Exposure and health effects follow-up study of residents near a former smelter site

Abstract

The Seo-Cheon Janghang Smelter in South Korea closed in 1989 owing to its contribution to environmental pollution. The emissions from the smelter likely affect various environmental media and also pose significant health risks to nearby residents, particularly in relation to exposure to heavy metals such as lead, cadmium, and arsenic. Although the environmental impacts of the smelter are known, long-term follow-up studies on heavy metal exposure in nearby residents remain limited, especially after remediation. This study aimed to assess the levels of heavy metal exposure and associated health effects, particularly on renal and bone health. We analyzed blood and urine samples from 37 volunteers, collecting demographic, lifestyle, and exposure-related data through interviews. Renal function tests and bone mineral density measurements were conducted. The geometric means for blood lead (bPb) and blood cadmium (bCd) were 1.95 μg/dL and 2.68 μg/L, respectively. The mean urinary cadmium (uCd) concentration was 3.74 μg/g cr. Urinary total and harmful arsenic concentrations were 165.7 μg/L and 1.00 μg/L, respectively. The bPb levels significantly decreased from 2008 to 2020, whereas cadmium levels did not show significant change overall. Among 28 participants tested in both years, bCd levels decreased for individuals living > 2 km from the smelter, while remaining stable for those closer. The uCd levels significantly decreased only in individuals who had relocated > 2 km away from the smelter. Despite remediation efforts, uCd levels remain persistently elevated. These findings underscore the need for continuous exposure monitoring and longitudinal health assessments of residents living near the former smelter.

Introduction

Although smelters have been essential to industrialization, they emit heavy metals into the surrounding environment [1]. These heavy metals—including lead (Pb), cadmium (Cd), arsenic (As), copper (Cu), and zinc (Zn)—are often found in base metal ores. During the smelting process, they may be released through chimneys, disposed of in landfills alongside other waste products, or dispersed as ore dust, thereby contaminating nearby soil and water sources [2].

In Korea, rapid industrialization led to the widespread and often unregulated establishment of pollutant-emitting facilities, which often negatively influenced the health and property of nearby residents. Consequently, residents living near smelters exhibit significantly higher levels of heavy metal exposure than those residing farther away [3, 4].

As, Pb and Cd are among the most hazardous substances, ranking first, second, and seventh, respectively, on the National Priority List (NPL) of the U.S. Agency for Toxic Substances and Disease Registry (ATSDR) [5]. Arsenic (As) is a well-established human carcinogen, with dietary exposure identified as the primary route of entry for the general population [6, 7]. Inorganic arsenic and its compounds are classified as Group 1 human carcinogens, indicating sufficient evidence for carcinogenicity in humans [8]. Moreover, arsenic exposure has been associated with cardiovascular disorders, reproductive toxicity, developmental delays in children, and immunosuppression [9]. Lead (Pb) is a potent neurotoxin, particularly in children, where it has been linked to reduced IQ, behavioral disorders, and impaired cognitive development—even at blood lead levels below 5 µg/dL [10, 11]. In adults, chronic lead exposure is associated with hypertension, kidney dysfunction, and reproductive toxicity, including reduced sperm count and increased risk of miscarriage [10–12]. Inorganic lead compounds are classified as “probably carcinogenic to humans” (Group 2A) [13]. Cadmium (Cd) is primarily transmitted through the consumption of contaminated food and water, inhalation of contaminated air, and, less frequently, through skin contact. Individuals residing near mining or industrial areas are at an increased risk of cadmium exposure due to environmental accumulation [14]. Upon entering the body, cadmium binds to proteins and circulates through the bloodstream, accumulating predominantly in organs such as the kidneys and liver. Notably, cadmium has an exceptionally long biological half-life, often exceeding a decade, leading to gradual accumulation over time [15]. Due to its persistence in the environment and bioaccumulate nature, Cd, remains a significant public health concern worldwide, necessitating continued monitoring and mitigation efforts, especially in communities near industrial or mining activities.

In 2008, following environmental pollution complaints from local residents, a detailed investigation of heavy metal contamination was conducted near the former Janghang Smelter in Seocheon-gun, Chungcheongnam-do, South Korea. The study found that soils within a 500-m radius of the smelter exceeded contamination standards for Cu, Zn, Pb, Cd, As, and Ni [16]. A subsequent health assessment showed that residents had significantly higher Cd and Pb exposure levels compared to a control group from a rural area approximately 15 km away. These findings confirmed the former smelter as a major source of heavy metal exposure [17, 18].

Following the 2008 findings, the Ministry of Environment implemented a series of measures, including acquiring heavily contaminated land and relocating residents between 2009 and 2012. These actions were followed by full-scale soil remediation projects that began in 2013. However, whether these policies effectively reduced heavy metal exposure among residents remains unclear.

Therefore, this study aims to evaluate the current levels of heavy metal exposure and associated health risks among residents living near the former smelter site and to assess the effectiveness of government intervention policies by comparing present data with those from the 2008 survey.

Materials and methods

Study participants

The participants in this study were 11 males and 26 females who resided near the former Seo-Cheon Janghang Smelter and had applied for damage relief through the Korea Institute of Environmental Science and Technology. All had lived within 4 km of the smelter for > 5 years and had no occupational exposure to heavy metals. Of these participants, 28 had taken part in the 2008 health impact survey of residents near the smelter. Prior to participation, all individuals were informed about the purpose of the study and provided written consent to participate in structured interviews. The survey covered their demographic and socioeconomic characteristics, smoking, drinking, dietary habits, and medical history. Physical measurements, blood pressure, and bone density were assessed, and blood and urine samples were collected. The study protocol was approved by the Institutional Review Board (IRB) of Chung-Ang University, South Korea (No. 1041078–202007-HRBR-137–01).

To compare current heavy metal exposure levels with those from 2008, data from a previous survey conducted by researchers were retrieved and analyzed. Blood Cd and lead concentrations were measured utilizing the same analytical methods as in this study. Urinary Cd and As concentrations were determined by atomic absorption spectrophotometry (AAs).

Determination of metal levels in blood and urine

To evaluate heavy metal exposure, ~ 4 mL of blood and 40 mL of urine were collected from each participant and stored at − 70 °C until analysis. Blood Pb and Cd concentrations were measured using graphite furnace atomic absorption spectrometry with Zeeman background correction (GFAAS; Model No. PinAAcle 900Z, PerkinElmer, Shelton, CT, USA). Whole blood samples were diluted to 0.2% in Triton X-100 containing 1% nitric acid and 0.2% diammonium hydrogen phosphate. Urinary Cd and As concentrations were analyzed using inductively coupled plasma mass spectrometry with a dynamic reaction cell (DRC) (ICP-MS; Agilent 7700 Series ICP-MS, Agilent Technologies, Santa Clara, CA, USA). Urine samples were diluted 1:10 with 1% nitric acid, and indium (¹¹⁵In) was used as the internal standard.

The urinary creatinine concentrations were measured using the colorimetric Jaffe reaction, based on the reaction with picric acid and NaOH, and analyzed with a microplate reader (Spectra 340) [19]. The urinary Cd concentrations were normalized to creatinine levels (μg/g creatinine) to control the effects of urine dilution.

The As species were analyzed using an ICP-MS coupled with high-performance liquid chromatography (HPLC; Agilent 1260 Infinity, Agilent Technologies). The measured species included As³⁺, As⁵⁺, monomethylarsonic acid (MMA), and dimethylarsinic acid (DMA). Hazardous As concentrations were defined as the sum of the As³⁺, As⁵⁺, and MMA. Urine samples were filtered through a 0.22-μm membrane filter (Sterile syringe filter, cellulose acetate N.A., PN: 28,145–477 supplied by VWR), then transferred into chromatographic vials and loaded onto autosampler trays.

Kidney injury biomarker measurements

The urinary N-acetyl-β-D-glucosaminidase (NAG) activity and β2-microglobulin (β2-MG) levels were measured as biomarkers of renal tubular damage. The NAG activity was determined using a NAG Quantitative Kit (Shionogi, Osaka, Japan), following the procedures of the manufacturer. The β2-MG levels were measured using a β2-MG Enzyme-Linked Immunosorbent Assay (ELISA) Kit (Immundiagnostik AG, Bensheim, Germany), following the instruction of the manufacturer. The estimated glomerular filtration rate (eGFR) was calculated using the serum creatinine and cystatin C levels based on the Chronic Kidney Disease-Epidemiology Collaboration (CKD-EPI) creatinine-cystatin Eq. (2012) [20].

Bone mineral density measurements

During participant health examinations at Chung-Ang University Hospital, the mineral density of the calcaneus (heel bone) was measured using high-accuracy dual-energy x-ray absorptiometry (DXA) to evaluate bone damage associated with Cd exposure.

Statistical analysis

All data were analyzed using IBM SPSS Statistics for Windows Version 26.0 (IBM Corp., Armonk, NY, USA). Heavy metal concentrations were log-transformed prior to analysis. Group means were compared using Student’s t-tests and analysis of variance (ANOVA). The change in heavy metal concentrations between 2008 and 2020 was assessed with a paired t-test. Analysis of covariance (ANCOVA) was performed to adjust for age and sex when comparing heavy metal concentrations. The chi-square test was applied to examine differences in frequency distributions between groups. Statistical significance was set at p < 0.05 and p < 0.001.

Results

Table 1 presents the demographic characteristics of the participants. The cohort included 26 females and 11 males, with a mean age of 79.6 years. Their mean residence duration was 62.9 years, and they all lived in the area for > 20 years. Thirteen participants (35.1%) resided within 2 km of the smelter, while 24 (64.9%) lived > 2 km away. Twenty-eight (75.7%) participants were non-smokers, 17 individuals (45.9%) were current alcohol consumers, and 20 (54.1%) had no history of alcohol consumption. The proportions of residents who obtained ≥ 50% and < 50% of their total rice intake from local sources were 67.6% and 32.4%, respectively. The participants consumed either tap water or purified water. Overall, 37.8% of the participants had previously worked at the smelter (Table 1). Table 2 presents the heavy metal concentrations in the blood and urine of participants. The geometric mean blood Pb concentration was 1.95 µg/dL, with 2.18 µg/dL in males and 1.86 µg/dL in females. In contrast, the mean blood Pb concentration was 4.14 µg/dL in 2008. The geometric mean blood Cd concentration was 2.68 µg/L, with 3.12 µg/L and 1.90 µg/L in females and males, respectively. The geometric mean blood Cd concentration was 2.64 µg/L in 2008. The geometric mean urinary Cd levels were 3.66 µg/g creatinine, with higher means observed in females (4.55 µg/g creatinine) than in males (2.18 µg/g creatinine). The geometric urinary Cd level was 2.72 µg/g creatinine in 2008. The geometric mean total urinary As concentration was 166.7 µg/L, with 186.8 µg/L and 157.5 µg/L in males and females, respectively. No significant difference was observed between the sexes. The geometric mean harmful As concentration (inorganic As + MMA) was 0.99 µg/L, with 1.11 µg/L and 0.94 µg/L in males and females, respectively. Table 3 presents heavy metal exposure stratified by smoking history, alcohol consumption, local rice intake, and residential area. Total urinary As concentration was higher in smokers (318.3 µg/L) than in non-smokers (134.3 µg/L) (p = 0.029). However, after adjusting for age and sex, the difference was no longer statistically significant. Blood and urinary Cd levels were higher in non-drinkers than in drinkers (p = 0.040 for bCd; p = 0.005 for uCd). After adjusting for age and sex, this difference also lost statistical significance (p = 0.729 for bCd; p = 0.539 for uCd). Urinary Cd concentrations were significantly higher among individuals who obtained > 50% of their rice from local sources (5.32 µg/g cr) than in those who did not (3.13 µg/g cr) (p = 0.017). However, this difference was not statistically significant after adjusting for age and sex (p = 0.285). Individuals residing within 2 km of the former smelter had significantly higher urinary Cd levels (5.49 µg/g cr) than those living > 2 km away (3.01 µg/g cr) (p = 0.005). However, this difference also lost statistical significance after age and sex adjustment (p = 0.138). Blood Pb and urinary iAs + MMA concentrations did not significantly differ by smoking status, alcohol consumption history, residential distance from the smelter, or local rice intake. Table 4 presents changes in heavy metal exposure by residential area and migration status among participants tested in both 2008 and 2020. Blood Pb levels were lower in 2020 than in 2008, regardless of residential area or migration status. Blood Cd levels were significantly lower in 2020 than in 2008 among residents living > 2 km from the smelter (p = 0.009), independent of migration status. In contrast, urinary Cd levels did not significantly differ by residential area. However, urinary Cd levels were significantly lower among residents who had migrated (p = 0.014) but not significantly different among those who remained in the same residence (p = 0.379). Tables 5 and 6 present the results of kidney function and bone density assessments evaluating the health effects of Cd exposure. Among participants assessed for Cd-related kidney damage, high NAG, high β2-MG, and low eGFR were observed in 16.2%, 29.7%, and 32.3%, respectively (Table 5). Osteoporosis was observed in 22.9% of participants evaluated for Cd-related bone demineralization (Table 6). However, the prevalence of abnormal findings did not significantly differ between individuals with urinary Cd levels above and below the reference standard.

Table 1.

Participant distribution in communities near former smelter sites based on epidemiological characteristics

Characteristics		Total (N = 37)
Age	< 69	3 (8.1)
	70–79	11 (29.7)
	≥ 80	23 (62.2)
	Mean ± SD	79.6 ± 8.35
Sex	Male	11 (29.7)
	Female	26 (70.3)
Duration of residence (years)	< 49	6 (16.2)
	50–69	18 (48.6)
	≥ 70	13 (35.1)
	Mean ± SD	62.9 ± 13.5
Distance from smelter, (km)	< 2.0	13 (35.1)
	≥ 2.0	24 (64.9)
Smoking status	Non-smoker	28 (75.7)
	Smoker	9 (24.3)
Alcohol consumption	Non-drinker	20 (54.1)
	Drinker	17 (45.9)
Local rice consumption (%)	< 50	25 (67.6)
	≥ 50	12 (32.4)
Drinking water source	Tap water/filter water	37 (100)
	Underground water	–
Occupational smelter exposure	Yes	14 (37.8)
	No	23 (62.2)

Mean arithmetic mean, SD standard deviation

Table 2.

Mean metal concentrations among study participants

Heavy metal	Sex	GM (GSD)	Range (min–max)	95th percentile	*2008 survey	**KoNEHS IV
					GM(GSD)	GM
Blood Pb (µg/dL)	Male	2.18 (1.56)	1.12–3.76	3.26	–	–
	Female	1.86 (1.76)	0.50–3.73	2.83	–	–
	Total	1.95 (1.69)	0.50–3.76	2.93	4.14 (1.54)	1.51*
Blood Cd (µg/L)	Male	1.90 (1.62)	0.59–3.46	2.43	–	–
	Female	3.12 (1.66)	1.36–7.85	4.05	–	–
	Total	2.68 (1.72)	0.59–7.85	3.68	2.72 (1.95)	0.39*
Urine Cd (µg/L)	Male	2.18 (1.92)	0.82–5.14	3.89	–	–
	Female	4.55 (1.66)	1.66–12.66	6.22	–	–
	Total	3.66 (1.90)	0.82–12.66	5.31	2.64 (1.77)	0.71**
Urinary Total As (µg/L)	Male	186.8 (3.73)	5.1–725.0	318.3	–	–
	Female	157.5 (2.55)	20.0–1,755.3	240.8	–	–
	Total	166.7 (2.84)	5.1–1,755.3	285.0	–	–
iAs + MMA (µg/L)	Male	1.11 (5.90)	0.11–12.95	4.08	–	–
	Female	0.94 (5.91)	0.11–10.51	4.10	–	–
	Total	0.99 (6.10)	0.11–12.95	4.08		–

GM geometric mean, GSD geometric standard deviation

^*2008 survey (blood Pb, N = 562; urine Cd, N = 437; blood Cd, N = 557; urine As, N = 441)

^*KoNEHS IV, Korean National Environmental Health Survey, 2018–2020

^**KNHANES, Korea National Health and Nutrition Examination Survey. 2016–2018

Table 3.

Heavy metal concentrations in blood and urine stratified by smoking status, alcohol consumption, occupation smelter exposure, local rice consumption, and residential proximity to smelter

Heavy metal		Smoking status		Alcohol consumption		Occupation smelter exposure		Local rice consumption		Residential proximity to smelter
		Yes	No	Yes	No	Yes	No	Yes	No	< 2.0 km	≥ 2.0 km
Blood Pb (µg/dL)	GM (GSD)	2.24 (1.50)	1.80 (1.65)	1.80 (1.65)	1.91 (1.72)	2.07 (1.58)	1.88 (1.78)	1.80 (1.65)	2.03 (1.73)	2.10 (1.49)	1.87 (1.82)
	P-value	0.378		0.527		0.601		0.527		0.547
Blood Cd (µg/L)	GM (GSD)	2.08 (1.35)	2.98 (1.76)	2.98 (1.76)	3.19 (1.60)	2.52 (1.55)	2.79 (1.84)	2.98 (1.76)	2.54 (1.71)	3.06 (1.64)	2.49 (1.76)
	P-value	0.109		0.411		0.595		0.411		0.279
Urinary Cd (µg/g cr)	GM (GSD)	2.83 (1.88)	5.32 (1.76)	5.32 (1.76)	4.91 (1.66)	3.58 (2.00)	3.84 (1.85)	5.32 (1.76)	3.13 (1.83)	5.49 (1.58)	3.01 (1.87)
	P-value	0.134		0.017		0.758		0.017		0.005
Urinary Total As (µg/L)	GM(GSD)	318.3 (2.43)	150.7 (2.18)	150.7 (2.18)	135.9 (2.38)	150.5 (3.92)	175.7 (2.28)	150.7 (2.18)	174.5 (3.25)	239.9 (2.19)	135.6 (3.09)
	P-value	0.029		0.689		0.669		0.689		0.114
iAs + MMA (µg/L)	GM (GSD)	1.71 (6.15)	1.88 (5.21)	1.88 (5.21)	1.04 (5.74)	0.65 (6.70)	1.31 (5.21)	1.88 (5.21)	0.72 (5.79)	0.96 (6.69)	1.03 (5.59)
	P-value	0.301		0.112		0.238		0.112		0.907

Mean arithmetic mean, SD standard deviation, GM geometric mean, GSD geometric standard deviation

Numbers in bold indicate significant differences (P < 0.05)

Table 4.

Geometric mean (GSD) concentrations of metals in urine and blood stratified by residential proximity and migration status (N = 28)

Heavy metal	Year	Distance		Migration status
		< 2 km	≥ 2 km	Yes	No
Blood Pb (µg/dL)	2008	4.93 (1.34)	4.51 (1.43)	4.45 (1.45)	4.94 (1.34)
	2020	2.04 (1.50)	1.88 (1.74)	1.90 (1.72)	2.00 (1.56)
	P-value	< 0.001	< 0.001	< 0.001	< 0.001
Blood Cd (µg /dL)	2008	3.93 (1.51)	3.70 (1.73)	3.53 (1.76)	4.08 (1.49)
	2020	3.00 (1.67)	2.70 (1.58)	2.68 (1.63)	2.97 (1.61)
	P-value	0.129	0.009	0.028	0.044
Urine Cd (μg/g cr)	2008	5.24 (1.30)	4.55 (1.62)	4.62 (1.67)	5.05 (1.30)
	2020	5.32 (1.59)	3.46 (1.87)	3.24 (1.90)	5.34 (1.53)
	P-value	0.552	0.053	0.014	0.379

GM geometric mean, GSD geometric standard deviation, cr creatinine

Numbers in bold indicate significant differences (P < 0.05)

Table 5.

Kidney function indices stratified by urinary cadmium levels

Variable		< 5 μg/g cr (N = 26)	≥ 5 μg/g cr (N = 11)	Total (N = 37)	Reference value
NAG (U/g cr)	Mean ± SD	9.20 ± 6.75	9.67 ± 3.70	9.34 ± 5.95	< 11.5
	Αbnormal (%)	4 (15.4%)	2 (18.2%)	6 (16.2%)
β2-MG (mg/g cr)	Mean ± SD	0.43 ± 1.30	1.16 ± 3.18	0.79 ± 2.29	< 0.3
	Αbnormal (%)	5 (19.2%)	4 (36.4%)	11 (29.7%)
Egfr (mL/min)	Mean ± SD	71.5 ± 22.7	70.5 ± 22.0	81.1 ± 21.2	< 60
	Αbnormal (%)	8 (30.7%)	4 (36.4%)	12 (32.3%)

Mean arithmetic mean, SD standard deviation, NAG N-acetyl-β-D-glucosaminidase, β2-MG β2-microglobulin, eGFR estimated glomerular filtration rate, cr creatinine

Abnormal: ≥ Reference value

Table 6.

Bone mineral density stratified by urinary cadmium levels

Variable		< 5 μg/g cr (N = 25)	≥ 5 μg/g cr (N = 10)	Total (N = 35)
Z-score (Spine)	Mean ± SD	0.39 ± 1.76	0.70 ± 1.34	0.48 ± 1.64
Z-score (Femur)	Mean ± SD	− 0.18 ± 0.40	− 0.01 ± 0.63	− 0.13 ± 0.47
Osteoporosis	N (%)	4 (16.0%)	4 (40.0%)	8 (22.9%)

Mean arithmetic mean, SD standard deviation, cr creatinine

Osteoporosis: − 2.5 ≤ T-score

Discussion

The area surrounding the former Seo-Cheon Janghang Smelter and nearby abandoned metal mines is among the regions most vulnerable to environmental pollution in South Korea. [16, 21, 22]. Although the smelter ceased operations in 1989, controversy regarding its environmental effects has persisted. In 2008, a comprehensive environmental pollution survey was conducted, accompanied by a detailed health effect assessment of residents living near the smelter. The assessment revealed that residents were exposed to Pb, Cd, and As and were potentially at risk of adverse health effects such as kidney damage. Soil remediation and resident relocation projects were implemented following the studies mentioned above. However, ongoing health effects assessments reveal that residents remain exposed to high levels of environmental pollutants. The present study examined the exposure levels and health effects of residents who applied for environmental pollution damage relief in 2020. It also compared the 2020 data to those from 2008 and assessed heavy metal exposure levels in the general population. The average participant age was 79.6 years, with most having lived in the area while the smelter was in full operation.

To facilitate a clearer comparison of heavy metal exposure over time and across populations, Table 7 summarizes the average levels of blood Pb, blood Cd, and urinary Cd from the present study and previous national or regional surveys. The average blood Pb level in this study (1.95 µg/dL) was lower than that reported in the 2008 survey (4.14 µg/dL), with no participants exceeding the environmental exposure threshold of 5 µg/dL.

Table 7.

Comparison of blood and urinary heavy metal levels (Pb and Cd) between the present study and previous studies

Study/Survey	Blood Pb (µg/dL)	Blood Cd (µg/L)	Urine Cd (µg/g cr)	Population	Year(s)
Present Study	1.95	2.68	3.74	Residents near smelter	2020
KoNEHS IV (Korea)	1.51	0.71	0.39	General Korean population	2018–2020
Abandoned Metal Mine Survey – Phase I	2.84	1.59	2.23	Residents near abandoned mine	2008–2011
Abandoned Metal Mine Survey – Phase II	2.27	1.42	1.66	Residents near abandoned mine	2013–2017
NHANES (U.S.)	1.38	0.38	0.23 µg/L*	General population	2017–2018
JNHNS (Japan)	1.77	0.58	0.58 µg/L*	General population	2019
CNHS (China)	3.50	0.45	0.30 µg/L*	General population	2018

KoNEHS IV Korea national environmental health survey, NHANES national health and nutrition examination survey, JNHNS Japan national health and nutrition survey, CNHS China national health survey

No participants in the present study had blood Pb concentrations exceeding the environmental exposure standard of 5 µg/dL. Blood Pb level did not differ significantly between participants employed as smelter workers and non-workers or between those who consumed locally grown rice and those who did not. Additionally, blood Pb levels did not significantly differ with lifestyle or residential area (Table 3). Analysis of participants measured in both 2008 and 2020 revealed a significant decline in blood Pb levels over time, regardless of residential area or migration status (Table 4). Comparing international populations, blood Pb levels in the present study were comparable to those in the US (1.38 µg/dL) and Japan (1.77 µg/dL) but lower than those in China (3.50 µg/dL) (Table 7) [23–25].

The mean blood Cd level was 2.68 µg/L, comparable to the 2008 level (2.64 µg/L) and consistently higher in females. This sex difference can be attributed to factors such as lifestyle differences, environmental exposure, and physiological characteristics [26]. No significant difference was observed in blood Cd level between smelter workers and non-workers or between participants who consumed locally grown rice and those who did not. Additionally, blood Cd levels did not significantly vary with lifestyle or residential area. Between 2008 and 2020, the mean blood Cd levels of residents within 2 km of the smelter remained significantly unchanged, while those of residents living > 2 km from the smelter decreased significantly. Levels in the study population exceeded those in the general populations of Korea, the US, Japan, and China (Table 7) [23–25, 27, 28]. Urinary Cd concentrations, adjusted for creatinine, were also elevated in this study (3.74 µg/g cr in 2020 vs. 2.72 µg/g cr in 2008), with 29.7% of participants exceeding the WHO reference value of 5 µg/g cr [29]. Creatinine adjustment of urinary Cd concentrations accounts for variations in urine dilution. Creatinine—a byproduct of muscle metabolism—is excreted in urine at a relatively constant rate. Normalizing urinary Cd concentrations to creatinine levels provides a more accurate assessment of cadmium exposure by minimizing the influence of variations in hydration status or urine volume [30]. This adjustment is crucial for standardizing measurements, thereby enhancing the reliability and comparability of Cd exposure assessments across individuals and populations [31]. In this survey, the urinary Cd concentrations in 32 participants (86.5%) exceeded the exposure threshold of 2.0 µg/g cr, a level recognized as indicative of cadmium-induced environmental pollution damage (Table 2) [32]. After adjusting for age and sex, no significant differences in urinary Cd concentrations were observed between participants who had worked at the smelter and those who had not, nor between those who consumed locally grown rice and those who did not. Moreover, urinary Cd concentration did not differ significantly by lifestyle factors or residential proximity. Analysis of multiple measurements revealed that urinary Cd concentrations significantly decreased in individuals who relocated, but no such change was observed in those who remained in that area (Table 3). These findings suggest that Cd exposure sources probably persisted within 2 km of the smelter and that relocating outside the affected area is associated with a significant reduction in exposure risk. Cd primarily accumulates in the liver and kidneys [33]. Blood and urinary Cd levels serve as indicators of current and cumulative exposures, respectively [6, 34, 35]. In this study, blood and urinary Cd levels remained high among residents living near the smelter. Multiple measurements revealed no significant change in blood Cd levels among those residing within 2 km of the smelter from 2008–2020. Hence, they were subjected to ongoing cadmium exposure. Urinary Cd concentrations did not significantly differ between 2008 and 2020 for residents living within 2 km of the smelter but were significantly lower in 2020 than in 2008 for those who relocated > 2 km away. In some residents, elevated urinary Cd concentrations probably indicate continued environmental Cd exposure rather than renal tubular damage and decreased Cd resorption. While the precise source of ongoing Cd exposure remains unclear, several potential environmental pathways warrant consideration. First, residual soil contamination near the smelter site represents a probable source, as Cd can persist in soil for decades and be absorbed by locally grown crops. Second, airborne dispersion of Cd-containing particulates from past smelter operations may have contributed to long-term environmental contamination, including household dust and surface water.

Environmental Cd exposure may cause renal tubular dysfunction [36]. Early signs of kidney damage include tubular dysfunction, characterized by the increased excretion of low-molecular-weight proteins such as β2-MG and NAG [37]. If left unchecked, early tubular damage can progress to more severe kidney damage. As early as 1950, decreased glomerular filtration rates were reported in cadmium-exposed workers [38]. eGFR—derived from blood cystatin C and creatinine levels—can be used to confirm the diagnosis of chronic kidney disease [20]. For both sexes, urinary Cd concentrations exhibited a positive correlation with NAG activity, β2-MG, and malondialdehyde levels, but these concentrations negatively correlated with eGFR and bone mineral density (BMD) values [37]. This present study demonstrated no significant correlation between urinary Cd exposure and the average values or proportions of individuals exceeding the threshold values for the kidney function indices mentioned (Table 5). No significant correlation was also observed between urinary Cd exposure and BMD or osteoporosis severity (Table 6).

In this study, total urinary As and hazardous As species—As³⁺  + As⁵⁺  + MMA—were separately quantified to assess As exposure. The total urinary and toxic As concentrations were 165.7 µg/L and 1.00 µg/L, respectively. A direct comparison between the 2008 and 2020 datasets was not feasible, as urinary arsenic concentrations in the earlier study (2008) were measured using AAS with the hydride generation technique.

The total As concentration measured in this study was higher than those reported in the recent Third Phase Health Effects Survey of Residents Around Abandoned Metal Mines (82.0–110.3 µg/L). Conversely, the concentration of toxic As levels reported in that survey (0.59–2.00 µg/L) is comparable to those observed in recent survey this present study. No significant differences in urinary As concentrations were observed between participants who had been employed at smelters and those who had not or between those who consumed locally grown rice and those who did not. Moreover, urinary As concentrations did not significantly vary according to lifestyle factors or residential area. Although the total arsenic concentrations observed in this study appeared somewhat elevated, comparable to those reported in other studies, the concentrations of hazardous arsenic species were not significantly different. These findings suggest that the elevated total arsenic levels are probably attributable to increased exposure to organic arsenic compounds, such as those derived from seafood consumption, rather than from environmental exposure to inorganic arsenic. Hence, dietary intake—especially of seafood—may have contributed significantly to the total urinary arsenic concentrations observed in this population [39, 40]. Supporting this interpretation, international comparisons reveal significant variability in urinary arsenic concentrations, probably reflecting differences in dietary patterns. For example, the average urinary arsenic concentration is 8.44 μg/L in the United States (NHANES 2017–2018) [23] and 10.5 μg/L in China (CNHS 2018) [25]. In Japan—where seafood consumption is relatively high—the average urinary arsenic concentration reaches 35.0 μg/L (JNHNS 2019) [24]. Arsenic—a metalloid or semimetal—is widely distributed throughout rocks, soil, water, and air. Inorganic As is commonly found in the groundwater sources consumed in countries such as Bangladesh, Chile, China, and other nations. Organic As compounds—such as arsenobetaine—are abundant in fish consumed by humans [40]. Arsenic is classified as a human carcinogen, with dietary intake recognized as the primary exposure route for the general population [41]. Mine tailings and other contaminated soils also represent potential sources of As exposure [42]. Soil measurement network data collected between 2014 and 2018 reported that the As levels do not exceed the established standards in any of the tested zones. Therefore, the soil remediation project implemented in the study area by the Ministry of the Environment was effective.

In this study, no significant differences in health outcomes, including renal impairment or osteoporosis, were observed based on cadmium exposure levels. This finding may be partially attributed to the relatively small sample size, which could have limited statistical power to detect meaningful associations. Furthermore, renal impairment may arise not only from heavy metal exposure, such as cadmium and arsenic, but also from underlying conditions, such as diabetes and hypertension. Given that most study participants were elderly and exhibited a high prevalence of these comorbidities, it became challenging to clearly distinguish renal effects specifically attributable to cadmium exposure. Regarding osteoporosis, the observed prevalence in this study was 22.9%, which is unexpectedly low considering the average participant age of 70 years. According to previous studies of the general Korean population, the prevalence of osteoporosis among individuals aged ≥ 50 years is approximately 22.4% [43]. The relatively low prevalence observed in this current study may be attributed to selection bias, as participation was voluntary and probably attracted individuals with relatively better overall health status.

This study has some limitations that should be considered. First, the relatively small sample size of 37 participants limited the generalizability of the findings. The absence of direct measurements of environmental factors, such as soil contamination or heavy metal concentrations in agricultural products, also limited our ability to ascertain specific exposure pathways. Variations in the analytical methodologies used to measure urinary cadmium concentrations may also affect the comparability of results. Nonetheless, a significant strength of this study is its longitudinal design, which was used to assess exposure levels in 28 participants at two-time points—2008 and 2020. This approach enabled the observation of temporal trends in cadmium exposure, offering valuable insights into the persistence of exposure despite remediation efforts.

The findings suggest that soil remediation efforts implemented since the closure of the Seo-Cheon Janghang Smelter in 1989 have significantly reduced overall heavy metal levels, particularly Pb and As exposure levels, in the vicinity of the facility. Conversely, the environmental Cd exposure risk remains relatively high within a 2-km radius of the smelter, raising concerns about declines in kidney function and BMD in the resident population. Therefore, continuous monitoring and appropriate compensation will be necessary for the affected individuals.

Author contributions

All authors contributed to the study’s conception and design. Material preparation and data collection were performed by Da-Som Lee, Heon Kim, Yong-Dae Kim, Young-Seoub Hong, Jung-Duck Park, and Byung-Sun Choi. Data analysis was conducted by Jung-Eum Lee and Young-Hun Kim. The first draft of the manuscript was written by Young-Hun Kim and Da-Som Lee, with all authors providing comments on earlier versions of the manuscript. All authors read and approved the final manuscript.

Funding

This work was supported by a Chung-Ang University Research Scholarship Grant in 2015.

Data availability

The data supporting the findings of this study are available from the corresponding author upon reasonable request.

Declarations

Conflict of interest

The authors have no relevant financial or non-financial interests to disclose.

Ethical approval

Heavy metal exposure levels were evaluated in this study by collecting biological samples, such as blood and urine, with the consent of local residents. The study design received approval from the Chung-Ang University Institutional Review Board (CAUIRB) (Approval No. 1041078–202007-HRB-1731).

Consent to participate

Participants were informed of the purpose of this study. Those who wished to participate provided written consent.

Consent to publish

Participants were informed of the purpose of the present study. Those who wished to participate provided written consent.