Exposure to polycyclic aromatic hydrocarbons, arsenic and environmental tobacco smoke, nutrient intake, and oxidative stress in Japanese preschool children

Co-exposure to multiple endocrine-disrupting chemicals and oxidative stress: Epidemiological evidence of nonmonotonic dose response curves

This study aimed to investigate the effect of multiple exposure to eight classes (parabens, bisphenols, glycidyl ethers, antimicrobials, benzophenones, phthalates, tri and dichlorophenols) of endocrine disrupting chemicals (EDCs) on oxidative stress levels of 8-hydroxy-2'-deoxyguanosine (8-OHdG). A cross-sectional study was conducted with 300 healthy Brazilian children and adolescents. Urinary levels of 65 EDCs, creatinine and 8-OHdG were analyzed by Liquid Chromatography-Tandem Mass Spectrometry. Elastic net was used to estimate the associations between the levels of EDCs and 8-OHdG. The optimal hyperparameters were estimated using ten-fold cross-validation. Bayesian Kernel machine regression (BKMR) was used to investigate potential interactions and 8-OHdG level response as a function of the co-exposure to EDCs. The elastic net analysis showed that 2,4-DCP (0.149; CI 95 %:-0.033, 0.335, p = 0.02) and BPA (0.21; CI 95 %: 0.08; 0.356, p < 0.005) were associated with urinary levels of 8-OHdG. The BKMR model indicated a positive nonlinear and nonmonotonic relationship between EDCs mixture and 8-OHdG with an inverted U-shaped dose-response curve. This study suggests the first epidemiological evidence of a complex, nonmonotonic relationship between urinary levels of EDCs and 8-OHdG. However, the lack of established reference ranges for 8-OHdG limited a deeper discussion of our findings' clinical significance. Therefore, further studies should focus on validating our results across diverse populations, particularly those affected by oxidative stress-related diseases, and investigate potential mechanisms for supporting this association.

Estimation of public exposure to PAH and environmental risks via wastewater-based epidemiology

The wastewater-based epidemiology (WBE) has the potential to monitor public health emergencies via the analysis of human urinary biomarkers in wastewater. This work proposes a novel approach utilizing WBE for the spatial and temporal evaluation of PAHs exposure using hydroxyl derivatives of PAHs. These are 1-hydroxynaphthalene, 2-hydroxynaphthalene, 2-hydroxyfluorene, 9-hydroxyfluorene, 9-hydroxyphenanthrene, 1-hydroxypyrene and 3-hydroxybenzo(a)pyrene. Most target markers were found at quantifiable concentrations in raw and treated wastewater. The total loads identified in raw sewage ranged from 88.33 g/day to 154.77 g/day during the summer period and from 137.66 g/day to 283.78 2 g/day during the winter period. The obtained results for the removal efficiencies of OH-PAHs indicate a seasonal dependency in their degradation. Removal efficiencies were higher in January compared to August. The results of the back calculations allowed to estimate that during the summer, on average, a resident of Krakow could absorb approximately 2.1 µg of the assessed OH-PAHs per day, while in winter, this value increased to 4.1 µg. This is close to the reported in the literature value that the total daily exposure to OH-PAHs is estimated at 3 µg/day. Moreover, the risk quotation (RQ) values on the base of acute and chronic data base for compounds present in effluents were calculated. The RQ values in January were relatively low, but in August the RQ values were higher, indicating a high concentration of effluent and nitrogen in summer as these compounds were removed in winter and summer. To the authors' knowledge, this is the first time wastewater profiling of OH-PAHs in wastewater for the evaluation of exposure to PAHs have been used, also their removal as well emission with effluent were determined.

Survey of Secondhand Smoke for 3-Year-Old Children in the Current Era of New Tobacco Products

AIM

To investigate children's exposure to secondhand smoke and aerosols in the current era of new tobacco products.

METHODS

A total of 200 children were recruited from among children who had undergone health checkups for 3-year-olds at the clinic. We investigated the smoking status of their families using a questionnaire and measured urinary cotinine concentrations in their children. The children were divided into four groups based on their families' smoking status: no smokers (n = 114), exclusive combustion cigarette smokers (n = 35), both combustion cigarette and heated tobacco product smokers (n = 12) and exclusive heated tobacco product smokers (n = 39).

RESULTS

Of the 200 children, 53 (26.5%) had detectable urinary cotinine levels. Of these, 12 (6.0%) were classified as having heavy exposure to secondhand smoke (urinary cotinine concentration ≥ 5 ng/mL). Urinary cotinine concentrations among children living with exclusive heated tobacco product smokers were significantly lower than those among children living with exclusive combustion cigarette smokers, but higher than those in children whose family members did not smoke at all. Relative to exclusive combustion cigarette smokers, exclusive heated tobacco product smokers were significantly more likely to smoke indoors.

CONCLUSIONS

Secondhand aerosol exposure from heated tobacco products may be reduced but cannot be completely eliminated.

Hair and urinary 2-hydroxynaphthalene levels in the people living in a region with frequent oil pipeline incidents in Iran: Health risk assessment

Oil spills from pipeline accidents can have long-lasting health effects on residents of polluted regions. Assessing the potential health risk of these accidents is crucial for effective environmental health management. This study analyzed the concentration of 2-OHNAP in urine and hair as biomarkers of PAHs exposure among the people living in a region with frequent oil pipeline incident in Iran. Fifty pairs of hair and urine samples were collected from residents along with demographic information and dietary habits via a questionnaire. The concentration of 2-OHNAP was analyzed using high performance liquid chromatography coupled with fluorescence detector (HPLC-FLD). 2-OHNAP was detected in 100% of urine and 88% of hair samples. The mean concentration of 2-OHNAP in urine was 16.65 ± 21.98 μg/g creatinine and in hair was 8.16±7.62 ng/g dry weight (dw). However, there was no significant correlations between the levels of 2-OHNAP in urine and hair. The mean values of HQ and CR were below 1 and 10-6, respectively. Moreover, some simulated health risk indices were near the threshold levels, and the carcinogenic risk above 70% of the simulated CRs was above 10-6 as well. Therefore, the health risk attributed to the exposure to the parent compound of 2-OHNAP in the study area is currently acceptable, but it is not negligible and may be worsened in the future. This study provides a valuable scientific information for regional decision makers and stakeholders about human health programs and identification of environmental health priorities.

Hormonal, liver, and renal function associated with electronic waste (e-waste) exposure in Dhaka, Bangladesh

Electronic waste (e-waste) contains numerous metals and organic pollutants that have detrimental impacts on human health. We studied 199 e-waste recycling workers and 104 non-exposed workers; analyzed blood, urine, and hair samples to measure heavy metals, hormonal, liver, and renal function. We used quantile regression models to evaluate the impact of Pb, Cd, and Hg on hormonal, liver and renal function, and the role of DNA oxidative damage in mediating the relationship between exposures and outcomes. Exposed workers had higher blood lead (Pb) (median 11.89 vs 3.63 µg/dL), similar blood cadmium (Cd) (1.04 vs 0.99 µg/L) and lower total mercury (Hg) in hair (0.38 vs 0.57 ppm) than non-exposed group. Exposed workers also had elevated median concentrations of total triiodothyronine (TT3), aspartate aminotransferase (AST), alanine aminotransferase (ALT), urinary albumin, albumin creatinine ratio (ACR) and estimated glomerular filtration rate (eGFR) were significantly higher than non-exposed group (p≤0.05). Sex hormones including luteinizing hormone, follicle stimulating hormone, estrogen, progesterone and testosterone concentrations were not significantly different between exposed and non-exposed (all p≥0.05). The median concentration of ALT was 4.00 (95% CI: 0.23, 7.77), urinary albumin was 0.09 (95% CI: 0.06, 0.12) and ACR was 1.31 (95% CI: 0.57, 2.05) units higher in the exposed group compared to non-exposed group. Pb was associated with a 3.67 unit increase in the ALP (95% CI: 1.53, 5.80), 0.01 unit increase in urinary albumin (95% CI: 0.002, 0.01), and 0.07 unit increase in ACR (95% CI: 0.01, 0.13). However, no hormonal, renal, and hepatic parameters were associated with Cd or Hg. Oxidative DNA damage did not mediate exposure-outcome relationships (p≥0.05). Our data indicate e-waste exposure impairs liver and renal functions secondary to elevated Pb levels. Continuous monitoring, longitudinal studies to evaluate the dose-response relationship and effective control measure are required to protect workers from e-waste exposure.

Association between urinary concentrations of toxic metals/metalloids and oxidative stress in Brazilians living in areas affected by the Fundão dam failure

The Fundão Dam failure has been the most significant environmental disaster in Brazil. The catastrophe released large amounts of mining waste into the environment, including toxic metals/metalloids, which are recognized to induce carcinogenic effects. The urinary levels of 8-hydroxy-2'-deoxyguanosine (8OHdG), a widely accepted oxidative stress and carcinogenesis biomarker, provide a potential tool for assessing the disaster's health implications. This study investigated the association between urinary levels of some toxic metals/metalloids and 8OHdG in Brazilian individuals living in areas affected by the Fundão dam failure. Urinary concentrations of arsenic (As), cadmium (Cd), mercury (Hg), nickel (Ni), and lead (Pb) were determined using inductively coupled plasma mass spectrometry, while 8OHdG was analyzed by liquid chromatography-tandem mass spectrometry. Non-parametric bootstrap regression was used to estimate the associations between the urinary levels of toxic elements and 8OHdG. The results showed that except for Hg, urinary concentrations of all metals/metalloids analyzed here exceeded the reference ranges for the Brazilian population. The regression analysis revealed that As (0.337; CI 95%: 0.203; 0.474), Cd (0.268; CI 95%: 0.036; 0.520), and Ni (0.296; CI 950.108; 0.469) were positively associated with creatinine-adjusted urinary 8OHdG levels. Associations were not found for Hg (0.0122; CI 95%: -0.155; 0.183) and Pb (0.201; CI 95%: -0.040; 0.498). The current findings suggest that high exposure to toxic metals/metalloids might increase 8OHdG levels with potential adverse health effects. This study is the first one in which the relationship between toxic metals/metalloids and oxidative stress biomarkers is investigated in populations affected by environmental disasters. Further prospective studies are necessary to monitor exposure levels and explore additional health impacts.

Biomarkers for polycyclic aromatic hydrocarbons in human excreta: recent advances in analytical techniques-a review

Polycyclic aromatic hydrocarbons (PAHs) are widespread environmental pollutants that are generated by the incomplete combustion of organic materials. The main anthropogenic sources of PAHs are the combustion of solid fuels for heating purposes, illegal waste incineration, road transport and industries based on fossil fuels. PAHs can easily enter the body because they are present in all elements of the environment, including water, soil, air, and food. Due to their ubiquitous presence, PAHs, may exert a harmful effect on human health. Assessing PAH exposure through biomonitoring mostly involve techniques to measure the concentration of 1-hydroxypyrene in human urine. Nevertheless, through recent progress in analytical techniques, other common metabolites of PAHs in human biospecimens can be detected. A scientific literature search was conducted to determine which hydroxy derivatives of PAHs are markers of PAHs exposure and to reveal the leading sources of these compounds. Techniques for analyzing biological samples to identify OH-PAHs are also discussed. The most frequently determined OH-PAH in human urine is 1-hydroxypyrene, the concentration of which reaches up to a dozen ng/L in urine. Apart from this compound, the most frequently determined biomarkers were naphthalene and fluorene metabolites. The highest concentrations of 1- and 2-hydroxynaphthalene, as well as 2-hydroxyfluorene, are associated with occupational exposure and reach approximately 30 ng/L in urine. High molecular weight PAH metabolites have been identified in only a few studies. To date, PAH metabolites in feces have been analyzed only in animal models for PAH exposure. The most frequently used analytical method is HPLC-FLD. However, compared to liquid chromatography, the LOD for gas chromatography methods is at least one order of magnitude lower. The hydroxy derivatives naphthalene and fluorene may also serve as indicators of PAH exposure.

The influence of the co-exposure to polycyclic aromatic hydrocarbons and toxic metals on DNA damage in brazilian lactating women and their infants: A cross-sectional study using machine learning approaches

Polycyclic aromatic hydrocarbons (PAHs) and toxic metals are widely spread pollutants of public health concern. The co-contamination of these chemicals in the environment is frequent, but relatively little is known about their combined toxicities. In this context, this study aimed to evaluate the influence of the co-exposure to PAHs and toxic metals on DNA damage in Brazilian lactating women and their infants using machine learning approaches. Data were collected from an observational, cross-sectional study with 96 lactating women and 96 infants living in two cities. The exposure to these pollutants was estimated by determining urinary levels of seven mono-hydroxylated PAH metabolites and the free form of three toxic metals. 8-Hydroxydeoxyguanosine (8-OHdG) levels in the urine were used as the oxidative stress biomarker and set as the outcome. Individual sociodemographic factors were also collected using questionnaires. Sixteen machine learning algorithms were trained using 10-fold cross-validation to investigate the associations of urinary OH-PAHs and metals with 8-OHdG levels. This approach was also compared with models attained by multiple linear regression. The results showed that the urinary concentration of OH-PAHs was highly correlated between the mothers and their infants. Multiple linear regression did not show a statistically significant association between the contaminants and urinary 8OHdG levels. Machine learning models indicated that all investigated variables did not present predictive performance on 8-OHdG concentrations. In conclusion, PAHs and toxic metals were not associated with 8-OHdG levels in Brazilian lactating women and their infants. These novelty and originality results were achieved even after applying sophisticated statistical models to capture non-linear relationships. However, these findings should be interpreted cautiously because the exposure to the studied contaminants was considerably low, which may not reflect other populations at risk.

Children's exposure to polycyclic aromatic hydrocarbon (PAHs): a review on urinary 1-hydroxypyrene and associated health effects

This article reviewed the published studies on the environmental exposure to polycyclic aromatic hydrocarbons (PAHs) among children and assessed the urinary 1-hydroxypyrene (1-OHP) level as a biomarker of exposure to PAHs. The current knowledge of the potential health effects of increased 1-OHP in children was reviewed. Additionally, the influence of genetic polymorphism on the urinary 1-OHP level was discussed in this review. The assembled data showed that children who are attending schools or living close to industrial and polluted urban areas might have greater exposure to higher concentrations of PAHs with a higher level of urinary 1-OHP when compared to those children living in rural areas. Urinary 1-OHP may be a reliable biomarker for determining the genotoxic effects, oxidative stress and inflammation caused by exposure to PAHs. Strong research evidence indicated that the total body burden of PAHs should be evaluated by biomonitoring of 1-OHP in line with other urinary PAHs metabolites (with 2-3 rings) to evaluate recent total exposure to PAHs. Overall, the study suggests implementing a mitigation plan to combat air pollution to provide a cleaner environment for children.

Passive smoking and urinary oxidative biomarkers: A pilot study of healthy travelers from Los Angeles to Beijing

There is a great heterogeneity in smoking prevalence and tobacco control policy across different countries. However, it is unknown whether this heterogeneity could cause increased passive smoking and adverse health effects among international travelers. In this pilot study, we collected 190 urine samples from 26 Los Angeles residents before (LA-before), during (Beijing), and after (LA-after) a 10-week visit to Beijing to measure biomarkers of passive smoking (cotinine), exposure to polycyclic aromatic hydrocarbons (OH-PAHs), and oxidative stress (malondialdehyde, 8-isoprostane, and uric acid). The geometric mean concentrations of urinary cotinine were 0.14, 1.52, and 0.22 μg/g creatinine in LA-before, Beijing, and LA-after, respectively. Likewise, OH-PAH levels were significantly higher in Beijing as compared to LA-before or LA-after, in association with the urinary cotinine levels. One-fold increase in urinary cotinine levels was associated with 10.1% (95% CI: 5.53-14.8%), 8.75% (95% CI: 2.33-15.6%), and 25.4% (95%CI: 13.1-39.1%) increases in urinary levels of malondialdehyde, 8-isoprotane, and uric acid, respectively. OH-PAHs mediated 9.1-23.3% of the pro-oxidative effects associated with passive smoking. Taken together, our findings indicate that traveling to a city with higher smoking prevalence may increase passive smoking exposure, in association with pro-oxidative effects partially mediated by PAHs.

Children's exposure to polycyclic aromatic hydrocarbons in the Valencian Region (Spain): Urinary levels, predictors of exposure and risk assessment

Polycyclic aromatic hydrocarbons (PAHs) are pollutants that are released into the environment during incomplete combustion of organic matter and which can have a negative effect on human health. PAHs enter the human body mostly through ingestion of food or inhalation of tobacco smoke. The purpose of the present study is to evaluate the internal levels of PAHs that children living in the Valencian Region (Spain) are exposed to. In total, we measured eleven biomarkers of exposure to naphthalene, fluorene, phenanthrene, pyrene, and benzo(a)pyrene in the urine of 566 children aged 5-12. The analytical method was based on a liquid-liquid extraction of the PAH metabolites from the urine samples, followed by their determination by liquid chromatography coupled to tandem mass spectrometry. In addition, we used a questionnaire to collect the socio-demographic characteristics and 72 h dietary recall information of the participants in our study. Overall, we detected PAH metabolites in more than 78% of the children, with the exception of 3-hydroxyfluorene and 3-hydroxybenzo(a)pyrene, which were found in less than 37% of the analyzed samples. The most abundant biomarker found was 2-hydroxynaphthalene, with a geometric mean of 10 ng·ml^-1. Reference values (RV₉₅) ranging from 0.11 (4-hydroxyphenanthrene) to 53 ng·ml^-1 (2-hydroxynaphthalene) in urine of Spanish children were derived from the present study. According to the statistical analysis, the factors that were significantly associated with the internal exposure to PAHs were province of residence, body mass index (BMI), children's age, consumption of plastic-wrapped food, and dietary habits. The estimated daily intakes in geometric mean terms ranged from 5 (fluorene) to 204 ng·kg-bw^-1·day^-1 (naphthalene). Risk assessment calculations showed higher hazard quotients and hazard indexes for children aged 5-8 than those aged 9-12, but all were below 1. In conclusion, no potential non-cancer health risk due to PAH exposure was observed in children living in Spain.

Decreased levels of urinary di-2-ethylhexyl phthalate (DEHP) metabolites and biomarkers of oxidative stress in children exposed to DEHP-tainted foods in Taiwan in 2011: A 44-month follow-up

A major health scandal involving DEHP-tainted (di-2-ethylhexyl phthalate) foodstuffs occurred in Taiwan in 2011. We investigated temporal relationships between urinary DEHP metabolites and biomarkers of oxidative stress in two cohorts of potentially affected children during that food scandal. One cohort was collected from Kaohsiung Medical University Hospital in southern Taiwan between May and June of 2011 (the KMUH cohort). This cohort was followed up at 2, 6, and 44 months. The other cohort was collected from a nationwide health survey conducted by Taiwan's National Health Research Institutes (the NHRI cohort) for potentially affected people between August 2012 and January 2013. Both cohorts only included children 10 years old and younger who had provided enough urine for analysis of urinary DEHP oxidative metabolites and two markers of oxidative stress: 8-oxo-2'-deoxyguanosine (8-OHdG) and malondialdehyde (MDA). The KMUH cohort had a simultaneous and significant decrease in urinary DEHP metabolites, 8-OHdG, and MDA, with the lowest concentrations found at the 6-month follow up and maintained until the 44-month follow up, consistent with those from NHRI cohort at ∼15-18 months post-scandal (p > 0.05). There were decreases in both DEHP metabolites and oxidative stress markers across the populations, but no association was observed between DEHP metabolites and oxidative stress markers in individuals in the two cohorts. Continued follow-up is needed to determine long-term health consequences in these children.

Association of internal exposure to polycyclic aromatic hydrocarbons with inflammation and oxidative stress in prediabetic and healthy individuals

Polycyclic aromatic hydrocarbons (PAHs) are key air pollutants that may contribute to the risk of numerous diseases by inducing inflammation and oxidative stress. Individuals with metabolic disorders may be more susceptible to PAH-induced inflammation and oxidative stress. To test this hypothesis, we designed a panel study involving 60 patients with pre-type 2 diabetes (pre-T2D) and 60 reference participants, and conducted up to seven repeated clinical examinations. Urinary metabolites of PAHs (i.e., OH-PAHs), measured as indicators of total PAH exposure, showed significant associations with markers of respiratory and systemic inflammation, including exhaled nitric oxide, interleukin (IL)-6 in exhaled breath condensate, and blood IL-2 and IL-8 levels and leucocyte count. The most significant effect was on urinary malondiadehyde (MDA), a marker of lipid peroxidation; a onefold increase of OH-PAHs was associated with 9.2-46.0% elevation in MDA in pre-T2D participants and 9.8-31.2% increase in healthy references. Pre-T2D participants showed greater increase in MDA, suggesting that metabolic disorder enhanced the oxidative damage induced by PAH exposure. This study revealed the association between PAH exposure and markers of inflammation and oxidative stress, and the enhanced responses of pre-T2D patients suggested that individuals with metabolic disorders were more susceptible to the adverse health effects of PAH exposure.

Emission-related Heavy Metal Associated with Oxidative Stress in Children: Effect of Antioxidant Intake

Heavy metals, the common pollutants emitted from industrial activities, are believed to cause harmful effects, partially through the mechanism of elevated oxidative stress, and antioxidant intake has been hypothesized to provide a potential protective effect against oxidative stress. This study aims to investigate the heavy metal exposure and the associated oxidative damage of young children living near a petrochemical complex and to assess the protective effect of antioxidant intake. There were 168 children recruited from the kindergartens near a huge petrochemical complex, with 87 as the high exposure group and 81 as the low exposure group. Urinary concentrations of eleven metals were detected by inductively coupled plasma mass spectrometry, and four biomarkers of oxidative stress were measured in urine by liquid chromatography-tandem mass spectrometry. The food frequency questionnaire was collected to assess participants’ intake of antioxidants. Multiple linear regression was performed to determine the predictors of metals for oxidative stress and to measure the beneficial effect of antioxidants. Weighted quantile sum regression was performed to determine the contributors among metals to the oxidative stress. Results showed that high exposure group had significantly higher concentrations of chromium, manganese, nickel, arsenic, strontium, cadmium, and lead when compared to those in low exposure group. There was no obviously difference on the total antioxidant intake and dietary profile between two groups. The elevated levels of two oxidative stress markers were significantly associated with most of the urinary metal concentrations in all study subjects after adjusting confounders, while no significant association was found between oxidative stress and antioxidant intake. Among the metals, mercury and strontium showed the dominated contributions for elevated levels of oxidative stress. It concluded that higher metal exposure was associated with elevated oxidative stress but with no protective effect by antioxidant intake among the young children residents near a petrochemical industry.

Effect of exposure to phthalates on association of polycyclic aromatic hydrocarbons with 8-hydroxy-2'-deoxyguanosine

BACKGROUND

Although polycyclic aromatic hydrocarbons (PAHs) and phthalates separately related to oxidative DNA damage have been reported, the joint effect of them on oxidative DNA damage need to be evaluated.

METHODS

In this pilot study, 106 participants were recruited from the community-dwelling residents (n=1240) of Wuhan city, China. Each individual provided three continuous days of spot urine samples for measuring the urinary monohydroxylated PAHs (OH-PAHs), phthalates metabolites and 8-hydroxy-2'-deoxyguanosine (8-OHdG) levels in the two seasons. Linear mixed effect model and Bayesian Kernel Machine Regression (BKMR) were used to analyze joint effect of urinary PAHs and phthalates metabolites on urinary 8-OHdG levels. We measured cellular and mitochondrial reactive oxygen species (ROS), malondialdehyde (MDA) and glutathione peroxidase (GSH-Px) levels as well as IL-6 and IL-8 secretions by the corresponding commercial kits in HepG2 cells treated with di (2-ethylhexyl) phthalate (DEHP, 62.5, 125.00, 250.00, 500.00 or 1000.00μM) alone, benzo[a]pyrene (BaP, 50.00μM) alone or both DEHP and BaP.

RESULTS

Linear mixed effect model showed that each of urinary PAHs metabolite was positively associated with urinary 8-OHdG levels; urinary level of mono (2-ethylhexyl) phthalate or monoisononyl phthalate was positively associated with urinary 8-OHdG levels; BKMR model indicated that a positive association of eight OH-PAHs with urinary 8-OHdG levels, nine urinary phthalates metabolites enhanced the association. We found that DEHP at the indicated concentration plus 50.00μM BaP increased cellular and mitochondrial ROS levels, IL-6 and IL-8 secretions at 24 and 48h as well as MDA levels and GSH-Px activities at 48h, compared to the solvent control.

CONCLUSIONS

Exposure to certain dose phthalates may attenuate the positive association of PAHs exposure with oxidative DNA damage in the body. DEHP at the certain concentrations enhanced BaP-induced mitochondrial ROS, pro-inflammatory response and the activation of the antioxidant defense system in HepG2 cells.

Determination of 3-Hydroxybenzo[a]pyrene Glucuronide/Sulfate Conjugates in Human Urine and Their Association with 8-Hydroxydeoxyguanosine

While 3-hydroxybenzo[a]pyrene (3-OHBaP) is a preferable biomarker to assess human exposure to benzo[a]pyrene (BaP), a sensitive and simple method is lacking. In this study, a specific and sensitive method based on liquid chromatography coupled with electrospray tandem mass spectrometry (LC-ESI-MS/MS) was developed for direct analysis of 3-OHBaP glucuronide and sulfate conjugates in human urine samples without enzymatic hydrolysis. The limits of detection (LODs) were 0.06 ng L^-1 for BaP-3-sulfate (BaP-3-S) and 0.16 ng L^-1 for BaP-3-glucuronide (BaP-3-G), which showed high sensitivity. Both compounds showed excellent linearity (r² > 0.99) in the range of 0.01-10 μg L^-1 in the instrumental calibration. The absolute recoveries of the target analytes spiked in human urine for the entire analytical procedure were 68.3 ± 4.96% (mean ± SD) and 63.7 ± 5.47% for BaP-3-S and BaP-3-G, respectively. This method was applied to quantify BaP-3-G and BaP-3-S in 150 urine samples collected from healthy volunteers. The mean concentration of BaP-3-S was 0.67 ng g^-1 creatinine (<LOD to 10.20 ng g^-1 creatinine), about 10-fold lower than that of BaP-3-G (6.73 ng g^-1 creatinine, < LOD to 52.64 ng g^-1 creatinine). For comparison, we also detected the concentration of free 3-OHBaP in 15 randomly selected samples without enzymatic hydrolysis and found at least >98% of 3-OHBaP is excreted mainly in these two conjugated forms in human urine. A statistically significant positive association was observed between urinary 3-OHBaP conjugates and urinary 8-OHdG levels (p < 0.001) in the general population. This study developed a sensitive and simple method to determine urinary glucuronide/sulfate conjugated BaP metabolites and for the first time found that BaP exposure associated with 8-OHdG levels in the general population.

Children environmental exposure to particulate matter and polycyclic aromatic hydrocarbons and biomonitoring in school environments: A review on indoor and outdoor exposure levels, major sources and health impacts

Children, an important vulnerable group, spend most of their time at schools (up to 10 h per day, mostly indoors) and the respective air quality may significantly impact on children health. Thus, this work reviews the published studies on children biomonitoring and environmental exposure to particulate matter (PM) and polycyclic aromatic hydrocarbons (PAHs) at school microenvironments (indoors and outdoors), major sources and potential health risks. A total of 28, 35, and 31% of the studies reported levels that exceeded the international outdoor ambient air guidelines for PM₁₀, PM_2.5, and benzo(a)pyrene, respectively. Indoor and outdoor concentrations of PM₁₀ at European schools, the most characterized continent, ranged between 7.5 and 229 μg/m³ and 21-166 μg/m³, respectively; levels of PM_2.5 varied between 4 and 100 μg/m³ indoors and 6.1-115 μg/m³ outdoors. Despite scarce information in some geographical regions (America, Oceania and Africa), the collected data clearly show that Asian children are exposed to the highest concentrations of PM and PAHs at school environments, which were associated with increased carcinogenic risks and with the highest values of urinary total monohydroxyl PAH metabolites (PAH biomarkers of exposure). Additionally, children attending schools in polluted urban and industrial areas are exposed to higher levels of PM and PAHs with increased concentrations of urinary PAH metabolites in comparison with children from rural areas. Strong evidences demonstrated associations between environmental exposure to PM and PAHs with several health outcomes, including increased risk of asthma, pulmonary infections, skin diseases, and allergies. Nevertheless, there is a scientific gap on studies that include the characterization of PM fine fraction and the levels of PAHs in the total air (particulate and gas phases) of indoor and outdoor air of school environments and the associated risks for the health of children. There is a clear need to improve indoor air quality in schools and to establish international guidelines for exposure limits in these environments.

Multiple-metal exposure, diet, and oxidative stress in Uruguayan school children

Oxidative stress (OS) is an important consequence of exposure to toxic metals but it is unclear to what extent low-level metal exposures contribute to OS in children. We examined the cross-sectional association between urinary concentrations of arsenic (As), cadmium (Cd), and lead (Pb) and urinary markers of OS: F₂-8α isoprostane and 8-hydroxy-2-deoxy-guanosine (8-OHdG). We also tested effect modification by dietary intakes. Of the 211 children aged 6-8 years living in Montevideo who were eligible for the study because they had at least one OS marker measured via ELISA, 143 were included in a complete-case analysis. Urinary metals were measured with inductively coupled plasma mass spectrometry (ICP-MS: Pb, Cd) and high-performance liquid chromatography online with hydride generation ICP-MS (As-metabolites); concentrations were log₂-transformed. All urinary markers were adjusted for specific gravity of urine. Two 24-h dietary recalls were conducted to estimate children's dietary intakes, including total fruit and vegetable consumption and vitamin C, zinc and fiber intake. Ordinary least square (OLS) and weighted quantile sum (WQS) regressions were used to estimate the association between metals and each OS marker as outcome. Metal exposure was generally low: median urinary As, Cd, Pb 9.6 μg/L, 0.06 μg/L and 1.9 μg/L, respectively. Median 8-isoprostane concentration was 1.1 and 8-OHdG 39.6 ng/mL. Log₂-transformed urinary As concentrations were positively associated with 8-OHdG concentrations (10.90 [3.82, 17.97]) in covariate-adjusted OLS models which also took account of exposure to Cd and Pb. In WQS, a mixture index was also associated with higher 8-OHdG (8.71 [1.12, 16.3] for each 25% increase in index value), mostly driven by As exposure. There was little evidence of effect modification by dietary antioxidants. In sum, even at low-level, As exposure is associated with detectable oxidative damage to the DNA.

Blood concentrations of lead, cadmium, mercury and their association with biomarkers of DNA oxidative damage in preschool children living in an e-waste recycling area

Reactive oxygen species (ROS)-induced DNA damage occurs in heavy metal exposure, but the simultaneous effect on DNA repair is unknown. We investigated the influence of co-exposure of lead (Pb), cadmium (Cd), and mercury (Hg) on 8-hydroxydeoxyguanosine (8-OHdG) and human repair enzyme 8-oxoguanine DNA glycosylase (hOGG1) mRNA levels in exposed children to evaluate the imbalance of DNA damage and repair. Children within the age range of 3-6 years from a primitive electronic waste (e-waste) recycling town were chosen as participants to represent a heavy metal-exposed population. 8-OHdG in the children's urine was assessed for heavy metal-induced oxidative effects, and the hOGG1 mRNA level in their blood represented the DNA repair ability of the children. Among the children surveyed, 88.14% (104/118) had a blood Pb level >5 μg/dL, 22.03% (26/118) had a blood Cd level >1 μg/dL, and 62.11% (59/95) had a blood Hg level >10 μg/dL. Having an e-waste workshop near the house was a risk factor contributing to high blood Pb (r _s  = 0.273, p < 0.01), while Cd and Hg exposure could have come from other contaminant sources. Preschool children of fathers who had a college or university education had significantly lower 8-OHdG levels (median 242.76 ng/g creatinine, range 154.62-407.79 ng/g creatinine) than did children of fathers who had less education (p = 0.035). However, we did not observe a significant difference in the mRNA expression levels of hOGG1 between the different variables. Compared with children having low lead exposure (quartile 1), the children with high Pb exposure (quartiles 2, 3, and 4) had significantly higher 8-OHdG levels (β _Q2 = 0.362, 95% CI 0.111-0.542; β _Q3 = 0.347, 95% CI 0.103-0.531; β _Q4 = 0.314, 95% CI 0.087-0.557). Associations between blood Hg levels and 8-OHdG were less apparent. Compared with low levels of blood Hg (quartile 1), elevated blood Hg levels (quartile 2) were associated with higher 8-OHdG levels (β _Q2 = 0.236, 95% CI 0.039-0.406). Compared with children having low lead exposure (quartile 1), the children with high Pb exposure (quartiles 2, 3, and 4) had significantly higher 8-OHdG levels.

Assessment of exposure to polycyclic aromatic hydrocarbons in preschool children: Levels and impact of preschool indoor air on excretion of main urinary monohydroxyl metabolites

The present work aimed to assess exposure of preschool children to polycyclic aromatic hydrocarbons (PAHs) by environmental monitoring (eighteen compounds in air) and biomonitoring (six urinary biomarkers of exposure (OH-PAHs)). The impact of preschool indoor air on excretion of urinary monohydroxyl metabolites was also evaluated. Gaseous and particulate-bound PAHs were simultaneously collected indoors and outdoors in two Portuguese preschools. PAHs and OH-PAHs were quantified by high-performance liquid chromatography with fluorescence and photodiode array detection. Total air (gaseous+total suspended particles) levels of PAHs (ΣPAHs) were higher indoors than outdoors. Gaseous phase (composed by ≥98% of 2-3 rings compounds) and particulate-bound PAHs (90-99% of 5-6 rings) accounted for 93-95% and 5-7% of ΣPAHs in indoor air, respectively. Total (including probable/possible) carcinogenic PAHs represented 26-45% of ΣPAHs; naphthalene and dibenz[a,h]anthracene were the strongest contributors. A similar distribution profile was observed between airborne PAHs and urinary OH-PAHs. Urinary 1-hydroxynaphthalene+1-hydroxyacenaphthene represented more than 78% of ΣOH-PAHs, being followed by 2-hydroxyfluorene, 1-hydroxypyrene, and 1-hydroxyphenanthrene. 3-hydroxybenzo[a]pyrene (PAH biomarker of carcinogenicity) was not detected. Results suggest that children had preschool indoor air as their major exposure source of naphthalene and acenaphthene, while no conclusion was reached regarding fluorene, phenanthrene and pyrene.

Environmental exposure to human carcinogens in teenagers and the association with DNA damage

BACKGROUND

We investigated whether human environmental exposure to chemicals that are labeled as (potential) carcinogens leads to increased (oxidative) damage to DNA in adolescents.

MATERIAL AND METHODS

Six hundred 14-15-year-old youngsters were recruited all over Flanders (Belgium) and in two areas with important industrial activities. DNA damage was assessed by alkaline and formamidopyrimidine DNA glycosylase (Fpg) modified comet assays in peripheral blood cells and analysis of urinary 8-hydroxydeoxyguanosine (8-OHdG) levels. Personal exposure to potentially carcinogenic compounds was measured in urine, namely: chromium, cadmium, nickel, 1-hydroxypyrene as a proxy for exposure to other carcinogenic polycyclic aromatic hydrocarbons (PAHs), t,t-muconic acid as a metabolite of benzene, 2,5-dichlorophenol (2,5-DCP), organophosphate pesticide metabolites, and di(2-ethylhexyl) phthalate (DEHP) metabolites. In blood, arsenic, polychlorinated biphenyl (PCB) congeners 118 and 156, hexachlorobenzene (HCB), dichlorodiphenyltrichloroethane (DDT) and perfluorooctanoic acid (PFOA) were analyzed. Levels of methylmercury (MeHg) were measured in hair. Multiple linear regression models were used to establish exposure-response relationships.

RESULTS

Biomarkers of exposure to PAHs and urinary chromium were associated with higher levels of both 8-OHdG in urine and DNA damage detected by the alkaline comet assay. Concentrations of 8-OHdG in urine increased in relation with increasing concentrations of urinary t,t-muconic acid, cadmium, nickel, 2,5-DCP, and DEHP metabolites. Increased concentrations of PFOA in blood were associated with higher levels of DNA damage measured by the alkaline comet assay, whereas DDT was associated in the same direction with the Fpg-modified comet assay. Inverse associations were observed between blood arsenic, hair MeHg, PCB 156 and HCB, and urinary 8-OHdG. The latter exposure biomarkers were also associated with higher fish intake. Urinary nickel and t,t-muconic acid were inversely associated with the alkaline comet assay.

CONCLUSION

This cross-sectional study found associations between current environmental exposure to (potential) human carcinogens in 14-15-year-old Flemish adolescents and short-term (oxidative) damage to DNA. Prospective follow-up will be required to investigate whether long-term effects may occur due to complex environmental exposures.

Co-exposure to polycyclic aromatic hydrocarbons, benzene and toluene and their dose-effects on oxidative stress damage in kindergarten-aged children in Guangzhou, China

Polycyclic aromatic hydrocarbons (PAHs), benzene and toluene (BT) are ubiquitous toxic pollutants in the environment. Children are sensitive and susceptible to exposure to these contaminants. To investigate the potential oxidative DNA damage from the co-exposure of PAHs and BT in children, 87 children (aged 3-6) from a kindergarten in Guangzhou, China, were recruited. Ten urinary PAHs and four BT metabolites, as well as 8-hydroxy-2'-deoxyguanosine (8-OHdG, a biomarker of oxidative DNA damage)in urine, were determined using a liquid chromatography tandem mass spectrometer. The results demonstrated that the levels of PAHs and BT in children from Guangzhou were 2-30 times higher than those in children from the other countries based on a comparison with recent data from the literature. In particular, the difference is more substantial for pyrene and volatile BT. Co-exposure to PAHs and BT could lead to additive oxidative DNA damage. Significant dose-effects were observed between the sum concentration of urinary monohydroxylated metabolites of PAHs (∑OH-PAHs), the sum concentration of the metabolites of BT (∑BT) and 8-OHdG levels. Every one percent increase in urinary PAHs and BT generated 0.33% and 0.02% increases in urinary 8-OHdG, respectively. We also determined that the urinary levels of PAHs and BT were negatively associated with the age of the children. Moreover, significant differences in the levels of ∑OH-PAHs and ∑BT were determined between 3- and 6-year-old children (p<0.05), which may be caused by different metabolism capabilities or inhalation frequencies. In conclusion, exposure to PAHs or BT could lead to oxidative DNA damage, and 8-OHdG is a good biomarker for indicating the presence of DNA damage. There exists a significant dose-effect relationship between PAH exposure, BT exposure and the concentration of 8-OHdG in urine. Toddlers (3-4 years old) face a higher burden of PAH and BT exposure compared with older children.

Levels of polycyclic aromatic hydrocarbons in maternal serum and risk of neural tube defects in offspring

Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous environmental pollutants, and have been reported to be a risk factor for human neural tube defects (NTDs). We investigated the relationship between PAH concentrations in maternal serum and NTD risk in offspring using a case-control study design, and explored the link between PAH concentrations to household energy usage characteristics and life styles. One hundred and seventeen women who had NTD-affected pregnancies (cases) and 121 women who delivered healthy infants (controls) were recruited in Northern China. Maternal blood samples were collected at pregnancy termination or at delivery. Twenty-seven PAHs were measured by gas chromatography-mass spectrometry. The concentrations of 13 individual PAHs detected were significantly higher in the cases than in the controls. Clear dose-response relationships between concentrations of most individual PAHs and the risk of total NTDs or subtypes were observed, even when potential covariates were adjusted for. High-molecular-weight PAHs (H-PAHs) showed higher risk than low-molecular-weight PAHs (L-PAHs). No associations between PAH concentrations and indoor life styles and energy usage characteristics were observed. It was concluded that maternal exposure to PAHs was associated with an increased risk of NTDs, and H-PAHs overall posed a higher risk for NTDs than L-PAHs.

Determination of low urinary 8-hydroxy-2`-deoxyguanosine excretion with capillary electrophoresis and molecularly imprinted monolith solid phase microextraction

As a sensitive biomarker, the level of 8-hydroxy-2`-deoxyguanosine (8-OHdG) indicates the extent of DNA oxidative damage of subject. However its determination in human urine is confounded by trace content and a complex matrix. In this study, a new approach of solid phase microextraction (SPME) coupled to capillary electrophoresis and electrochemical detection was developed with molecularly imprinted monolithic column as extraction sorbent. The tailor made monolith exhibited high extraction efficiency with the enrichment factor 73 for 8-OHdG owing to its special porous structure and inherent selectivity. Under optimal conditions, appreciable sensitivity had been achieved with a limit of detection of 2.61 nmol/L (signal/noise=3) and a limit of quantification of 8.63 nmol/L (signal/noise=10), respectively. As an alternative of precise 8-OHdG determination, wide range linearity had been achieved with 0.01-1.50 μmol/L and RSDs with 3.70% for migration time and 4.80% for peak current (10-1000 nmol/L). 106 samples with relative low extents of DNA oxidative damage were collected and analyzed which including coke plant workers, traffic policemen, taxi drivers and healthy students. Elevated urinary 8-OHdG excretions of subjects may correlate to working condition, occupational exposure, or lifestyle.

Concentrations and profiles of urinary polycyclic aromatic hydrocarbon metabolites (OH-PAHs) in several Asian countries

Concentrations of 12 hydroxylated polycyclic aromatic hydrocarbons (OH-PAHs) were determined in 306 urine samples collected from seven Asian countries (China, India, Japan, Korea, Kuwait, Malaysia, and Vietnam) by high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS). The total concentrations of OH-PAHs found in the seven Asian countries were in the following increasing order: Malaysia (median: 2260 pg/mL) < Japan (4030 pg/mL) < China (5770 pg/mL) < India (6750 pg/mL) < Vietnam (8560 pg/mL) < Korea (9340 pg/mL) < Kuwait (10170 pg/mL). The measured urinary concentrations of 1-hydroxypyrene (1-PYR) in samples from Malaysia, Korea, and Japan (∼ 100 pg/mL) were similar to those reported for North America and Western Europe. The concentrations of 1-PYR in urine samples from China, India, and Vietnam were 4-10 times higher than those reported for other countries, thus far. Among the 12 OH-PAH compounds analyzed, hydroxynaphthalene (NAP: sum of 1-hydroxynaphthalene and 2-hydroxynaphthalene) was the dominant compound (accounting for 60-90% of total OH-PAHs), followed by hydroxyphenanthrene (PHEN: sum of 2-hydroxyphenanthrene, 3-hydroxyphenanthrene, 4-hydroxyphenanthrene, and 9-hydroxyphenanthrene [3-16%]), 2-hydroxyfluorene (3-20%), and 1-PYR (2-8%). The total daily intakes (DIs) of PAHs were estimated based on the urinary concentrations of their metabolites. The DIs of naphthalene were found to be higher for populations in Korea, Kuwait, and Vietnam (> 10 μg/day) than those of the other countries studied (∼ 5 μg/day). The DIs of phenanthrene and pyrene (> 10 μg/day) in the populations of China, India, and Vietnam were higher than those estimated for the populations in the other countries studied (∼ 5 μg/day).

Polycyclic aromatic hydrocarbons (PAHs) as determinants of various anthropometric measures of birth outcome

Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous environmental contaminants that are known to induce oxidative stress. There have been several reports about the link between PAH exposure and complications in pregnancy. This cross-sectional study was conducted to: (1) measure the levels of benzo(a)anthracene (BaA), chrysene (Ch), benzo(b)fluoranthene (BbF), benzo(a)pyrene (BaP), and dibenzo(a,h)anthracene (DBahA) in placentas and maternal and -umbilical cord blood obtained at delivery from 1578 women between June 2005 and 2006 in the area of Al-Kharj, Saudi Arabia; (2) assess their influence on various anthropometric measures of birth outcome taking into consideration the carcinogenic properties of these PAHs; and (3) determine the degree of PAH-related oxidative DNA damage and birth outcome. Among the five tested PAHs, only BaP was carcinogenic; therefore, the levels of the other four probable or possible carcinogenic PAHs (BaA, Ch, BaF, and DBahA) were summed as ∑4-PAHs. Levels of 1-hydroxypyrene (1-HP) were determined in maternal urine samples as a biomarker of PAH internal dose. Urinary cotinine (COT) was measured as an index of smoking. The following markers of oxidative stress were selected: malondialdehyde (MDA) in cord (C-MDA) and maternal (M-MDA) serum and 8-hydroxy-2-deoxyguanosine (8-OHdG) in maternal urine. None of the tested PAHs was found in maternal or cord blood. However, all five PAH compounds were detected in placentas; Ch was the highest (6.582 μg/kg dry wt.), and BaA was the lowest (0.236 μg/kg dry wt.). The mean concentration of urinary 1-HP found in this study was 0.216 ± 0.856 μg/g Cr. After adjusting for gestational age and other confounding variables, regression models revealed an inverse relationship between placental weight, cord length and placental BaP. A similar trend was observed between cord length and ∑4-PAHs in placental tissues. Urinary 1-HP, though, cannot be used as an unequivocal biomarker of PAH exposure, but it can be an appropriate indicator of exposure to environmental tobacco smoke (ETS). The data demonstrate that ETS exposure (as measured by urinary COT) may adversely affect birth outcome as shown by reduced head circumference, birth weight, and birth length, as well as increased cephalization index. The positive relationship between 8-OHdG levels and 1-HP in urine provides evidence of an oxidative stress mechanism. Although this study provides no direct evidence of an association between PAH exposure and DNA damage, increased oxidative stress in the form of lipid peroxidation significantly affected various birth measures. Therefore, there is a need for studies regarding PAH exposure and its associated biological effects to determine the extent of potential fetal damage as well as possible long-term effects, such as cancer.

Exposure to chemical mixtures in Mexican children: high-risk scenarios

In developing countries, the management of environmental toxicants is inadequate, thus, humans may be exposed to levels higher than normal levels (background levels). Therefore, the aim of this study was to evaluate the exposure level of Mexican children to dichlorodiphenyltrichloroethane (DDT), dichlorodiphenyldichloroethylene (DDE), lead, and polycyclic aromatic hydrocarbons [using 1-hydroxypyrene (1-OHP) as exposure biomarker] and to assess the percentage of children exposed to these four compounds at concentrations higher than normal in each community studied. We performed random sampling in eight communities in Mexico (five communities in Chiapas State and three communities in San Luis Potosi State). DDT and DDE were analyzed by gas chromatography/mass spectrometry, the quantification of lead in blood was performed using atomic absorption spectrophotometry, and 1-OHP analyses were performed using HPLC with a fluorescence detector. Elevated DDT, DDE, and 1-OHP levels were found in children living in the indigenous communities of Chiapas State, while higher blood lead levels were found in two communities in San Luis Potosí. Approximately 30 % of children living in Chiapas were exposed to all four compounds at concentrations above the guidelines for each compound, whereas 48 % of children studied were exposed to all four contaminants at concentrations higher than normal in a community in San Luis Potosí State. As expected, our results showed that in hot spots, children are exposed to levels higher than normal. Therefore, child environmental health programs are urgently needed.

Delineating the degree of association between biomarkers of arsenic exposure and type-2 diabetes mellitus

Non-carcinogenic effects in low-level (< 100 μgL(-1)) arsenic (As)-impacted populations, such as the development and progression of type-2 diabetes mellitus (T2DM), are often neglected given the primary emphasis of public health authorities on As carcinogenicity. We gathered studies reporting urinary biomarkers of As exposure (U-As) and biomarkers associated with T2DM and its complications (U-T2DM), such as renal damage, oxidation stress, low-grade inflammation, and endothelial damage. Studied U-T2DM biomarkers were: 8-hydroxy-2'deoxyguanosine, N-acetyl-β-d-glucosaminidase, β2-microglobulin, and albumin. Data was expressed as: either arithmetic means and standard deviations, or geometric means and geometric standard deviations, or correlation coefficients of U-As and U-T2DM. Urinary As concentrations were consistently associated with the aforementioned biomarkers of T2DM pathologic complications. Despite the limited selectivity of the selected T2DM biomarkers, a per unit change in As exposure level was reflected in the corresponding T2DM biomarker urinary concentrations. Our systematic review provides new evidence on the role of environmental As exposures influencing the T2DM disease process. Additional epidemiologic studies onto the association between As and T2DM should incorporate both urinary As and T2DM biomarkers, as suggested in this study, in order to evaluate subclinical effects of low-level As exposures.

Effect of mercury (Hg) dental amalgam fillings on renal and oxidative stress biomarkers in children

We examined the effect of mercury (Hg) associated with dental amalgam fillings on biomarkers of renal and oxidative stress in children between the ages of 5-15.5 years. Urine samples were analyzed for N-acetyl-β-D-glucosaminidase (NAG), α(1)-microglobulin (α(1)-MG), β(2)-microglobulin (β(2)-MG), retinol binding protein (RBP), albumin (ALB), 8-hydroxy-2-deoxyguanosine (8-OHdG) and malondialdehyde (MDA). The level of urinary Hg (UHg-C) was calculated as μg/g creatinine. Multiple regression analyses revealed that the excretion of urinary NAG was significantly associated with the presence of dental amalgam fillings (β=0.149, P=0.03) and the levels of UHg-C (β=0.531, P=0), with an interaction between the two (P=0). The increase in urinary NAG in relation to UHg-C levels had a dose-effect pattern. The lowest observed effect was seen at UHg-C levels above 1.452 μg/g creatinine, which is lower than previously reported. In contrast, α(1)-MG was negatively associated with the presence of dental amalgam fillings (β=-0.270, P=0), but positively with UHg-C levels (β=0.393, P=0). There were 7 children without, and one child with, dental amalgam fillings with urinary α(1)-MG levels above the reference limit of >7 mg/g creatinine. Even though α(1)-MG seems to be a reliable biomarker for early changes in renal functions, it might exert its effect only at a higher level of exposure. An inverse relationship was also observed between urinary 8-OHdG levels and the presence of dental amalgam fillings. This might suggest that the dental amalgam does not increase DNA damage but reduces the capacity to repair DNA, leading to lower urinary excretion of 8-OHdG. On the other hand, we found that Hg affected the excretion of urinary 8-OHdG in a dose-related pattern that was mostly associated with long-term exposure to low Hg levels. Urinary NAG levels were positively associated with urinary MDA levels (β=0.516, P=0) but not with 8-OHdG (β=0.134, P=0.078) after adjustment for potential confounders. Both UHg-C and the presence of dental amalgam fillings remained predictors of the NAG model. Our data provide evidence that low exposure to Hg from dental amalgam fillings exerts an effect on kidney tubular functions in children. Oxidative stress may have played a role in this mechanism. The results of this study would also suggest that urinary NAG is the most sensitive of all the investigated renal biomarkers. These results should be confirmed with further investigation.