Methylmercury in fish: a review of residue levels, fish consumption and regulatory action in the United States

A novel approach to assessing the joint effects of mercury and fish consumption on neurodevelopment in the New Bedford Cohort

Understanding health risks from methylmercury (MeHg) exposure is complicated by its link to fish consumption, which may confound or modify toxicities. One solution is to include fish intake and a biomarker of MeHg exposure in the same analytical model, but resulting estimates do not reflect the independent impact of accumulated MeHg or fish exposure. In fish-eating populations, this can be addressed by separating MeHg exposure into fish intake and average mercury content of the consumed fish. We assessed the joint association of prenatal MeHg exposure (maternal hair mercury level) and fish intake (among fish-eating mothers) with neurodevelopment in 361 children aged 8 years from the New Bedford Cohort (New Bedford, Massachusetts; born in 1993-1998). Neurodevelopmental assessments used standardized tests of IQ, language, memory, and attention. Covariate-adjusted regression assessed the association of maternal fish consumption, stratified by tertile of estimated average fish mercury level, with neurodevelopment. Associations between maternal fish intake and child outcomes were generally beneficial for those in the lowest average fish mercury tertile but detrimental in the highest average fish mercury tertile, where, for example, each serving of fish was associated with 1.3 fewer correct responses (95% CI, -2.2 to -0.4) on the Boston Naming Test. Standard analyses showed no outcome associations with hair mercury level or fish intake. This article is part of a Special Collection on Environmental Epidemiology.

Dietary oily fish intake is inversely associated with moderate-to-severe intracranial artery stenosis in older adults of indigenous Ecuadorian ancestry

BACKGROUND AND AIMS

Information on the association between dietary oily fish intake and intracranial atherosclerosis is limited and contradictory. Inconsistencies might be in part related to heterogeneous designs and differences in race/ethnicity of study populations. We aim to assess whether oily fish intake is inversely associated with intracranial artery stenosis (ICAS) in frequent fish consumers of indigenous ancestry living in coastal Ecuador.

METHODS

The study included 384 participants aged ≥60 years enrolled in the Atahualpa Project Cohort. Dietary oily fish intake was quantified systematically via validated surveys and all participants received a time-of-flight MRA of intracranial vessels. Poisson regression models, adjusted for demographics, level of education, traditional risk factors and severe tooth loss, were fitted to assess the association between amounts of oily fish intake and the number of intracranial arteries with moderate-to-severe (≥50 %) stenosis.

RESULTS

Participants had a mean age of 67.7 ± 7 years, and 56 % were women. The mean oily fish intake was 8.9 ± 5.2 servings/week; 283 (74 %) participants consumed ≥5.2 servings/week (2nd to 4th quartiles of fish intake). Forty-three (11 %) participants had at least one major intracranial artery with moderate-to-severe stenosis. Both univariate and multivariate models showed a significant inverse association between consumption of oily fish in the 2nd to 4th quartiles and ≥50 % stenosis in at least one artery (β: 0.46; 95 % C.I.: 0.27-077, and β: 0.52; 95 % C.I.: 0.30-0.90, respectively).

CONCLUSIONS

Consumption of more than five oily fish servings/week is associated with lower prevalence of moderate-to-severe ICAS in indigenous Ecuadorians.

Activatable Probes for Ratiometric Imaging of Endogenous Biomarkers In Vivo

Dynamic variations in the concentration and abnormal distribution of endogenous biomarkers are strongly associated with multiple physiological and pathological states. Therefore, it is crucial to design imaging systems capable of real-time detection of dynamic changes in biomarkers for the accurate diagnosis and effective treatment of diseases. Recently, ratiometric imaging has emerged as a widely used technique for sensing and imaging of biomarkers due to its advantage of circumventing the limitations inherent to conventional intensity-dependent signal readout methods while also providing built-in self-calibration for signal correction. Here, the recent progress of ratiometric probes and their applications in sensing and imaging of biomarkers are outlined. Ratiometric probes are classified according to their imaging mechanisms, and ratiometric photoacoustic imaging, ratiometric optical imaging including photoluminescence imaging and self-luminescence imaging, ratiometric magnetic resonance imaging, and dual-modal ratiometric imaging are discussed. The applications of ratiometric probes in the sensing and imaging of biomarkers such as pH, reactive oxygen species (ROS), reactive nitrogen species (RNS), glutathione (GSH), gas molecules, enzymes, metal ions, and hypoxia are discussed in detail. Additionally, this Review presents an overview of challenges faced in this field along with future research directions.

Factors associated with blood mercury concentrations and their interactions with three glutathione S-transferase genes (GSTT1, GSTM1, and GSTP1): an exposure assessment study of typically developing Jamaican children

BACKGROUND

Jamaican soil is abundant in heavy metals including mercury (Hg). Due to availability and ease of access, fish is a traditional dietary component in Jamaica and a significant source of Hg exposure. Mercury is a xenobiotic and known neuro-toxicant that affects children's neurodevelopment. Human glutathione S-transferase (GST) genes, including GSTT1, GSTM1, and GSTP1, affect Hg conjugation and elimination mechanisms.

METHODS

In this exposure assessment study we used data from 375 typically developing (TD) 2-8-year-old Jamaican children to explore the association between environmental Hg exposure, GST genes, and their interaction effects on blood Hg concentrations (BHgCs). We used multivariable general linear models (GLMs).

RESULTS

We identified the child's age, consumption of saltwater fish, canned fish (sardine, mackerel), string beans, grain, and starches (pasta, macaroni, noodles) as the environmental factors significantly associated with BHgCs (all P < 0.05). A significant interaction between consumption of canned fish (sardine, mackerel) and GSTP1 in relation to BHgC using either a co-dominant or recessive genetic model (overall interaction P = 0.01 and P < 0.01, respectively) indicated that consumption of canned fish (sardine, mackerel) was significantly associated with higher mean BHgC only among children with the GSTP1 Ile105Val, Ile/Ile [Ratio of mean Hg (95% CI) = 1.59 (1.09, 2.32), P = 0.02] and Ile/Val [Ratio of mean Hg (95% CI) = 1.46 (1.12, 1.91), P = 0.01] genotypes.

CONCLUSIONS

Since this is the first study from Jamaica to report these findings, replication in other populations is recommended.

Dietary oily fish intake reduces the risk of all-cause mortality in frequent fish consumers of Amerindian ancestry living in coastal Ecuador: the Atahualpa project

PURPOSE

To assess the relationship between dietary oily fish intake and all-cause mortality in a population of frequent fish consumers of Amerindian ancestry living in rural Ecuador.

METHODS

Individuals aged ≥ 40 years enrolled in the prospective population-based Atahualpa Project cohort received annual questionnaires to estimate their dietary oily fish intake. Only fish served broiled or cooked in the soup were included for analysis. Poisson regression and Cox-proportional hazards models adjusted for demographics, education level and cardiovascular risk factors were obtained to estimate mortality risk according to the amount of oily fish intake stratified in tertiles.

RESULTS

Analysis included 909 individuals (mean age: 55.1 ± 12.8 years) followed by a median of 7.5 ± 3 years. Mean oily fish intake was 9.4 ± 5.7 servings per week. A total of 142 (16%) individuals died during the follow-up. The mortality rate for individuals in the first tertile de oily fish intake (0.0-6.29 servings) was 2.87 per 100 person-years, which decreased to 1.78 for those in the third tertile (10.59-35.0 servings). An adjusted Cox-proportional hazards model showed that individuals allocated to the second (HR 0.61; 95% CI 0.41-0.92) and third (HR 0.60; 95% CI 0.40-0.91) tertiles of dietary oily fish intake had significantly lower mortality risk than those in the first tertile.

CONCLUSION

Sustained oily fish intake of more than six servings per week reduces mortality risk in middle-aged and older adults of Amerindian ancestry.

Methylmercury formation in biofilms of Geobacter sulfurreducens

Introduction

Mercury (Hg) is a major environmental pollutant that accumulates in biota predominantly in the form of methylmercury (MeHg). Surface-associated microbial communities (biofilms) represent an important source of MeHg in natural aquatic systems. In this work, we report MeHg formation in biofilms of the iron-reducing bacterium Geobacter sulfurreducens.

Methods

Biofilms were prepared in media with varied nutrient load for 3, 5, or 7 days, and their structural properties were characterized using confocal laser scanning microscopy, cryo-scanning electron microscopy and Fourier-transform infrared spectroscopy.

Results

Biofilms cultivated for 3 days with vitamins in the medium had the highest surface coverage, and they also contained abundant extracellular matrix. Using 3 and 7-days-old biofilms, we demonstrate that G. sulfurreducens biofilms prepared in media with various nutrient load produce MeHg, of which a significant portion is released to the surrounding medium. The Hg methylation rate constant determined in 6-h assays in a low-nutrient assay medium with 3-days-old biofilms was 3.9 ± 2.0 ∙ 10^-14  L ∙ cell^-1 ∙ h^-1, which is three to five times lower than the rates found in assays with planktonic cultures of G. sulfurreducens in this and previous studies. The fraction of MeHg of total Hg within the biofilms was, however, remarkably high (close to 50%), and medium/biofilm partitioning of inorganic Hg (Hg(II)) indicated low accumulation of Hg(II) in biofilms.

Discussion

These findings suggest a high Hg(II) methylation capacity of G. sulfurreducens biofilms and that Hg(II) transfer to the biofilm is the rate-limiting step for MeHg formation in this systems.

Targeted Intracellular Demethylation of Methylmercury Enhances Elimination Kinetics and Reduces Developmental Toxicity in Transgenic Drosophila

Methylmercury (MeHg) persists today as a priority public health concern. Mechanisms influencing MeHg metabolism, kinetics, and toxicity outcomes are therefore essential knowledge for informing exposure risks. Evidence points to different toxic potencies of MeHg and inorganic mercury (Hg2+), highlighting the role for biotransformation (demethylation) in regulating MeHg toxicokinetics/dynamics. Whereas microbial MeHg demethylation in the gut is seen to influence elimination kinetics, the potential for systemic demethylation in tissues and target organs to influence MeHg toxicity remains uncertain. To investigate the consequences of systemic MeHg demethylation across development, we engineered transgenic Drosophila to express the bacterial organomercurial lyase enzyme (merB) in a targeted and tissue-specific manner. With all combinations of merB-induced demethylation, ubiquitously (via an actin promoter) or in a tissue-specific manner (ie, gut, muscle, neurons), we observe a rescue of MeHg-induced eclosion failure at the pupal to adult transition. In MeHg-fed larvae with ubiquitous or targeted (gut and muscle) merB expression, we see a significant decrease in MeHg body burden at the pupal stage relative to control flies. We also observe a significant increase in the MeHg elimination rate with merB demethylation induced in adults (control, t1/2 = 7.2 days; merB flies, t1/2 = 3.1 days). With neuronal-specific merB expression, we observe a rescue of MeHg-induced eclosion failure without a decrease in Hg body burden, but a redistribution of Hg away from the brain. These results demonstrate the previously unidentified potential for intracellular MeHg demethylation to promote transport and elimination of Hg, and reduce developmental MeHg toxicity. Impact Statement: These findings demonstrate the potential for MeHg demethylation in situ to contribute significantly to the MeHg elimination and distribution kinetics of whole animals and thereby affords a means of protection against the toxic insult of MeHg. Therefore, this study reveals important insight into processes that can determine an individual's resistance or susceptibility to MeHg and provides rationale for therapies targeting a novel metabolism-based pathways to alleviate toxicity risk stemming from MeHg exposure.

Comparative Study on the Distribution of Essential, Non-Essential Toxic, and Other Elements across Trophic Levels in Various Edible Aquatic Organisms in Sri Lanka and Dietary Human Risk Assessment

Thirty-six elements are categorized as essential but toxic in excess amount (EBTEs), non-essential toxic (NETs), and Other in 29 different edible aquatic species dwelling in offshore pelagic, and coastal and estuarine (CE) ecosystems were investigated in Sri Lanka. Elements were analyzed using an energy-dispersive X-ray fluorescence (EDXRF) spectrometer, and an NIC MA-3000 Mercury Analyzer. EBTEs showed a negative relationship, whereas NETs showed a positive relationship between the concentration (mg/kg wet weight) and trophic levels in both ecosystems. EBTEs showed trophic dilution, whereas NETs showed trophic magnification. Some elements in a few organisms exceeded the maximum allowable limit which is safe for human consumption. There was a positive relationship (R² = 0.85) between the concentration of mercury and body weight of yellowfin tuna (YFT). For the widely consumed YFT, the calculated hazard index (HI) for the non-carcinogenic health and exposure daily intake of NETs for adults were 0.27 and 9.38 × 10^-5 mg/kg bw/day, respectively. The estimated provisional tolerable weekly intake (PTWI) (μg/kg bw/w) was 0.47 for arsenic and 0.05 for antimony, cadmium, mercury, and lead. The HI and PTWI values were below the recommended limits; thus, consumption of YFT does not pose any health risk for Sri Lankan adults.

Mercury Concentrations in Four Marine Fishery Resources from Rio de Janeiro Coast, SW Atlantic, and Potential Human Health Risk Via Fish Consumption

Mercury (Hg) contamination has caused ecological and socioeconomic problems worldwide. One of the main Hg contamination routes by the human populations is through fish ingestion. Herein, we analyzed the total Hg concentrations (THg) in highly consumed marine fish species: Brazilian flathead Percophis brasiliensis, Atlantic bigeye Priacanthus arenatus, Stripped weakfish Cynoscion guatucupa, and Jamaica weakfish C. jamaicensis. The specimens were collected from fishing landings off the Rio de Janeiro, SW Atlantic. Additionally, we calculate the estimated weekly intakes (EWI) and the maximum amount of fish (MAF) that can be safely ingested, both based on the provisional tolerable weekly intake (PTWI). The highest THg concentrations were recorded in P. brasiliensis with a mean of 340.59 μg/kg (dry weight) and the lowest in P. arenatus (115.75 μg/kg). THg concentrations were positively related to the δ¹⁵N ratios indicating an increase in contamination with trophic level. All samples showed THg concentrations below the established limits by Brazilian and international regulation. Hg intake via human fish consumption does not exceed the PTWI. The EWI varied from 1.41% (P. arenatus size class I) to 11.52% (P. brasiliensis class II) of the PTWI, while the estimated EWI for "fish consumers" varied between 8.35 and 68.07% PTWI. The MAF estimated for an adult (70 kg) could safely consume between 1277.85 and 7075.50 g/week. This study is an important baseline for monitoring and future comparisons. Therefore, it is important to maintain monitoring of mercury levels in fish species in different marine regions, especially those species most consumed by humans.

Contamination levels and habitat use influence Hg accumulation and stable isotope ratios in the European seabass Dicentrarchus labrax

Hg accumulation in marine organisms depends strongly on in situ water or sediment biogeochemistry and levels of Hg pollution. To predict the rates of Hg exposure in human communities, it is important to understand Hg assimilation and processing within commercially harvested marine fish, like the European seabass Dicentrarchus labrax. Previously, values of Δ¹⁹⁹Hg and δ²⁰²Hg in muscle tissue successfully discriminated between seven populations of European seabass. In the present study, a multi-tissue approach was developed to assess the underlying processes behind such discrimination. We determined total Hg content (THg), the proportion of monomethyl-Hg (%MeHg), and Hg isotopic composition (e.g. Δ¹⁹⁹Hg and δ²⁰²Hg) in seabass liver. We compared this to the previously published data on muscle tissue and local anthropogenic Hg inputs. The first important finding of this study showed an increase of both %MeHg and δ²⁰²Hg values in muscle compared to liver in all populations, suggesting the occurrence of internal MeHg demethylation in seabass. This is the first evidence of such a process occurring in this species. Values for mass-dependent (MDF, δ²⁰²Hg) and mass-independent (MIF, Δ¹⁹⁹Hg) isotopic fractionation in liver and muscle accorded with data observed in estuarine fish (MDF, 0-1‰ and MIF, 0-0.7‰). Black Sea seabass stood out from other regions, presenting higher MIF values (≈1.5‰) in muscle and very low MDF (≈-1‰) in liver. This second finding suggests that under low Hg bioaccumulation, Hg isotopic composition may allow the detection of a shift in the habitat use of juvenile fish, such as for first-year Black Sea seabass. Our study supports the multi-tissue approach as a valid tool for refining the analysis of Hg sourcing and metabolism in a marine fish. The study's major outcome indicates that Hg levels of pollution and fish foraging location are the main factors influencing Hg species accumulation and isotopic fractionation in the organisms.

Mercury in neonatal and juvenile blacktip sharks (Carcharhinus limbatus). Part I: exposure assessment

Elasmobranchs are exposed to mercury (Hg) through a variety of pathways in the environment. This study assessed maternal offloading and diet-based Hg exposure for neonatal and juvenile blacktip sharks (Carcharhinus limbatus) from Charlotte Harbor located along southwest Florida's coast, a recognized Hg hotspot. Neonates (n = 57) had highest total Hg (THg) concentrations in the kidney (0.56 ± 0.26 mg kg^-1; n = 38) and muscle (0.53 ± 0.17 mg kg^-1; n = 57), followed by liver (0.31 ± 0.11 mg kg^-1; n = 38), and blood (0.05 ± 0.033 mg kg^-1; n = 57). Juveniles (n = 13) exhibited a different distribution with highest THg in the liver (0.868 ± 0.54 mg kg^-1; n = 6), followed by the muscle (0.84 ± 0.28 mg kg^-1; n = 13), kidney (0.55 ± 0.22 mg kg^-1; n = 6), and blood (0.11 ± 0.04 mg kg^-1; n = 11). The distribution of THg among tissues and liver-to-muscle ratios indicated that Hg originated primarily from maternal offloading in neonates, whereas juveniles continued to accumulate Hg through dietary exposure post-parturition. Additionally, comparisons between results of the present study and previous Florida blacktip shark surveys suggested that Hg levels have not declined in southwest Florida estuaries for over two decades.

Neurobehavioral and immune-toxic impairments induced by organic methyl mercury dietary exposure in Nile tilapia Oreochromis niloticus

Although substantial knowledge of mercury toxicity in fish has been assembled; until now, studies investigating the toxic impacts in Nile tilapia (Oreochromis niloticus) following dietary exposure to organic methyl mercury (MeHg) are less prolific. Accordingly, the current study aimed to evaluate the impacts of MeHg on neurobehavioral and immune integrity in Nile tilapia after dietary exposure. Two hundred and twenty-five juvenile Nile tilapia (19.99 ± 0.33 g) were allocated into five groups in triplicates (15 fish/replicate). G1, G2, G3, G4, and G5. O. niloticus were fed corresponding basal diets containing 0, 0.5, 1, 1.5, and 2 mg/kg diet MeHg chloride (MeHgCl) daily for 30 days, zero value represented the control G1 group. The results showed that MeHg induced significant alterations in O. niloticus behavior, the swimming behavior was significantly decreased, while scratching, biting, and fin tugging behaviors were significantly augmented. Moreover; chasing, mouth pushing, and butting behaviors were significantly increased in all the exposed groups. MeHg significantly decreased brain acetylcholine esterase (AChE) and serum immunoglobulin M (IgM) levels in all the exposed groups. Meanwhile, serum levels of lysozyme (LYZ), nitric oxide (NO), superoxide dismutase (SOD) malondialdehyde (MDA), protein carbonyl (PCO), and 8 hydroxy 2 deoxyguanosine (8OH2dG) were significantly elevated in all the exposed groups except for serum reduced glutathione (GSH) content was significantly decreased implying oxidative stress (OS), lipid peroxidation (LPO), protein, DNA damage and impaired immune response of the exposed tilapia. MeHg significantly altered transcriptional expression of immune-related genes including (TNF-α, IL-1β, and IL-8, and IL-10) in all the exposed groups. From the obtained outcomes, the present research is the premier to investigate that dietary MeHg exposure in O. niloticus significantly induced neurobehavioral and immune defense impairments in a dose-related manner. This study exhibits that dietary MeHg may pose a potential threat to the O. niloticus populations.

Blood and Urine Inorganic and Organic Mercury Levels in the United States from 1999 to 2016

BACKGROUND

Mercury is an environmental hazard. Organic mercury is biologically more toxic than inorganic mercury. Therefore, we studied recent trends in the blood levels of organic and inorganic mercury in the United States.

METHODS

A total of 56,445 participants that had blood mercury and urine mercury measurements in National Health and Nutrition Examination Survey (NHANES) 1999-2016 were included. The organic mercury level was obtained by subtracting the inorganic mercury level from the total mercury level. Results were analyzed using SPSS complex sample module version 25. Pregnant women, children ages <20 years, and different ethnicities were analyzed as subgroups.

RESULTS

Blood organic mercury level increased from (geometric mean [95% confidence interval]) 0.08 [0.07-0.10] to 0.17 [0.16-0.18] µg/L during 1999-2016. It increased significantly (P <0.001) from 0.03 [0.02-0.03] to 0.07 [0.06-0.07] µg/L in children ages <20 and from 0.14 [0.09-0.21] to 0.36 [0.16-0.83] µg/L in pregnant women in this period (P <0.001). In 2013-2016, non-Hispanic Asians had the highest blood organic mercury level among different ethnicities, 0.93 [0.82-1.05] µg/L (P <0.001). Blood inorganic mercury level decreased from 0.31 [0.31-0.31] in 1999-2000 to 0.21 [0.21-0.22] µg/L in 2015-2016 (P <0.001). Urine mercury level decreased from 0.75 [0.71-0.80] in 1999-2000 to 0.16 [0.16-0.17] µg/L in 2015-2016 (P <0.001).

CONCLUSION

Blood organic mercury increased over the period 1999-2016 in the US population, including children and pregnant women, whereas there was a steady decline in both blood inorganic mercury and urine mercury levels.

The fish or the egg: Maternal transfer and subcellular partitioning of mercury and selenium in Yellow Perch (Perca flavescens)

Mercury (Hg) is a trace element of particular concern since it is ubiquitous in the environment and because its methylated form (MeHg) readily bioaccumulates and biomagnifies in food webs. This latter process leads to elevated Hg concentrations in fish and may thus induce toxicity. Maternal transfer of bioaccumulated contaminants to offspring is a suggested mechanism of impaired reproductive success in fish. The purpose of this study was to assess the toxicity potential of Hg during maternal transfer in Yellow Perch from Lake Saint-Pierre (Quebec, Canada) using a subcellular partitioning approach. We also evaluated potential protective effects of selenium, as this element has been shown to alleviate Hg toxicity through sequestration. A customized subcellular partitioning protocol was used to separate liver and gonad of Yellow Perch into various subcellular fractions. Results show that, in the liver, MeHg was primarily (51%) associated to the subcellular fraction containing cytosolic enzymes. Furthermore, 23% and 15% of MeHg was found in hepatic and gonadal mitochondria, respectively, suggesting that Yellow Perch is not effectively detoxifying this metal. There was also a strong relationship (R² = 0.73) between MeHg bioaccumulation in the liver and MeHg concentrations in gonadal mitochondria, which corroborates the potential risk linked to MeHg maternal transfer. On the other hand, we also found that selenium might have a protective effect on Hg toxicity at a subcellular level. In fact, Se:Hg molar ratios in subcellular fractions were systematically above 1 in all tissues and fractions examined, which corresponds to the suggested protective threshold. This study provides the first assessment of subcellular Se:Hg molar ratios in fish. Since early developmental stages in aquatic biota are particularly sensitive to Hg, this study represents a step forward in understanding the likelihood for toxic effects in wild fish through maternal transfer.

Mercury Contamination in Riverine Sediments and Fish Associated with Artisanal and Small-Scale Gold Mining in Madre de Dios, Peru

Artisanal and small-scale gold mining (ASGM) in Madre de Dios, Peru, continues to expand rapidly, raising concerns about increases in loading of mercury (Hg) to the environment. We measured physicochemical parameters in water and sampled and analyzed sediments and fish from multiple sites along one ASGM-impacted river and two unimpacted rivers in the region to examine whether Hg concentrations were elevated and possibly related to ASGM activity. We also analyzed the 308 fish samples, representing 36 species, for stable isotopes (δ¹⁵N and δ¹³C) to estimate their trophic position. Trophic position was positively correlated with the log-transformed Hg concentrations in fish among all sites. There was a lack of relationship between Hg concentrations in fish and either Hg concentrations in sediments or ASGM activity among sites, suggesting that fish Hg concentrations alone is not an ideal bioindicator of site-specific Hg contamination in the region. Fish Hg concentrations were not elevated in the ASGM-impacted river relative to the other two rivers; however, sediment Hg concentrations were highest in the ASGM-impacted river. Degraded habitat conditions and commensurate shifts in fish species and ecological processes may influence Hg bioaccumulation in the ASGM-impacted river. More research is needed on food web dynamics in the region to elucidate any effects caused by ASGM, especially through feeding relationships and food sources.

Comparative study on toxicity of methylmercury chloride and methylmercury hydroxide to the human neuroblastoma cell line SH-SY5Y

Toxicities of methylmercury chloride (CH₃HgCl) and methylmercury hydroxide (CH₃HgOH) to cultured neuroblastoma cell line SH-SY5Y in vitro are evaluated. This is the comparative study between two methylmercury compounds to find out the extent of toxicity of these compounds are toxic to SH-SY5Y cell line. Both cytotoxicity and genotoxicity experiments were carried out to find out the more toxic compound. For cytotoxicity study, four staining assay methods independently with trypan blue (TB), acridine orange/ethidium bromide (AO/EB), 3-(4,5-dimethylthiazol-2-yl) 2,5-diphenyl tetrazolium bromide (MTT), and neutral red (NR) were used and the comet assay method was done for genotoxicity study. The obtained toxicity data were used for probit analysis. In cytotoxicity, CH₃HgCl had minimum inhibitory concentration (MIC) value in each assay method as 3 mg/L invariably; LC₂₅ values were in the range 7.41 to 10.23 mg/L, and LC₅₀ values were 14.79 to 15.48 mg/L; while LC₇₅ values were 20.89 to 26.91 mg/L. Moreover, LC₁₀₀ value was 30 mg/L, known from comet assay experiments for CH₃HgCl. Similarly for CH₃HgOH, the MIC value in each assay method was invariably 3 mg/L, the LC₂₅ values were in the range 12.58 to 16.59 mg/L, and LC₅₀ values were 19.49 to 23.44 mg/L; LC₇₅ values were 27.54 to 30.90 mg/L and LC₁₀₀ value was 42 mg/L in each assay done for cytotoxicity and genotoxicity studies. Computed DNA fragmentation indices in comet assays were 98.6 ± 0.57 30 mg/L with CH₃HgCl and 76 ± 5.29 30 mg/L with CH₃HgOH. This study clearly indicated that methylmercury chloride is more toxic than methylmercury hydroxide to SH-SY5Y cell line. Toxicity of Hg had been quantified with in vitro cultured human neuroblastoma cell line; since it has neurotoxic effects, its neural evaluation has implications in environmental health issues.

Mercury levels of marine fish commonly consumed in Peninsular Malaysia

This study was conducted to determine the concentration of total mercury in the edible portion of 46 species of marine fish (n = 297) collected from selected major fish landing ports and wholesale markets throughout Peninsular Malaysia. Samples were collected in June to December 2009. Prior to analysis, the fish samples were processed which consisted of drying at 65 °C until a constant weight was attained; then, it was grounded and digested by a microwave digestion system. The analytical determination was carried out by using a mercury analysis system. Total mercury concentration among fish species was examined. The results showed that mercury concentrations were found significantly higher (p < 0.001) in demersal fish (the range was from 0.173 to 2.537 mg/kg in dried weight) compared to pelagic fish (which ranged from 0.055 to 2.137 mg/kg in dried weight). The mercury concentrations were also higher in carnivorous fish especially in the species with more predatory feeding habits. Besides, the family group of Latidae (0.537 ± 0.267 mg/kg in dried weight), Dasyatidae (0.492 ± 0.740 mg/kg in dried weight), and Lutjanidae (0.465 ± 0.566 mg/kg in dried weight) showed significantly (p < 0.001) higher mercury levels compared to other groups. Fish collected from Port Klang (0.563 ± 0.509 mg/kg in dry weight), Kuala Besar (0.521 ± 0.415 mg/kg in dry weight), and Pandan (0.380 ± 0.481 mg/kg in dry weight) were significantly higher (p = 0.014) in mercury concentrations when compared to fish from other sampling locations. Total mercury levels were significantly higher (p < 0.002) in bigger fish (body length >20 cm) and were positively related with fish size (length and weight) in all fish samples. Despite the results, the level of mercury in marine fish did not exceed the permitted levels of Malaysian and JECFA guideline values at 0.5 mg/kg methylmercury in fish.

Assessment of total and organic mercury levels in blue sharks (Prionace glauca) from the south and southeastern Brazilian coast

Mercury occurrence was evaluated in samples of edible muscle tissue of 27 blue sharks (Prionace glauca) caught in the Atlantic Ocean, adjacent to the south and southeastern Brazilian coast, indicating a slight increase in comparison with previous data obtained for the same studied area and being higher than those fish caught at different sites of the Atlantic Ocean. Total Hg concentrations ranged from 0.46 to 2.40 mg kg(-1) with the organic Hg fraction ranging between 0.44 and 2.37 mg kg(-1). A negative correlation between total Hg concentration in muscle tissue and blue shark size was obtained, and 40% of samples analyzed had Hg concentrations higher than 1.0 mg kg(-1) Hg, the maximum concentration permitted in Brazilian predator fish. Data obtained showed that total Hg can be used as a reliable predictor of organic Hg in blue shark muscle because 95 to 98% of the total Hg measured was found to be organic mercury. The wide range of Hg concentrations obtained for our set of samples can be explained by the heterogeneity of sampled population and the large size of the studied area. Given the adverse toxicological effects of Hg on animals and humans, a regular monitoring program of Hg contamination in Brazilian marine ecosystem can be recommended.

Improved chronic fatigue symptoms after removal of mercury in patient with increased mercury concentration in hair toxic mineral assay: a case

Clinical manifestations of chronic exposure to organic mercury usually have a gradual onset. As the primary target is the nervous system, chronic mercury exposure can cause symptoms such as fatigue, weakness, headache, and poor recall and concentration. In severe cases chronic exposure leads to intellectual deterioration and neurologic abnormality. Recent outbreaks of bovine spongiform encephalopathy and pathogenic avian influenza have increased fish consumption in Korea. Methyl-mercury, a type of organic mercury, is present in higher than normal ranges in the general Korean population. When we examine a patient with chronic fatigue, we assess his/her methyl-mercury concentrations in the body if environmental exposure such as excessive fish consumption is suspected. In the current case, we learned the patient had consumed many slices of raw tuna and was initially diagnosed with chronic fatigue syndrome. Therefore, we suspected that he was exposured to methyl-mercury and that the mercury concentration in his hair would be below the poisoning level identified by World Health Organization but above the normal range according to hair toxic mineral assay. Our patient's toxic chronic fatigue symptoms improved after he was given mercury removal therapy, indicating that he was correctly diagnosed with chronic exposure to organic mercury.

Which fish should I eat? Perspectives influencing fish consumption choices

BACKGROUND

Diverse perspectives have influenced fish consumption choices.

OBJECTIVES

We summarized the issue of fish consumption choice from toxicological, nutritional, ecological, and economic points of view; identified areas of overlap and disagreement among these viewpoints; and reviewed effects of previous fish consumption advisories.

METHODS

We reviewed published scientific literature, public health guidelines, and advisories related to fish consumption, focusing on advisories targeted at U.S. populations. However, our conclusions apply to groups having similar fish consumption patterns.

DISCUSSION

There are many possible combinations of matters related to fish consumption, but few, if any, fish consumption patterns optimize all domains. Fish provides a rich source of protein and other nutrients, but because of contamination by methylmercury and other toxicants, higher fish intake often leads to greater toxicant exposure. Furthermore, stocks of wild fish are not adequate to meet the nutrient demands of the growing world population, and fish consumption choices also have a broad economic impact on the fishing industry. Most guidance does not account for ecological and economic impacts of different fish consumption choices.

CONCLUSION

Despite the relative lack of information integrating the health, ecological, and economic impacts of different fish choices, clear and simple guidance is necessary to effect desired changes. Thus, more comprehensive advice can be developed to describe the multiple impacts of fish consumption. In addition, policy and fishery management interventions will be necessary to ensure long-term availability of fish as an important source of human nutrition.

The prenatal toxic effect of methylmercury on the development of the appendicular skeleton of rat fetuses and the protective role of vitamin E

Methylmercury (MeHg) is an environmental contaminant that is found in many ecosystems. Many studies reported that MeHg toxicity is accompanied by increased lipid peroxidation that may lead to oxidative damage to DNA, RNA, and proteins. Vitamin E is considered as the most effective antioxidant preventing lipid peroxidation. The aim of this study was to evaluate the effects of MeHg exposure during pregnancy on the development of the appendicular skeleton in rat fetuses and whether vitamin E administration could reduce this toxicity. Positively mated adult female Sprague-Dawley rats were used and divided into the following experimental groups: control group, received only deionized water, and four MeHg treated groups received 1 mg of MeHg/kg/d, 2 mg of MeHg/kg/d, 1 mg of MeHg/kg/d plus 150 mg of vitamin E/kg/d, and 2 mg of MeHg/kg/d, plus 150 mg of vitamin E/kg/d starting from Day 0 of gestation. On Day 20 of gestation, the fetuses from the pregnant rats were extracted and the fetal growth parameters were evaluated. Skeletal evaluation of ossification of both fore- and hind-limbs, and coxal bones were undertaken. Results showed that treatment with MeHg caused adverse effects on fetal growth parameters and ossification of the bones. The coadministration of vitamin E with MeHg revealed an improvement in these parameters. These results suggest that vitamin E may ameliorate some aspects of MeHg developmental toxicity. The underlying and human health implications warrant further investigations.

State calculations of cultural survival in environmental risk assessment: consequences for Alaska Natives

In 2007, the Alaska Division of Public Health issued their first-ever fish consumption advisory to reduce exposure to methylmercury. Interestingly, they utilized a toxicity level in their calculations of risk that is four times higher than the U.S. Environmental Protection Agency's (EPA) level, arguing that the EPA's calculation is "inappropriately restrictive" for Alaskans. This article explores the institutional reasoning and scientific calculations behind the state's fish consumption advice, with special attention paid to the consequences for Alaska Natives. I argue that a discourse of "Alaskan exceptionalism" is utilized by the health department to justify their assessment of risk. Although this exceptionalist discourse is intended to accommodate the unique lifestyles of Alaskan citizens, it may actually serve to undermine the very lifeways and traditions that it presumes to preserve. This article contributes insights into the ways that states can influence the social and material reproduction of communities through the deployment of "cultural difference" during the risk-assessment process.

The clinical content of preconception care: environmental exposures

Environmental origins of disease risk and harm to health have been increasingly acknowledged for numerous outcomes, in both adult and pediatric populations. Adverse reproductive and developmental effects have also been linked to environmental exposures. In addition to the current queries about a patient's alcohol and smoking history, key determinants of a future pregnancy outcome should also be elicited during the preconception visit. These determinants include: (1) mercury intake via fish consumption; (2) nitrate exposure from well water sources; (3) exposure to chemical, physical, or biologic hazards on the job; and (4) lead and other toxic exposures--possibly from hobbies or the use of lead-glazed dinnerware in the home. Eliciting a detailed environmental history permits tailored recommendations to optimize the woman's health and that of her future pregnancy.

Mercury in seafood: mechanisms of accumulation and consequences for consumer health

Mercury is a largely uncontrollable heavy metal contaminant in that it is globally ubiquitous, and environmentally persistent. The element has the potential for global mobilization following liberation from environmental stores, which can occur as a consequence of either anthropogenic activities or natural processes. Furthermore, organic forms like methylmercury accumulate in biological tissues with an exceptionally long biological half-life, facilitating the magnification of this toxin along trophic food chains. Bioaccumulation is particularly evident in aquatic environments, in which long-lived piscivorous fishes and marine mammals are reported with a mercury burden one-million times that of the surrounding water body, typically attaining mercury burdens exceeding 1 microg g(-1). Mercury levels in other seafood, however, are typically reported in the range of 0.1 to 0.2 microg g(-1) and usually less then 0.5 microg g(-1). The primary source of human exposure to environmental mercury is through seafood consumption. The dangers associated with the consumption of large amounts of methylmercury accumulated in seafood are well recognized from past poisoning incidents, in which fish with mercury burdens in the range of 9 to 24 microg g(-1) were consumed. Nevertheless, the toxicological consequence of chronic low-level mercury exposure from habitual seafood consumption is an area of contention. This review discusses the mechanisms of mercury accumulation and distribution in fish tissues and the toxicological consequences of mercury exposure from seafood consumption with regard to international safety guidelines.

Benchmark concentrations for methyl mercury obtained from the 9-year follow-up of the Seychelles Child Development Study

Methyl mercury (MeHg) is highly toxic to the developing nervous system. Human exposure is mainly from fish consumption since small amounts are present in all fish. Findings of developmental neurotoxicity following high-level prenatal exposure to MeHg raised the question of whether children whose mothers consumed fish contaminated with background levels during pregnancy are at an increased risk of impaired neurological function. Benchmark doses determined from studies in New Zealand, and the Faroese and Seychelles Islands indicate that a level of 4-25 parts per million (ppm) measured in maternal hair may carry a risk to the infant. However, there are numerous sources of uncertainty that could affect the derivation of benchmark doses, and it is crucial to continue to investigate the most appropriate derivation of safe consumption levels. Earlier, we published the findings from benchmark analyses applied to the data collected on the Seychelles main cohort at the 66-month follow-up period. Here, we expand on the main cohort analyses by determining the benchmark doses (BMD) of MeHg level in maternal hair based on 643 Seychellois children for whom 26 different neurobehavioral endpoints were measured at 9 years of age. Dose-response models applied to these continuous endpoints incorporated a variety of covariates and included the k-power model, the Weibull model, and the logistic model. The average 95% lower confidence limit of the BMD (BMDL) across all 26 endpoints varied from 20.1 ppm (range=17.2-22.5) for the logistic model to 20.4 ppm (range=17.9-23.0) for the k-power model. These estimates are somewhat lower than those obtained after 66 months of follow-up. The Seychelles Child Development Study continues to provide a firm scientific basis for the derivation of safe levels of MeHg consumption.

Antepartum seafood consumption and mercury levels in newborn cord blood

OBJECTIVE

The purpose of this study was to determine the level of fetal mercury exposure by measuring mercury levels in newborn cord blood and to analyze the association with fish consumption during pregnancy.

STUDY DESIGN

A total of 308 women who met the eligibility criteria were enrolled in the study. Of these, 275 women completed a dietary survey; after delivery, cord blood was collected and analyzed for mercury levels.

RESULTS

The mean mercury level in cord blood was 4.82 microg/L; 28.3% of the participants had measured mercury levels above the US Environmental Protection Agency's recommended reference dose (5.8 microg/L). A significant relationship was noted between the amount of fish consumed during pregnancy and rising mercury levels in cord blood.

CONCLUSION

In an island state with high levels of fish consumption, women were 3 times more likely to have elevated cord blood mercury levels, compared with the national average.

Fish and shellfish as dietary sources of methylmercury and the omega-3 fatty acids, eicosahexaenoic acid and docosahexaenoic acid: risks and benefits

Fish and shellfish supply the human diet with not only complex nutrients including the omega-3 fatty acids, but also highly toxic chemicals including methylmercury. The dietary essential fatty acids are linoleic and alpha-linolenic acid. Two omega-3 fatty acids with longer carbon chains, eicosahexaenoic acid (EPA) and docosahexaenoic acid (DHA), can be synthesized in humans from alpha-linolenic precursors. Though not required in the diet per se, EPA and DHA have important roles in metabolism. The almost exclusive source of preformed dietary DHA is fish and shellfish. These foods are also an important source of EPA. In marked contrast to the benefits of fish and shellfish as sources of preformed omega-3 fatty acids, fish and shellfish are almost exclusively the dietary source of methylmercury. Fortunately, these chemicals are not uniformly distributed across many species of fish and shellfish. The purpose of this article is to provide information on the comparative distribution of these chemicals and nutrients to help groups formulating dietary recommendations.

Organic mercury compounds: human exposure and its relevance to public health

Humans may be exposed to organic forms of mercury by either inhalation, oral, or dermal routes, and the effects of such exposure depend upon both the type of mercury to which exposed and the magnitude of the exposure. In general, the effects of exposure to organic mercury are primarily neurologic, while a host of other organ systems may also be involved, including gastrointestinal, respiratory, hepatic, immune, dermal, and renal. While the primary source of exposure to organic mercury for most populations is the consumption of methylmercury-contaminated fish and shellfish, there are a number of other organomercurials to which humans might be exposed. The antibacterial and antifungal properties of organomercurials have resulted in their long use as topical disinfectants (thimerosal and merbromin) and preservatives in medical preparations (thimerosal) and grain products (both methyl and ethyl mercurials). Phenylmercury has been used in the past in paints, and dialkyl mercurials are still used in some industrial processes and in the calibration of certain analytical laboratory equipment. The effects of exposure to different organic mercurials by different routes of exposure are summarized in this article.

Technical report: mercury in the environment: implications for pediatricians

Mercury is a ubiquitous environmental toxin that causes a wide range of adverse health effects in humans. Three forms of mercury (elemental, inorganic, and organic) exist, and each has its own profile of toxicity. Exposure to mercury typically occurs by inhalation or ingestion. Readily absorbed after its inhalation, mercury can be an indoor air pollutant, for example, after spills of elemental mercury in the home; however, industry emissions with resulting ambient air pollution remain the most important source of inhaled mercury. Because fresh-water and ocean fish may contain large amounts of mercury, children and pregnant women can have significant exposure if they consume excessive amounts of fish. The developing fetus and young children are thought to be disproportionately affected by mercury exposure, because many aspects of development, particularly brain maturation, can be disturbed by the presence of mercury. Minimizing mercury exposure is, therefore, essential to optimal child health. This review provides pediatricians with current information on mercury, including environmental sources, toxicity, and treatment and prevention of mercury exposure.

Methylmercury: a new look at the risks

In the US, exposure to methylmercury, a neurotoxin, occurs primarily through consumption of fish. Data from recent studies assessing the health impact of methylmercury exposure due to consumption of fish and other sources in the aquatic food web (shellfish, crustacea, and marine mammals) suggest adverse effects at levels previously considered safe. There is substantial variation in human methylmercury exposure based on differences in the frequency and amount of fish consumed and in the fish's mercury concentration. Although virtually all fish and other seafood contain at least trace amounts of methylmercury, large predatory fish species have the highest concentrations. Concerns have been expressed about mercury exposure levels in the US, particularly among sensitive populations, and discussions are underway about the standards used by various federal agencies to protect the public. In the 1997 Mercury Study Report to Congress, the US Environmental Protection Agency summarized the current state of knowledge on methylmercury's effects on the health of humans and wildlife; sources of mercury; and how mercury is distributed in the environment. This article summarizes some of the major findings in the Report to Congress and identifies issues of concern to the public health community.

Alterations in immune parameters associated with low level methylmercury exposure in mice

Methylmercury (MeHg) is a known toxicant and continues to be a significant environmental contaminant. While the neurotoxicity and developmental toxicity of MeHg are well established, the immunotoxic effects of MeHg are just now being studied and described. This study evaluated strain and gender specific effects of low level, prolonged MeHg exposure in mice. Mice were exposed to MeHg in the drinking water (0, 3 or 10 ppm) for 4 weeks. Splenocytes and thymocytes were evaluated for alterations in immunophenotype, GSH levels, and intracellular Ca2+ flux after mitogen stimulation. MeHg exposure resulted in alterations in splenocyte and thymocyte subsets and a dose dependent decrease in GSH levels (as measured by monochlorobimane fluorescence and flow cytometry) of all splenocyte subsets. This decrease in GSH was further confirmed by biochemical assay in splenocytes. In addition, there was a dose response related decrease in mitogen stimulated Ca2+ flux and in the percentages of CD4+ splenocytes and CD8+ splenocytes from mice exposed to 10 ppm of MeHg. These results suggest that low-level chronic MeHg exposure may cause immune disfunction by disturbing thiol redox balance, transmembrane signaling and splenic cellularity.

Biological monitoring for mercury within a community with soil and fish contamination

To assess the impact of elevated levels of inorganic mercury in soil and dust and organic mercury in fish, biological monitoring was conducted among Native Americans living next to an inactive mercury mine in Clear Lake, California. Of resident tribal members, 46% (n = 56) participated in biomonitoring. Urine mercury levels are equivalent to background, indicating that soil and dust exposures among study participants are not substantial. The average blood organic mercury level among study participants is 15.6 +/- 8.8 micrograms/l (n = 44), which is higher than levels reported by others among those who do not consume fish (2 micrograms/l). Consistent with results from other studies, a correlation between fish consumption and blood organic mercury is observed (p = 0.03). The margin between observed and established adverse effect levels for adults is examined for blood organic mercury and found to be less than 10-fold for 20% of the study population. Protective public health efforts for the study population and other similarly exposed populations, notably those who consume commercial fish products, are considered.

Imported seabass as a source of mercury exposure: a Wisconsin case study

The Wisconsin Division of Health investigated mercury exposure in a 40-year-old man, his 42-year-old wife, and their 2.5-year-old son. At the time of our investigation, these individuals had blood mercury levels ranging from 37 to 58 micrograms/L (normal < 5 micrograms/L) and hair samples from the adults contained 10-12 micrograms mercury/g dry weight. A personal interview and home inspection failed to identify any occupational or household sources of mercury exposure. The family's diet included three to four fish meals per week. The fish was purchased from a local market and included Lake Superior whitefish, Lake Superior trout, farm-raised trout and salmon, and imported seabass. Analysis of these fish found that only one species, the imported seabass, contained significant mercury levels. Two samples of the seabass obtained from the vendor on different days contained mercury concentrations of 0.5 and 0.7 mg/kg. Based on consumption estimates, the average daily mercury intakes for these individuals ranged from 0.5 to 0.8 micrograms/kg body weight. Six months after the family stopped consuming the seabass, blood mercury levels in this man and woman were 5 and 3 micrograms/L, respectively. Analysis of sequential blood samples confirmed that mercury elimination followed first-order kinetics with a half-life of approximately 60 days.

Speciation of organomercurials in biological and environmental samples by gas chromatography with microwave-induced plasma atomic emission detection

The applicability of a commercial microwave-induced plasma atomic emission detector with capillary gas chromatography for mercury speciation in environmental samples was examined. The chromatographic conditions were optimized in order to obtain an adequate resolution of the methylmercury peak vs. interfering carbon signals. Under the proposed operational conditions, the detection limit (signal-to-noise ratio = 3) was 1.2 pg with a linear range of 1-40 ng ml-1 (as methylmercury in samples). Certified reference material (DORM-1) was used to evaluate the accuracy. The results of the proposed procedure were compared with those obtained by means of the usual GC method with electron-capture detection.

Re-evaluation of the reference dose for methylmercury and assessment of current exposure levels

Methylmercury (Me-Hg) is widely distributed through freshwater and saltwater food chains and human consumption of fish and shellfish has lead to widespread exposure. Both the U.S. EPA Reference Dose (0.3 micrograms/kg/day) and the FAO/WHO Permissible Tolerable Weekly Intake (3.3 micrograms/kg/week) are currently based on the prevention of paraesthesia in adult and older children. However, Me-Hg exposure in utero is known to result in a range of developmental neurologic effects including clinical CNS symptoms and delayed onset of walking. Based on a critical review of developmental toxicity data from human and animal studies, it is concluded that current guidelines for the prevention of paraesthesia are not adequate to address developmental effects. A dose of 0.07 micrograms/kg/day is suggested as the best estimate of a potential reference dose for developmental effects. Data on nationwide fish consumption rates and Me-Hg levels in fish/seafood weighted by proportion of the catch intended for human consumption are analyzed in a Monte Carlo simulation to derive a probability distribution of background Me-Hg exposure. While various uncertainties in the toxicologic and exposure data limit the precision with which health risk can be estimated, this analysis suggests that at current levels of Me-Hg exposure, a significant fraction of women of childbearing age have exposures above this suggested reference dose.

A relationship between vitamin B12, folic acid, ascorbic acid, and mercury uptake and methylation

Ingestion of megadoses of certain vitamins appears to influence the in vivo methylation of mercuric chloride in guinea pigs. The addition of megadoses of vitamin B12 fed either singularly or in combination with folic acid resulted in increased methylmercury concentrations in the liver. Moreover, percent methylmercury levels were significantly increased with B12 treatment in the liver (B12 only and B12/folic acid) and brain (B12/vitamin C). Incorporation of high levels of folic acid into the dietary regime also increased the methylmercury concentration particularly in the liver and hair tissues. The addition of vitamin C in the diet, particularly in combination with B12 (brain) or folic acid (muscle) resulted in increased methylmercury levels in these tissues and percent methylmercury values with B12 in the muscle and brain tissue.