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Background: Rice is an important dietary source for methylmercury; however, rice does not contain the same beneficial nutrients as fish. Our main objective was to assess associations of prenatal methylmercury exposure through rice ingestion with child neurodevelopment in rural China.Methods: Eligible peripartum women were enrolled (n = 391), provided peripartum hair samples, and children's neurodevelopment was assessed at 12 months (n = 264, 68%) and 36 months (n = 190, 48%) using the Bayley Scales of Infant Development, 2nd Edition, including the Mental Developmental Index (MDI) and the Psychomotor Developmental Index (PDI). Associations between prenatal methylmercury exposure during the third trimester [log2 maternal hair total mercury (THg)] and child's neurodevelopment were assessed using linear mixed models for repeated measures.Results: In adjusted models, a doubling in maternal hair THg corresponded to a 1.3-point decrement in the MDI score [95% confidence interval (CI): - 2.6, - 0.14], and a 1.2-point decrement in the PDI score (95% CI: - 2.6, 0.14). Overall, adverse associations between maternal hair THg and MDI scores attenuated over time. However, associations were robust and stable over time among children whose primary caregiver was their parent(s). During the study follow-up, an increasing proportion of children were raised by grandparents (12 months: 9% versus 36 months: 27%), a trend associated with rural-to-urban parental migration for work.Conclusions: For young children living in rural China, a biomarker of prenatal methylmercury exposure was associated with decrements in cognitive function assessed between 12 and 36 months of age. Changes in the family structure over the study follow-up time interval potentially impacted children's sensitivity to prenatal methylmercury exposure. [ABSTRACT FROM AUTHOR]

We investigated cross-sectional associations between children's neurodevelopment and their gut microbiota composition. Study children (36 months of age) lived in rural China (n = 46). Neurodevelopment was assessed using the Bayley Scales of Infant Development, 2nd Edition, yielding the Mental Developmental Index (MDI) and Psychomotor Developmental Index (PDI). Children's gut microbiota was assessed using 16S rRNA gene profiling. Microbial diversity was characterized using alpha diversity patterns. Additionally, 3 coabundance factors were determined for the 25 most abundant taxa. Multivariable linear regression models were constructed to examine the relationships between Bayley scores (MDI and PDI) and children's gut microbiota. In adjusted models, MDI and PDI scores were not associated with alpha diversity indices. However, in adjusted models, MDI and PDI scores were positively associated with the first coabundance factor, which captured positive loadings for the genera Faecalibacterium, Sutterella, and Clostridium cluster XIVa. For an interquartile range increase in the first coabundance factor, MDI scores increased by 3.9 points [95% confidence interval (CI): 0, 7.7], while PDI scores increased by 8.6 points (95% CI 3.1, 14). Our results highlight the potential for gut microbial compositional characteristics to be important correlates of children's Bayley Scales performance at 36 months of age. [ABSTRACT FROM AUTHOR]

The a article discusses the seminal study by D. Mergler and colleagues concerning the intergenerational effects of methyl mercury (MeHG) poisoning on children's mental health. The researchers used structural equation models (SEMs) to assess the intergenerational effects of grandmaternal (G0) and maternal (G1) MeHg poisoning on children's mental health. The results of the study suggest that MeHG toxicity may have profound intergenerational effects on children's mental health.

Gut microorganisms contribute to the metabolism of environmental toxicants, including methylmercury (MeHg). Our main objective was to investigate whether associations between biomarkers for prenatal MeHg exposure and maternal gut microbiota differed between early and late gestation. Maternal blood and stool samples were collected during early (8.3–17 weeks, n=28) and late (27–36 weeks, n=24) gestation. Total mercury and MeHg concentrations were quantified in biomarkers, and inorganic mercury was estimated by subtraction. The diversity and structure of the gut microbiota were investigated using 16S rRNA gene profiling (n = 52). Biomarkers were dichotomized, and diversity patterns were compared between high/low mercury concentrations. Spearman's correlation was used to assess bivariate associations between MeHg biomarkers (stool, blood, and meconium), and 23 gut microbial taxa (genus or family level, >1% average relative abundance). Within-person and between-person diversity patterns in gut microbiota differed between early/late gestation. The overall composition of the microbiome differed between high/low MeHg concentrations (in blood and stool) during early gestation, but not late gestation. Ten (of 23) taxa were significantly correlated with MeHg biomarkers (increasing or decreasing); however, associations differed, depending on whether the sample was collected during early or late gestation. A total of 43% of associations (69/161) reversed the direction of correlation between early/late gestation. The time point at which a maternal fecal sample is collected may yield different associations between gut microorganisms and MeHg biomarkers, which may be due in part to remodeling of maternal microbiota during pregnancy. Our results suggest the effectiveness of dietary interventions to reduce prenatal MeHg exposure may differ between early and late gestation. • Pregnant mothers donated blood and stool samples during early/late gestation. • Total mercury and methylmercury (MeHg) were determined in both biomarkers. • Gut microbiota community structure was determined using 16S rRNA gene profiling. • Within- and between-person diversity patterns differed between early/late gestation. • Associations between gut microbiota and MeHg biomarkers differed longitudinally. [ABSTRACT FROM AUTHOR]

Background Rice is an important dietary source for methylmercury (MeHg), a potent neurotoxin, and inorganic arsenic (As), a human carcinogen. Rice baby cereals are a dietary source of inorganic As; however, less is known concerning MeHg concentrations in rice baby cereals and rice teething biscuits. Methods MeHg concentrations were measured in 36 rice baby cereals, eight rice teething biscuits, and four baby cereals manufactured with oats/wheat (n = 48 total). Arsenic (As) species, including inorganic As, were determined in rice baby cereals and rice teething biscuits (n = 44/48), while total As was determined in all products (n = 48). Results Rice baby cereals and rice teething biscuits were on average 61 and 92 times higher in MeHg, respectively, and 9.4 and 4.7 times higher in total As, respectively, compared to wheat/oat baby cereals. For a 15-g serving of rice baby cereal, average MeHg intake was 0.0092 μg day −1 (range: 0.0013–0.034 μg day −1 ), while average inorganic As intake was 1.3 μg day −1 (range: 0.37–2.3 μg day −1 ). Inorganic As concentrations in two brands of rice baby cereal (n = 12/36 boxes of rice cereal) exceeded 100 ng/g, the proposed action level from the U.S. Food and Drug Administration. Log 10 MeHg and inorganic As concentrations in rice baby cereals were strongly, positively correlated (Pearson's rho = 0.60, p < 0.001, n = 36). Conclusions Rice-containing baby cereals and teething biscuits were a dietary source of both MeHg and inorganic As. Studies concerning the cumulative impacts of MeHg and inorganic As on offspring development are warranted. [ABSTRACT FROM AUTHOR]

Mercury (Hg) isotopic signatures were characterized in polished rice samples from China, U.S., and Indonesia (n = 45). Hg isotopes were also analyzed in paired hair samples for participants from China (n = 21). For the latter, we also quantified the proportion of methylmercury intake through rice (range: 31-100%), and the weekly servings of fish meals (range: 0-5.6 servings/weekly). For these participants, 29% (n = 6) never ingested fish, 52% (n = 11) ingested fish < twice/weekly, and 19% (n = 4) ingested fish ? twice/weekly. In rice and hair, both mass-dependent fractionation (MDF, reported as ?202Hg) and mass-independent fractionation (MIF, reported as ?199Hg) of Hg isotopes were observed. Compared to rice, hair ?202Hg values were enriched on average (±1 standard deviation) by 1.9 ± 0.61‰, although the range was wide (range: 0.45‰, 3.0‰). Hair ?199Hg was significantly inversely associated with %methylmercury intake from rice (Spearman's rho = -0.61, p < 0.01, n = 21), i.e., as the proportion of methylmercury intake from rice increased, MIF decreased. Additionally, hair ?199Hg was significantly higher for participants ingesting fish ? twice/weekly compared to those who did not ingest fish or ingested fish < twice/weekly (ANOVA, p < 0.05, n = 21); Overall, results suggest that Hg isotopes (especially MIF) in human hair can be used to distinguish methylmercury intake from rice versus fish. [ABSTRACT FROM AUTHOR]

Rice farmers are pressured to grow rice using less water. The impacts of water-saving rice cultivation methods on rice methylmercury concentrations are uncertain. Rice ( Oryza sativa L. cv. Nipponbare) was cultivated in fields using four water management treatments, including flooded (no dry-downs), alternating wetting and drying (AWD) (with one or three dry-downs), and furrow-irrigated fields (nine dry-downs) (n = 16 fields). Anoxic bulk soil was collected from rice roots during the rice maturation phase, and rice grain was harvested after fields were dried. Total mercury and methylmercury concentrations were determined in soil and polished rice samples, and the soil microbiome was analyzed using 16S (v4) rRNA gene profiling. Soil total mercury did not differ between fields. However, compared to continuously flooded fields, soil and rice methylmercury concentrations averaged 51% and 38% lower in the AWD fields, respectively, and 95% and 96% lower in the furrow-irrigated fields, respectively. Compared to flooded fields, grain yield was reduced on average by < 1% in the AWD fields and 34% in the furrow-irrigated fields. Additionally, using 16S (v4) rRNA gene profiling, the relative abundance of genera (i.e., highest resolution via this method) known to contain mercury methylators averaged 2.9-fold higher in flooded and AWD fields compared to furrow-irrigated fields. These results reinforce the benefits of AWD in reducing rice methylmercury concentrations with minimal changes in rice production yields. In the furrow-irrigated fields, a lower relative abundance of genera known to contain mercury methylators suggests an association between lower concentrations of soil and rice methylmercury and specific soil microbiomes. [ABSTRACT FROM AUTHOR]

Background: Dietary methylmercury intake can occur not only through fish ingestion but also through rice ingestion; however, rice does not contain the same beneficial micronutrients as fish.Objectives: In rural China, where rice is a staple food, associations between prenatal methylmercury exposure (assessed using maternal hair mercury) and impacts on offspring neurodevelopment were investigated.Methods: A total of 398 mothers were recruited at parturition at which time a sample of scalp hair was collected. Offspring (n=270, 68%) were assessed at 12 months using the Bayley Scales of Infant Development-II, yielding age-adjusted scores for the Mental Developmental Index (MDI) and Psychomotor Developmental Index (PDI).Results: Among 270 mothers, 85% ingested rice daily, 41% never or rarely ingested fish/shellfish and 11% ingested fish/shellfish at least twice/weekly. Maternal hair mercury averaged 0.41μg/g (median: 0.39μg/g, range: 0.079-1.7μg/g). In unadjusted models, offspring neurodevelopment (both MDI and PDI) was inversely correlated with hair mercury. Associations were strengthened after adjustment for fish/shellfish ingestion, rice ingestion, total energy intake (kcal), and maternal/offspring characteristics for both the MDI [Beta: -4.9, 95% Confidence Interval (CI): -9.7, -0.12] and the PDI (Beta: -2.7, 95% CI: -8.3, 2.9), although confidence intervals remained wide for the latter.Conclusions: For 12-month old offspring living in rural China, prenatal methylmercury exposure was associated with statistically significant decrements in offspring cognition, but not psychomotor development. Results expose potential new vulnerabilities for communities depending on rice as a staple food. [ABSTRACT FROM AUTHOR]

Purpose The mechanisms by which gut microbiota contribute to methylmercury metabolism remain unclear. Among a cohort of pregnant mothers, the objectives of our pilot study were to determine (1) associations between gut microbiota and mercury concentrations in biomarkers (stool, hair and cord blood) and (2) the contributions of gut microbial mercury methylation/demethylation to stool methylmercury. Methods Pregnant women (36–39 weeks gestation, n = 17) donated hair and stool specimens, and cord blood was collected for a subset ( n = 7). The diversity of gut microbiota was determined using 16S rRNA gene profiling ( n = 17). For 6 stool samples with highest/lowest methylmercury concentrations, metagenomic whole genome shotgun sequencing was employed to search for the mercury methylation gene ( hgcA ), and two mer operon genes involved in methylmercury detoxification ( merA and merB ). Results Seventeen bacterial genera were significantly correlated (increasing or decreasing) with stool methylmercury, stool inorganic mercury, or hair total mercury; however, aside from one genus, there was no overlap between biomarkers. There were no definitive matches for hgcA or merB , while merA was detected at low concentrations in all six samples. Major conclusions Proportional differences in stool methylmercury were not likely attributed to gut microbiota through methylation/demethylation. Gut microbiota potentially altered methylmercury metabolism using indirect pathways. [ABSTRACT FROM AUTHOR]

Background In animal studies obesity is associated with higher blood and tissue mercury concentrations; however human studies are lacking. Although the mechanism underlying this association is uncertain, obesity may alter the metabolism and distribution of methylmercury. Objectives We determined whether obesity influenced blood mercury levels, the majority of which was methylmercury, for U.S. non-pregnant adults (≥20 years) and children (2–19 years) after controlling for methylmercury intake through fish and shellfish consumption, and other confounders. Methods We completed secondary data analysis of the National Health and Nutrition Examination Survey (NHANES) (2007–2010) for participants who consumed fish/shellfish within 24 h of blood collection for mercury analysis. Weighted least squares regression models related blood mercury levels (the dependent variable) to methylmercury exposure (μg) from fish consumed in the previous 24 h, body mass index (BMI) (for adults), BMI z -scores (for children), and other confounders. Results In adjusted models, blood mercury levels were inversely correlated with BMI for adults [ β , 95% confidence interval (CI)=−0.54 (−0.90, −0.18)]. For children, blood mercury levels were inversely correlated with BMI z -scores but the trend was not significant [β (95% CI)=−0.016 (−0.066, 0.035)]. When obese adults or children were compared with those who were overweight/normal weight, blood mercury averaged 22% lower for obese adults (95% CI: −33%, −8.2%), while blood mercury did not differ significantly for obese children [β (95% CI)=−1.7% (−31%, +39%)]. Conclusions After adjusting for the main, if not exclusive, exogenous source of methylmercury exposure (through fish/shellfish intake) and other confounders, our results support potential changes in the metabolism, distribution or excretion of methylmercury with increasing BMI (for adults). [ABSTRACT FROM AUTHOR]

Rice cultivation practices from field preparation to post-harvest transform rice paddies into hot spots for microbial mercury methylation, converting less-toxic inorganic mercury to more-toxic methylmercury, which is likely translocated to rice grain. This review includes 51 studies reporting rice total mercury and/or methylmercury concentrations, based on rice ( Orzya sativa ) cultivated or purchased in 15 countries. Not surprisingly, both rice total mercury and methylmercury levels were significantly higher in polluted sites compared to non-polluted sites (Wilcoxon rank sum, p <0.001). However, rice percent methylmercury (of total mercury) did not differ statistically between polluted and non-polluted sites (Wilcoxon rank sum, p =0.35), suggesting comparable mercury methylation rates in paddy soil across these sites and/or similar accumulation of mercury species for these rice cultivars. Studies characterizing the effects of rice cultivation under more aerobic conditions were reviewed to determine the mitigation potential of this practice. Rice management practices utilizing alternating wetting and drying (instead of continuous flooding) caused soil methylmercury levels to spike, resulting in a strong methylmercury pulse after fields were dried and reflooded; however, it is uncertain whether this led to increased translocation of methylmercury from paddy soil to rice grain. Due to the potential health risks, it is advisable to investigate this issue further, and to develop separate water management strategies for mercury polluted and non-polluted sites, in order to minimize methylmercury exposure through rice ingestion. [ABSTRACT FROM AUTHOR]

Abstract: Accumulation of total Hg (THg) and methylmercury (MeHg) was investigated among 50 indica rice varieties cultivated in 3 sites in Guizhou, China, classified as highly-contaminated, moderately-contaminated, and background sites. Concentrations of soil and pore water (depth: 0–2cm) THg and MeHg were poor predictors of THg and MeHg concentrations in polished white rice and bran, with significantly higher accumulation in the moderately-contaminated site compared to the other 2 sites (ANOVA, p<0.0001). Results indicated other environmental factors played a critical role in the translocation of Hg species from paddy soil to rice grain. We hypothesized alkaline conditions at the highly-contaminated site (surface water pH 11, other 2 sites pH 7.6–8.0), mitigated the uptake of Hg species by decreasing the solubility of micronutrients needed for plant growth, or by reducing the bioavailability of Hg species. White rice MeHg concentrations were associated with genotype but not inorganic Hg(II) concentrations (IHg=THG–MeHg) (MeHg: p<0.001, IHG: p=0.44), while bran MeHg and IHg concentrations were not significantly associated with genotype (p>0.05 for both analyses), indicating there may be genetic markers for the translocation of MeHg from the caryopsis to the endosperm, i.e., from the maternal to the filial tissue. Lastly, calculation of daily MeHg ingestion rates confirmed international guidelines for MeHg exposure were exceeded at the moderately-contaminated site (background: 0.013±0.0052μgkg−1 d−1, n=46; highly-contaminated: 0.066±0.034μgkg−1 d−1, n=49; moderately-contaminated: 0.42±0.13μgkg−1 d−1, n=49). However, MeHg exposure at this site may be decreased up to 69% by cultivating low Hg-accumulating rice varieties. [Copyright &y& Elsevier]

Abstract: Atmospheric mercury (Hg) species, including gaseous elemental mercury (GEM), reactive gaseous mercury (RGM) and particulate-bound mercury (Hgp), were monitored near three sites, including a cement plant (monitored in 2007 and 2008), an urban site and a rural site (both monitored in 2005 and 2008). Although the cement plant was a significant source of Hg emissions (for 2008, GEM: 2.20 ± 1.39 ng m−3, RGM: 25.2 ± 52.8 pg m−3, Hgp 80.8 ± 283 pg m−3), average GEM levels and daytime average dry depositional RGM flux were highest at the rural site, when all three sites were monitored sequentially in 2008 (rural site, GEM: 2.37 ± 1.26 ng m−3, daytime RGM flux: 29 ± 40 ng m−2 day−1). Photochemical conversion of GEM was not the primary RGM source, as highest net RGM gains (75.9 pg m−3, 99.0 pg m−3, 149 m−3) occurred within 3.0–5.3 h, while the theoretical time required was 14–23 h. Instead, simultaneous peaks in RGM, Hgp, ozone (O3), nitrogen oxides, and sulfur dioxide in the late afternoon suggested short-range transport of RGM from the urban center to the rural site. The rural site was located more inland, where the average water vapor mixing ratio was lower compared to the other two sites (in 2008, rural: 5.6 ± 1.4 g kg−1, urban: 9.0 ± 1.1 g kg−1, cement plant: 8.3 ± 2.2 g kg−1). Together, these findings suggested short-range transport of O3 from an urban area contributed to higher RGM deposition at the rural site, while drier conditions helped sustain elevated RGM levels. Results suggested less urbanized environments may be equally or perhaps more impacted by industrial atmospheric Hg emissions, compared to the urban areas from where Hg emissions originated. [Copyright &y& Elsevier]

Abstract: Hg species (total mercury, methylmercury, reactive mercury) in precipitation were investigated in the vicinity of the Lehigh Hanson Permanente Cement Plant in the San Francisco Bay Area, CA., USA. Precipitation was collected weekly between November 29, 2007 and March 20, 2008, which included the period in February and March 2008 when cement production was minimized during annual plant maintenance. When the cement plant was operational, the volume weighted mean (VWM) and wet depositional flux for total Hg (HgT) were 6.7 and 5.8 times higher, respectively, compared to a control site located 3.5 km east of the cement plant. In February and March, when cement plant operations were minimized, levels were approximately equal at both sites (the ratio for both parameters was 1.1). Due to the close proximity between the two sites, meteorological conditions (e.g., precipitation levels, wind direction) were similar, and therefore higher VWM HgT levels and HgT deposition likely reflected increased Hg emissions from the cement plant. Methylmercury (MeHg) and reactive Hg (Hg(II)) were also measured; compared to the control site, the VWM for MeHg was lower at the cement plant (the ratio = 0.75) and the VWM for Hg(II) was slightly higher (ratio = 1.2), which indicated the cement plant was not likely a significant source of these Hg species to the watershed. [Copyright &y& Elsevier]

Of the ∼780 U.S. EPA approved mercury total maximum daily loads (TMDLs), most specify a reduction in total mercury (HgT) loads to reduce methylmercury levels in fish tissue, assuming a 1:1 correspondence. However, mercury methylation is more complex, and therefore, proposed load reductions may not be adequate. Using multiple regression with microlevel and macrolevel variables, the potential efficacy of mercury TMDLs on decreasing aqueous methylmercury levels was investigated in four coastal watersheds: Mugu Lagoon (CA), San Francisco Bay Estuary, Long Island Sound, and south Florida. HgT and methylmercury levels were positively correlated in all watersheds except in Long Island Sound, where spatial differences explained over 40% of the variability in methylmercury levels. A mercury TMDL would be least effective in Long Island Sound due to spatial heterogeneity but most effective in south Florida, where the ratio between aqueous HgT and methylmercury levels was close to 1 and the 95% confidence interval was narrow, indicating a probable reduction in aqueous methylmercury levels if HgT loads were reduced. [ABSTRACT FROM AUTHOR]

BACKGROUND: A critical challenge in genomic medicine is identifying the genetic and environmental risk factors for disease. Currently, the available data links a majority of known coding human genes to phenotypes, but the environmental component of human disease is extremely underrepresented in these linked data sets. Without environmental exposure information, our ability to realize precision health is limited, even with the promise of modern genomics. Achieving integration of gene, phenotype, and environment will require extensive translation of data into a standard, computable form and the extension of the existing gene/phenotype data model. The data standards and models needed to achieve this integration do not currently exist. OBJECTIVES: Our objective is to foster development of community-driven data-reporting standards and a computational model that will facilitate the inclusion of exposure data in computational analysis of human disease. To this end, we present a preliminary semantic data model and use cases and competency questions for further community-driven model development and refinement. DISCUSSION: There is a real desire by the exposure science, epidemiology, and toxicology communities to use informatics approaches to improve their research workflow, gain new insights, and increase data reuse. Critical to success is the development of a community-driven data model for describing environmental exposures and linking them to existing models of human disease. [ABSTRACT FROM AUTHOR]

Platinum Group Element (PGE) pollution on the Indian subcontinent is a growing concern because vehicle sales in India have rapidly increased over the last decade, and it is well known that automobile catalytic converters are one of the major source of anthropogenic PGE in the environment. Despite the rapid growth of the Indian automobile industry, the sources and magnitude of PGE contamination in Indian airborne particles are unknown. In this study we report PGE and mercury (Hg) concentrations, as well as osmium isotope ratios ( 187 Os/ 188 Os) of airborne particles (PM 10 ) collected in Kanpur, a large industrial city in India. We estimate that 61 ± 22%, 32 ± 24%, and 7 ± 3% of the total Os fraction are derived from eroding upper continental crust, catalytic converters fitted in the exhaust system of motor vehicles, and fossil fuel combustion, respectively. Only one sample had a ten times higher (∼76%) than average contribution from fossil fuel. Unlike Os, Pt is predominantly (84 ± 10%) derived from anthropogenic sources. Platinum Group Element and Hg concentrations are not well correlated. However, the highest concentration of particulate Hg corresponds to the most radiogenic 187 Os/ 188 Os isotope ratios (4.6). Our results further indicated that PGE/Ir ratios could be successfully used to quantify the relative proportions of natural and anthropogenic PGE sources in aerosol samples. Since PGE and Hg data on Indian environmental samples are scarce, this study provides an interpretive framework that calls for additional assessments of PGE and Hg concentrations in environmental samples from India. [ABSTRACT FROM AUTHOR]

Background Rice ingestion is an important dietary exposure pathway for methylmercury. There are few studies concerning prenatal methylmercury exposure through rice ingestion, yet the health risks are greatest to the developing fetus, and thus should be investigated. Objectives Our main objective was to quantify dietary methylmercury intake through rice and fish/shellfish ingestion among pregnant mothers living in southern China, where rice was a staple food and mercury contamination was considered minimal. Methods A total of 398 mothers were recruited at parturition, who donated scalp hair and blood samples. Total mercury and/or methylmercury concentrations were measured in biomarkers, in rice samples from each participant's home, and in fish tissue purchased from local markets. Additional fish/shellfish mercury concentrations were obtained from a literature search. Dietary methylmercury intake during the third trimester was equivalent to the ingestion rate for rice (or fish/shellfish)×the respective methylmercury concentration. Results Dietary methylmercury intake from both rice and fish/shellfish ingestion averaged 1.2±1.8 µg/day (median=0.79 µg/day, range=0–22 µg/day), including on average 71% from rice ingestion (median: 87%, range: 0–100%), and 29% from fish/shellfish consumption (median 13%, range: 0–100%). Median concentrations of hair total mercury, hair methylmercury, and blood total mercury were 0.40 µg/g (range: 0.08–1.7 µg/g), 0.28 µg/g (range: 0.01–1.4 µg/g), and 1.2 µg/L (range: 0.29–8.6 µg/L), respectively, and all three biomarkers were positively correlated with dietary methylmercury intake through rice ingestion (Spearman's rho=0.18–0.21, p≤0.0005), although the correlations were weak. In contrast, biomarkers were not correlated with fish/shellfish methylmercury intake (Spearman's rho=0.04–0.08, p=0.11–0.46). Conclusions Among pregnant mothers living in rural inland China, rice ingestion contributed to prenatal methylmercury exposure, more so than fish/shellfish ingestion. [ABSTRACT FROM AUTHOR]

Abstract: The Wanshan Hg mining area in Guizhou, China, was one of the world’s largest Hg producing regions. Numerous mine-waste and calcines still remain, leaching Hg to local rivers and streams and potentially impacting the local population. Several studies have been published on local environmental impacts of these mining and retorting residues, but a comprehensive, regional survey on the distribution of Hg in the rivers in the region, as presented in this paper, has not previously been conducted. This study focuses on the regional distribution and temporal variation of aqueous Hg fractions in the five main watercourses draining the Wanshan Hg mining and retorting area, covering more than 700 km2. Three sampling campaigns were carried out in 2007 and 2008, covering high flow, normal flow and low flow periods. Total (THg), particulate (PHg), dissolved (DHg) and reactive (RHg) Hg fractions were determined. All rivers had the highest Hg concentrations at sample sites about 100–500m downstream of the mine wastes. Total Hg concentrations ranged from extremely high (up to 12,000ngL−1) at the sample site just 100m below mine wastes, to quite low in tributary streams (1.9ngL−1, about 14km downstream of the mine wastes). Total Hg and PHg concentrations were usually highest during high flow periods in the Hg-contaminated areas (i.e. THg⩾50ngL−1), while in the less-impacted downstream areas (with THg<50ngL−1) the Hg concentrations were usually lowest during high flow periods. Although highly elevated concentrations of Hg in water samples were found just downstream of the mine wastes, the concentrations decreased sharply to well below 50ngL−1 (US EPA Hg concentration standard for protection of fresh water), within only 6–8km downstream. Concentrations of THg were highly dominated by and correlated with PHg (R 2 =0.996–0.999, P <0.001); PHg constituted more than 80% of THg in Hg-contaminated areas, and could account for 99.6% of the THg close to the mine wastes. [Copyright &y& Elsevier]