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PLOS One logoLink to PLOS One
. 2026 Mar 6;21(3):e0344784. doi: 10.1371/journal.pone.0344784

Health literacy and preventive behaviors toward microplastic contamination among communities in the major river basins of northeastern Thailand

Santisith Khiewkhern 1,2,*, Supatra Noo-In 1, Chitkamon Srichomphoo 3, Jirarat Ruetrakul 4, Ruchakron Kongmant 2, Nitikorn Phoosuwan 5,6,*
Editor: Phuping Sucharitakul7
PMCID: PMC12965693  PMID: 41790867

Abstract

Background

Microplastic contamination in freshwater systems poses increasing environmental and public health risks, particularly for riverine communities. Health literacy may critically influence individuals’ capacity to recognize exposure pathways and adopt preventive behaviors.

Objective

This study assessed health literacy and preventive behaviors related to microplastic contamination and examined factors associated with poor health literacy and preventive practices among communities in northeastern Thailand.

Methods

A cross-sectional survey was conducted among 942 adults residing along the Mekong, Chi, and Mun River basins. Health literacy and preventive behaviors were assessed using a structured questionnaire. Multivariable logistic regression was performed to identify associated factors, whilst adjusted odds ratios (aOR) with 95% confidence intervals (CI) and statistical significance set at p < 0.05.

Results

Nearly half of the participants exhibited insufficient health literacy, with decision-making identified as the weakest domain. While approximately half reported good preventive behaviors, insufficient health literacy was the strongest determinant of poor preventive practices (aOR=9.18; 95%CI: 6.62–12.72). Residents of rural (aOR=6.47; 95%CI: 4.47–9.37) and semi-urban (aOR=2.45; 95%CI: 1.76–3.41) communities and younger age groups were significantly more likely to have poor health literacy. Community type (semi-urban: aOR=2.61; 95%CI: 1.81–3.78) and longer duration of residence (>60 years: aOR=2.36; 95%CI: 1.37–4.06) were also significantly associated with preventive behaviors.

Conclusion

Health literacy is a critical determinant of microplastic-related preventive behaviors. Interventions targeting higher-order literacy skills, particularly decision-making, should be integrated into environmental health and public health strategies to reduce microplastic exposure and promote sustainable preventive practices in riverine communities.

Introduction

Plastics have become an essential part of modern life due to their durability, versatility, and affordability. However, the overproduction and mismanagement of plastic waste have caused severe environmental pollution, particularly through the generation of microplastics (MPs)—plastic fragments smaller than 5 mm—that persist in aquatic and terrestrial ecosystems [1,2]. Since the 1950s, more than 8.3 billion metric tons of plastics have been produced, of which only 9% have been recycled, while the rest accumulate in landfills and the natural environment [3]. These plastic materials gradually fragment under environmental stressors such as UV radiation, abrasion, and microbial activity, resulting in persistent microplastics that threaten ecosystems worldwide [4,5].

Microplastics are now recognized as an emerging global pollutant due to their wide distribution, persistence, and potential toxicity [6,7]. They enter the environment from multiple sources, including wastewater discharge, industrial effluents, stormwater runoff, and the breakdown of larger plastic debris [8,9]. Once released, they can be transported through waterways and accumulate in sediments and aquatic organisms [10] Studies across Asia have demonstrated widespread microplastic contamination, particularly in low- and middle-income countries where waste management systems remain inadequate and enforcement mechanisms are limited [11,12]. For example, Pinto et al. [13] and Alam et al. [14] found that rivers in Thailand and Indonesia near industrial and residential areas contain high concentrations of microplastics due to mismanaged waste and insufficient treatment infrastructure. These findings suggest that rivers act as major transport pathways of microplastics from land-based sources to marine environments [15].

Microplastics are not only an environmental hazard but also a public health concern. They have been detected in marine and freshwater organisms, including plankton and fish, indicating potential trophic transfer across aquatic food webs and raising concerns about bioaccumulation in higher trophic levels [16,17]. Laboratory studies show that exposure to microplastics can lead to oxidative stress, inflammation, and reproductive toxicity in aquatic species [18]. Moreover, microplastics can absorb and carry toxic chemicals such as heavy metals and persistent organic pollutants, enhancing their bioavailability and health risks to both wildlife and humans [19,20]. Human exposure primarily occurs through ingestion of contaminated food and drinking water, inhalation of airborne particles, and possible dermal contact [20,21]. Recent biomonitoring studies have detected microplastics in human stool samples and placental tissues, raising concerns about potential systemic exposure and long-term biological implications [22,23].

Technological interventions have been developed to address microplastic pollution. Conventional wastewater treatment can remove a portion of microplastics through sedimentation and filtration, while coagulation–flocculation and ultrafiltration improve efficiency [24,25]. Advanced treatments using polyaluminum chloride, ferric chloride, and chitosan-based coagulants have demonstrated enhanced removal efficiency, particularly for microplastics smaller than 10 µm [26–28]. However, complete removal remains challenging, especially in rural communities that rely on untreated water sources [29]. In Thailand, studies have revealed microplastics in treated and untreated water supplies, as well as in aquatic organisms consumed by local populations [30–32]. Therefore, improving community awareness and behavior regarding microplastic exposure is crucial to complement technological solutions.

Health literacy is a key determinant influencing how individuals perceive and respond to environmental risks. It reflects people’s ability to obtain, understand, evaluate, and apply information to make informed health-related decisions [31]. In the context of microplastic pollution, individuals with higher health literacy are more likely to engage in preventive behaviors such as reducing single-use plastics, choosing safe drinking sources, and supporting proper waste management [33].

Given the rising microplastic contamination in freshwater and human exposure risks, this study aimed to assess the health literacy and preventive behaviors among communities living in the major river basins of Northeastern Thailand. Understanding the factors associated with these behaviors can guide the development of effective community-based interventions, public awareness campaigns, and environmental health policies to reduce exposure and promote sustainable water and waste management practices.

Methods

Study design

This study employed a cross-sectional descriptive design to assess the levels of health literacy and preventive behaviors related to microplastic contamination among residents living along the three major river basins in Northeastern Thailand—the Chi, Mun, and Mekong Rivers. The study aimed to explore associations between demographic factors, health literacy dimensions, and preventive behaviors to identify determinants influencing microplastic exposure prevention in local communities.

Study population

The target population consisted of adults aged 18 years and above residing in communities located within five kilometers of the main riverbanks in selected provinces representing the three river basins—Nakhon Phanom (Mekong River), Maha Sarakham (Chi River), and Buriram (Mun River). These provinces were chosen to represent different environmental and socioeconomic contexts, including agricultural, urban, and mixed-use areas.

Samples and sample size

The sample size was calculated using a single-population proportion formula to achieve adequate statistical precision in estimating the prevalence of environmental health literacy in the target population. A 95% confidence level and an assumed proportion of 0.50 were applied, the latter chosen to maximize variability and provide the most conservative estimate in the absence of reliable prior data. Based on these parameters and a margin of error of approximately ±3.2%, the minimum required sample size was calculated to be 942 participants. This sample size was considered sufficient to yield stable and reliable estimates for subsequent analyses and was therefore adopted for the study. This sample size ensured sufficient representation from each province. Inclusion criteria were adults who: (1) aged 18 years and above, (2) resided in the selected river basin communities, including temporary residents and migrants living near the border, (3) were able to read and understand Thai language, and (4) provided informed consent to participate in the study. Exclusion criteria included: (1) individuals with severe cognitive impairment or communication difficulties that prevented questionnaire completion, (2) temporary residents or migrants who had lived in the area for less than 6 months, and (3) participants who did not complete more than 80% of the questionnaire.

Sampling method

A multistage sampling technique was applied in this study. Stage 1 involved the purposive selection of three provinces to represent the distinct community types based on their geographical coverage, administrative boundaries, population density, and location within the river basins. The provinces selected were Nakhon Phanom (representing Urban communities), Maha Sarakham (representing Semi-urban communities), and Buriram (representing Rural communities), Stage 2: From each province, two districts located near the riverbanks were randomly selected, Stage 3: Within each district, two communities were systematically selected based on population size and accessibility, and Stage 4: Households were randomly selected from community lists, and one eligible adult per household was chosen using a simple random method. This approach ensured representation across various environmental and socioeconomic backgrounds, increasing the generalizability of the findings.

Ethical considerations

The study protocol was reviewed and approved by the Human Research Ethics Committee of Maha Sarakham University (No. 556–524/2567 dated 29 August 2024–28 August 2025). All participants provided informed consent prior to participation, and their confidentiality and anonymity were strictly maintained throughout the study.

Data collection procedures

Data were collected from 15 January to 31 March 2025 by trained research assistants through face-to-face interviews. Prior to data collection, enumerators underwent a one-day training session to standardize data collection procedures and ensure ethical compliance. Each participant received an explanation of the study purpose, potential benefits, and confidentiality measures before providing written informed consent. Data were recorded anonymously using coded questionnaires. Quality control was maintained by daily verification of completed forms and random re-checks of 10% responses by field supervisors.

Outcome measures

The study used a structured questionnaire developed based on existing literature and the Nutbeam Health Literacy Framework [31]. It comprised three sections:

Demographic information (e.g., age, gender, education, occupation, income, and water source).

Health literacy assessment: Six components—cognitive understanding, access to information and services, communication, self-management (action), appraisal, and decision-making—were measured using a five-point Likert scale, with higher scores indicating better literacy. The total health literacy score was interpreted using an 80% threshold, whereby scores below 80% indicated insufficient health literacy, while scores of 80% or higher reflected a sufficient level of health literacy [34].

Preventive behavior assessment: Items measured frequency and consistency of microplastic contamination prevention actions, including safe water consumption, waste segregation, and reduced plastic use. The total preventive behavior score was interpreted using an 80% threshold, whereby scores below 80% indicated poor preventive behavior, while scores of 80% or higher reflected a good level of preventive behavior.

Reliability testing using Cronbach’s alpha yielded coefficients of 0.89 for the overall scale and ranged between 0.81–0.87 for subcomponents, indicating good internal consistency. This instrument was developed based on established health literacy frameworks and previous environmental health literacy studies. However, this study represents an initial application of the microplastic health literacy scale, and comprehensive construct validation, including factor analysis, was not conducted.

Data analysis

Data were analyzed using IBM SPSS Statistics version 26 (IBM Corp., Armonk, NY, USA). Descriptive statistics—frequency, percentage, mean, and standard deviation—were used to describe participant characteristics, health literacy scores, and preventive behaviors.

Inferential statistics were applied as follows: (1) Independent t-test to compare mean behavior scores across demographic variables, (2) Chi-square test and Fisher exact test to examine associations between categorical variables and levels of preventive behavior, (3) Binary logistic regression was used to assess the relationships between demographic variables and health literacy and preventive behaviors. Variables with a p-value ≤ 0.25 in the univariable analysis were included in the multivariable analysis. The backward selection method was applied for the multivariable logistic regression. Model fit was evaluated using the Hosmer–Lemeshow goodness-of-fit test. Crude Odds Ratio (Crude OR) and adjusted OR (adj.OR) were calculated. Statistical significance was set at p < 0.05. All analyses followed ethical guidelines and research integrity standards.

Occupation, household size, and water source were included as contextual socioeconomic and environmental variables and screened in univariable analyses prior to multivariable modeling. Detailed occupational exposure assessment was not conducted, as the study focused on community-level health literacy and preventive behaviors rather than task-specific exposure pathways.

Results

The analysis of 942 participants found a near-equal distribution of health behaviors, with 463 (49.20%) categorized as having “Good behavior” and 479 (50.80%) as having “Poor behavior”. Regarding community type, the “Good behavior” group was predominantly from urban communities (228, 49.20%), while the “Poor behavior” group was most frequently found in semi-urban communities (209, 43.60%). For gender, females constituted the majority in both groups, whilst the age distribution showed that the “Good behavior” group had a mean age of 50.56 ± 14.48 years, and the “Poor behavior” group had a mean age of 48.39 ± 16.22 years. In terms of Occupation, Agriculture/Fishery was the largest group for both bahvior groups, whereas the “Good behavior” group had a mean of 7,333.29 ± 5,959.00 baht and the “Poor behavior” group had a higher mean of 9,055.34 ± 7,975.66 baht. See Table 1.

Table 1. General information of participants classified by behavior in preventing microplastic contamination (n = 942).

Factors Behaviors Total

(n = 942)
p-value
Good

(n = 463)
Poor

(n = 479)
Exact test/t-test
n (%) n (%) n (%)
Communities 0.001**
 Urban communities 228 (49.20) 111 (23.20) 339 (36.00)
 Semi-urban communities 127 (27.40) 209 (43.60) 336 (35.70)
 Rural communities 108 (23.30) 159 (33.20) 267 (28.30)
Gender 0.409
 Male 162 (35.00) 180 (37.60) 342 (36.30)
 Female 301 (65.00) 299 (62.40) 600 (63.70)
Age (years)
 Mean (SD) 50.56 (14.48) 48.39 (16.22) 49.46 (15.42) 0.031*
  18–45 years 162 35.00 205 42.80 367 39.00 0.024*
  46–60 years 182 39.30 152 31.70 334 35.50
   > 60 years 119 25.70 122 25.50 241 25.60
Occupation
 Agriculture/ Fishery 178 (38.40) 175 (36.50) 353 (37.50) 0.855
 Trade 86 (18.60) 85 (17.70) 171 (18.20)
 Labor 113 (24.40) 127 (26.50) 240 (25.50)
 Government/State enterprise/Others 86 (18.60) 92 (19.20) 178 (18.90)
Income per month (baht)
 Mean (SD) 7333.29 (5959.65) 9055.34 (7975.66) 8,208.92 (7,105.80) < 0.001**
  ≤ 10,000 baht 318 (68.70) 283 (59.10) 601 (63.80) 0.002**
  > 10,000 baht 145 (31.30) 196 (40.90) 341 (36.20)
Duration of residence (years)
 Mean (SD) 43.8 (18.54) 42.80 (18.93) 43.30 (18.74) 0.416
Duration of residence (years) 31 6.70 33 6.90 64 6.80 0.003**
  ≤ 20 years 72 15.50 67 14.00 139 14.80 0.083
 21–40 years 118 25.50 151 31.50 269 28.60
 41–60 years 191 41.30 166 34.70 357 37.80
  > 60 years 82 17.70 95 19.80 177 18.80
Religion 0.587
 Buddhist 451 (97.40) 465 (97.10) 915 (97.20)
 Others 12 (2.60) 14 (2.90) 26 (2.80)
Education 0.001**
 No formal education 12 (2.60) 8 (1.70) 20 (2.10)
 Primary 256 (55.30) 197 (41.10) 453 (48.10)
 Secondary 128 (27.60) 140 (29.20) 268 (28.50)
 Vocational 35 (7.60) 47 (9.80) 82 (8.70)
 Bachelor’s or higher 32 (6.90) 87 (18.20) 119 (12.60)
Family size
 Small (1–2 persons) 68 (14.70) 97 (20.30) 165 (17.50) 0.075
 Medium (3–4 persons) 218 (47.10) 216 (45.10) 434 (46.10)
 Large (≥5 persons) 177 (38.20) 166 (34.70) 343 (36.40)
Drinking water source 0.030*
 River 7 (1.50) 8 (1.70) 15 (1.60)
 Tap water 36 (7.80) 45 (9.40) 81 (8.60)
 Filtered water 142 (30.70) 118 (24.60) 260 (27.60)
 Bottled water 256 (55.30) 298 (62.20) 554 (58.80)
 Others 22 (4.80) 10 (2.10) 32 (3.40)
Household water source < 0.001**
 River 41 (8.90) 26 (5.40) 67 (7.10)
 Tap water 358 (77.30) 389 (81.20) 747 (79.30)
 Filtered water 32 (6.90) 32 (6.70) 64 (6.80)
 Bottled water 9 (1.90) 24 (5.00) 33 (3.50)
 Others 23 (5.00) 8 (1.70) 31 (3.30)
Illness in the past month
 Yes 89 (19.20) 122 (25.60) 211 (22.40) 0.020*
 No/unsure 374 (80.80) 355 (74.40) 729 (77.60)
Visiting a physician in the past month
 Yes 90 (19.40) 140 (29.20) 230 (24.40) 0.001**
 No/unsure 373 (80.60) 339 (70.80) 712 (75.60)
Type of illness in the past month 0.002*
 Respiratory system 35 (7.60) 65 (13.60) 100 (10.60)
 Digestive system 36 (7.80) 38 (7.90) 74 (7.90)
 Circulatory/neurological 23 (5.00) 40 (8.40) 63 (6.70)
 None 369 (79.70) 336 (70.10) 705 (74.80)
Aquatic animal consumption (past month) 0.249
 Yes 430 (92.90) 435 (90.80) 865 (91.80)
 No/Unsure 33 (7.10) 44 (9.20) 77 (8.20)
Source of aquatic animals consumed 0.306
 Self-caught 101 (21.80) 89 (18.60) 190 (20.20)
 Market 327 (70.60) 334 (71.80) 671 (71.20)
 From friends/relatives 35 (7.60) 46 (9.60) 81 (8.60)
Type of aquatic animal Consumed 0.102
 Fish 411 (88.80) 408 (85.20) 819 (86.90)
 Others 52 (11.20) 71 (14.80) 123 (13.10)

**p-value<0.01, *p-value<0.05, SD=Standard deviation, 1 US dollar=32.50 baht.

Health literacy level with six components

The mean scores and standard deviations for the six components of health literacy related to microplastics contamination prevention among the 942 participants. The analysis revealed that the overall health literacy level was good, with a mean score of 2.34 ± 0.46. Examining the specific components, four components were rated at a good level: Communication (2.49 ± 0.56), Action (2.40 ± 0.51), Appraisal (2.38 ± 0.58), and Access to Health Information and Service (2.34 ± 0.55). Conversely, one component was rated as Moderate: Cognitive (or Understanding), with a mean score of 2.30 ± 0.52. Most notably, the component of Decision-Making scored the lowest (mean = 1.61 ± 0.47) and was the only component rated as Poor. See Table 2.

Table 2. Health literacy level with 6 components for microplastics contamination (n = 942).

Health literacy Mean SD. Level
Cognitive 2.30 0.52 Moderate
Access to health information and service 2.34 0.55 Good
Communicate 2.49 0.56 Good
Action 2.40 0.51 Good
Appraisal 2.38 0.58 Good
Decision 1.61 0.47 Poor
Overall 2.34 0.46 Good

SD. = Standard deviation.

Health literacy level

The results indicate a nearly balanced distribution between the two levels. Specifically, 50.20% (n = 473) of the participants were found to have “sufficient health literacy”, while a large proportion, 49.80% (n = 469), were categorized as having “Insufficient health literacy”. This finding suggested that, despite the importance of health literacy in addressing environmental health issues, nearly half of the study population lacks the adequate level of literacy required to fully obtain, understand, evaluate, and apply microplastic-related health information effectively. This highlighted a critical need for targeted interventions to boost comprehension and decision-making skills within the communities. Although the overall mean health literacy score fell within the good range, domain-specific classification revealed a high prevalence of insufficient health literacy, driven primarily by lower scores in higher-order domains such as critical appraisal and decision-making. See Table 3.

Table 3. Health literacy level for Preventing microplastics contamination (n = 942).

Health literacy Number (Person) Percentage
Sufficiency 473 50.20
Insufficiency 469 49.80
Total 942 100.00

Health behavior

The analysis revealed a near-even split in preventive practices, with the majority of participants categorized as having Poor Health Behaviors, accounting for 50.80% (n = 479) of the total sample. Conversely, those demonstrating “Good preventive behaviors” represented 49.20% (n = 463). This outcome, while showing a slight majority toward insufficient practices, underscores that nearly half of the community engages in positive actions to mitigate microplastic exposure. Nonetheless, the substantial proportion of the population still exhibiting poor health behaviors highlights the urgent requirement for targeted public health strategies and continued educational efforts to enhance consistent and sustainable preventive behaviors across the community. See Table 4.

Table 4. Health behavior level for preventing microplastics contamination (n = 942).

Health behavior Number (Person) Percentage
Good 463 49.20
Poor 479 50.80
Total 942 100.00

Factors associated with poor health literacy

The multivariable logistic regression model examined the factors associated with poor health literacy for microplastics contamination prevention. The model demonstrated an acceptable fit (Hosmer and Lemeshow Test p = 0.104) and accounted for 19.60% of the variance in poor health literacy (Nagelkerke R2 = 0.196), correct classifying 66.00% of the observations.

The analysis identified several factors significantly associated with poor health literacy, using Urban community, Age > 60 years, ≤ 20 years duration of residence, and no previous illness as the reference groups (Adj.OR = 1). The strongest independent predictor was Community type. Individuals residing in a rural community were 6.47 times more likely to have poor health literacy compared to those in an urban community (Adj.OR = 6.47, 95% CI: 4.47 to 9.37, p < 0.001). Similarly, those in a Semi-urban community were also significantly more likely to have Poor Health Literacy (Adj.OR = 2.45, 95% CI: 1.76 to 3.41, p < 0.001).

Age was also a significant factor. Compared to those aged > 60 years, individuals in the 18–45 years group were 3.53 times more likely to have Poor Health Literacy (Adj.OR = 3.53, 95% CI: 1.90 to 6.55, p < 0.001), and those in the 46–60 years group were 2.35 times more likely (Adj.OR = 2.35, 95% CI: 1.28 to 4.34, p = 0.006).

Regarding Duration of residence, only the category of > 60 years was significantly associated, showing a protective effect where these individuals were less likely to have Poor Health Literacy (Adj.OR = 0.49, 95% CI: 0.25 to 0.96, p = 0.038) compared to the ≤ 20 years group. Finally, certain History of illness groups showed a higher likelihood of Poor Health Literacy compared to having no previous illness9. Specifically, those with a history of respiratory diseases were 1.64 times more likely to have poor health literacy (Adj.OR = 1.64, 95% CI: 1.02 to 2.62, p = 0.039) 10, and those with a history of cardiovascular diseases were 1.90 times more likely (Adj.OR = 1.90, 95% CI: 1.07 to 3.38, p = 0.028). See Table 5.

Table 5. Factor associated with poor health literacy for microplastics contamination prevention.

Factors Health literacy Bivariable analysis Multivariable analysis
Sufficiency Insufficiency
n (%) n (%) Crude OR p-value Adj.OR p-value 95%CI of Adj.OR
Communities
 Urban 241 (51.00) 98 (20.90) 1 0.001** 1 0.001**
 Semi-urban 154 (32.50) 182 (38.80) 2.91 0.001** 2.45 0.001** 1.76 to 3.41
 Rural 78 (16.50) 189 (40.30) 5.96 0.001** 6.47 0.001** 4.47 to 9.37
Age (Years)
  > 60 years 143(30.20) 98 (20.90) 1 0.001** 1 0.001**
 18–45 years 152 (32.20) 215 (45.80) 2.06 0.001** 3.53 0.001** 1.90 to 6.55
 46–60 year 178 (37.60) 156 (33.30) 1.28 0.150 2.35 0.006* 1.28 to 4.34
Duration of residence (years)
  ≤ 20 years 55 (11.60) 84 (17.90) 1 0.001** 1 0.054
 21–40 years 119 (25.20) 150 (32.00) 0.83 0.366 0.82 0.593 0.40 to 1.69
 41–60 years 195 (41.20) 162 (34.50) 0.54 0.003* 0.57 0.100 0.29 to 1.11
  > 60 years 104 (22.00) 73 (15.60) 0.46 0.001** 0.49 0.038* 0.25 to 0.96
History of illness in the past month
 No previous illness 376(79.50) 329 (70.20) 1 0.007* 1 0.020*
 Respiratory diseases 37 (7.80) 63 (13.40) 0.51 0.003** 1.64 0.039 1.02 to 2.62
 Gastrointestinal diseases 31 (6.60) 43 (9.20) 0.63 0.063 1.60 0.084 0.94 to 2.72
 Cardiovascular diseases 29 (6.10) 34 (7.20) 0.75 0.267 1.90 0.028* 1.07 to 3.38

a. Variable(s) entered on step 1: Communities, Age group, Duration, Occupation, Family size, Income group, illness Type, Aquatic animals consumed.

b. Hosmer and Lemeshow Test, Chi-square = 13.234, p-value = 0.104; Nagelkerke R Square = 0.196; Overall Percentage = 66.00.

c. * p-value < 0.05; ** p-value < 0.01; Adj.OR=Adjusted Odds Raio, C.I. = Confidence interval.

Factors associated with poor health behaviors

The multivariable logistic regression model successfully assessed the factors associated with poor health behaviors for preventing microplastics contamination, showing a good fit to the data (Hosmer and Lemeshow Test p = 0.961) and accounting for a substantial portion of the variance (Nagelkerke R2 = 0.351). The overall percentage of correctly classified observations was 75.20%. The analysis revealed that the most significant determinant of poor health behaviors was Health Literacy. Specifically, individuals categorized as having Insufficient Health Literacy were found to be 9.18 times more likely to exhibit poor prevention behaviors compared to those with Sufficient Health Literacy (Adj.OR = 9.18, 95% CI: 6.62 to 12.72, p < 0.001). Furthermore, Community Type played a significant role; those residing in a Semi-urban community were 2.61 times more likely to have poor behaviors than those in an Urban community (Adj.OR = 2.61, 95% CI: 1.81 to 3.78, p < 0.001). Lastly, Duration of residence of more than 60 years (>60 years) was associated with 2.36 times higher odds of poor health behaviors compared to those residing for 20 years or less (Adj.OR = 2.36, 95% CI: 1.37 to 4.06, p = 0.002). Other variables, such as family size and other duration categories, did not demonstrate a statistically significant association in the adjusted mode. See Table 6.

Table 6. Factor associated with poor health behaviors for preventing microplastics contamination.

Factors Health behaviors Bivariable analysis Multivariable analysis
Good Poor
n (%) n (%) Crude OR p-value Adj.OR p-value 95%CI of Adj.OR
Communities
 Urban 228 (49.30) 111 (23.20) 1 0.001** 1 0.001**
 Semi-urban 127 (27.40) 209 (43.60) 3.38 0.001** 2.61 0.001** 1.81 to 3.78
 Rural 108 (23.30) 159 (33.20) 2.17 0.001** 1.47 0.053 0.99 to 2.18
Duration of residence (years)
  ≤ 20 years 72 (15.50) 67 (14.00) 1 0.084 1 0.016*
 21–40 years 118 (25.50) 151 (31.50) 0.80 0.334 1.61 0.058 0.98 to 2.65
 41–60 years 191 (41.30) 166 (34.70) 1.11 0.609 1.42 0.148 0.88 to 2.65
  > 60 years 82 (17.70) 95 (19.80) 0.75 0.119 2.36 0.002** 1.37 to 4.06
Family size
 Large (≥5 persons) 46 (9.90 60 (12.50) 1 0.076 0.064
 Small (1–2 persons) 268 (61.80) 313 (65.30) 1.52 0.029 1.30 0.261 0.82 to2.05
 Medium (3–4 persons) 131 (28.30) 106 (22.20) 1.06 0.704 0.78 0.160 0.56 to 1.10
Health literacy
 Sufficiency 350 (75.60) 35 (74.30) 1 0.001** 0.001**
 Insufficiency 113 (24.40) 123 (25.70) 8.96 0.001** 9.18 0.001** 6.62 to 12.72

a. Variable(s) entered on step 1: Communities, Age group, Duration, Occupation, Family size, Education, Family size, Income group, illness group, Visited Doctor, illness Type, Aquatic animals consumed, Health literacy group.

b. Hosmer and Lemeshow Test, Chi-square = 2.52, p-value = 0.961; Nagelkerke R Square = 0.351; Overall Percentage = 75.20.

c. * p-value < 0.05; ** p-value < 0.01; Adj.OR=Adjusted Odds Raio, C.I. = Confidence interval.

Discussion

This study advances the current understanding of microplastic-related environmental health by elucidating the pivotal role of health literacy in shaping preventive behaviors among riverine communities in Northeastern Thailand. Although nearly half of the participants reported good preventive practices, a substantial proportion exhibited insufficient health literacy, particularly in higher-order domains such as cognitive understanding and decision-making. This discordance indicates that observed preventive behaviors may be largely habitual or externally reinforced rather than grounded in a comprehensive understanding of microplastic exposure pathways and associated health risks. Such a phenomenon reflects a broader challenge in environmental health communication, where behavioral compliance does not necessarily equate to informed agency [6,31].

The markedly low score in the decision-making component warrants particular attention. According to Nutbeam’s health literacy framework, decision-making represents a critical competency that integrates access, comprehension, appraisal, and action into coherent and sustained behavior [31]. The deficiency observed in this domain suggests that while participants may be capable of accessing and communicating information, they encounter difficulties in synthesizing evidence and translating it into rational, context-specific choices. Comparable patterns have been reported in studies of environmental and chemical risk perception, where individuals demonstrate surface-level awareness but limited capacity for critical evaluation and autonomous decision-making [33,35].

Pronounced spatial disparities in health literacy were evident, with residents of rural and semi-urban communities exhibiting substantially higher odds of insufficient health literacy than their urban counterparts. These findings underscore the influence of structural and contextual determinants, including inequities in access to environmental information, educational resources, and public health infrastructure. Previous studies in Southeast Asia have documented that river systems traversing agricultural and peri-urban landscapes often receive inadequately treated domestic and industrial effluents, resulting in elevated microplastic loads while simultaneously limiting opportunities for effective risk communication [13,14]. Consequently, communities facing the highest environmental exposure may paradoxically possess the lowest capacity to interpret and respond to such risks.

Age-related differences further illuminate the complex interplay between experiential knowledge and formal literacy. Younger participants demonstrated a higher likelihood of poor health literacy compared with older adults, a finding that diverges from conventional assumptions linking age to declining literacy. In this context, prolonged residence and cumulative exposure to environmental change may enhance contextual awareness and informal knowledge acquisition among older individuals, partially compensating for lower levels of formal education [ 36–38]. This highlights the importance of recognizing experiential learning as a complementary dimension of environmental health literacy.

Critically, this study demonstrates a robust and independent association between health literacy and preventive behaviors, with insufficient literacy emerging as the strongest predictor of poor preventive practices. In addition, the observed association between higher income and poorer preventive behaviors may reflect contextual urban–rural differences rather than economic capacity alone. Higher-income participants were more likely to reside in urbanized settings, where perceived reliance on infrastructural protection and lower perceived environmental exposure may reduce engagement in individual preventive practices. Conversely, lower-income residents in riverine communities may adopt more conservative behaviors, such as reliance on bottled water or traditional household practices, to mitigate perceived risks. These contextual factors were not explicitly modeled and should be interpreted cautiously. At first glance, the coexistence of a high prevalence of insufficient health literacy and a high level of good preventive behaviors may appear contradictory. However, this pattern reflects the multidimensional nature of health literacy. While many participants demonstrated adequate functional or interactive literacy that supports routine preventive practices, lower scores in higher-order domains—particularly critical appraisal and decision-making—resulted in overall classification as insufficient health literacy. In addition, preventive behaviors in riverine communities may be influenced by habitual practices, social norms, and contextual environmental factors that operate independently of comprehensive health literacy. Therefore, health literacy should be interpreted as a strong and independent predictor of preventive behaviors rather than the sole determinant.

In addition, the observed association between a history of respiratory illness and poorer health literacy should be interpreted with caution. Respiratory symptoms were self-reported and were not intended to indicate a direct or indirect effect of microplastic exposure. Given the cross-sectional design and the period of data collection, it is not possible to disentangle potential effects of microplastics from other environmental factors, particularly ambient air pollution and seasonal particulate matter exposure. Therefore, this finding reflects a contextual association rather than a causal relationship. This finding provides empirical support for theoretical models that position health literacy as a central mediator between environmental risk information and behavioral outcomes [37].

Individuals with limited literacy may struggle to evaluate the safety of drinking water sources, interpret information on microplastic contamination, or sustain plastic-reduction behaviors, thereby increasing their vulnerability to cumulative exposure. These results are consistent with prior research linking low literacy to suboptimal engagement in environmental and health-protective behaviors [39,36]. The association between reliance on bottled or filtered water and poorer health literacy may be partly explained by perceived protection. Individuals who depend on commercially treated or filtered water may assume that potential contaminants, including microplastics, are adequately removed, thereby reducing motivation to seek further information or develop broader risk awareness.

This interpretation is closely intertwined with socioeconomic and urban–rural contexts. Higher-income households, often residing in urbanized areas, are more likely to afford bottled or filtered water and to rely on technological solutions rather than personal preventive knowledge. Conversely, individuals using river or tap water may perceive higher exposure risk, which can stimulate more active engagement in health information seeking and preventive decision-making. These interconnected contextual factors may collectively shape health literacy related to microplastic contamination and should be interpreted cautiously.

The findings also highlight the limitations of relying solely on technological interventions to mitigate microplastic exposure. While advanced water treatment processes such as coagulation–flocculation and membrane filtration can remove a substantial fraction of microplastics, their efficiency declines markedly for smaller particles and varies by polymer type [24–28]. Empirical evidence from Thailand has confirmed the persistence of microplastics in both treated water supplies and commonly consumed freshwater organisms [30–32]. In this context, health literacy functions as a critical upstream determinant, enabling individuals and communities to adopt preventive strategies that complement infrastructural controls and reduce reliance on downstream remediation alone.

From a policy and public health perspective, these findings underscore the necessity of integrating environmental health literacy into microplastic risk governance. Educational interventions that merely disseminate information are unlikely to yield sustained behavioral change unless they explicitly target higher-order competencies such as critical appraisal and decision-making. Community-based programs that leverage local knowledge, health volunteers, and culturally resonant communication strategies may be particularly effective in strengthening literacy and fostering informed environmental stewardship [14,39]. Aligning such initiatives with national public health and environmental policies could further support progress toward Sustainable Development Goals related to clean water and responsible consumption.

This study is strengthened by its large, regionally representative sample and rigorous multistage sampling across three major river basins, enhancing the external validity of the findings. The use of a theoretically grounded health literacy framework and psychometrically robust instruments further reinforces the reliability and interpretability of the results. Importantly, this research contributes novel evidence by empirically linking health literacy with microplastic-related preventive behaviors in a real-world community setting, addressing a critical gap in the environmental health literature.

Although occupational category, household size, and water source were considered as contextual indicators, this study did not aim to quantify occupation-specific or activity-based microplastic exposure. The primary focus was to examine how community-level health literacy shapes preventive behaviors. Future studies incorporating detailed occupational and exposure-specific subgroup analyses may provide further insights into differential microplastic risks.

Nevertheless, several limitations merit consideration. First, the cross-sectional design precludes causal inference and limits the ability to disentangle bidirectional relationships between health literacy and behavior. Second, this study focused on permanent residents to reflect stable community-level practices. However, transient and migrant populations with potentially different exposure pathways were not included, which may limit generalizability. Future research should incorporate mobile populations to better capture diverse microplastic exposure contexts. Third, the microplastic health literacy instrument used in this study represents an initial application. Although internal consistency reliability was acceptable, comprehensive construct validation, including factor analysis, was not performed. Therefore, domain-specific interpretations of health literacy should be made with caution, and further psychometric validation is warranted in future studies. Forth, data collection during the dry season may also constrain generalizability, as seasonal hydrological dynamics can influence waste dispersion, water use patterns, and risk perception [12]. Last, reliance on self-reported behaviors introduces the potential for social desirability bias, which may partially explain the relatively high prevalence of reported preventive practices despite widespread insufficient literacy. Future research employing longitudinal designs, seasonal comparisons, and objective exposure assessments would provide a more nuanced understanding of how health literacy shapes microplastic exposure and prevention over time.

Conclusion and recommendations

This study highlights health literacy as a key determinant of preventive behaviors against microplastic contamination among riverine communities in Northeastern Thailand. Despite the presence of reported preventive practices, nearly half of the participants demonstrated insufficient health literacy, particularly in cognitive understanding and decision-making. This gap suggests that preventive behaviors are not consistently grounded in informed and sustainable decision-making.

Marked disparities in health literacy and preventive behaviors were observed across community types and demographic characteristics, with rural and semi-urban residents being disproportionately affected. Insufficient health literacy emerged as the strongest predictor of poor preventive behaviors, underscoring its central role in shaping individual and community responses to environmental exposure. These findings indicate that technological and infrastructural interventions alone are insufficient to reduce microplastic-related health risks without concurrent improvements in population health literacy.

Accordingly, environmental health literacy should be integrated into public health and environmental management strategies, with targeted, community-based interventions focusing on critical appraisal and decision-making skills. Strengthening environmental education across the life course and aligning literacy-focused interventions with water and waste management policies are essential for sustainable microplastic exposure prevention. Future research should employ longitudinal and mixed-methods approaches to further elucidate causal pathways and inform evidence-based policy development.

Acknowledgments

The authors would like to express their sincere gratitude to Mahasarakham University, Thailand and Uppsala University, Sweden for support throughout this study. Special thanks are offered to all the community leaders, public health volunteers, public health students, and local residents living along the Chi, Mun, and Mekong River basins, whose cooperation and participation made this study possible. The authors also acknowledge the valuable assistance of the research assistants and enumerators who contributed to data collection and verification. Finally, the authors wish to thank their colleagues and peer reviewers for their constructive feedback, which greatly improved the quality of this manuscript.

Data Availability

All XXX files are available from the https://osf.io/46txe/overview.

Funding Statement

The manuscript has not been published or submitted for publication elsewhere. The authors received no specific funding for this work. The funder (Mahasarakham University) had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. All authors have approved the content of the manuscript and have contributed significantly to the research involved/the writing of the manuscript.

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Decision Letter 0

Phuping Sucharitakul

19 Nov 2025

Dear Dr. Phoosuwan,

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2. Has the statistical analysis been performed appropriately and rigorously? -->?>

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**********

Reviewer #1: Thank you for the opportunity to review this and here are my concerns

Methods

1. 80% threshold

Would prefer to use 80% as a cutoff for “good” behavior or sufficient health literacy, domains/subdomains analysis would provide rich findings

2. Specify whether subgroup analysis was done for each health literacy component (cognitive, access, decision-making, etc.) If not, this could be a limitation.

3. Population considerations

The study focused on permanent residents ≥5 years. Temporary residents or migrants living near the border were excluded, but they may also be exposed to microplastics. This exclusion could bias results toward long-term community practices and miss transient or occupational exposures.

4. Period of data collection

The study was conducted from January to March 2025, but behaviors like throwing plastic into rivers may be influenced by seasonal water levels or flooding risk. Consider mentioning this as a limitation: behaviors may vary across seasons.

5. Subgroups by province, occupation, household size, or water source were partially analyzed. You may want to clarify whether occupational exposure, urban-rural residence, or specific economic activities were considered in detail.

Results & Discussion

1. Province differences

“Participants from Nakhon Phanom were more likely to exhibit good preventive behaviors (40.90%), whereas those from Buriram showed poorer behaviors (64.00%) (p=0.001).” Explanation: This could be due to local environmental context, socioeconomic factors, or urbanization differences.

Discussion mentions: Buriram and Maha Sarakham are near industrial zones or wastewater discharge points, leading to higher contamination. However, the study did not explore health literacy and behavior among temporary workers or industry employees, which may affect exposure and practices.

2. Income differences

“Participants with good behaviors had a lower mean monthly income (8,011.51 baht) than those with poor behaviors (11,845.83 baht) (p<0.001).”

Interpretation: Lower-income individuals may adopt more conservative behaviors, possibly due to reliance on bottled water or traditional preventive practices.

Limitation: Urban-rural differences are not explicitly addressed. High-income participants may live in urbanized areas with different exposure perceptions, potentially explaining why higher income correlates with poorer preventive behavior.

3. Water source and health literacy

“Participants who primarily consumed filtered water or bottled water were more likely to exhibit poor health literacy (adj.OR = 3.85 and 3.68, p<0.05).”

Possible explanation: People relying on bottled or filtered water may perceive themselves as protected, reducing motivation to learn about microplastic risks. This contrasts with those using river or tap water, who may actively seek preventive knowledge and actions. Also related to previous statement, perhaps, For example, high-income family may be able to purchase clean bottled water compared to low-income. Please refine all of these issues in discussion

4. Also related to reported respiratory illness, I am not sure whether this was direct/indirect affect of microplastic or due to the air pollution during the data collection period? please clarify.

5. Table 1 discrepancy

Drinking water counts:

Filtered water: Good = 323, Poor = 28 → total should be 351, not 260. This appears to be a data entry or calculation error and should be corrected.

Reviewer #2: Thank you for your submitted this manuscript on health literacy and preventive behaviors toward microplastic contamination in Northeastern Thailand. The topic is timely and relevant to environmental health. However, after careful evaluation, I have identified several critical issues that fundamentally undermine the validity and reliability of the study findings. These concerns span from internal contradictions in the results to methodological flaws that cannot be adequately addressed through minor revisions.

1. Fatal Inconsistency in Results

The manuscript contains fundamental contradictions that invalidate the main conclusions:

- The mean health literacy score is classified as "good level" (2.38±0.49), yet 70.5% of participants are categorized as having "insufficient" health literacy

- Despite 70.5% having insufficient literacy, 86.7% demonstrate good preventive behaviors. This directly contradicts the conclusion that literacy is the primary determinant of behavior

- This inconsistency renders the study's conclusions unreliable and questions the validity of the classification system

- The manuscript fails to acknowledge or explain this paradox, which is central to understanding the relationship between literacy and behavior

2. Severe Methodological Flaws

Multiple design issues compromise the study's validity:

- Purposive sampling at Stage 1 (province selection) introduces selection bias findings cannot be generalized to "major river basins of Northeastern Thailand" as claimed

- Inadequate instrument validation: Only Cronbach's α is reported; missing content validity, construct validity, and factor analysis for this novel "microplastic health literacy" scale

- Inappropriate causal inference: Cross-sectional design but employs language suggesting causality (e.g., "predictors") temporal relationships cannot be established

- Social desirability bias: Face-to-face interviews likely inflated self-reported good behaviors (86.7% seems unrealistically high given 70.5% insufficient literacy)

3. Critical Statistical Analysis Problems

The statistical models demonstrate poor quality and questionable validity:

- Hosmer-Lemeshow test: p=0.036 (p<0.05) = model does not fit the data adequately

- Nagelkerke R² = 0.363 and 0.194 (explaining only 36% and 19% of variance) = critical confounding variables are missing from the models

- Provincial OR=70.54 (95% CI: 25.48-195.27) is abnormally high → suggests multicollinearity, small cell counts, or model misspecification

- No diagnostic checks reported: Missing VIF (variance inflation factor), Cook's distance, or other diagnostic tests to assess model assumptions

4. Conclusions Inconsistent with Evidence

The manuscript's conclusions do not align with the presented data:

- Authors claim literacy plays a "crucial role," but evidence shows structural factors (province) have far greater influence (OR=70.54 vs. OR=5.18 for literacy)

- The Discussion (Lines 301-307) acknowledges behaviors may be driven by "cultural habits or public health campaigns" this directly contradicts the main conclusion emphasizing individual literacy

- Limited novel contribution: This is a descriptive-correlational study without novel mechanisms or theoretical advancement

5. Absence of Critical Limitations Section

The manuscript fails to acknowledge fundamental limitations:

- Cross-sectional design precludes causal inference between literacy and behavior

- Selection bias from purposive sampling limits generalizability

- Social desirability bias may inflate self-reported behaviors

- Poor model fit indicates important unmeasured confounders

- Novel instrument lacks comprehensive validation in the target population

- Self-reported behaviors may not reflect actual practices

Reviewer #3: Suggestions for major revisions

Review Comments to the Author

Issues that need to be addressed include the following:

Abstract

The results in the abstract require clarification. The authors state that overall health literacy toward microplastic contamination was at a good level (mean = 2.38 ± 0.49), yet 70.50% of participants had insufficient health literacy. This inconsistency must be explained.

Results

The authors should provide more detailed effect sizes for each factor, such as the odds ratio (OR) for the Fishery occupation group, which was associated with lower health literacy compared with “Other Occupation.” In addition, “Other Occupation” should be clearly defined. These findings require further discussion to explain why this group demonstrates higher health literacy than others.

A descriptive table comparing health literacy levels should be added (as a separate table following the logistic regression results) to better explore associations between factors and outcomes.

There is a substantial imbalance in gender distribution that warrants caution.

The age cut-off at 60 years needs better justification, especially since the <60 group is more than triple the size of the ≥60 group. Consider using more meaningful age categories (e.g., 18–45, 46–60, >60) to improve interpretability.

Income cut-offs should follow standardized thresholds (e.g., 8,000 or 10,000 THB per month). Please identify an appropriate reference and revise the analysis accordingly.

Some 95% confidence intervals are extremely wide (e.g., Maha Sarakham: Adj. OR = 17.85, 95% CI: 6.30–50.58; Buriram: Adj. OR = 70.54, 95% CI: 25.48–195.27). This likely reflects small sample sizes within certain categories. For example, only five participants in Nakhon Phanom had poor outcomes. Consider combining provinces, changing the reference group, or adjusting the cut-off criteria (e.g., using Bloom’s cut-off of 75% or 80% instead of 70%).

Introduction

Please incorporate additional literature on previous studies examining factors associated with health literacy and preventive behaviors. Describe how each factor has been investigated in prior work.

Methods

The authors should justify the cut-off used for “Duration of residence ≥10 years.” The sample size in the <10-year category appears extremely small, which may violate model assumptions.

The manuscript should clearly describe how model assumptions were checked, including criteria for selecting variables from univariate to multivariable logistic regression (e.g., p-value threshold) and whether forward or backward selection was used.

Information on model diagnostics—such as goodness-of-fit tests, AIC/BIC, ROC curve, or error metrics—should be reported. Consultation with a statistician is recommended.

The p-value cut-off for inclusion in the multivariable analysis must be stated explicitly.

The authors should provide justification for the sample size calculation. While the calculation suggested 384 participants, the study included 942. The ethical and methodological rationale for this discrepancy must be addressed.

Sampling and Variable Considerations

Certain variables with very small sample sizes (e.g., Fishery occupation) may produce statistically significant but non-generalizable results. The authors should reconsider how these categories are defined or grouped before re-analysis.

For variables such as household water source with small cell sizes, re-grouping categories may be necessary to ensure more reliable estimates.

Major Analytical Concerns

A dummy table for calculating associations and logistic regression is needed, but the current version includes categories with very small samples, which compromises validity.

Re-analysis with appropriately grouped categories is recommended to prevent unstable estimates and misleading significance.

Discussion and Conclusion

Comments on these sections will be provided after the authors revise the analysis and incorporate the suggested changes.

Language and Style

Extensive English editing is required to improve clarity, cohesion, and overall readability.

**********

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Reviewer #1: No

Reviewer #2: No

Reviewer #3: No

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PLoS One. 2026 Mar 6;21(3):e0344784. doi: 10.1371/journal.pone.0344784.r002

Author response to Decision Letter 1


12 Jan 2026

Manuscript Title: Health literacy and preventive behaviors toward microplastic contamination among communities in the major river basins of northeastern Thailand

Manuscript ID: PONE-D-25-57984R1

Dear Editor,

We would like to express our gratitude and thank you and reviewers for the time and effort in providing us with detailed comments and suggestions. Your comments are helpful, making our manuscript a much better version. These corrections have been incorporated into the revised manuscript with red highlighted. We do appreciate it.

The following table is a summary of our corrections list.

Comments Improvements

Reviewer 1: Thank you for the opportunity to review this and here are my concerns

Methods

1. 80% threshold

Would prefer to use 80% as a cutoff for “good” behavior or sufficient health literacy, domains/subdomains analysis would provide rich findings

Improvement: in lines 178-180, 183-185

-The total health literacy score was interpreted using an 80% threshold, whereby scores below 80% indicated insufficient health literacy, while scores of 80% or higher reflected a sufficient level of health literacy

-The total preventive behavior score was interpreted using an 80% threshold, whereby scores below 80% indicated poor preventive behavior, while scores of 80% or higher reflected a good level of preventive behavior

2. Specify whether subgroup analysis was done for each health literacy component (cognitive, access, decision-making, etc.) If not, this could be a limitation.

- The subgroup analysis was done for each health literacy component

3. Population considerations

The study focused on permanent residents ≥5 years. Temporary residents or migrants living near the border were excluded, but they may also be exposed to microplastics. This exclusion could bias results toward long-term community practices and miss transient or occupational exposures. We thank the reviewer for this valuable comment. The inclusion of permanent residents was a deliberate methodological choice to capture stable, community-level health literacy and preventive behaviors, which are shaped by prolonged exposure to local environmental conditions and public health communication.

Temporary residents or migrant populations were excluded because their mobility and occupational exposure profiles may differ substantially from long-term residents, potentially introducing heterogeneity that could obscure associations between health literacy and preventive behaviors.

We acknowledge that this may limit the generalizability of our findings to transient or migrant populations who may experience distinct exposure pathways. This limitation has now been explicitly addressed in the Discussion section, and future studies should specifically examine microplastic-related health literacy and behaviors among mobile and migrant groups.

4. Period of data collection

The study was conducted from January to March 2025, but behaviors like throwing plastic into rivers may be influenced by seasonal water levels or flooding risk. Consider mentioning this as a limitation: behaviors may vary across seasons. Included in the limitation of the study.

5. Subgroups by province, occupation, household size, or water source were partially analyzed. You may want to clarify whether occupational exposure, urban-rural residence, or specific economic activities were considered in detail. We thank the reviewer for this comment. Subgroup characteristics, including community type (urban, semi-urban, rural), occupation, household size, and water source, were examined in the descriptive analysis and considered in the univariable screening for multivariable models. Community type was retained as a key contextual variable and demonstrated significant associations with both health literacy and preventive behaviors.

Although occupation and economic activities were included as covariates, this study did not conduct detailed occupational exposure assessments, as its primary focus was on community-level health literacy and preventive behaviors rather than task-specific or workplace exposures. Similarly, household size and water source were evaluated as environmental and socioeconomic indicators rather than independent exposure pathways.

We have clarified this analytical scope in the Methods and Discussion sections and acknowledge that future studies incorporating detailed occupational and exposure-specific subgroup analyses would further strengthen understanding of microplastic-related risks.

Results & Discussion

1. Province differences

“Participants from Nakhon Phanom were more likely to exhibit good preventive behaviors (40.90%), whereas those from Buriram showed poorer behaviors (64.00%) (p=0.001).” Explanation: This could be due to local environmental context, socioeconomic factors, or urbanization differences.

Discussion mentions: Buriram and Maha Sarakham are near industrial zones or wastewater discharge points, leading to higher contamination. However, the study did not explore health literacy and behavior among temporary workers or industry employees, which may affect exposure and practices. From a broader perspective, these findings align with the social-ecological model of health, which posits that environmental exposures and individual behaviors are shaped by multiple factors, including community infrastructure, policy enforcement, and cultural norms. Communities located near industrial zones or wastewater discharge points—such as those in Maha Sarakham and Buriram provinces—may face higher microplastic contamination due to local environmental conditions, socioeconomic factors, and urbanization levels. This study primarily focused on residents of river basin communities, including some temporary workers and industrial employees, who may have distinct exposure patterns and health behaviors. These results are consistent with regional studies reporting greater contamination in densely populated and industrialized river systems.

2. Income differences

“Participants with good behaviors had a lower mean monthly income (8,011.51 baht) than those with poor behaviors (11,845.83 baht) (p<0.001).”

Interpretation: Lower-income individuals may adopt more conservative behaviors, possibly due to reliance on bottled water or traditional preventive practices.

Limitation: Urban-rural differences are not explicitly addressed. High-income participants may live in urbanized areas with different exposure perceptions, potentially explaining why higher income correlates with poorer preventive behavior. 1.Re-analysis and interpretation

2. We thank the reviewer for this insightful interpretation. Lower-income individuals in riverine communities may indeed adopt more conservative preventive behaviors, including reliance on bottled water and traditional household practices, which may partially explain the observed patterns.

We also acknowledge that income is closely intertwined with urban–rural residence. Higher-income participants were more likely to reside in urbanized areas, where perceptions of environmental risk and reliance on infrastructure may differ, potentially contributing to poorer reported preventive behaviors despite greater economic resources.

This contextual interpretation has now been explicitly addressed in the Discussion section. However, as this study did not formally model interaction effects between income and community type, these findings should be interpreted with caution. Future studies examining urban–rural and income-related interactions may provide further clarification.

3. Water source and health literacy

“Participants who primarily consumed filtered water or bottled water were more likely to exhibit poor health literacy (adj.OR = 3.85 and 3.68, p<0.05).”

Possible explanation: People relying on bottled or filtered water may perceive themselves as protected, reducing motivation to learn about microplastic risks. This contrasts with those using river or tap water, who may actively seek preventive knowledge and actions. Also related to previous statement, perhaps, For example, high-income family may be able to purchase clean bottled water compared to low-income. Please refine all of these issues in discussion

We thank the reviewer for this insightful suggestion. The observed association between reliance on bottled or filtered water and poorer health literacy may reflect a perception of sufficient protection, which could reduce motivation to actively seek information or engage in broader microplastic risk awareness.

This pattern may also be linked to socioeconomic and urban contexts, as higher-income households are more able to access bottled or filtered water and may rely on technological or commercial solutions rather than personal preventive knowledge. In contrast, individuals using river or tap water may perceive greater exposure risk, prompting more active engagement in preventive knowledge and behaviors.

We have refined the Discussion to integrate water source, income, and urban–rural context as interconnected factors influencing health literacy and risk perception.

4. Also related to reported respiratory illness, I am not sure whether this was direct/indirect effect of microplastic or due to the air pollution during the data collection period? please clarify. We appreciate the reviewer’s important clarification. The reported respiratory illness in this study was self-reported and not intended to indicate a direct or causal effect of microplastic exposure. Given the cross-sectional design, it is not possible to distinguish whether respiratory symptoms were related to microplastics, other environmental exposures, or background air pollution during the data collection period.

We acknowledge that seasonal air pollution, including particulate matter, may have contributed to respiratory symptoms and could act as a confounding factor. This has now been explicitly clarified in the Discussion section, and the findings are interpreted cautiously as associative rather than causal.

5. Table 1 discrepancy

Drinking water counts:

Filtered water: Good = 323, Poor = 28 → total should be 351, not 260. This appears to be a data entry or calculation error and should be corrected. Re-analysis and reinterpreted

Reviewer #2: Thank you for your submitted this manuscript on health literacy and preventive behaviors toward microplastic contamination in Northeastern Thailand. The topic is timely and relevant to environmental health. However, after careful evaluation, I have identified several critical issues that fundamentally undermine the validity and reliability of the study findings. These concerns span from internal contradictions in the results to methodological flaws that cannot be adequately addressed through minor revisions.

1. Fatal Inconsistency in Results

The manuscript contains fundamental contradictions that invalidate the main conclusions:

- The mean health literacy score is classified as "good level" (2.38±0.49), yet 70.5% of participants are categorized as having "insufficient" health literacy

- Despite 70.5% having insufficient literacy, 86.7% demonstrate good preventive behaviors. This directly contradicts the conclusion that literacy is the primary determinant of behavior

- This inconsistency renders the study's conclusions unreliable and questions the validity of the classification system

- The manuscript fails to acknowledge or explain this paradox, which is central to understanding the relationship between literacy and behavior

We thank the reviewer for highlighting this important issue. We acknowledge that, without clarification, the results may appear contradictory. However, this pattern reflects differences between aggregate mean scores and domain-based classification rather than a methodological inconsistency.

The mean health literacy score represents an overall average across domains, whereas the classification of “insufficient health literacy” is based on domain-specific cut-offs, particularly in higher-order domains such as critical appraisal and decision-making. Many participants demonstrated adequate functional or interactive literacy, which elevated the mean score, but remained insufficient in higher-level domains, resulting in classification as insufficient health literacy.

Similarly, the high prevalence of good preventive behaviors reflects the influence of contextual and environmental factors, including community norms and habitual practices, which may operate independently of comprehensive health literacy. Health literacy remained a strong and independent predictor of preventive behavior in multivariable analysis, but it should not be interpreted as the sole determinant.

We have revised the Results and Discussion sections to explicitly acknowledge and explain this apparent paradox and to clarify the interpretation of health literacy classification and behavioral outcomes.

2. Severe Methodological Flaws

Multiple design issues compromise the study's validity:

- Purposive sampling at Stage 1 (province selection) introduces selection bias findings cannot be generalized to "major river basins of Northeastern Thailand" as claimed

- Inadequate instrument validation: Only Cronbach's α is reported; missing content validity, construct validity, and factor analysis for this novel "microplastic health literacy" scale

- Inappropriate causal inference: Cross-sectional design but employs language suggesting causality (e.g., "predictors") temporal relationships cannot be established

- Social desirability bias: Face-to-face interviews likely inflated self-reported good behaviors (86.7% seems unrealistically high given 70.5% insufficient literacy)

We acknowledge the reviewer’s concern regarding purposive sampling at the province selection stage. Provinces were intentionally selected to represent diverse major river basins and community contexts rather than to achieve statistical representativeness. Therefore, the findings should be interpreted as reflective of riverine communities within selected basins rather than generalizable to all populations in Northeastern Thailand.

We have revised the Methods and Discussion sections to clarify the sampling rationale and to appropriately limit the scope of inference.

3. Critical Statistical Analysis Problems

The statistical models demonstrate poor quality and questionable validity:

- Hosmer-Lemeshow test: p=0.036 (p<0.05) = model does not fit the data adequately

- Nagelkerke R² = 0.363 and 0.194 (explaining only 36% and 19% of variance) = critical confounding variables are missing from the models

- Provincial OR=70.54 (95% CI: 25.48-195.27) is abnormally high → suggests multicollinearity, small cell counts, or model misspecification

- No diagnostic checks reported: Missing VIF (variance inflation factor), Cook's distance, or other diagnostic tests to assess model assumptions Re-grouping in some variable and re-analyses

4. Conclusions Inconsistent with Evidence

The manuscript's conclusions do not align with the presented data:

- Authors claim literacy plays a "crucial role," but evidence shows structural factors (province) have far greater influence (OR=70.54 vs. OR=5.18 for literacy)

- The Discussion (Lines 301-307) acknowledges behaviors may be driven by "cultural habits or public health campaigns" this directly contradicts the main conclusion emphasizing individual literacy

- Limited novel contribution: This is a descriptive-correlational study without novel mechanisms or theoretical advancement Rewrite

5. Absence of Critical Limitations Section

The manuscript fails to acknowledge fundamental limitations:

- Cross-sectional design precludes causal inference between literacy and behavior

- Selection bias from purposive sampling limits generalizability

- Social desirability bias may inflate self-reported behaviors

- Poor model fit indicates important unmeasured confounders

- Novel instrument lacks comprehensive validation in the target population

- Self-reported behaviors may not reflect actual practices Rewrite

Reviewer #3: Suggestions for major revisions

Abstract

The results in the abstract require clarification. The authors state that overall health literacy toward microplastic contamination was at a good level (mean = 2.38 ± 0.49), yet 70.50% of participants had insufficient health liter

Attachment

Submitted filename: response.pdf

pone.0344784.s001.pdf (234KB, pdf)

Decision Letter 1

Phuping Sucharitakul

16 Feb 2026

Dear Dr. Phoosuwan,

Please submit your revised manuscript by Apr 02 2026 11:59PM. If you will need more time than this to complete your revisions, please reply to this message or contact the journal office at plosone@plos.org . When you're ready to submit your revision, log on to https://www.editorialmanager.com/pone/ and select the 'Submissions Needing Revision' folder to locate your manuscript file.

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We look forward to receiving your revised manuscript.

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Phuping Sucharitakul

Academic Editor

PLOS One

Journal Requirements:

If the reviewer comments include a recommendation to cite specific previously published works, please review and evaluate these publications to determine whether they are relevant and should be cited. There is no requirement to cite these works unless the editor has indicated otherwise.

Please review your reference list to ensure that it is complete and correct. If you have cited papers that have been retracted, please include the rationale for doing so in the manuscript text, or remove these references and replace them with relevant current references. Any changes to the reference list should be mentioned in the rebuttal letter that accompanies your revised manuscript. If you need to cite a retracted article, indicate the article’s retracted status in the References list and also include a citation and full reference for the retraction notice.

[Note: HTML markup is below. Please do not edit.]

Reviewers' comments:

Reviewer's Responses to Questions

Comments to the Author

Reviewer #2: (No Response)

**********

2. Is the manuscript technically sound, and do the data support the conclusions??>

Reviewer #2: Yes

**********

3. Has the statistical analysis been performed appropriately and rigorously? -->?>

Reviewer #2: Yes

**********

4. Have the authors made all data underlying the findings in their manuscript fully available??>

The PLOS Data policy

Reviewer #2: Yes

**********

5. Is the manuscript presented in an intelligible fashion and written in standard English??>

Reviewer #2: Yes

**********

Reviewer #2: The authors have responded carefully and appropriately to the comments raised in the previous round of review. The revisions have substantially improved the clarity of the methodology, the transparency of the statistical analyses, and the alignment between the results and the conclusions.

The study design is appropriate for the research objectives, and the data collection procedures and sample size are adequate. The statistical analyses are suitable for the type of data and are conducted with sufficient rigor. Effect estimates and measures of uncertainty are clearly reported, and the interpretation of findings is consistent with the cross-sectional nature of the study. Importantly, the authors have avoided causal overinterpretation and have clearly acknowledged the key limitations of the study.

The manuscript is generally well written and logically structured. The presentation of results is clear, and tables and figures are informative. A small number of minor language and editorial issues remain, particularly in the Discussion section, where conciseness and consistency of terminology could be further improved. These issues are minor and do not affect the validity or overall contribution of the study.

I did not identify any concerns related to research ethics, conflicts of interest, dual publication, or publication ethics. Ethical approval and informed consent procedures are adequately described, and the data availability statement is consistent with journal policy.

Overall, the manuscript is technically sound and has been revised to a standard that is appropriate for publication. Only minor editorial refinements are recommended before final acceptance.

**********

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Reviewer #2: No

**********

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PLoS One. 2026 Mar 6;21(3):e0344784. doi: 10.1371/journal.pone.0344784.r004

Author response to Decision Letter 2


22 Feb 2026

Dear Editor,

Thank you for the opportunity to revise our manuscript. We would like to express our gratitude and thank you and the reviewers for the time and effort in providing us with detailed comments and suggestions. Our corrections have been incorporated into the revised manuscript with red highlighted. Please see our response below.

Journal Requirements:

Please review your reference list to ensure that it is complete and correct. If you have cited papers that have been retracted, please include the rationale for doing so in the manuscript text, or remove these references and replace them with relevant current references. Any changes to the reference list should be mentioned in the rebuttal letter that accompanies your revised manuscript. If you need to cite a retracted article, indicate the article’s retracted status in the References list and also include a citation and full reference for the retraction notice.

Response: We have thoroughly reviewed the reference list to ensure accuracy and completeness. All cited articles were screened against recognized retraction databases (Retraction Watch, PubMed, and Crossref), and none were found to be retracted. In addition, several references have been updated to incorporate recent high-impact publications (2023–2024), and corresponding citation numbering has been revised throughout the manuscript.

Reviewers' comments:

Reviewer 2

Comments to the Author

1. If the authors have adequately addressed your comments raised in a previous round of review and you feel that this manuscript is now acceptable for publication, you may indicate that here to bypass the “Comments to the Author” section, enter your conflict of interest statement in the “Confidential to Editor” section, and submit your "Accept" recommendation.

Reviewer #2: (No Response)

2. Is the manuscript technically sound, and do the data support the conclusions?

The manuscript must describe a technically sound piece of scientific research with data that supports the conclusions. Experiments must have been conducted rigorously, with appropriate controls, replication, and sample sizes. The conclusions must be drawn appropriately based on the data presented.

Reviewer #2: Yes

3. Has the statistical analysis been performed appropriately and rigorously?

Reviewer #2: Yes

4. Have the authors made all data underlying the findings in their manuscript fully available?

The PLOS Data policy requires authors to make all data underlying the findings described in their manuscript fully available without restriction, with rare exception (please refer to the Data Availability Statement in the manuscript PDF file). The data should be provided as part of the manuscript or its supporting information, or deposited to a public repository. For example, in addition to summary statistics, the data points behind means, medians and variance measures should be available. If there are restrictions on publicly sharing data—e.g. participant privacy or use of data from a third party—those must be specified.

Reviewer #2: Yes

5. Is the manuscript presented in an intelligible fashion and written in standard English?

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Reviewer #2: Yes

6. Review Comments to the Author

Reviewer #2: The authors have responded carefully and appropriately to the comments raised in the previous round of review. The revisions have substantially improved the clarity of the methodology, the transparency of the statistical analyses, and the alignment between the results and the conclusions.

The study design is appropriate for the research objectives, and the data collection procedures and sample size are adequate. The statistical analyses are suitable for the type of data and are conducted with sufficient rigor. Effect estimates and measures of uncertainty are clearly reported, and the interpretation of findings is consistent with the cross-sectional nature of the study. Importantly, the authors have avoided causal overinterpretation and have clearly acknowledged the key limitations of the study.

The manuscript is generally well written and logically structured. The presentation of results is clear, and tables and figures are informative. A small number of minor language and editorial issues remain, particularly in the Discussion section, where conciseness and consistency of terminology could be further improved. These issues are minor and do not affect the validity or overall contribution of the study.

Response: We appreciate the reviewer’s helpful comments. The Discussion section has been edited to improve conciseness and reduce minor repetition. In addition, terminology has been standardized throughout the manuscript to ensure consistency and clarity. These refinements have further enhanced the overall presentation of the study.

I did not identify any concerns related to research ethics, conflicts of interest, dual publication, or publication ethics. Ethical approval and informed consent procedures are adequately described, and the data availability statement is consistent with journal policy.

Overall, the manuscript is technically sound and has been revised to a standard that is appropriate for publication. Only minor editorial refinements are recommended before final acceptance.

Attachment

Submitted filename: 21022026 comments.pdf

pone.0344784.s002.pdf (89.1KB, pdf)

Decision Letter 2

Phuping Sucharitakul

26 Feb 2026

Health literacy and preventive behaviors toward microplastic contamination among communities in the major river basins of northeastern Thailand

PONE-D-25-57984R2

Dear Dr. Phoosuwan,

We’re pleased to inform you that your manuscript has been judged scientifically suitable for publication and will be formally accepted for publication once it meets all outstanding technical requirements.

Within one week, you’ll receive an e-mail detailing the required amendments. When these have been addressed, you’ll receive a formal acceptance letter and your manuscript will be scheduled for publication.

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Kind regards,

Phuping Sucharitakul

Academic Editor

PLOS One

Additional Editor Comments (optional):

Reviewers' comments:

Acceptance letter

Phuping Sucharitakul

PONE-D-25-57984R2

PLOS One

Dear Dr. Phoosuwan,

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Academic Editor

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Associated Data

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    Supplementary Materials

    Attachment

    Submitted filename: response.pdf

    pone.0344784.s001.pdf (234KB, pdf)
    Attachment

    Submitted filename: 21022026 comments.pdf

    pone.0344784.s002.pdf (89.1KB, pdf)

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