Using exposure biomarkers in children to compare between-child and within-child variance and calculate correlations among siblings for multiple environmental chemicals

Associations between exposure to phthalates, phenols, and parabens with objective and subjective measures of sleep health among Mexican women in midlife: a cross-sectional and retrospective analysis

Endocrine-disrupting chemicals (EDCs) may impact sleep during the menopausal transition by altering sex hormones. However, these studies are scarce among Latin American women. This investigation utilized cross-sectional and retrospective data from midlife women enrolled in the Early Life Exposure in Mexico to Environmental Toxicants (ELEMENT) study to examine associations between exposure to EDCs (phthalates, phenols, and parabens) and sleep health measures. For cross-sectional analyses, single spot urine samples were collected between 2017-2019 from a pilot sample of women (N = 91) of midlife age to estimate the urinary concentration of individual phthalates, phenols, and parabens and to calculate the summary concentration of phthalate mixtures. Seven-day nightly sleep duration, midpoint, and fragmentation were obtained from wrist-actigraphy devices and estimated from the actigraphy data using a pruned dynamic programming algorithm. Self-reported poor sleep quality was assessed by one item from the Pittsburgh Sleep Quality Index (PSQI). We examined associations between urinary summary phthalate mixtures, phthalate metabolites, phenol, and paraben analytes with each sleep measure using linear or logistic (to compute odds of poor sleep quality only) regression models adjusted for specific gravity, age, and socioeconomic status. We ran similar regression models for retrospective analyses (N = 74), except that urine exposure biomarker data were collected in 2008 when women were 24-50 years old. At the 2017-2019 midlife visit, 38% reported poor sleep quality. Cross-sectionally, EDCs were associated with longer sleep duration, earlier sleep timing, and more fragmented sleep. For example, every 1-unit IQR increase in the phenol triclosan was associated with a 26.3 min per night (95% CI: 10.5, 42.2; P < 0.05) longer sleep duration and marginally associated with 0.2 decimal hours (95% CI: -0.4, 0.0; P < 0.10) earlier sleep midpoint; while every 1-unit IQR increase in the phthalate metabolite MEHP was associated with 1.1% higher sleep fragmentation (95% CI: 0.1, 2.1; P < 0.05). Retrospective study results generally mirrored cross-sectional results such that EDCs were linked to longer sleep duration, earlier sleep timing, and more fragmented sleep. EDCs were not significantly associated with odds of self-reported poor sleep quality. Results from cross-sectional and retrospective analyses revealed that higher exposure to EDCs was predictive of longer sleep duration, earlier sleep timing, and more fragmented sleep among midlife women.

Pesticide exposure in New Zealand school-aged children: Urinary concentrations of biomarkers and assessment of determinants

This study aimed to assess pesticide exposure and its determinants in children aged 5-14 years. Urine samples (n = 953) were collected from 501 participating children living in urban areas (participant n = 300), rural areas but not on a farm (n = 76), and living on a farm (n = 125). The majority provided two samples, one in the high and one in the low spraying season. Information on diet, lifestyle, and demographic factors was collected by questionnaire. Urine was analysed for 20 pesticide biomarkers by GC-MS/MS and LC-MS/MS. Nine analytes were detected in > 80% of samples, including six organophosphate insecticide metabolites (DMP, DMTP, DEP, DETP, TCPy, PNP), two pyrethroid insecticide metabolites (3-PBA, trans-DCCA), and one herbicide (2,4-D). The highest concentration was measured for TCPy (median 13 μg/g creatinine), a metabolite of chlorpyrifos and triclopyr, followed by DMP (11 μg/g) and DMTP (3.7 μg/g). Urine metabolite levels were generally similar or low compared to those reported for other countries, while relatively high for TCPy and pyrethroid metabolites. Living on a farm was associated with higher TCPy levels during the high spray season. Living in rural areas, dog ownership and in-home pest control were associated with higher levels of pyrethroid metabolites. Urinary concentrations of several pesticide metabolites were higher during the low spraying season, possibly due to consumption of imported fruits and vegetables. Organic fruit consumption was not associated with lower urine concentrations, but consumption of organic food other than fruit or vegetables was associated with lower concentrations of TCPy in the high spray season. In conclusion, compared to other countries such as the U.S., New Zealand children had relatively high exposures to chlorpyrifos/triclopyr and pyrethroids. Factors associated with exposure included age, season, area of residence, diet, in-home pest control, and pets.

Prenatal maternal pesticide exposure in relation to sleep health of offspring during adolescence

STUDY OBJECTIVES

The neurobiological processes involved in establishing sleep regulation are vulnerable to environmental exposures as early as seven weeks of gestation. Studies have linked in utero pesticide exposure to childhood sleep-disordered breathing. However, the impact of in utero pesticide exposure on the sleep health of adolescents remains unexplored.

MATERIALS AND METHODS

Data from 137 mother-adolescent pairs from a Mexico City cohort were analyzed. We used maternal urinary 3-phenoxybenzoic acid (3-PBA, pyrethroid metabolite) and 3, 5, 6-trichloro-2-pyridinol (TCPy, chlorpyrifos metabolite) from trimester three to estimate in utero pesticide exposure. Among adolescents, we obtained repeated measures of objectively assessed sleep duration, midpoint, and fragmentation using wrist-actigraphy devices for 7 consecutive days in 2015 and 2017. Unstratified and sex-stratified associations between maternal urinary 3-PBA and TCPy and adolescent sleep measures were examined using generalized linear mixed models (GLMMs). We also examined the interactive effects of maternal pesticide exposure and offspring sex on sleep outcomes.

RESULTS

3-PBA and TCPy were detected in 44.4% and 93% of urine samples, respectively. Adjusted findings demonstrated that higher exposure to maternal TCPy was associated with longer sleep duration and later sleep timing. Findings from interaction tests between maternal pesticide exposure and offspring sex were not statistically significant, although adjusted sex-stratified findings showed that the association between TCPy with duration and midpoint was evident only among female offspring. To illustrate, those in the highest tertile of exposure had a 59 minute (95% CI: 12.2, 104.8) (p, trend = 0.004) longer sleep duration and a 0.6 hour (95% CI: 0.01, 1.3) (p, trend = 0.01) later sleep midpoint. We found no significant associations between 3-PBA and sleep outcomes.

CONCLUSION

Within a cohort of mother-adolescent pairs, we found associations between maternal prenatal pesticide exposure and longer sleep duration and later sleep timing among adolescent offspring. Further, this association may be female-specific.

Association between pesticide exposure and sleep health among a representative sample of US adults: evidence from NHANES 2009-2014

BACKGROUND

Data suggest that pesticides interact with the melatonin receptor, which may influence sleep. However, the link between pesticides and sleep remains unexplored among the general adult population. This study evaluated unstratified and sex-stratified associations between urinary pesticide exposure (N = 4,478) and self-reported acute household pesticide exposure (N = 14,956), with sleep health outcomes within a nationally representative sample of US adults.

METHODS

Data from the National Health and Nutrition Examination Surveys (NHANES) 2009-2014 were combined for analysis of aim 1 and aim 2. Urinary pesticide metabolite concentrations served as biomarkers of pesticide exposure. Acute household pesticide exposure (if any chemical products were used in the home in the past seven days to control pests) was self-reported (yes/no). Insufficient sleep duration (< 7 h/night) and trouble sleeping (yes/no) were self-reported. Log-binomial regression models that accounted for complex survey weights and adjusted for confounders were used to compute prevalence ratios and 95% CI.

RESULTS

Log urinary 3-phenoxybenzoic acid (3-PBA) was related to a higher probability of insufficient sleep [1.09 (95% CI: 1.00, 1.20), p = 0.04] and trouble sleeping [1.14 (95% CI: 1.02, 1.27), p = 0.02] among males. Self-reported acute household pesticide exposure was associated with a higher probability of insufficient sleep duration [1.16 (95% CI: 1.02, 1.32), p = 0.03] and trouble sleeping [1.20 (95% CI: 1.01, 1.44), p = 0.04] in the unstratified sample. Sex-stratified findings showed that associations between acute household pesticide exposure and trouble sleeping only persisted  among males [1.69 (95% CI: 1.27, 2.24), p < .001].

CONCLUSIONS

In summary, acute pesticide exposure may be detrimental to adult sleep health, particularly among US males.

Development of a questionnaire-based insecticide exposure assessment method and comparison with urinary insecticide biomarkers in young Australian children

Environmental and behavioural factors assessed via an online questionnaire were compared to insecticide metabolite concentrations in urine collected from 61 children from South East Queensland, Australia. Metabolite concentrations (μg/L urine) were transformed using the natural logarithm prior to regression analysis and adjusted for age and creatinine. A significant dietary association was reported for vegetable intake and 3-phenoxybenzoic acid (3-PBA) (β: 1.47 for top quartile of intake versus bottom quartile of intake 95% CI: 0.36, 2.57). Intake of vegetables and fruit were also positively associated with sum non-specific organophosphate metabolites (ƩnsOP). ƩnsOP concentrations were lower when fruits and vegetables were always or almost always washed prior to cooking or eating (β: -0.69 95% CI: -1.25, -0.12). In multivariable modelling 3-PBA concentrations were also associated with hand-washing frequency (β: 1.69 95% CI: 0.76, 2.61 for <1 day versus > 3 day), presence of a dog in the home (β: 0.73 95% CI: 0.07, 1.38), frequency of pest-spray use in the summer months (β: 0.88 95% CI: 0.22, 1.54 weekly versus less than weekly) and season (β: 0.88 95% CI: 0.32, 1.44 for spring/summer versus winter/autumn). This is the first study in Australia to report dietary, behavioural and environmental factors associated with biomarkers of insecticide exposure in young children.

Lead exposure during childhood and subsequent anthropometry through adolescence in girls

INTRODUCTION

Cross-sectional studies suggest that postnatal blood lead (PbB) concentrations are negatively associated with child growth. Few studies prospectively examined this association in populations with lower PbB concentrations. We investigated longitudinal associations of childhood PbB concentrations and subsequent anthropometric measurements in a multi-ethnic cohort of girls.

METHODS

Data were from The Breast Cancer and the Environment Research Program at three sites in the United States (U.S.): New York City, Cincinnati, and San Francisco Bay Area. Girls were enrolled at ages 6-8 years in 2004-2007. Girls with PbB concentrations collected at ≤10 years old (mean 7.8 years, standard deviation (SD) 0.82) and anthropometry collected at ≥3 follow-up visits were included (n = 683). The median PbB concentration was 0.99 μg/d (10th percentile = 0.59 μg/dL and 90th percentile = 2.00 μg/dL) and the geometric mean was 1.03 μg/dL (95% Confidence Interval (CI): 0.99, 1.06). For analyses, PbB concentrations were dichotomized as <1 μg/dL (n = 342) and ≥1 μg/dL (n = 341). Anthropometric measurements of height, body mass index (BMI), waist circumference (WC), and percent body fat (%BF) were collected at enrollment and follow-up visits through 2015. Linear mixed effects regression estimated how PbB concentrations related to changes in girls' measurements from ages 7-14 years.

RESULTS

At 7 years, mean difference in height was -2.0 cm (95% CI: -3.0, -1.0) for girls with ≥1 μg/dL versus <1 μg/dL PbB concentrations; differences persisted, but were attenuated, with age to -1.5 cm (95% CI: -2.5, -0.4) at 14 years. Mean differences for BMI, WC, and BF% at 7 years between girls with ≥1 μg/dL versus <1 μg/dL PbB concentrations were -0.7 kg/m² (95% CI: -1.2, -0.2), -2.2 cm (95% CI: -3.8, -0.6), and -1.8% (95% CI: -3.2, -0.4), respectively. Overall, these differences generally persisted with advancing age and at 14 years, differences were -0.8 kg/m² (95% CI: -1.5, -0.02), -2.9 cm (95% CI: -4.8, -0.9), and -1.7% (95% CI: -3.1, -0.4) for BMI, WC, and BF%, respectively.

CONCLUSIONS

These findings suggest that higher concentrations of PbB during childhood, even though relatively low by screening standards, may be inversely associated with anthropometric measurements in girls.

Human biomarker interpretation: the importance of intra-class correlation coefficients (ICC) and their calculations based on mixed models, ANOVA, and variance estimates

Human biomonitoring is the foundation of environmental toxicology, community public health evaluation, preclinical health effects assessments, pharmacological drug development and testing, and medical diagnostics. Within this framework, the intra-class correlation coefficient (ICC) serves as an important tool for gaining insight into human variability and responses and for developing risk-based assessments in the face of sparse or highly complex measurement data. The analytical procedures that provide data for clinical and public health efforts are continually evolving to expand our knowledge base of the many thousands of environmental and biomarker chemicals that define human systems biology. These chemicals range from the smallest molecules from energy metabolism (i.e., the metabolome), through larger molecules including enzymes, proteins, RNA, DNA, and adducts. In additiona, the human body contains exogenous environmental chemicals and contributions from the microbiome from gastrointestinal, pulmonary, urogenital, naso-pharyngeal, and skin sources. This complex mixture of biomarker chemicals from environmental, human, and microbiotic sources comprise the human exposome and generally accessed through sampling of blood, breath, and urine. One of the most difficult problems in biomarker assessment is assigning probative value to any given set of measurements as there are generally insufficient data to distinguish among sources of chemicals such as environmental, microbiotic, or human metabolism and also deciding which measurements are remarkable from those that are within normal human variability. The implementation of longitudinal (repeat) measurement strategies has provided new statistical approaches for interpreting such complexities, and use of descriptive statistics based upon intra-class correlation coefficients (ICC) has become a powerful tool in these efforts. This review has two parts; the first focuses on the history of repeat measures of human biomarkers starting with occupational toxicology of the early 1950s through modern applications in interpretation of the human exposome and metabolic adverse outcome pathways (AOPs). The second part reviews different methods for calculating the ICC and explores the strategies and applications in light of different data structures.

Prenatal phthalate exposures and child temperament at 12 and 24 months

INTRODUCTION

Gestational phthalate exposures have been adversely associated with attention, externalizing, and internalizing behaviors in childhood. Early childhood temperament may be a marker of later behavioral patterns. We therefore sought to determine whether gestational phthalate exposures were associated with infant and toddler temperament.

METHODS

The Mount Sinai Children's Environmental Health Study is a prospective cohort study of children born between May 1998 and July 2001 in New York City (N=404). Phthalate metabolites were measured in spot urine samples collected from pregnant women in their third trimester. Child temperament was assessed by parental report at 12-months using the Infant Behavior Questionnaire (IBQ) (N=204) and at 24-months using the Toddler Behavior Assessment Questionnaire (TBAQ) (N=279). We used multiple linear regression to evaluate associations between urinary phthalate metabolites and eleven temperament domains.

RESULTS

Phthalate biomarker concentrations were weakly associated with lower gross motor activity levels as well as higher duration of orienting at the 12-month assessment. Mono(3-carboxypropyl) phthalate (MCPP), monobenzyl phthalate (MBzP) and the sum of metabolites of di(2-ethylhexyl) phthalate (∑DEHP) were associated with lower levels of smiling and laughing at 12 months. At 24-months, social fear and lower pleasure was linked to higher concentrations of MCPP and MBzP, and higher ∑DEHP was weakly associated with increased anger levels at 24-months.

CONCLUSIONS

Though we observed some weak associations between biomarkers of prenatal exposure to phthalates and temperament at 12- and 24-months, overall phthalates biomarkers were not strongly associated with alterations in temperament.

Associations of urinary phthalate and phenol biomarkers with menarche in a multiethnic cohort of young girls

To study potential environmental influences on puberty in girls, we investigated urinary biomarkers in relation to age at menarche. Phenols and phthalates were measured at baseline (6-8 years of age). Menarche was ascertained over 11 years for 1051 girls with menarche and biomarkers. Hazards ratios were estimated from Cox models adjusted for race/ethnicity and caregiver education (aHR, 95% confidence intervals [CI] for 5th vs 1st quintile urinary biomarker concentrations). 2,5-Dichlorophenol was associated with earlier menarche (aHR 1.34 [1.06-1.71]); enterolactone was associated with later menarche (aHR 0.82 [0.66-1.03]), as was mono-3-carboxypropyl phthalate (MCPP) (aHR 0.73 [0.59-0.91]); the three p-trends were <0.05. Menarche differed by 4-7 months across this range. Enterolactone and MCPP associations were stronger in girls with below-median body mass index. These analytes were also associated with age at breast development in this cohort. Findings from this prospective study suggest that some childhood exposures are associated with pubertal timing.

Urinary cotinine levels and environmental tobacco smoke in mothers and children of Romania, Portugal and Poland within the European human biomonitoring pilot study

The aim of this study was to explore data from the DEMOCOPHES study population for Romania, Portugal and Poland, in order to assess smoking patterns and the extent of ETS exposure and compare the national study samples with reference to the respective anti-smoking laws. The subset of the DEMOCOPHES study sample consisted of 360 children and their mothers (120 in each of the three countries - Romania (RO), Portugal (PT) and Poland (PL). Smoking was assessed using a detailed questionnaire for the participants, which addresses both active and passive smoking. This assessment uses exposure-relevant questionnaire data, in particular on the home environment and residence, socio-demographic characteristics, lifestyle such as nutrition, smoking behavior, other exposure-relevant behavior and occupational history, as well as urinary cotinine and creatinine measurements. We performed general statistical analysis and innovative receiver operating characteristic (ROC) curve analyses. Smoking prevalence as evaluated by the questionnaire was generally high, and higher than official statistics, which suggests some under-reporting in the countries, particularly in Romania. Urinary cotinine levels provided biochemical confirmation of the high and similar smoking prevalence for the three countries. Concerning ETS exposure, Romania presented significantly higher levels, for children as well as for non-smoking mothers, with Portugal showing significantly lower levels. Compared to non-smoking mothers, the children showed relatively higher ETS exposure levels in all three countries. The established country-specific optimal cut-off values in urinary cotinine to distinguish smokers from non-smokers vary more than those to discriminate ETS exposure extent in non-smoking mothers and children. Although different between countries, these values are a valuable output to monitor effectiveness of both national antismoking laws and educational programs in the three countries. The findings of this study point to the urgent need for stronger, more effective and well enforced smoke-free legislation in the three countries.

Assessing exposure of young children to common endocrine-disrupting chemicals in the home environment: a review and commentary of the questionnaire-based approach

BACKGROUND

Although infants and young children are particularly vulnerable to endocrine disrupting chemical (EDC) exposure, there is an absence of comprehensive exposure data for this age group. As young children spend the majority of their time indoors, improved methods of exposure assessment are needed to characterise the health risks from exposures in the home environment. Biologic assessment, which has been considered the gold standard for exposure assessment in recent years, is difficult to conduct in young children. Questionnaires are an alternative and indirect method of predicting exposure, which may overcome some of the limitations of direct exposure assessment.

RESEARCH PROBLEM

The feasibility of using a questionnaire-based approach to predict exposure of young children to EDCs in the home has yet to be comprehensively reviewed. Moreover, there is no one questionnaire that has been validated for predicting the exposure of infants to common EDCs in the home.

AIMS AND OBJECTIVES

The aim of this review is to discuss the use and validation of the questionnaire-based approach to predict exposure of children to chemicals from three common classes of EDCs in the home, namely, plasticisers, flame retardants, and insecticides. We discuss the strengths and weaknesses of the questionnaire-based approach as well as the important pathways of exposure in the home environment, by which to guide the design and validation of future exposure questionnaires.

RESULTS

The findings from our review indicate that the questionnaire-based approach is a valuable tool in the prediction of exposure to persistent organic pollutants, as well as to toxicants that have consistent patterns of exposure. With improvements to the design and validation process, the questionnaire-based approach may also prove to be a reliable instrument in predicting exposure to EDCs with short-half lives, including bisphenol A, phthalates, and pyrethroid and organophosphate insecticides.

Within- and between-child variation in repeated urinary pesticide metabolite measurements over a 1-year period

BACKGROUND

Children are exposed to pesticides from many sources and routes, including dietary and incidental ingestion, dermal absorption, and inhalation. Linking health outcomes to these exposures using urinary metabolites requires understanding temporal variability within subjects to avoid exposure misclassification.

OBJECTIVES

We characterized the within- and between-child variability of urinary organophosphorus and pyrethroid metabolites in 23 participants of the Children's Pesticide Exposure Study-Washington over 1 year and examined the ability of one to four spot urine samples to categorize mean exposures.

METHODS

Each child provided urine samples twice daily over 7- to 16-day sessions in four seasons in 2003 and 2004. Samples were analyzed for five pyrethroid and five organophosphorus (OP) metabolites. After adjusting for specific gravity, we used a customized maximum likelihood estimation linear mixed-effects model that accounted for values below the limit of detection to calculate intraclass correlation coefficients (ICC) and conducted surrogate category analyses.

RESULTS

Within-child variability was 2-11 times greater than between-child variability. When restricted to samples collected during a single season, ICCs were higher in the fall, winter, and spring than in summer for OPs, and higher in summer and winter for pyrethroids, indicating an increase in between-person variability relative to within-person variability during these seasons. Surrogate category analyses demonstrated that a single spot urine sample did not categorize metabolite concentrations well, and that four or more samples would be needed to categorize children into quartiles consistently.

CONCLUSIONS

Urinary biomarkers of these short half-life pesticides exhibited substantial within-person variability in children observed over four seasons. Researchers investigating pesticides and health outcomes in children may need repeated biomarker measurements to derive accurate estimates of exposure and relative risks.

Are metals accumulated in human hair affected by naturally occurring asbestos fiber contamination? A case study from a rural area of china

Little is known about the link between metals accumulated in human and asbestos fiber contamination in the environment. Therefore, hair samples of 368 subjects (128 males and 240 females) from a rural area contaminated by crocidolite asbestos fibers were collected to investigate the distributions of 17 metals accumulated in human. The results showed that the mean concentrations of As, Al, Ba, Cd, Co, Cr, Cu, Fe, Hg, Mg, Mn, Mo, Na, Ni, Pb, Sr, and Zn in hair of the total subjects were 0.23, 23.36, 4.33, 0.11, 0.05, 0.70, 10.53, 29.74, 0.37, 241.57, 3.52, 0.08, 153.21, 0.72, 4.26, 10.96, and 113.35 mg/kg, respectively. Moreover, approximately 86.14, 52.17, 73.91, 85.05, 80.98, 74.46, and 53.80 % of the hair samples of the total subjects contained much higher concentrations of Al, Ba, Fe, Mg, Mn, Na, and Sr compared with the highest reference values, respectively. The mean concentrations of the determined metals (except for As, Co, Cr, Hg, and Mo) significantly varied among different age groups for both male and females. The results of correlation analysis and cluster analysis revealed that strong correlations were found between Al, Fe, Zn, Mg, and Na accumulated in human from the study area. These might suggest that Al, Ba, Fe, Mg, Mn, Na, and Sr were significantly derived from contamination of crocidolite asbestos fibers. Zn, Mg, and Na might also originate from diet. However, Cd, Mo, Co, As, Cr, Hg, Ni, Mn, Pb, and Ba accumulated in human seemed to be mainly derived from soil. It can be concluded that metals accumulated in human hair have a link with asbestos fiber contamination in the environment.

Estimating lifetime risk from spot biomarker data and intraclass correlation coefficients (ICC)

Human biomarker measurements in tissues including blood, breath, and urine can serve as efficient surrogates for environmental monitoring because a single biological sample integrates personal exposure across all environmental media and uptake pathways. However, biomarkers represent a "snapshot" in time, and risk assessment is generally based on long-term averages. In this study, a statistical approach is proposed for estimating long-term average exposures from distributions of spot biomarker measurements using intraclass correlations based upon measurement variance components from the literature. This methodology was developed and demonstrated using a log-normally distributed data set of urinary OH-pyrene taken from our own studies. The calculations are generalized for any biomarker data set of spot measures such as those from the National Health and Nutrition Evaluation Studies (NHANES) requiring only spreadsheet calculations. A three-tiered approach depending on the availability of metadata was developed for converting any collection of spot biomarkers into an estimated distribution of individual means that can then be compared to a biologically relevant risk level. Examples from a Microsoft Excel-based spreadsheet for calculating estimates of the proportion of the population exceeding a given biomonitoring equivalent level are provided as an appendix.

Association between lung function in school children and exposure to three transition metals from an e-waste recycling area

The informal processing of electronic waste or e-waste contributes to the release of high concentrations of transition metals into the ambient air. The damage caused by chromium, nickel and manganese exposure on lung function in school children from an e-waste recycling area and the role of oxidative stress in this process were evaluated. We recruited school children (n=144, 8-13 years) from an e-waste recycling area in China compared with the control. Spirometry was performed to assess lung function status. The blood levels of chromium, nickel and manganese, antioxidant enzyme activities and lipid peroxidation of the subjects were examined. The concentrations of blood manganese (bMn) and serum nickel (sNi) in the exposed group were significantly higher than those in controls for all three age groups. The forced vital capacity value of boys aged 8-9 years was significantly lower than that of the control. Malondialdehyde levels and superoxide dismutase activities increased significantly in children aged 8-9 years from e-waste environment, but catalase activities declined. School children from an e-waste recycling area were exposed to high levels of the three transition metals. The accumulation of bMn and sNi may be risk factors for oxidative damage and decreased pulmonary function.

Interpreting variability in population biomonitoring data: role of elimination kinetics

Biomarker concentrations in spot samples of blood and urine are implicitly interpreted as direct surrogates for long-term exposure magnitude in a variety of contexts including (1) epidemiological studies of potential health outcomes associated with general population chemical exposure, and (2) cross-sectional population biomonitoring studies. However, numerous factors in addition to exposure magnitude influence biomarker concentrations in spot samples, including temporal variation in spot samples because of elimination kinetics. The influence of half-life of elimination relative to exposure interval is examined here using simple first-order pharmacokinetic simulations of urinary concentrations in spot samples collected at random times relative to exposure events. Repeated exposures were modeled for each individual in the simulation with exposure amounts drawn from lognormal distributions with varying geometric standard deviations. Relative variation in predicted spot sample concentrations was greater than the variation in underlying dose distributions when the half-life of elimination was shorter than the interval between exposures, with the degree of relative variation increasing as the ratio of half-life to exposure interval decreased. Results of the modeling agreed well with data from a serial urine collection data set from the Centers for Disease Control. Data from previous studies examining intra-class correlation coefficients for a range of chemicals relying upon repeated sampling support the importance of considering the half-life relative to exposure frequency in design and interpretation of studies using spot samples for exposure classification and exposure estimation. The modeling and data sets presented here provide tools that can assist in interpretation of variability in cross-sectional biomonitoring studies and in design of studies utilizing biomonitoring data as markers for exposure.