Blood mercury mediates the associations between fish consumption and serum uric acid levels among Chinese adults: A nationally representative study.

Fish consumption can increase purine load in human body, and the enrichment of mercury in fish may affect the glomerular filtration function, both resulting in increased serum uric acid (SUA) levels. The data of blood mercury (BHg), fish consumption frequency and SUA levels of 7653 participants aged 18 years or older was from China National Human Biomonitoring (2017-2018). The associations between fish consumption frequency, ln-transformed BHg and SUA levels were explored through weighted multiple linear regressions. The mediating effect of BHg levels between fish consumption frequency and SUA levels was evaluated by mediation analysis. We found that both the fish consumption frequency and BHg were positively associated with SUA levels in both sexes. Compared to participants who had never consumed fish, participants who consumed fish once a week or more had higher SUA levels [ß (95% confidence interval, CI): 20.39 (2.16, 38.62) in males; ß (95% CI): 10.06 (0.76, 19.37) in females] and ln-transformed BHg [ß (95% CI): 0.97 (0.61, 1.34) in males; ß (95% CI): 0.84 (0.63, 1.05) in females]. Each 1-unit increase in ln-transformed BHg, the SUA levels rose by 4.78 (95% CI: 0.01, 9.54) µmol/L for males and 3.81 (95% CI: 1.60, 6.03) µmol/L for females. The association between fish consumption with SUA levels was mediated by ln-transformed BHg with the percent mediated of 34.66% in males and 26.58% in females. It revealed that BHg played mediating roles in the elevation of SUA levels caused by fish consumption. This study's findings could promote the government to intervene in mercury pollution in fish, so as to ensure the safety of fish consumption.

Fish and Shellfish Consumption, Cognitive Health and Mortality from Alzheimer's Disease among US Adults Aged 60 and Older.

BACKGROUND: Relationships of fish-shellfish consumption, cognitive health and mortality from Alzheimer's disease (AD) among US adults aged 60 years and older have not been adequately studied. OBJECTIVES: To determine the relationship of fish-shellfish consumption, cognitive health and mortality from AD in US adults aged 60 years and older. DESIGN, SETTING AND PARTICIPANTS: The data of this cross-sectional study of US adults aged 60 years and older were from the National Nutrition and Health Examination Survey (NHANES) datasets. Frequency of fish-shellfish consumption, its association with subjective cognitive decline (SCD) and AD mortality of these participants between 1999 and 2018 and cognitive assessment scores between 2011 and 2014 were analyzed. MEASUREMENTS AND RESULTS: US adults aged 60 years and older consumed fish-shellfish 1.2 times/week and had a blood Hg of 1.63 ug/L on average between 1999 and 2018. Participants aged 60 years and older in the highest quartile of fish-shellfish consumption (~3 times/week) had significantly higher cognitive assessment scores than those in the lowest quartile (rare or no fish-shellfish consumption). Adults in the highest quartile of fish-shellfish consumption had a 30% lower risk (odds ratio 0.7, 95%CI 0.57-0.87) of SCD, and 44% lower risk (hazard ratio 0.56, 95%CI 0.35-0.9) of AD mortality than those in the lowest quartile. CONCLUSION: Increased fish-shellfish consumption was associated with improved scores of cognitive assessment and reduced risks of SCD and AD mortality.

Genome-Wide Association Study of Blood Mercury in European Pregnant Women and Children.

Mercury has high industrial utility and is present in many products, and environmental contamination and occupational exposure are widespread. There are numerous biological systems involved in the absorption, metabolism, and excretion of Hg, and it is possible that some systems may be impacted by genetic variation. If so, genotype may affect tissue concentrations of Hg and subsequent toxic effects. Genome-wide association testing was performed on blood Hg samples from pregnant women of the Avon Longitudinal Study of Parents and Children (n = 2893) and children of the Human Early Life Exposome (n = 1042). Directly-genotyped single-nucleotide polymorphisms (SNPs) were imputed to the Haplotype Reference Consortium r1.1 panel of whole genotypes and modelled againstlog-transformed Hg. Heritability was estimated using linkage disequilibrium score regression. The heritability of Hg was estimated as 24.0% (95% CI: 16.9% to 46.4%) in pregnant women, but could not be determined in children. There were 16 SNPs associated with Hg in pregnant women above a suggestive p-value threshold (p < 1 × 10-5), and 21 for children. However, no SNP passed this threshold in both studies, and none were genome-wide significant (p < 5 × 10-8). SNP-Hg associations were highly discordant between women and children, and this may reflect differences in metabolism, a gene-age interaction, or dose-response effects. Several suggestive variants had plausible links to Hg metabolism, such as rs146099921 in metal transporter SLC39A14, and two variants (rs28618224, rs7154700) in potassium voltage-gated channel genes. The findings would benefit from external validation, as suggestive results may contain both true associations and false positives.

Association of blood mercury levels with bone mineral density in adolescents aged 12-19.

Bone mass increases rapidly in adolescence, and achieving higher bone mineral density (BMD) during this period can help prevent osteoporosis. However, the effects of metallic mercury on bone health remain controversial. Previous studies have discussed perimenopausal women and older adults, while the association of blood mercury with BMD in adolescents is yet to be studied. Date was collected from the National Health and Nutrition Examination Survey (NHANES) 2011-2018. Weighted multiple linear regression models were used to explore the association of blood mercury levels with BMD in adolescents, while smooth curve fittings and weighted generalized additive models were used to identify the potential nonlinear association. We found that blood mercury levels were negatively associated with BMD in adolescents, though not significantly, based on the results of statistical analyses of 2818 participants. Additionally, the trend in BMD with changes in blood mercury was different in male and female adolescents. We also found an inverted U-shaped association between blood mercury and BMD in male and Mexican-American adolescents. This suggests that increased blood mercury levels within a range may benefit bone health in male adolescents (inflection point: 5.44 nmol/L) and Mexican-American adolescents (inflection point: 5.49 nmol/L), while higher blood mercury levels may harm bone health. More prospective research is needed to confirm our findings.

Association of Blood Mercury Level with Liver Enzymes in Korean Adults: An Analysis of 2015-2017 Korean National Environmental Health Survey.

Increased liver enzymes as a result of exposure to mercury and their toxic effects are not well understood in Korea at the population level. The effect of blood mercury concentration on alanine aminotransferase (ALT) and aspartate aminotransferase (AST) was evaluated after adjusting for sex, age, obesity, alcohol consumption habit, smoking, and exercise parameters in 3712 adults. The risk of abnormal liver function was measured using a multiple logistic regression analysis. Blood mercury concentration was divided into quartiles, and liver enzyme levels were compared for each quartile. ALT and AST levels were 10-20% higher in the second, third, and fourth quartiles compared to the first quartile. The risk of liver dysfunction or elevated liver enzymes was significantly higher in the second, third, and fourth quartiles than in the first quartile. As blood mercury levels increased, liver enzymes and mercury-induced hepatotoxicity increased. The increase in liver enzymes caused by mercury was more pronounced in the low-mercury concentration range. To reduce the long-standing problem of abnormal liver enzymes and liver function in Korea and other similar settings, it is important to decrease exposure to mercury through effective implementation of specific health and environmental strategies.

Association of blood mercury exposure with depressive symptoms in the Chinese oldest old.

Depressive symptoms have a significant impact on the quality-of-life among the oldest old (aged ≥ 80 years) in the population. Current research on the association of blood mercury with depressive symptoms has mainly targeted the general population. However, it is unclear whether this association is present in the oldest old. We used data from the Healthy Aging and Biomarker Cohort Study carried out in 2017-2018, with 1154 participants aged ≥ 80 years eligible for analysis. Inductively coupled plasma mass spectrometry (ICP-MS) was employed to detect blood mercury (Hg) levels, while the CES-D10 depression scale was used to assess depressive symptoms. The association between blood mercury levels and depressive symptoms was investigated using log-binomial and Poisson regression models. We also used restricted cubic splines (RCS) to assess the linear or nonlinear association of blood mercury with depressive symptoms scores. The 1154 participants ranged in age from 80 to 120 years, while the geometric mean of blood mercury concentration was 1.01 µg/L. After adjustment for covariates, log-binomial and Poisson regression analyses revealed a statistically significant, positive association of blood mercury with depressive symptoms. In comparison to the first tertile, the adjusted relative risks of blood mercury and the presence of depressive symptoms in the second and third tertiles were 1.55 (1.20-1.99) and 1.45 (1.11-1.90), respectively. The RCS model showed a linear association between blood mercury level and depressive symptoms scores. In conclusion, among the oldest old, we demonstrated that blood mercury levels were positively associated with depressive symptoms. Further surveys, especially cohort studies and clinical trials are needed to confirm these results.

Mercury may reduce the protective effect of sea fish consumption on serum triglycerides levels in Chinese adults: Evidence from China National Human Biomonitoring.

Sea fish contain omega-3 polyunsaturated fatty acids (omega-3 PUFAs) which have been found to reduce triglyceride (TG) levels. However, sea fish may contain pollutants such as mercury which cause oxidative stress and increase TG levels. Therefore, the relationship between sea fish and TG remains unclear. We aimed to explore whether blood mercury (BHg) can affect the effect of sea fish consumption frequency on TG level among Chinese adults. A total of 10,780 participants were included in this study. BHg levels were measured using inductively coupled plasma mass spectrometry (ICP-MS). The associations of sea fish consumption frequency with BHg and TG levels as well as the association of BHg with TG levels were evaluated using multiple linear regression. Causal mediation analysis was used to evaluate the mediation effect of BHg levels on the association of sea fish consumption frequency with TG levels. The frequency of sea fish consumption showed a negative association with TG level. Compared with the participants who never ate sea fish, the TG level decreased by 0.193 mmol/L in those who ate sea fish once a week or more [ß (95%CI): -0.193 (-0.370, -0.015)]. Significant positive associations were observed of BHg with TG levels. With one unit increase of log2-transformed BHg, the change of TG level was 0.030 mmol/L [0.030 (0.009, 0.051)]. The association between sea fish consumption and TG was mediated by log2-transformed BHg [total effect = -0.037 (-0.074, -0.001); indirect effect = 0.009 (0.004, 0.015)], and the proportion mediated by log2-transformed BHg was 24.25%. BHg may reduce the beneficial effect of sea fish consumption frequency on TG levels among Chinese adults. Overall, sea fish consumption has more benefits than harms to TG.

Effect of heavy metals on ventricular repolarization and depolarization in the Metropolitan Manila Development Authority (MMDA) traffic enforcers' health study.

We examined the relationships between blood heavy metals [cadmium (B-Cd), mercury (B-Hg), and lead (B-Pb)] and heart rate-corrected QT interval (QTc), JT interval (JTc), and QRS complex duration (QRSc), electrocardiogram markers of ventricular repolarization and depolarization among 60 traffic enforcers in the MMDA traffic enforcers' health study. We fitted regression models to estimate the mean change effect on QTc, JTc, and QRSc, of B-Cd, B-Hg, and B-Pb concentrations, adjusted for potential confounding factors. We looked at effect modification by sex and smoking status. An interquartile range increase in B-Cd (0.9 µg/L) was related to a 6.6% increase in mean QRSc [95% confidence interval (CI): 2.5, 10.8], and a 1.7% increase in mean QTc (95% CI: 0.2, 3.3). We also found that the associations between B-Cd and QRSc and QTc were higher among participants who were never smokers than ever smokers. Moreover, the association between B-Cd and QRSc was also higher among males than females.

Mercury Exposure in Artisanal Mining: Assessing the Effect of Occupational Activities on Blood Mercury Levels Among Artisanal and Small-Scale Goldminers in Ghana.

A cross-sectional survey of 425 male artisanal and small-scale goldminers (ASGM) was conducted to examine the relationship between the occupational activities of the miners and their blood mercury levels while controlling for relevant biosocial and socio-cultural factors. The data was subjected to descriptive and inferential statistics. Initial findings showed that 43.29% of the ASGM miners had blood mercury levels above the occupational exposure threshold. Among the occupational factors, ASGM miners who amalgamate gold, burn amalgam, and ASGM miners who smelt gold were 2.260, 1.881, and 2.094 times respectively more likely to have high blood mercury levels as compared to ASGM miners who did not carry out these activities. Also, ASGM miners who suck excess mercury with their mouth (OR = 0.197, p < 0.001) were less likely to have high blood mercury levels. For the biosocial and socio-cultural attributes, high blood mercury levels was less likely among older ASGM miners (OR = 0.507, p < 0.05). Inversely, high blood mercury levels was more likely among ASGM miners who are married (OR = 1.627, p < 0.05), ASGM miners with junior (OR = 2.240, p < 0.001) and senior (OR = 1.575, p < 0.05) high school education, and ASGM miners who have 6-10 years (OR = 3.802, p < 0.001) and above 10 years (OR = 2.591, p < 0.001) work experience. ASGM miners who amalgamate gold, burn amalgam, and smelt gold are exposed to mercury and are at risk of mercury poisoning. This could, however, be minimized with the right capturing devices and personal protective equipment. This notwithstanding, unsafe, and unsustainable occupational practices such as working in mercury contaminated water and sucking excess mercury with the mouth should be discouraged.

Associations of total blood mercury and blood methylmercury concentrations with diabetes in adults: An exposure-response analysis of 2005-2018 NHANES.

OBJECTIVE: To examine the exposure-response relationship between mercury exposure and diabetes in adults, and to explore the possible effect modifications by selenium and omega-3 fatty acids. METHODS: Biomarker data (total blood mercury and blood methylmercury) from individuals ≥20 years of age were obtained from the 2005-2018 NHANES. Diabetes was defined through questionnaires, fasting plasma glucose, 2 -h plasma glucose and hemoglobin A1c levels. The exposure-response relationship between mercury exposure and diabetes was assessed with logistic regression and restricted cubic splines. RESULTS: Comparing the highest to lowest quartile of exposure, the multivariable-adjusted odds ratio (95 % CI) of diabetes was 0.76 (0.63-0.92) with total blood mercury and 0.82 (0.66-1.00) with blood methylmercury. The inverse associations between total blood mercury [0.55 (0.40-0.77)] and blood methylmercury [0.61 (0.38-0.97)] and diabetes were observed among individuals having higher intakes of selenium (Pfor interaction<0.05). Trends toward lower odds of diabetes with mercury exposure were mainly confined to individuals having higher intakes of omega-3 fatty acid, but the interactions were not significant. The inverse associations between total blood mercury and blood methylmercury and diabetes remained in sensitivity analyses after excluding patients with hypertension that may change their dietary intake of fish. Exposure-response analyses showed an initial decrease in odds of diabetes followed by a platform or a weaker decrease beyond 3 µg/L of total blood mercury and methylmercury concentrations, respectively. CONCLUSIONS: Total blood mercury and blood methylmercury concentrations were inversely associated with diabetes in adults, and the associations were modified by selenium.

Role of MT1A Polymorphism and Environmental Mercury Exposure on the Montreal Cognitive Assessment (MoCA).

PURPOSE: Many age-related structural and functional changes in the brain have important consequences. Long-term exposure to mercury and the impact of functional polymorphisms of metal-regulating proteins such as metallothioneins (MTs) can result in neurological-neurobehavioral effects in elderly individuals. Therefore, the aims of this study are to examine the associations between biomarkers of mercury exposure and cognitive impairment and to investigate the effect of the rs8052394 single nucleotide polymorphism (SNP) of the potential modifier gene MT1A on different domains of the Montreal Cognitive Assessment (MoCA). MATERIALS AND METHODS: We studied 436 participants aged ≥55 years from the Electricity Generating Authority of Thailand study. They underwent a physical examination, an extensive cognitive assessment with the MoCA (cutoff <26 points), and a biochemical analysis related to diabetes and dyslipidemia. The blood mercury level was determined by inductively coupled plasma mass spectrometry. Genotyping of the MT1A rs8052394 SNP was performed by the restriction fragmentation length polymorphism method. RESULTS: The mean age of the study population was 58.8±3.01 years, and most had ≥12 years of education (75.7%). The primary study finding was that the prevalence of mild cognitive impairment (MCI) in older Thai adults was 39.7%. The frequency distributions of the G allele of the rs8052394 SNP of the MT1A gene were significantly associated with the total and sub-domain MoCA scores. The prevalence of MCI was significantly associated with increased age, hypertriglyceridemia, hyperhomocysteinemia, the third tertile of blood mercury concentration, and the rs8052394 variant genotype of MT1A (P values for all odds ratios <0.05). CONCLUSION: These findings suggested that neurocognitive effects associate with mercury exposure and genetic susceptibility in toxicokinetics. Public health strategies can be used to implement as a comprehensive action plan to educate vulnerable populations on how to reduce mercury exposure. Concurrently, impact of such genetic predisposition requires replication for identifying and protecting susceptible individuals from mercury toxicity.

Blood Mercury in Three Populations of Endangered Whooping Crane (Grus americana).

We investigated concentrations of blood total mercury (THg) in three extant populations of endangered Whooping Crane (Grus americana). Blood THg was greater in cranes reintroduced during 2001-2008 that range in the eastern US (median = 0.31 ug/g ww) than both wild cranes in central North America (median = 0.11 ug/g ww) and from captivity (median = 0.01 ug/g ww). The median THg blood concentrations in the two free-ranging populations of Whooping Cranes were low compared to reproductive toxic thresholds suggested for other large bird species (> 4.3 ug/g ww), but a singular elevated concentration was observed in one crane (1.04 ug/g ww; 6% of samples from the reintroduced population). These results likely reflect variable dietary Hg exposure among these populations, but should prompt additional biomonitoring to discern risk of greater Hg exposure nearer to the time of breeding and potential effects on productivity.

Associations of Metabolic Genes (GSTT1, GSTP1, GSTM1) and Blood Mercury Concentrations Differ in Jamaican Children with and without Autism Spectrum Disorder.

We investigated interactive roles of three metabolic glutathione S-transferase (GST) genes (GSTP1, GSTT1, and GSTM1) and autism spectrum disorder (ASD) status in relation to blood Hg concentrations (BHC) of Jamaican children. We used data from 266 children (2-8 years) with ASD and their 1:1 age- and sex-matched typically developing (TD) controls. After adjusting General Linear Models for child's age, socioeconomic status, consumption of leafy vegetables, fried plantain, canned fish, and the interaction between GSTP1 and GSTT1, we found significant interactions between GSTP1 and ASD status in relation to BHC either in a co-dominant or dominant genetic model for GSTP1(P < 0.001, P = 0.007, respectively). In the co-dominant model for the Ile105Val GSTP1 polymorphism, geometric mean (GM) BHC in ASD cases with genotype Ile/Ile were significantly higher than in cases with the Ile/Val genotype (0.73 vs. 0.48 µg/L, P = 0.01). In contrast, in TD controls with the Ile/Val genotype GM BHC were significantly higher than in those with the Ile/Ile genotype (0.72 vs. 0.49 µg/L, P = 0.03) or the Val/Val genotype (0.72 vs. 0.51 µg/L, P = 0.04). Although our findings are consistent with the role of GSTP1 in detoxification of Hg, replication in other populations is warranted.

Per- and Polyfluoroalkyl Substances in Human Serum Samples of Selected Populations from Ghana.

The aims of this study were to assess serum concentrations of per- and polyfluoroalkyl substances (PFASs) in selected populations from Ghana, including workers engaged in the repair of electronic equipment (ERWs), and to elucidate PFAS concentrations in relation to blood mercury concentrations (B-Hg) as a biomarker of seafood consumption. In all, 219 participants were recruited into the study, of which 26 were women and 64 were ERWs. Overall, the PFAS concentrations were low. The most abundant components were perfluorooctane sulfonate (PFOS) and perfluorohexane sulfonic acid (PFHxS). Women had generally lower PFAS concentration than men. The ERWs had statistically significantly higher concentrations of perfluorooctanoate (PFOA), which was associated with the concentration of tin in urine. This could indicate exposure during soldering. The concentration of B-Hg was associated with several of the PFASs such as PFOA, PFOS and perfluoroheptane sulfonate (PFHpS). Additionally, the concentrations of perfluorodecanoic acid (PFDA) and perfluoroundecanoate (PFUnDA) were highly associated with the concentrations of B-Hg. It is noteworthy that the linear isomer of PFHxS was strongly associated with B-Hg while the branched isomers of PFHxS were not. In conclusion, the PFAS concentrations observed in the present study are low compared to other populations previously investigated, which also reflects a lower PFAS exposure within the Ghanaian cohorts. ERWs had significantly higher PFOA concentrations than the other participants. Several PFASs were associated with B-Hg, indicating that seafood consumption may be a source of PFAS exposure.

The Relationship between Mercury Exposure Indices and Dietary Intake of Fish and Shellfish in Women of Childbearing Age.

Women of childbearing age who are susceptible to mercury exposure were studied to understand the relation between mercury intake through fish and shellfish consumption and mercury exposure indices from blood, hair, and urine samples. A total of 711 women of childbearing age from coastal areas with a high concentration of mercury exposure in Korea were studied. Data were collected on demographic characteristics, dietary intake of fish and shellfish using the simple Food Frequency Questionnaire. Mercury concentration was estimated from the collected samples of blood, hair, and urine. The geometric mean of blood methyl mercury concentration of mercury exposure through seafood was 3.06 µg/L for the low tertile, 3.12 µg/L for the middle tertile, and 3.60 µg/L for the high tertile, indicating a clear tendency of blood methyl mercury to increase as the mercury exposure by fish and shellfish intake ascended. For total blood mercury and hair mercury, the middle and high tertiles had higher values than the low. Mercury exposure through fish and shellfish intake is a main factor for an increase of blood methyl mercury concentration in women of childbearing age. More attention needs to be paid to mercury exposure through seafood intake, considering the serious effect mercury concentration has on women of childbearing age.

Association between Blood Heavy Metal Levels and Predicted 10-Year Risk for A First Atherosclerosis Cardiovascular Disease in the General Korean Population.

BACKGROUND: Atherosclerotic cardiovascular disease (ASCVD) is a preventable type of disease, thus, specifying factors that increase the occurrence of this type of disease is needed. Heavy metals such as cadmium (Cd), lead (Pb), and mercury (Hg) have been suggested as possible factors influencing the development of cardiovascular disease. We aimed to link blood heavy metal levels (Cd, Pb, Hg) with 10-year ASCVD risk scores. METHODS: A population of 993 men and 1431 women who participated in the Korea National Health and Nutrition Examination Survey (KNHANES) were included. The 2013 American College of Cardiology/American Heart Association (ACC/AHA) pooled cohort equations risk prediction model and Korean Risk Prediction Model (KRPM) were used as means for risk prediction. Following multivariate adjustment; blood Cd; Pb; and Hg levels were divided into quartiles for analysis using linear trends estimation and multiple regression models. RESULTS: There was an overall positive trend between blood Cd, Pb, and Hg levels and 10-year ASCVD risk scores; KRPM risk score increasing by quartile for blood Cd (men p < 0.0001, women p = 0.0024), Pb (men p = 0.0097, women p = 0.0330), Hg (men p = 0.0096, women p = 0.0030) rates and pooled cohort equations risk score increasing by quartile for Cd (men p < 0.0001, women p = 0.0034) and Hg (men p = 0.0099, women p = 0.0010) with linear trends. Urban population showed a stronger relationship between blood Cd, Pb, and Hg levels and 10-year ASCVD risk score especially among men with multiple regression analysis. CONCLUSION: Blood Cd, Pb, and Hg levels are associated with ASCVD risk. Thus, they should be considered while developing preventive measures for ASCVD.

Association of Blood Mercury Level with the Risk of Depression According to Fish Intake Level in the General Korean Population: Findings from the Korean National Health and Nutrition Examination Survey (KNHANES) 2008-2013.

Mercury is a cumulative neurotoxic agent, exposure to high levels of which may increase the risk of psychiatric symptoms. The purpose of this study was to examine the associations between blood mercury and depression risk in Korean adults. We analyzed the Korean National Health and Nutrition Examination Survey (KNHANES) with 11,754 participants (male: 5834 female: 5920) aged ≥19 years from 2008 to 2013. The associations of blood mercury with risk of depression were estimated using multivariate logistic regression after adjustment for potential confounders. We found a significantly increased risk of depression in the highest quintile for blood mercury (multivariate OR = 2.05; 95% CI = 1.20-3.48; P trend = 0.03) among female, but not male. A stratification analysis by fish intake showed that the association between depression and blood mercury was strengthened (OR = 4.00; 95% CI = 1.51-10.6; P trend = 0.015) among females with the lowest tertile of fish intake. The results of this study suggest that higher levels of blood mercury, especially in cases of lower fish intake, are positively associated with the risk of depression in Korean women.

Do songbirds in wetlands show higher mercury bioaccumulation relative to conspecifics in non-wetland habitats?

Environmental conditions in wetlands facilitate favorable biogeochemical conditions for the conversion of inorganic mercury into methylmercury. For this reason, wetlands are increasingly classified as mercury hotspots, places where biota exhibit elevated mercury concentrations. While it is clear that wetlands play an important role in methylmercury production, factors such as geographic variation in mercury deposition, wetland type, and trophic dynamics can cause variation in mercury dynamics and bioaccumulation in biota occupying wetlands or connected to wetland trophic systems. Here, we use songbirds as bioindicators in a two-pronged approach aimed at evaluating the state of our understanding of mercury bioaccumulation by songbirds in wetland ecosystems. First, we use a case study in southeast Missouri to compare blood mercury concentrations in tree swallows (Tachycineta bicolor) and eastern bluebirds (Sialia sialis) occupying wetland and non-wetland habitats to test the hypothesis that songbirds in wetlands will have higher mercury bioaccumulation than those in non-wetlands. Adult tree swallows in wetlands had significantly higher blood mercury concentrations than those in non-wetlands; however, no difference between ecosystems was detected in eastern bluebirds. Second, we present a review of the current literature on mercury in songbirds in wetland ecosystems across North America. Mercury concentrations in songbirds varied among wetland types and with geographic location, often in an unpredictable manner. Mercury concentrations in songbird blood varied 3-10 fold at locations separated only by ~10 to several hundred kilometers. This magnitude of difference in blood mercury concentrations among wetlands exceeds documented differences between wetland and non-wetland ecosystems. Therefore, we caution against the automatic assumption that songbirds occupying wetlands will have higher mercury bioaccumulation than conspecifics living in other habitats.

Wetland water-management may influence mercury bioaccumulation in songbirds and ducks at a mercury hotspot.

Mercury is a persistent, biomagnifying contaminant that can cause negative behavioral, immunological, and reproductive effects in wildlife and human populations. We examined the role of wetland water-management on mercury bioaccumulation in songbirds and ducks at Kellys Slough National Wildlife Refuge Complex, near Grand Forks, North Dakota USA. We assessed mercury concentrations in blood of wetland-foraging songbirds (80 common yellowthroats [Geothlypis trichas] and 14 Nelson's sparrows [Ammospiza nelsoni]) and eggs of upland-nesting ducks (28 gadwall [Mareca strepera], 19 blue-winged teal [Spatula discors], and 13 northern shoveler [S. clypeta]) across four wetland water-management classifications. Nelson's sparrow blood mercury concentrations were elevated (mean: 1.00 µg/g ww; 95% CL: 0.76-1.31) and similar to those reported 6 years previously. Mercury in songbird blood and duck eggs varied among wetland water-management classifications. Songbirds and ducks had 67% and 49% lower mercury concentrations, respectively, when occupying wetlands that were drawn down with water flow compared to individuals occupying isolated-depressional wetlands with no outflow. Additionally, songbirds within impounded and partially drawn-down wetland units with water flow had mercury concentrations that were 26-28% lower, respectively, than individuals within isolated-depressional wetlands with no outflow. Our results confirm that mercury concentrations in songbirds at Kellys Slough continue to be elevated and suggest that water-management could be an important tool for wetland managers to reduce bioaccumulation of mercury in birds.

Explaining variation in Colorado songbird blood mercury using migratory behavior, foraging guild, and diet.

Methylmercury is a contaminant of growing global concern that has been shown to accumulate in a variety of taxa, including songbirds. Birds in the same area can accumulate mercury to strikingly different levels. While diet and trophic level clearly play an important role in mercury bioaccumulation and biomagnification, other factors including foraging guilds and migratory behavior may influence mercury levels as well. Here we examine interspecific variation in blood mercury levels in songbirds living in the Fountain Creek watershed on the Front Range of Colorado. We found that the species with the highest mercury had blood mercury concentrations over 75 times higher than the species with the lowest levels. Carnivores had the highest blood mercury levels, but ground foraging and long distance migration also were correlated with higher mercury concentrations. This information may shed light on what species are most at risk from mercury pollution and help to target conservation resources at contaminated sites.