Tracing Sources and Stage‐Specific Impacts of Heavy Metal Contamination in Farmed Tilapia (Oreochromis niloticus): Implications for Human Health Risk

Abstract

Objective

The levels of five heavy metals—zinc (Zn), lead (Pb), chromium (Cr), cadmium (Cd) and arsenic (As)—in soil, water, feed and fish were investigated in this study at different culture phases (early, nursery, grower and harvest) of Oreochromis niloticus (tilapia). Unlike previous studies that focused on one or two sources, this research provides a comprehensive assessment across all major inputs during the entire production cycle, offering new insight into potential contamination pathways.

Results

Heavy metal accumulation varied across sources and stages. Cr and As in sediment, and Cr in feed at the early stage, exceeded the permissible boundaries set by the Food and Agriculture Organization (FAO) and the World Health Organization (WHO). As the culture progressed, sediment showed increasing levels of Pb, Cr and As, all surpassing safe thresholds during the nursery to harvest phases. Feed also retained elevated Cr concentrations throughout. In contrast, water samples showed minimal contamination, and heavy metal levels in fish stayed within acceptable bounds for human consumption, although Zn and Cr gradually increased toward harvest. These findings suggest that sediment and feed are the primary sources of heavy metal accumulation, with water contributing minimally.

Conclusion

The results indicate that tilapia raised in contaminated environments may not pose an immediate risk to consumers, but long‐term exposure through sediment and feed can lead to gradual metal build‐up. Therefore, routine monitoring of feed quality and sediment conditions is critical for safe aquaculture practices. These findings offer valuable guidance for hatchery operators and fish farmers, emphasising the need for preventive strategies to ensure the sustainable and safe production of tilapia.

The results indicate that tilapia raised in contaminated environments may not pose an immediate risk to consumers, but long‐term exposure through sediment and feed can lead to gradual metal build‐up. Therefore, routine monitoring of feed quality and sediment conditions is critical for safe aquaculture practices. These findings offer valuable guidance for hatchery operators and fish farmers, emphasising the need for preventive strategies to ensure the sustainable and safe production of tilapia.

1. Introduction

Pollution of waterways by various pollutants has become a significant global environmental issue, posing threats to biodiversity, ecosystem health, and human safety (Lin et al. 2022). Among these pollutants, heavy metals (HMs) are of particular concern due to their toxicity, persistence and bio‐accumulative nature (Kahal et al. 2020; Ghafarifarsani et al. 2024). Aquatic environments are polluted by HMs such as arsenic (As), chromium (Cr), cadmium (Cd), lead (Pb) and zinc (Zn) from both natural sources like rock weathering and erosion, and human activities like improper waste disposal, agricultural runoff and industrial emissions. According to Kang et al. (2019), Akindele et al. (2020), and Liu et al. (2020), factors like pH, temperature and salinity can affect how easily these metals move and how available they are, making it harder to clean up the contamination. The presence of HMs in aquatic environments threatens the health of fish and other aquatic living things by disrupting physiological and biochemical functions (Ullah et al. 2019; Taslima et al. 2022). Such toxic effects can reduce fish growth, reproduction and survival rates, ultimately impacting aquaculture productivity and ecosystem balance. In addition, HMs build up in fish tissues, and eating contaminated fish can seriously harm human health, as these metals can collect in important organs like the liver, kidneys and bones, leading to long‐term health issues such as cancer, brain problems and organ damage. Given the critical role of fish as a primary source of animal protein and essential nutrients for millions worldwide (El‐Sorogy et al. 2018; Ali et al. 2020), understanding and managing HM contamination is vital for food safety and public health.

In Bangladesh, tilapia (Oreochromis niloticus) has gained popularity as an affordable and accessible source of high‐quality protein and essential minerals such as iron, calcium, zinc, magnesium and sodium (Job et al. 2015; Rahman et al. 2021). Its widespread farming and consumption, particularly among low‐income populations, have led to the nickname ‘fish for all’ (Rahman et al. 2021). Despite its economic and nutritional importance, there is limited comprehensive data on the extent and dynamics of HM contamination in tilapia farms, especially regarding how contamination levels vary across different culture phases and environmental sources. Most existing research tends to focus on singular components—either the fish tissue or water quality—without integrating data from feed, sediment and water throughout the production cycle. This fragmented approach limits understanding of contamination pathways and hinders the development of effective intervention strategies. Furthermore, many studies rely on outdated or regionally narrow data, leaving a gap in up‐to‐date, holistic assessments in key aquaculture areas. To address these gaps, this study conducts a thorough assessment of Zn, Cd, Cr, Pb and As concentrations in tilapia and its surrounding environment—including feed, water and sediment—across various culture stages (early, nursery, grower and harvest) at a major fish farm in Trishal, Mymensingh district, Bangladesh. This region is a leading centre for tilapia production, so the findings are especially relevant for national aquaculture practices. In addition, the study evaluates human health risks by calculating hazard indices such as target hazard quotient (THQ), lifetime cancer risk (TR) and hazard index (HI), which offer important information about the safety of consuming farmed tilapia from this area. The results aim to guide farmers, hatchery operators and policymakers in adopting safer and more sustainable aquaculture practices, ultimately protecting consumer health and supporting the growth of Bangladesh's aquaculture industry.

2. Materials and Methods

2.1. Study Site

Tilapia of different stages (nursery, grower and harvest) were taken from a well‐known fish farm (Biswas Hatchery and Agro Fishery Ltd.) in Trishal, Mymensingh, Bangladesh (Figure 1). The average temperature of the pond water was between 28°C and 30°C during the experiment. Digestion of the fish sample and analysis of HMs were carried out at Bangladesh Agricultural University (BAU), Bangladesh, which has two laboratories—the Laboratory of Fish Nutrition and the Multidisciplinary Institute for Food Security (IIFS) Laboratory.

FIGURE 1.

Study area.

2.2. Sample Collection

Fish, feed, water and sediment were collected at four (3, 33, 93 and 153 days) different times of the total tilapia culture period. Bottom sediment, pond water, feed and fish were collected in polyethylene bags, fresh new plastic bottles, plastic jars and oxygenated polyethylene bags, respectively. From each pond, we collected 3 fish and used the average result from these fish. We also collected the sediment in a polybag. Each polybag contains 500 g of sediment on a wet basis. After air drying, we used these sediments for our analysis. The research farm used commercial Biswas floating feed, and we collected the feed from their feed bag, which they used in their experimental pond.

2.3. Preparing the Sample

Sediment and feed samples were air‐dried in the Fish Nutrition laboratory, BAU. After proper drying, the samples were finely ground. Fish samples were cut into small pieces, oven‐dried at 105°C for 24 h and ground finely. Next, 1.0 g of each sediment, feed and fish sample was placed into a micro Kjeldahl flask. Using an electrothermal heater, 5 mL of perchloric acid and 10 mL of nitric acid were added to the flask, which was then heated to 80°C for 25–30 min. Finally, the digested samples were cooled down at room temperature. The required amount of distilled water was added to get the volume up to 100 mL. The prepared solutions were then filtered using Whatman no. 42 filter paper and stored in airtight plastic bottles for later analysis. However, clean plastic bottles were used to collect water samples after being rinsed two to three times with pond water. After passing through Whatman filter paper number 42, the water was stored in an airtight plastic bottle.

2.4. Blank Preparation

All of the same digestive reagents and acid ratios were present in the blank solution as in the original samples. The same procedure was followed for the blank solution preparation of the sediment, water and feed. These blank solutions were used to check whether impurities from other chemicals influence the accuracy of the result. The measured blank value by AAS was subtracted from every sample value to get the actual value.

2.5. Method Validation, Accuracy Check and Sample Analysis

The Shimadzu AA‐7000 type flame atomic absorption spectrophotometer was used to measure the amounts of HMs. Acetylene gas served as the fuel, while compressed air acted as the oxidiser during the analysis. Metal concentrations were quantified based on calibration curves prepared from standard solutions, following the manufacturer's instructions. The analytical protocol was carried out in compliance with EC567/2002 standards. To ensure precise metal detection, hollow cathode lamps specific to Zn, Cd, Cr, As and Pb were used, operating at wavelengths of 213.9, 228.8, 357.9, 193.7 and 283.3 nm, respectively. Each sample was analysed in triplicate to determine the average concentration of metals. Once calibration curves were established, the limits of detection (LOD) for each metal were calculated. The accuracy of the analytical process was verified using certified reference materials, including DORM‐4 (fish protein) provided by BCR‐142Q (sewage sludge amended soil) from the Community Bureau of Reference. The measured values showed strong agreement with certified standards, with recovery rates ranging between 90% and 98%. All reagents and chemicals used in the process were of analytical grade to maintain the reliability of the results.

2.6. Analysis of HM Concentration

The samples' HMs concentration was analysed using the GFAAS technique. To analyse the sample, standard solutions were made for GFAAS. In Graphite Furnace Atomic Absorption Spectroscopy (GFAAS), the samples were placed into small graphite tubes that were either uncoated or coated with pyrolytic carbon. The samples were then placed in GFAAS and converted into atomic vapours by the atomisation process. The calibration curves derived from the standard solutions were used to calculate the metal concentration. The average results of three replicate samples served as the basis for each determination.

2.7. Human Health Risk Assessment

To determine each HM's THQ, a scientific formula was used; Equation 1 by USEPA (2010) to assess the potential health risk.

$$\mathrm{THQ}=\frac{E_D\times F_{\mathrm{IR}}\times E_F\times C_i}{R_{\mathrm{FD}}\times W_{\mathrm{AB}}\times T_A}\times {10}^{-3}$$ (1)

Where, as per USEPA (2010), E_D stands for exposure duration (average life span, 72.32 years), F _IR for daily ingestion rate (2.43 gm/person/day, based on an online survey with 5000 respondents nationwide), E_F for exposure frequency (365 days/year), C_i for concentration of the respective HM (mg/kg), R _FD for reference oral dose in mg/kg/day (0.001 for Cd, 0.004 for Pb, 1.5 for Cr, 0.3 for Zn and 0.001 for As), W _AB for average body weight for an adult consumer (54.6 kg for Bangladesh, according to the online based survey) and T_A for average exposure time, calculated as E_D × E_F .

The overall HI was calculated using following formula (Equation 2) according to USEPA (2010)

$$\mathrm{HI}=\mathrm{TH}{\mathrm{Q}}_{\mathrm{Zn}}+\mathrm{TH}{\mathrm{Q}}_{\mathrm{Cd}}+\mathrm{TH}{\mathrm{Q}}_{\mathrm{Cr}}+\mathrm{TH}{\mathrm{Q}}_{\mathrm{As}}+\mathrm{TH}{\mathrm{Q}}_{\mathrm{Pb}}+\mathrm{TH}{\mathrm{Q}}_{\mathrm{Ni}}$$ (2)

where Cd, Cr, As and Pb were identified as strong carcinogens among the HMs that were examined. To estimate the potential cancer risk from the identified HMs, the following equation was applied. (Equation 3; Bonsignore et al. 2018):

$$\mathrm{TR}=\frac{E_D\times F_{\mathrm{IR}}\times E_F\times C_i\times C_{\mathrm{SF}}}{W_{\mathrm{AB}}\times T_A}\times {10}^{-3}$$ (3)

The cancer slope factor (CSF) values used in this study were obtained from the USEPA (2010) for cadmium (6.3 mg/kg/day) and lead (0.0085 mg/kg/day), while the values for arsenic (0.91 mg/kg/day) and chromium (0.5 mg/kg/day) were sourced from Zeng et al. (2015). The detailed schematic illustration of HMs analysis and related health risks is shown in Figure 2.

FIGURE 2.

Schematic illustrations of heavy metals analysis and associated health issues.

2.8. Data Processing

The HM concentration data collected throughout the study were examined using one‐way ANOVA to identify significant changes over time. Any difference with a p value below 0.05 was deemed statistically significant. For all statistical computations, Microsoft Excel 2010 was used.

3. Results

3.1. Concentration of Toxic Metals

To clarify the statistical significance of the results, we have used one‐way Analysis of Variance (ANOVA) to assess the variation in HM concentrations across different culture stages in sediment, water, feed and fish samples. The results section of the updated paper makes it explicit that the significant differences were calculated at the 95% confidence level (p < 0.05). Each metal's concentration showed statistically significant variation over time, with distinct trends across different sample types. Superscript letters (a, b, c, d) have been used in Table 1 to indicate statistically different means, allowing easy comparison among stages. We have also emphasised the highest and lowest values observed and their respective stages to better reflect the pattern of changes in metal concentrations. These revisions aim to improve the clarity and interpretation of our statistical findings.

TABLE 1.

Heavy metal concentration in sediment, water, feed and fish at different stages of tilapia's culture period (3–153 days age of fish).

Elements	Days	Zn	Cd	Cr	Pb	As
Sediment	03	7.34 ± 0.43a	0.13 ± 0.01a	0.47 ± 0.02a	0.68 ± 0.01a	1.35 ± 0.01a
	33	8.16 ± 1.48a	0.26 ± 0.01b	0.58 ± 0.01b	2.07 ± 0.01b	1.68 ± 0.02b
	93	8.25 ± 2.22a	0.30 ± 0.01c	1.11 ± 0.01c	4.36 ± 0.01c	1.83 ± 0.03c
	153	16.26 ± 0.11b	0.46 ± 0.01d	1.35 ± 0.01d	5.6 ± 0.01d	1.90 ± 0.02d
p value
Level of significance		0.000 **	0.000*	0.000 **	0.000 **	0.000 **
Water	03	0.00 ± 0.00a	0.00 ± 0.00a	0.04 ± 0.04	0.15 ± 0.02ab	0.00 ± 0.00a
	33	0.00 ± 0.00a	0.00 ± 0.00a	0.06 ± 0.03	0.09 ± 0.08a	0.00 ± 0.00a
	93	0.03 ± 0.01b	0.01 ± 0.01a	0.06 ± 0.05	0.05 ± 0.01a	0.00 ± 0.00a
	153	1.47 ± 0.01c	0.30 ± 0.01b	0.06 ± 0.03	0.20 ± 0.06b	0.04 ± 0.02b
p value
level of significance		0.000 **	0.000 **	0.858S	0.039 **	0.001 **
Feed	03	6.15 ± 1.71a	0.01 ± 0.01a	0.53 ± 0.01a	0.00 ± 0.00a	0.00 ± 0.00a
	33	6.59 ± 2.05a	0.27 ± 0.02c	0.62 ± 0.01b	0.00 ± 0.00a	0.00 ± 0.00a
	93	9.73 ± 0.19b	0.29 ± 0.01d	0.64 ± 0.02b	0.90 ± 0.01b	0.03 ± 0.01b
	153	6.79 ± 0.10a	0.25 ± 0.01b	0.68 ± 0.01c	0.00 ± 0.00a	0.00 ± 0.00a
p value
level of significance		0.055 **	0.000 **	0.000 **	0.000 **	0.000 **
Fish	03	8.74 ± 1.02a	0.00 ± 0.00a	0.00 ± 0.00a	0.00 ± 0.00a	0.00 ± 0.00a
	33	11.33 ± 1.01b	0.03 ± 0.01b	0.00 ± 0.00a	0.00 ± 0.00a	0.00 ± 0.00a
	93	14.2 ± 0.47c	0.04 ± 0.01b	0.00 ± 0.00a	0.00 ± 0.00a	0.00 ± 0.00a
	153	17.84 ± 1.65d	0.25 ± 0.02c	0.02 ± 0.01b	0.35 ± 0.01b,	0.01 ± 0.01a
p value
level of significance		0.000 **	0.000 **	0.000 **	0.000 **	0.095NS

Note: There is no significant (p < 0.05) difference between columns in the table that have the same letter.

^**The mean difference is significant at the 0.05 level.

The minimum, maximum and average values of HMs (Zn, Cr, Cd, Pb and As) in sediment, water, feed and fish at different culture periods of tilapia were determined in Trishal, Mymensingh (Table 1, Figures 3, 4, 5, 6). Furthermore, Table 2 presents a comparison of the concentration of HMs (mg/kg) in this work with those in earlier Bangladeshi investigations, along with their respective safety limits. The ANOVA results showed that in sediment, the abundance of Zn, Cd, Cr, Pb and As has increased with the experiment days and varied significantly (p < 0.05). Among all these elements, Zn exhibited the highest abundance in sediment on the final day (16.26 ± 0.11), whereas it contained the lowest mean concentration of Cr (0.46 ± 0.01). In the case of water, all the elements showed a significant (p < 0.05) increase over the experiment, except for Cr. Similar to the sediment on the final day, Zn (1.47 ± 0.01) is the most abundant element found in water as well, while the lowest is As (0.04 ± 0.02). In the feed, the abundance of all elements increased until the 93rd day but reduced on the final day, except for Cr, but all the elements showed significant variation (p < 0.05). Like sediment and water findings, Zn showed the highest mean concentration (6.79 ± 0.10) in feed as well. Pb and As weren't found in the feed on the final day. In fish, all elements showed a significant (p < 0.05) increase over the experiment days except for As. Like all other samples, Zn (1.47 ± 0.01) was the most abundant element found in fish as well, but the lowest mean concentration was of As (0.01 ± 0.01) on the final day.

FIGURE 3.

Average heavy metals (Zn, Cd, Cr, Pb and As) concentration (mg/kg) of sediment during 30, 60, 90 and 120 days of culture period of tilapia.

FIGURE 4.

Average heavy metals (Zn, Cd, Cr, Pb and As) concentration (mg/kg) of water during 30, 60, 90 and 120 days of culture period of tilapia.

FIGURE 5.

Average heavy metals (Zn, Cd, Cr, Pb and As) concentration (mg/kg) of feed during 30, 60, 90 and 120 days of culture period of tilapia.

FIGURE 6.

Average heavy metals (Zn, Cd, Cr, Pb and As) concentration (mg/kg) of fish during 30, 60, 90 and 120 days of culture period of tilapia.

TABLE 2.

Comparison of the determined concentrations of heavy metals in farmed fish of Mymensingh with other studies in Bangladesh as well as around the world.

Study area		Measured heavy metals concentration (mg/kg) in the present study together with the reported literature and other standards in different geographic location
		Zn	Cr	Pb	Cd	As	References
Trishal	1st stage	7.8505 ± 1.21	NF	NF	NF	NF	This study
	2nd stage	13.4027 ± 1.21	0.0235 ± 0.01	NF	NF	NF
	3rd stage	14.0312 ± 1.21	0.0365 ± 0.01	NF	NF	NF
	4th stage	18.0859 ± 1.21	0.2507 ± 0.01	0.0196 ± 0.02	0.3612 ± 0.01	0.0154 ± 0.01
Karnaphuli River Estuary		31.54–1458.68	0.059–1.605	0.025–0.385	NA	NA	Mohiuddin et al. (2022)
Laxmipur, Noakhali		31.1–50.5	BDL	4.4–8.0	0.04–0.08	NA	Hossain et al. (2022)
Noakhali fish market		89.91–142.78	BDL ‐9.685	0.202–0.68	NA	NA	Hossain et al. (2022)
Southern Part of Bangladesh		NA	4.71–8.98	4.35–8.03	0.87–1.35	0.17–0.28	Saha et al. (2021)
Bangshi River		42.83–418.1	0.47–2.07	1.76–10.27	NA	NA	Rahman et al. (2012)
Meghna River Estuary		NA	0.62–1.19	2.76–4.63	NA	NA	Ahmed et al. (2015)
WHO Safe limit		100	1.0	2.0	1.0	1.0	World Health Organization (1989)
FAO Safe limit		100	1.0	1‐5	2.0	1.0	Food and Agricultural Organization (1983)
EU Safe limit			1.0	5.0	2.0	1.0	European Union (2001)

3.2. Zn Concentration

The average Zn concentration (mg/kg) in the early stage in sediment, water, feed and fish was 7.34 ± 7.34 ± 0.43^a, 0.00 ± 0.00^a, 6.15 ± 1.71^a and 8.74 ± 1.02^a, respectively (Table 1), while the Zn concentration at the nursery stage in the above‐mentioned samples was 8.16 ±  8.16 ± 1.48^a, 0.00 ± 0.00^a, 6.15 ± 1.71^a and 8.74 ± 1.02^a, respectively (Table 1). However, Zn concentrations in the grower stage in sediment, water, feed and fish were 8.25 ± 8.25 ± 2.22^a, 0.03 ± 0.01^b, 9.73 ± 0.19^b and 14.2 ± 0.47^c, respectively (Table 1), and at the harvest stage were 16.26 ± 0.11^b, 1.47 ± 0.01^c, 6.79 ± 0.10^a and 17.84 ± 1.65^d, respectively (Table 1). The highest Zn concentrations in sediment (16.26 ± 0.11^b), water (1.47 ± 0.01^c) and fish (17.84 ± 1.65^d) were observed in the harvest stage, while in feed, the highest (9.73 ± 0.19^b) was found at the grower stage. The lowest Zn concentration in sediment (7.34 ± 7.34 ± 0.43^a) was found in the early stage and in water (0.00 ± 0.00^a) in the grower stage, and was not detected in water in the early and nursery stages. In fish and feed, the lowest amount of Zn in fish (8.74 ± 1.02^a) and feed (6.15 ± 1.71^a) was found in the early stage.

3.2.1. Cd Concentration

The average Cd concentrations (mg/kg) at the early stage in sediment, water, feed and fish were 0.13 ± 0.01^a, 0.00 ± 0.00^a, 0.01 ± 0.01^a and 0.00 ± 0.00^a, respectively (Table 1), while Cd concentrations at the nursery stage in the above‐mentioned samples were 0.26 ± 0.01^b, 0.00 ± 0.00^a, 0.27 ± 0.02^c and 0.03 ± 0.01^b, respectively (Table 1). However, average Cd concentrations in the grower stage in sediment, water, feed and fish were 0.30 ± 0.01^c, 0.01 ± 0.01^a, 0.29 ± 0.01^d and 0.04 ± 0.01^b, respectively (Table 1), and at the harvest 0.46 ± 0.01^d, 0.30 ± 0.01^b, 0.25 ± 0.01^b and 0.68 ± 0.01^c, respectively (Table 1). The highest Cd concentrations in sediment (0.46 ± 0.01^d), water (0.30 ± 0.01^b) and fish (0.25 ± 0.02^c) were found in the harvest stage, while the highest concentration in feed (0.29 ± 0.01^d) was found in the grower stage. The lowest Cd concentration in sediment (0.13 ± 0.01^a) was found in the early stage, and in water in the grower stage (0.01 ± 0.01^a). However, Cd was not found in the early and nursery stages. In fish, the lowest Cd (0.03 ± 0.01^b) concentration was found in the nursery stage, while in feed, the lowest (0.01 ± 0.01^a) Cd concentration was found in the early stage.

3.2.2. Cr Concentration

The average Cr concentrations in sediment, water, feed and fish at the early stage were 0.47 ± 0.02^a, 0.04 ± 0.04, 0.53 ± 0.01^a and 0.00 ± 0.00^a, respectively (Table 1). At the nursery stage, Cr concentrations in sediment, water, feed and fish were 0.58 ± 0.01^b, 0.06 ± 0.03, 0.62 ± 0.01^b and 0.00 ± 0.00^a, respectively (Table 1). In the grower and harvest stages, the average Cr concentrations in sediment, water, feed and fish were 1.11 ± 0.01^c, 0.06 ± 0.05, 0.64 ± 0.02^b and 0.00 ± 0.00^a, respectively (Table 1), and 1.35 ± 0.01^d, 0.06 ± 0.03, 0.68 ± 0.01^c and 0.02 ± 0.01^b, respectively (Table 1). The highest Cr concentrations in sediment (1.35 ± 0.01^d), in water (0.06 ± 0.03), in fish (0.02 ± 0.01^b) and in feed (0.68 ± 0.01^c) were found in the harvest stage. However, the lowest Cr concentration in sediment (0.47 ± 0.02^a) and in water (0.04 ± 0.04) was found in the early stage and the nursery stage, respectively.

3.2.3. Pb Concentration

The average Pb concentrations in sediment, water, feed and fish at the early stage and the nursery stage were 0.68 ± 0.01^a, 0.15 ± 0.02^ab, 0.00 ± 0.00^a and 0.00 ± 0.00^a, respectively (Table 1), and 2.07 ± 0.01^b, 0.09 ± 0.08^a, 0.00 ± 0.00^a and 0.00 ± 0.00^a, respectively (Table 1). In the grower and harvest stages, the average Pb concentrations in sediment, water, feed and fish were 4.36 ± 0.01^c, 0.05 ± 0.01^a, 0.90 ± 0.01^b and 0.00 ± 0.00^a, respectively (Table 1), and 5.6 ± 0.01^d, 0.20 ± 0.06^b, 0.00 ± 0.00^a and 0.35 ± 0.01^b, respectively (Table 1). The highest Pb concentrations in sediment (5.6 ± 0.01^d), in water (0.20 ± 0.06^b), and in fish (0.35 ± 0.01^b) were found at the harvest stage, while in feed, the highest concentration (0.90 ± 0.01^b) was found in the grower stage. The lowest Pb concentration in sediment (0.68 ± 0.01^a) was found in the early stage, whereas in water (0.05 ± 0.01^a), it was found in the nursery stage.

3.2.4. As Concentration

The average As concentrations in the early stage in sediment, water, feed and fish were 1.35 ± 0.01^a, 0.00 ± 0.00^a, 0.00 ± 0.00^a and 0.00 ± 0.00, respectively (Table 1). In the nursery stage, concentrations in sediment, water, feed and fish were 1.68 ± 0.02^b, 0.00 ± 0.00^a, 0.00 ± 0.00^a and 0.00 ± 0.00, respectively (Table 1). In the grower and harvest stages, the average As concentrations in sediment, water, feed and fish were 1.83 ± 0.03^c, 0.00 ± 0.00^a, 0.03 ± 0.01^b and 0.00 ± 0.00, respectively (Table 1), and 1.90 ± 0.02^d, 0.04 ± 0.02^b, 0.00 ± 0.00^a and 0.01 ± 0.01^a, respectively (Table 1). The highest As concentrations in sediment (1.90 ± 0.02^d), water (0.04 ± 0.02^b) and fish (0.01 ± 0.01^a) were found in the harvest stage, while in feed (0.03 ± 0.01^b), it was found in the grower stage. The lowest As concentration in sediment (1.35 ± 0.01^a) was found in the early stage.

3.3. Human Health Risk Assessment

For several samples, the THQ values for Zn, Pb, Cr, Cd and As were consistently significantly less than 1 (Table 3). Similarly, the HI for all fish was less than 1, which is extremely low. Conversely, the TR values for Cd, Pb, Zn and Cr ranged from 1.52 × 10⁻⁹ to 1.29×10⁻¹¹. Certain fish occasionally fall below detectable levels, which, according to recommended values, indicate their safety for human consumption (USEPA 2010).

TABLE 3.

Values of target hazard quotient (THQ), hazard index (HI) and lifetime cancer risk (TR) calculated for tilapia fish species.

Risk indexes	1st stage	2nd stage	3rd stage	4th stage
THQ
THQZn	0.001165	0.001988	0.002082	0.002683
THQCd	0.0	7.47057E‐06	1.16032E‐05	7.96966E‐05
THQCr	0.0	0.0	0.0	5.81538E‐07
THQPb	0.0	0.0	0.0	0.004019
THQAs	0.0	0.0	0.0	0.000685
HI	0.001165	0.001995	0.002094	0.007468
TR
TRCd	0	2.09E−09	3.25E−09	2.23E−08
TRCr	0	0	0	1.29 E−11
TRPb	0	0	0	1.52 E−09

4. Discussion

This study investigated HM concentrations in pond sediment, water, supplied feed and fish at different culture periods of tilapia (O. niloticus) at Trishal, Mymensingh, Bangladesh, and identified the main source of fish bioaccumulation of HMs to determine whether the concentrations could be hazardous to human health. Fish tissue may be used to screen heavy metallic contamination in aquatic structures; thus, they may be an important biomarker to assess their presence in aquatic systems (Weber et al. 2013).

4.1. Zn

The highest permissible amount of Zn is 100 mg/kg (Food and Agriculture Organization [FAO] 1983; World Health Organization [WHO] 1989). The current study found the Zn concentration in water, silt, feed and fish in every stage was below the recommended amount and much lower than the value revealed by the study in Laxmipur, Noakhali (Hossain et al. 2022) and Bangshi River (Rahman et al. 2012). Therefore, from the point of view of health safety issues, the fish from this site did not have hazardous impacts on consumers' health. However, excess levels of Zn in fish may result in several complications, including anaemic and lethargic conditions, nausea and other health hazards (Prasad 1984). Prolonged exposure to zinc chloride can lead to respiratory ailments.

4.2. Cd

According to FAO (1983) and WHO (1989), the maximum allowable limit for Cd is 1.00 mg/kg. This investigation discovered that the Cd concentration at all stages in sediment, water, feed and fish was less than the uppermost allowable level. A similar, lower level of Cd in fishes was observed in fishes from Laxmipur, Noakhali (Hossain et al. 2022). On the contrary, high levels (1.09–1.21 mg/kg) of Cd were found in fish from the Shitalakhya River, Bangladesh (Ahmed et al. 2009). However, these variations may be due to the seasonal effects that may influence Cd uptake by fish. However, the Cd level in the fish in this study may be sourced from different intermediary activities during fish culture. Besides, feed, water and soil can also be a great source of this metal. Excess Cd in fish interrupts the immune system functionalities as well as having several carcinogenic impacts (Gray et al. 2005; Thomson et al. 2008).

4.3. Cr

The highest permissible level of Cr is 0.05 mg/kg (FAO 1983; WHO 1989). This study revealed that the Cr concentration in all stages in sediment and feed was above the mentioned highest amount, while in water and fish, the Cr concentration was below the maximum permissible limit in all stages. Similar studies from Bangladesh have also revealed lower Cr levels in fishes from different riverine sources (Mourtaja 2008; Ali et al. 2019; Ahmed et al. 2019). Mahmuda et al. (2020) revealed that the average concentration of Cr in O. niloticus was 0.9735 mg/kg, which was better than the current findings and higher than the maximum permissible limit. Though Cr, especially organic Cr, is important from a nutritional point of view (Akter et al. 2021), excess levels can cause malfunctions of organs, including the liver and kidney (Ali et al. 2020), as well as result in complexity in fish respiration (Ahmed et al. 2016).

4.4. Pb

The maximum permissible limit of Pb is 2.0 mg/kg (FAO 1983; WHO 1989). This study revealed that the Pb concentration in all states, except the early stage in the sediment, was higher than the maximum permissible limit. However, the opposite scenario was found in the Pb concentrations at all stages in water, feed and fish. In tilapia fish samples, Alauddin (2016) found Pb values ranging from 9.92 to 14.83 mg/kg. Pb concentrations in the feed samples were 9.25–10.12 mg/kg. The average Pb concentration in tilapia (O. niloticus) was 1.1496 mg/kg, while the range in the special fish market was 0.3058–3.2441 mg/kg. These values were higher than the current findings in fish, water and feed but lower than those in sediment and above the maximum permissible threshold, according to Mahmuda et al. (2020). These Pb's health effects include harm to the kidneys, liver, brain, nerves and other organs. In addition, especially in men, exposure to lead can raise the risk of high blood pressure and heart disease. High levels of lead exposure harm a developing foetus's and young child's brain and nerves, resulting in learning disabilities, seizures, behavioural issues, mental retardation and decreased IQ. Effects from Pb exposure are less severe at lower concentrations.

4.5. As

The maximum permissible concentration of As is 2.0 mg/kg (FAO 1983; WHO 1989). The As concentration at all stages in the sediment was found to be higher than the maximum permissible restriction. However, the As concentrations at all levels in water, feed and fish were below the highest permissible level. Mahmuda et al. (2020) found that As concentration was very low in O. niloticus, which was even lower than the present findings. Sloth et al. (2005) found that concentrations of As and inorganic As varied between 3.4–8.3 and 0.010–0.061 mg/kg for feed, which was better than the prevailing results. The typical level of As in dyke soil and outside in the farm soil was 0.1799 and 0.1758, respectively, which is above the maximum permissible restriction. It was also found that the As concentration in the soil in that vicinity was higher than the maximum permissible concentration, indicating that the area was not appropriate for fish cultivation based on As concentrations, which represented a major threat of As‐associated complexities in fish. It has been noted that there is a correlation between fish age and steel concentration. Excessive levels of As may cause harm to its consumers, resulting in heart diseases, respiratory problems, muscular dystrophy, sclerosis, keratosis and lesions in the skin (Smith et al. 2000; Jarup 2003).

Despite providing valuable insights into HM concentrations during different culture phases of O. niloticus, this study faced several limitations that may have influenced the overall findings. The research focused on total metal concentrations in whole fish samples, without evaluating how these metals are distributed in specific organs. This limits understanding of both toxicological impact and food safety risk, as some tissues may accumulate metals more intensely than others. Furthermore, the study investigated only five HMs (Zn, Cr, Cd, Pb and As). Other potentially harmful elements, including mercury (Hg), nickel (Ni) and copper (Cu), were not analysed, potentially underestimating the full spectrum of contamination. In addition, the research appears to have been carried out in a limited geographic area, possibly involving a single or a few aquaculture sites. To build on these findings, future studies should consider continuous and more frequent sampling across all culture phases to capture seasonal and short‐term variations in metal concentrations. Including farms from various geographic regions would strengthen the applicability and broader relevance of the findings. Further investigation should focus on tracing the origins and transmission pathways of HMs using advanced techniques like isotopic fingerprinting or source apportionment models. This would help identify and mitigate the primary sources of contamination.

4.6. Human Health Risk Assessment

This study found that the average THQ values at all stages remained below 1, which is the safety threshold set by the USEPA (2010). Since all THQ values were under this recommended limit for the metals analysed across the fish species, it suggests that the exposure levels are within safe bounds. Furthermore, the HI measured did not surpass the allowable limit, implying that consuming these fish is unlikely to cause any non‐cancer health issues for consumers. One must keep in mind that people can be affected by multiple pollutants simultaneously, which may increase health risks (Huang, et al. 2013; Kong, et al. 2013). The target risk (TR) values for cadmium, chromium and lead, which ranged from 10⁻⁸ to 10⁻⁹, fall within acceptable limits, indicating no significant cancer risk from eating fish at any stage of the farming cycle. These results are in agreement with earlier studies conducted by Saha et al. (2021), Hossain et al. (2022) and Ali et al. (2019).

5. Conclusion

This research explored the accumulation of five HMs—arsenic, chromium, cadmium, lead and zinc—in the culture environment, feed and tissues of O. niloticus at different farming stages. The data revealed a consistent increase in HM concentrations, particularly in sediment and feed, as the culture period progressed. Although most values in water and fish remained within internationally accepted safety limits, certain metals—specifically chromium in feed and chromium, lead and arsenic in sediment—exceeded recommended thresholds during the nursery, grower and harvest stages. These results indicate that sediment quality and feed composition are key factors influencing metal uptake in cultured tilapia. The study emphasises the importance of regular environmental assessments and careful feed selection to reduce contamination risk. Implementing routine monitoring, ensuring clean feed inputs and adopting best management practices can significantly enhance the safety of farmed fish. These actions not only protect consumer health but also promote the long‐term sustainability of aquaculture systems. In addition to technical measures, addressing HM contamination requires broader policy engagement and community involvement. Since these pollutants can accumulate in fish and pose risks to human health, there is a clear need for stronger enforcement of environmental regulations and food safety standards. Government bodies should increase surveillance efforts while also promoting environmental awareness through education initiatives. Trained non‐governmental organisations and local authorities can play a vital role in raising public consciousness and encouraging responsible practices. These combined efforts are essential to protect aquatic ecosystems, ensure food safety and support a more sustainable future for aquaculture.

Author Contributions

Md. Hamidur Rahman: conceptualisation, investigation, writing – original draft, methodology, writing – review and editing, formal analysis, data curation, resources. Dalal Sulaiman Alshaya: writing – review and editing, project administration, resources, funding acquisition. Haitham Ramadan: funding acquisition, writing – review and editing, project administration. KOTB A. Attia: funding acquisition, writing – review and editing, project administration. Nadira Sultana: methodology, formal analysis. Md. Fazle Rohani: writing – review and editing, formal analysis, data curation. Anugrah Ricky Wijaya: writing – review and editing, formal analysis, data curation, resources. Md. Sazzad Hossain: conceptualisation, supervision, funding acquisition, validation, resources, investigation.

Ethics Statement

The authors have nothing to report.

Conflicts of Interest

The authors declare no conflicts of interest.

Peer Review

The peer review history for this article is available at https://www.webofscience.com/api/gateway/wos/peer‐review/10.1002/vms3.70562.

Rahman, M. H. , Alshaya D. S., Ramadan H., et al. 2025. “Tracing Sources and Stage‐Specific Impacts of Heavy Metal Contamination in Farmed Tilapia (Oreochromis niloticus): Implications for Human Health Risk.” Veterinary Medicine and Science 11, no. 5: 11, e70562. 10.1002/vms3.70562

Data Availability Statement

The authors have nothing to report.