The influence of fish length on tissue mercury dynamics: implications for natural resource management and human health risk

An evaluation of fish and invertebrate mercury concentrations in the Caribbean Region

Mercury is a ubiquitous pollutant of global concern but the threat of exposure is not homogenously distributed at local, regional, or global scales. The primary route of human exposure to mercury is through consumption of aquatic foods, which are culturally and economically important in the wider Caribbean Region, especially for Small Island Developing States (SIDS). We compiled more than 1600 samples of 108 unique species of fish and aquatic invertebrates collected between 2005 and 2023 from eleven countries or territories in the wider Caribbean Region. There was wide variability in total mercury concentrations with 55% of samples below the 0.23 µg/g wet weight (ww) guideline from the U.S. FDA/EPA (2022) for 2 or 3 weekly servings and 26% exceeding the 0.46 µg/g ww guideline consistent with adverse effects on human health from continual consumption, particularly for sensitive populations. Significant relationships were found between total mercury concentrations and taxonomic family, sampling country, fish length, and trophic level. The data analyzed here support the need for further sampling with concrete geospatial data to better understand patterns and mechanisms in mercury concentrations and allow for more informed decision making on the consumption of fish and invertebrates from the wider Caribbean Region as well as supporting efforts to evaluate the effectiveness of national, regional, and international mercury policies.

Measuring Total Mercury Through Freeze-Thaw Cycles

Total mercury (THg) analysis of fish tissue requires the samples to be frozen for long-term storage or analyzed immediately after the fish sample has been obtained. Such rigid field sampling protocols do not account for the logistical challenges that can occur if sampling is conducted in remote areas or collaboratively via community-based monitoring initiatives. Here we present a study that examines the loss of THg from Walleye tissue that has thawed for 3 and 5 days, mimicking potential thaw during transport from remote locations. THg concentrations were not significantly influenced (Kruskal-Wallace, p-value > 0.05) by the thaw and refreeze events. The mean THg concentration per day group was 0.67 ug/g, SD = 0.03, 0.65 ug/g, SD = 0.01, and 0.72 ug/g, SD = 0.01 for the control (no thaw), 3-day thaw and 5-day thaw, respectively. Results from this study suggest the analytical integrity of samples may be maintained if freeze-thaw situations arise when conducting community-based mercury monitoring programs.

Mercury accumulation and biomarkers of exposure in two popular recreational fishes in Hawaiian waters

Mercury (Hg) exposure has not been examined in many recreational nearshore fish species that are commonly consumed around the Hawaiian Islands. Specific gene transcripts, such as metallothionein (MET) and thioredoxin reductase (TrxR), can be used to examine Hg exposure responses in aquatic organisms. This study measured total mercury (THg) in four species from two groups of Hawaiian nearshore fishes: giant trevally (Caranx ignobilis, n = 13), bluefin trevally (C. melampygus, n = 4), sharp jaw bonefish (Albula virgata, n = 2), and round jaw bonefish (A. glossodonta, n = 19). Total Hg accumulation and abundance profiles of MET and TrxR were evaluated for muscle, liver, and kidney tissues. Total Hg in round jaw bonefish and giant trevally tissues accumulated with length and calculated age. In round jaw bonefish tissues, mean THg was greater in kidney (1156 ng/g wet mass (wm)) than liver (339 ng/g wm) and muscle (330 ng/g wm). Giant trevally muscle (187 ng/g wm) and liver (277 ng/g wm) mean THg did not differ significantly. Fish species in this study were compared to commercial and local fish species with state and federal muscle tissue consumption advisories based on THg benchmarks developed by the U.S. Food and Drug Administration (FDA) and Environmental Protection Agency (EPA). Both bonefishes had mean muscle THg that exceeded benchmarks suggesting consumption advisories should be considered. MET transcript in round jaw bonefish kidney tissue and kidney THg exhibited a marginally significant positive correlation, while TrxR transcript in liver tissue negatively correlated with increasing liver THg. These results contribute to our understanding of Hg exposure associated health effects in fish.

Analysis of the Mercury Content in Fish for Human Consumption in Poland

Mercury (Hg) is a metal with toxic effects on the environment, including living organisms. Organic Hg derivatives readily penetrate biological membranes and pose a particular health risk. Food of aquatic origin is the main source of human exposure to methylmercury (MeHg). In Poland, the consumption of fishery and aquaculture products has been gradually increasing. The aim of this study was to determine the content of Hg in fish intended for human consumption and purchased in Poland. The total Hg content of the edible parts of different species of marine and freshwater fish was analysed. The range of Hg content in all fish was 0.004-0.827 mg/kg, with an arithmetic mean of 0.084 mg/kg. The concentration of Hg in marine fish (0.100 mg/kg) was higher than in freshwater fish (0.063 mg/kg). The highest concentration of Hg was found in tuna. The Estimated Hazard Quotient (EHQ) calculated for the tuna samples analysed was >1. This may represent a potential health risk for consumers. The consumption of the other fish analysed was considered safe on the basis of the EHQ. The Hg content of the analysed fish samples did not exceed the current limits for food.

Mercury Contamination of an Introduced Generalist Fish of Intermediate Trophic Level

Mercury contamination is a global issue because mercury concentrations in aquatic systems are influenced by both natural and anthropogenic pathways. Here, liver and muscle total mercury (THg) concentrations in black crappie Pomoxis nigromaculatus from three boreal lakes in southeastern Manitoba, Canada, were related to age, morphology and physiological traits to better understand the dynamics of mercury accumulation in an introduced generalist fish species. These THg concentrations were then compared to black crappie mercury concentrations in other Canadian water bodies and to mercury concentrations in other freshwater fishes in southeastern Manitoba. Age and size had strong positive correlations (P < 0.001, r ≥ 0.60) with muscle mercury concentrations. No evidence of acute point source contamination or physiological impairment in black crappie was found in the study area. Analysis of liver THg revealed the possible impacts of seasonal and ontogenetic differences in diet on exposure. Furthermore, THg analysis of liver and muscle tissue showed how generalist foraging may curb the progressively greater mercury exposure and resultant physiological consequences expected from ontogenetic diet shifts in black crappie. Although there appeared to be temporally varied levels of mercury exposure (i.e., liver THg) by sex, there was no sex effect observed in long-term mercury accumulation in the muscle. Black crappie bioaccumulated less mercury at age than primary piscivore species in the region. These results will help foster a better understanding of mercury biomagnification within a region impacted by legacy mercury.

Risk assessment of heavy metals in tuna from Japanese restaurants in the Republic of Korea

Background

Studies on the risk of mercury (Hg) in Korean fishery products focus primarily on total Hg levels as opposed to methylmercury (MeHg) levels. None of the few studies on MeHg in tuna investigated tuna from Japanese restaurants. Few have evaluated lead (Pb), cadmium (Cd) and arsenic (As) in tuna. Thus, this study aimed to conduct a risk assessment by evaluating heavy metal concentrations in tuna from Japanese restaurants.

Methods

Thirty-one tuna samples were collected from Japanese restaurants in the Republic of Korea. They were classified according to region and species. The concentration of heavy metals in the samples was analyzed using the Ministry of Food and Drug Safety Food Code method. The rate of exceedance of maximum residue levels (MRLs) and the risk compared to the provisional tolerable weekly intake (PTWI) set by the Joint Food and Agriculture Organization/World Health Organization Expert Committee on Food Additives (%PTWI) were evaluated for risk assessment.

Results

The mean of MeHg, Pb, Cd and As concentrations were 0.56 ± 1.47 mg/kg, 33.95 ± 3.74 μg/kg, 14.25 ± 2.19 μg/kg and 1.46 ± 1.89 mg/kg, respectively. No sample exceeded the MRLs of Pb and Cd, but 9.7% of the samples exceeded the MRL of MeHg. The %PTWIs of MeHg, Pb, Cd and As were 4.2037, 0.0162, 0.0244 and 1.1627, respectively. The %PTWI of MeHg by age group and sex was highest among men aged 19-29 years (10.6494), followed by men aged 30-49 years (7.2458) and women aged 19-29 years (4.8307).

Conclusions

We found that 3 out of 31 samples exceeded the MRL of MeHg. The %PTWI of MeHg showed significant differences based on age and sex, and the value was likely to exceed a safe level depending on individuals' eating behaviors. Therefore, improved risk management for MeHg is required.

Mercury Sources, Emissions, Distribution and Bioavailability along an Estuarine Gradient under Semiarid Conditions in Northeast Brazil

In the semiarid coast of northeast Brazil, climate change and changes in land use in drainage basins affect river hydrodynamics and hydrochemistry, modifying the estuarine environment and its biogeochemistry and increasing the mobilization of mercury (Hg). This is particularly relevant to the largest semiarid-encroached basin of the region, the Jaguaribe River. Major Hg sources to the Jaguaribe estuary are solid waste disposal, sewage and shrimp farming, the latter emitting effluents directly into the estuary. Total annual emission reaches 300 kg. In that estuary, the distribution of Hg in sediment and suspended particulate matter decreases seaward, whereas dissolved Hg concentrations increase sharply seaward, suggesting higher mobilization at the marine-influenced, mangrove-dominated portion of the estuary, mostly in the dry season. Concentrations of Hg in rooted macrophytes respond to Hg concentrations in sediment, being higher in the fluvial endmember of the estuary, whereas in floating aquatic macrophytes, Hg concentrations followed dissolved Hg concentrations in water and were also higher in the dry season. Animals (fish and crustaceans) also showed higher concentrations and bioaccumulation in the marine-influenced portion of the estuary. The variability of Hg concentrations in plants and sediments agrees with continental sources of Hg. However, Hg fractionation in water and contents in the animals respond to higher Hg availability in the marine-dominated end of the estuary. The results suggest that the impact of anthropogenic sources on Hg bioavailability is modulated by regional and global environmental changes and results from a conjunction of biological, ecological and hydrological characteristics. Finally, increasing aridity due to global warming, observed in northeast Brazil, as well as in other semiarid littorals worldwide, in addition to increased water overuse, augment Hg bioavailability and environmental risk and exposure of the local biota and the tradition of human populations exploiting the estuary's biological resources.

Factors related to fish mercury concentrations in Iowa lakes

Mercury contamination in aquatic ecosystems is a global concern due to the health risks of consuming contaminated fishes. Fish mercury concentrations are influenced by a range of biotic and abiotic factors that vary among regions, but these complex interactions are difficult to disentangle. We collected bluegill (Lepomis macrochirus), white and black crappie (Pomoxis annularis; P. nigromaculatus), largemouth bass (Micropterus salmoides), walleye (Sander vitreus), muskellunge (Esox masquinongy), and northern pike (E. lucius) from waterbodies throughout Iowa and analyzed them for mercury concentrations. We used land use, water chemistry, and fish characteristics to explain variation in mercury concentrations among and within systems. Mercury concentrations were generally low and undetectable (< 0.05 mg/kg) in 43% of fish analyzed. Detected mercury concentrations were highest in largemouth bass, muskellunge, northern pike, and walleye, lowest in black and white crappie and bluegill, and positively related to fish length and age. Mean lake depth, pH, watershed area to lake area ratio, and percent of watershed as open water were positively related to fish mercury concentrations whereas lake area and percent of watershed as agriculture, developed, forested, and grassland were negatively related to mercury concentrations. Additionally, mercury concentrations were higher in shallow natural lakes compared to other lake types. Our results indicate fish mercury concentrations are lower in Iowa lakes compared to other regions. Models we developed in this study can be used to identify other waterbodies that may have elevated mercury concentrations that can guide fish mercury monitoring programs.

Human risk assessment of toxic elements (As, Cd, Hg, Pb) in marine fish from the Amazon

The present study evaluated As, Hg, Pb and Cd burdens in both ecologically and commercially important 314 marine fishes belonging to 47 species sampled along the Amazon Coast. We specifically investigated variations in these four elements among different habitats and their relationships with trophic position and estimated potential human health risk by calculating the hazard quotient (HQ), hazard index (HI), and target cancer risk (TR). Our analyses revealed that Hg concentrations in reef-associated fish were over 2-fold those recorded in demersal fish (p < 0.001). A stable isotope analysis indicated that most of the fish species analyzed herein are secondary consumers (i.e., TP > 2.9) and their trophic positions exhibited a significant negative correlation to As, Pb and Cd. Positive significant relationships were noted between As-Cd, As-Pb, As-Hg, Hg-Cd and Cd-Pb, suggesting that these elements exhibit similar dispersion properties and bioaccumulation homology, probably arising from natural fluvial inputs from the Amazon basin system. Detected As concentrations were higher than established guidelines and legal limits in 63.8% of the examined species (n = 30), whereas Cd, Hg and Pb levels were generally very low. Estimated daily intake (EDI) of iAs, Hg and Pb were above reference dose (RfD) in more almost half of species analyzed and HQ values were each found to pose potential non-carcinogenic health risks if high amounts are consumed over time. HI indicates that the determined elements attained levels considered as potential human health hazards trough consumption of eight cartilaginous fish. The TR values of iAs and Pb were higher than the guideline value and given this, individuals who continuously consume cartilaginous fish contaminated with the toxic elements determined here will likely be under increased cancer risks in the long term.

A Quantitative Assessment and Biomagnification of Mercury and Its Associated Health Risks from Fish Consumption in Freshwater Lakes of Azad Kashmir, Pakistan

Issues regarding biomagnification of mercury (Hg) due to its persistence, bioaccumulation, and toxicity in freshwater lakes have gained much attention in the last two decades especially in remote regions of the world where anthropogenic inputs are considered as negligible. In this study, spatial distribution of total mercury (THg), interspecific accumulation patterns, trophic transfer, and associated health risks in fish of freshwater lakes (357-3107 masl) in Azad Kashmir, Pakistan, were investigated. THg concentrations in the regions were 0.20 ± 0.08 μg g^-1 in glacial, 0.54 ± 0.21 μg g^-1 in rural, and 1.35 ± 0.46 μg g^-1 in urban region. Omnivorous, herbivorous, and carnivorous fish showed THg concentrations of 0.94, 0.85, and 0.49 μg g^-1. Regional, lake, trophic level, and specie-specific differences of THg accumulation were found significant in the study. Among growth parameters, length and age varied significantly among species, trophic levels, and lakes, whereas weight showed significant variation among lakes as well. Condition factor (K) showed significant differences within species, lakes, and trophic levels. Biomagnification was observed in all lakes with the trophic magnification slopes (TMS) ranging from 0.03 to 0.20 with an average of 0.094 ± 0.07. Isotopic values of nitrogen (δ¹⁵N) and condition factor were found to dominate THg accumulation trends; however, no significant health risks were found in the study.

Mercury in fish tissues in the area of Malachov Hg-ore deposit (Slovakia)

The abandoned Malachov deposit belongs among the most important historic Hg deposits in the world. The soil, groundwater, surface water, plants, and animals are still heavily contaminated by potentially toxic elements such as As and Cd, but mainly by Hg. This article is focused on the Hg contamination of aquatic plants and animals in the Malachov creek. Mercury concentrations were measured in fresh water (on average 3 µg L^-1), in the zoobenthos (on average 362.47 µg kg^-1), and in the phytobenthos (on average 578.36 µg kg^-1). Higher Hg concentrations were determined in the muscles of Salmo trutta morpha fario (on average 362.47 µg kg^-1) and lower in Cottus poecilopus (on average 352.75 µg kg^-1). The Hg concentrations were higher in the internal tissues (578.36-1185.75 µg kg^-1) than in the muscles of the fish. The Hg content in fresh water exceeded Regulation of the Slovak Government No. 269/2010, which stipulates the criteria for achieving a proper water balance, but the Hg content in the fish muscles of both fish species was below the specified limit of the Food Code of Governmental Regulation of the Slovak Republic No. 608/3/2004-100. The Hg contamination in fishes is controlled by their weight and age. The presented data may be used as the base information for future studies in order to be able to estimate consumption recommendations and warnings.

Interactions between mercury and environmental factors: A chemometric assessment in seafood from an eutrophic estuary in southeastern Brazil

Guanabara Bay (GB) is an estuary in Brazil, constantly the target of pollutants, such as mercury (Hg). Thus, our study aimed to evaluate (i) total mercury (THg) content in shrimp and squid species from GB; (ii) associate THg content to contamination in swimming crabs; (iii) explore potential differences between species, and size; (iv) correlate abiotic water data to the determined THg contents; (v) verify if Hg concentrations are below acceptable limits. Swimming crabs showed greater Hg contamination compared to other species. For shrimp only biometric variables are related to Hg, while for squid, only abiotic. Only squids did not show a correlation between Hg and animal size. Finally, the detected Hg values are below the tolerable limits established by legislations. Our results indicate that the dynamics of Hg contamination differs between groups and that further studies are needed to elucidate the mechanisms that affect bioaccumulation in different species.

Amyotrophic Lateral Sclerosis Risk, Family Income, and Fish Consumption Estimates of Mercury and Omega-3 PUFAs in the United States

Most amyotrophic lateral sclerosis (ALS) cases are considered sporadic, without a known genetic basis, and lifestyle factors are suspected to play an etiologic role. We previously observed increased risk of ALS associated with high nail mercury levels as an exposure biomarker and thus hypothesized that mercury exposure via fish consumption patterns increases ALS risk. Lifestyle surveys were obtained from ALS patients (n = 165) and n = 330 age- and sex-matched controls without ALS enrolled in New Hampshire, Vermont, or Ohio, USA. We estimated their annual intake of mercury and omega-3 polyunsaturated fatty acid (PUFA) via self-reported seafood consumption habits, including species and frequency. In our multivariable model, family income showed a significant positive association with ALS risk (p = 0.0003, adjusted for age, sex, family history, education, and race). Neither the estimated annual mercury nor omega-3 PUFA intakes via seafood were associated with ALS risk. ALS incidence is associated with socioeconomic status; however, consistent with a prior international study, this relationship is not linked to mercury intake estimated via fish or seafood consumption patterns.

Use of occupancy modelling to identify sample sizes and waterbodies with fish exceeding mercury consumption advisory thresholds

Identifying waterbodies where fish methylmercury concentrations are elevated is critical for development of consumption guidelines. However, mercury concentrations vary among waterbodies and fishes due to a suite of environmental conditions and detection of elevated mercury concentrations is imperfect, resulting in inaccurate consumption guidelines. Occupancy models may be a useful approach for addressing these issues but have not been used for these purposes. Our objectives were to use occupancy modeling to (1) estimate number of samples needed to detect mercury levels surpassing >0.30 mg/kg wet weight in fish at a waterbody (2) identify individual fish-level factors associated with detection probability, and (3) identify environmental-level factors linked to elevated mercury levels in fish at a waterbody. Mercury concentrations were estimated from >500 largemouth bass Micropterus salmoides and walleye Sander vitreus from 30 waterbodies throughout Iowa, USA to identify individuals with concentrations > or <0.30 mg/kg. Probability of detecting mercury concentrations >0.30 mg/kg varied between species and increased with fish length; consequently, more samples were needed to detect elevated mercury concentrations in small versus large fish. The probability of a waterbody having fish with elevated mercury levels increased with the percent grassland and declined with percent agriculture in the watershed, providing prioritization metrics for mercury surveillance programs. Our results demonstrate that occupancy models can be a valuable tool for mercury surveillance due to their ability to estimate necessary sample sizes and identify fish sizes and waterbodies with elevated mercury concentrations while accounting for imperfect detection probabilities.

Mercury concentrations in Baja California Sur fish: Dietary exposure assessment

Total mercury concentrations ([THg]) in muscle were determined in commercial finfish and elasmobranchs from Baja California Sur (BCS), Mexico to evaluate dietary Hg exposure for BCS communities, including the relationship of trophic ecology, length and mass with [THg] that might drive future consumption advice (e.g., recommend limited consumption of large fish for some species). The [THg] ranged from 0.06 to 528.02 μg kg^-1 ww in finfish and 17.68-848.26 μg kg^-1 ww in elasmobranchs. Relative to the consumption threshold set for predatory fish in Mexico, all species had a concentration below 1000 μg kg^-1 ww. As expected, 16 (4.02%) and 75 (18.84%) individual fish were above advisory thresholds of 500 and 200 μg kg^-1 ww, respectively. The hazard quotients (HQs) in most species were significantly <1.0, only banded guitarfish showed a significant median HQ > 1.0. Thus, the relative level of risk of high Hg exposure is low for most species.

Mercury in fish from streams and rivers in New York State: Spatial patterns, temporal changes, and environmental drivers

Mercury (Hg) concentrations in freshwater fish across the state of New York frequently exceed guidelines considered harmful to humans and wildlife, but statewide distribution and temporal changes are not well known for the state's streams and rivers. We analyzed existing data to describe recent spatial patterns, identify key environmental drivers, and assess temporal changes. Size classes within sportfishes and prey fishes formed 'functional taxa' (FT), and standardized scores were generated from 2007-2016 data for 218 sites. Muscle Hg in ≥1 sportfish FT exceeded human-health guidelines of 50 ng/g (sensitive populations) and 300 ng/g (general population, GP) at 93 and 56% of sites, respectively, but exceeded 1000 ng/g (a state threshold) at only 10% of sites. Whole-body Hg in ≥1 prey fish FT exceeded wildlife thresholds of 40 ng/g and 100 ng/g at 91 and 51% of sites, respectively. Environmental drivers of recent spatial patterns include extent of forest cover and storage, the latter an indicator of wetlands. Standardized Hg scores increased with increasing atmospheric Hg deposition and storage across rural 'upland' regions of New York. However, scores were not related to atmospheric deposition in more-developed 'lowland' regions due to the limited methylation potential of urban landscapes. Comparisons of 2010-2015 sportfish Hg concentrations with those of 1998 and 2000-2005 showed inconsistent temporal changes both among and within eight sites examined. Some recent stream and river fish Hg spatial patterns differed from those of lake-based studies, highlighting the importance of New York's flowing waters to future Hg monitoring and risk assessment.

Prenatal Mercury Exposure in Pregnant Women from Suriname's Interior and Its Effects on Birth Outcomes

Prenatal mercury (Hg) exposure was determined in a sub-cohort of the Caribbean Consortium for Environmental and Occupational Health’s environmental epidemiologic prospective cohort study of pregnant women living in Suriname’s interior. The associations between Hg exposure, low birth weight (LBW, <2500 g) and preterm birth (PTB, <37 weeks) were explored. Correlation analysis, Fisher’s exact test and logistic regression analyses were conducted to evaluate the associations between maternal hair Hg levels and birth weight, LBW and PTB, and between potential confounders, LBW and PTB, respectively. Among 204 singleton births were 198 live births, five stillbirths and one miscarriage. The mean participant age was 26 years; 15.7% of participants had PTBs and 8.1% delivered a child with a LBW. The median hair Hg level was 3.48 μg/g hair. Low hair Hg exposure, based on lowest tertile < 2.34 μg/g, was associated with LBW (OR = 7.2; 95% CI 1.5–35.6; p = 0.015); this association was independent of maternal age, ethnic background, household income and village location, and no correlation was found between hair Hg and PTB. Young maternal age was associated with PTB (RR = 5.09, 95% CI: 1.92–13.85; p = 0.0004) while maternal age was not associated with hair Hg or LBW. The impact of prenatal Hg exposure on pediatric neurodevelopment is currently being evaluated in the infant sub-cohort.

Mercury bioaccumulation in freshwater fishes of the Chesapeake Bay watershed

Chemical contaminants are a threat to the Chesapeake Bay watershed, with mercury (Hg) among the most prevalent causes of impairment. Despite this, large-scale patterns of Hg concentrations, and the potential risks to fish, wildlife, and humans across the watershed, are poorly understood. We compiled fish Hg data from state monitoring programs and recent research efforts to address this knowledge gap and provide a comprehensive assessment of fish Hg concentrations in the watershed's freshwater habitats. The resulting dataset consisted of nearly 8000 total Hg (THg) concentrations from 600 locations. Across the watershed, fish THg concentrations spanned a 44-fold range, with mean concentrations varying by 2.6- and 8.8-fold among major sub-watersheds and individual 8-digit hydrological units, respectively. Although, mean THg concentrations tended to be moderate, fish frequently exceeded benchmarks for potential adverse health effects, with 45, 48, and 36% of all samples exceeding benchmarks for human, avian piscivore, and fish risk, respectively. Importantly, the percentage of fish exceeding these benchmarks was not uniform among species or locations. The variation in fish THg concentrations among species and sites highlights the roles of waterbody, landscape, and ecological processes in shaping broad patterns in Hg risk across the watershed. We outline an integrated Hg monitoring program that could identify key factors influencing Hg concentrations across the watershed and facilitate the implementation of management strategies to mitigate the risks posed by Hg.

Mercury Levels in Freshwater Fish: Estimating Concentration with Fish Length to Determine Exposures Through Fish Consumption

Methylmercury (MeHg) is a neurotoxic pollutant that bioaccumulates and biomagnifies in aquatic food webs, impacting the health of piscivorous wildlife and human consumers of predatory fish. While fish mercury levels have been correlated with various biotic and abiotic factors, many studies only measure adults to characterize the health of locally fished populations, omitting information about how local fish bioaccumulate mercury relative to their growth. In this study, we sought to establish length: total mercury (THg) concentration relationships in juvenile and adult fish of four genera (sunfish, yellow perch, white perch, and killifish) across six freshwater pond systems of Nantucket Island to determine safe consumption sizes across species and environmental conditions. A wide length range (2-21 cm) was utilized to develop linear regression models of ln-THg versus fish length. In most cases, different genera within the same pond indicated similar slopes, supporting that all four genera share comparable features of feeding and growth. Comparing individual species across ponds, differences in ln-THg versus fish length were attributable to known environmental Hg-modulators including surface water MeHg levels, pH, and watershed area. Referencing human health and wildlife criteria, our results confirm that numerous Nantucket freshwater ecosystems contain elevated fish THg levels, which could impact the health of not only piscivorous wildlife in all measured ponds but also recreational fishers in at least two measured systems. Future studies should measure THg levels across juvenile and adult fish to detect potential differences in the slope of THg concentration across fish length relevant for local consumption advice.

Elemental composition of aquaculture fish from West Bengal, India: nutrition versus food safety

Aquaculture production continues to grow in West Bengal, where on average people consume 8.2 kg capita^-1 of fish each year, and an extensive mosaic of aquaculture ponds has developed along the River Hugli as clay pits are repurposed. The adjacent brickworks and industry (especially tanneries) are a source of environmental pollution, with potential for bioaccumulation of potentially harmful elements (PHEs) in fish farmed in these ponds. Fish from aquaculture present an opportunity to meet food sufficiency in West Bengal; however, an investigation to assess their effectiveness for micronutrient supply balanced against food safety is required. Five ponds close to industrial brick manufacture (urban) and three from rural areas were assessed for the degree of pollution within their pond sediments and waters. Fish were also sampled from each location including a subset from the market in Kolkata to determine the concentrations of PHEs in their fish muscle tissue. Dietary intake and PHE loading were calculated for four fish species to evaluate their nutrient content with respect to recommended daily intakes for adults, e.g. calcium (Ca), potassium (K), magnesium (Mg), iron (Fe), zinc (Zn) and selenium (Se), and to establish whether the provisional maximum tolerable intakes (PMTIs) are exceeded for PHEs, e.g. aluminium (Al), arsenic (As), mercury (Hg), chromium (Cr), tin (Sn), copper (Cu) and lead (Pb). Preliminary results suggest that aquaculture is making an important contribution to nutrition, with fish being a good source of Se. However, in contrast to small wild-caught fish, aquaculture fish in the present study were poor sources of Fe, Ca and Zn. The fish also made substantial contributions (> 10%) to the PMTI of Hg and As. Therefore, there is an urgent need for ongoing monitoring and an expanded sampling programme, as well as research into approaches which might improve the nutritional quality of the farmed fish.

Health Risk Assessment of Metals (Cu, Pb, Zn, Cr, Cd, As, Hg, Se) in Angling Fish with Different Lengths Collected from Liuzhou, China

Wild fish caught by anglers (WFAs) were confirmed to be usually contaminated with metals, and the contamination status is radically affected by the growth and length of the fish. To determine the contamination levels of metals and health risks in WFAs with different length ranges of fish, this study ascertained the concentration of eight metals, including Cu, Pb, Zn, Cr, Cd, As, Hg and Se, in 171 wild fishes collected from the watershed of Liujiang River. The assessment of metal pollution and health risks from the consumption of these fishes with seven length ranges were accomplished. The obtained results implied a relatively high concentration of Zn, Cr, and Cd up to 109.294 mg/kg, 4.226 mg/kg, and 0.196 mg/kg (wet weight), respectively, which exceed the corresponding Maximum Residue Limit (MRL). The negative correlation between Cu, Zn, Cr, and Cd was observed to be significant with fish length, signifying a possible occurrence of biological dilution on these metals. The WFAs were mostly contaminated with Cr and Cd irrespective of the length ranges of fish, which were denoted by the average pollution index (Pi) of Cr and Cd and were commonly found to be beyond 0.2. Based on the results of health risk assessment analysis, most of the target hazard quotient (THQ) values of Cr were below 1, implying that the consumption of wild fish for adults has insignificant health risk. For children, the total target hazard quotient (TTHQ) values of beyond 1 were found in fishes with the length range of <25 cm, particularly a TTHQ value 1.627 in the range of 10–15 cm, indicating that children are being prone to serious health risks owing to the consumption of WFAs. The weekly recommended consumption of WFAs with the length range of 10–15 cm for adults and children was 0.298 kg/week and 0.149 kg/week, respectively. These are substantially lower than the current rate of fish consumption (0.42 kg/week), and therefore, the wild fish with the length range of 10–15 cm should be avoided for consumption.

Impact and consequences of dietary riboflavin deficiency treatment on flesh quality loss in on-growing grass carp (Ctenopharyngodon idella)

Fish is among the cheapest and most promising sources of animal protein. The main edible portion of fish is muscle. This study explored the impact of dietary riboflavin on fish flesh quality and showed the possible role of muscle antioxidant defense in flesh quality in relation to dietary riboflavin. On-growing grass carp (initial average weight of 275.82 ± 0.57 g) were fed diets containing graded levels of riboflavin (0.63, 1.95, 3.98, 6.02, 7.96, and 10.04 mg kg-1 diet) for eight weeks. The results indicated that compared with the optimal riboflavin levels (3.98 and/or 6.02 mg riboflavin per kg diet), riboflavin deficiency treatment (0.63 mg riboflavin per kg diet) significantly reduced the muscle nutrients, including the protein, lipid, flavor amino acid, and total essential amino acid contents. Furthermore, the muscle shear force, pH value, and hydroxyproline concentration were reduced, while the muscle cooking loss and lactic acid content increased (P < 0.05). Compared with optimal riboflavin levels, the riboflavin deficiency treatment increased the reactive oxygen species (ROS), malondialdehyde (MDA), and protein carbonyl contents, while riboflavin treatments of 3.98-10.04 mg riboflavin per kg diet showed the lowest ROS and MDA contents (P < 0.05). Compared with the optimal riboflavin levels, the riboflavin deficiency treatment decreased the activities of copper/zinc superoxide dismutase (CuZnSOD), glutathione reductase (GR), catalase (CAT), and glutathione peroxidase (GPx), and reduced the glutathione (GSH) content (P < 0.05). Furthermore, the relative mRNA levels of antioxidant enzymes, including CuZnSOD, CAT, GR and GPx, and antioxidant-related signaling molecules, including NF-E2-related factor 2 (Nrf2) and casein kinase 2, were down-regulated, while those of Kelch-like ECH-associated protein 1b were up-regulated (P < 0.05). Collectively, the present study indicates that riboflavin deficiency treatment reduces the flesh quality, partly due to inhibition of the antioxidant defense through the Nrf2 signaling pathway, while optimal riboflavin levels reverse these negative effects.

Mercury in aquatic fauna contamination: A systematic review on its dynamics and potential health risks

Mercury is an important pollutant, released into aquatic ecosystems both naturally and by anthropogenic action. This element is transferred to aquatic organisms in different ways, causing potential health risks. In addition, mercury can be accumulated by humans, especially through the consumption of contaminated food. This systematic review aims to present mercury pathways, the major routes through which this element reaches the aquatic environment and its transformations until becoming available to living animals, leading to bioaccumulation and biomagnification phenomena. The key biotic and abiotic factors affecting such processes, the impact of mercury on animal and human health and the issue of seafood consumption as a source of chronic mercury contamination are also addressed. A total of 101 articles were retrieved from a standardized search on three databases (PubMed, Emabse, and Web of Science), in addition to 28 other studies not found on these databases but considered fundamental to this review (totaling 129 articles). Both biotic and abiotic factors display fundamental importance in mediating mercurial dynamics, i.e., muscle tropism, and salinity, respectively. Consequently, mercurial contamination in aquatic environments affects animal health, especially the risk of extinction species and also on human health, with methylmercury the main mercury species responsible for acute and chronic symptomatology.

Biomarkers of Exposure to Chemical Contamination in the Commercial Fish Species Lepidopus caudatus (Euphrasen, 1788): A Particular Focus on Plastic Additives

In recent years, the Mediterranean Sea has become an accumulation zone for waste generated by the 22 countries bordering its shores. Although the effects of plastic litter on the marine environment and on organisms have recently been studied in other areas, further information is needed for the Mediterranean Sea and, in particular, about plastics additives inputs and interactions with the biota and the trophic network, such as phthalates and bisphenol A. Plastic material production, use and disposal contribute also to the release of heavy metals into the environment, such as mercury (Hg), often used during the production of chlorine, the primary ingredient in PVC, lead (Pb) and cadmium (Cd), which are used as stabilizers in PVC and leach out of products during use and disposal. Our research aims to evaluate phthalates, bisphenol A and heavy metals contamination in Lepidopus caudatus (Pisces, Trichiuridae), which could be considered as a potential sentinel species. For the evaluation of toxicological effects, we evaluated the expression of vitellogenin and metallothioneins 1. In all samples analyzed, we have not found microplastics in the gastrointestinal tract but chemical analysis revealed the presence of high content of phthalates, and in particular high quantities of DIDP, DEHP, bis-benzylester phthalate, bis-butyl ester phthalate and mono-N-butyl ester phthalate in different organs. Instead, trace elements detected in tissue revealed a trend of concentrations generally higher in liver and intestine than gill and muscle tissues. Immunohistochemical analysis for anti-metallothionein 1 antibody showed a strong positivity of liver cells, both in females and males. Analysis for the anti-vitellogenin antibody showed in females a strong positivity both in the liver cells and in the gonads, in male specimens was found to be always negative except for a specimen, in which it was highlighted a positivity in some areas of the liver and of the gonad.

Potentially toxic elements (PTEs) and polycyclic aromatic hydrocarbons (PAHs) in fish and prawn in the Persian Gulf, Iran

This study aimed to speciate and quantify potentially toxic elements (PTEs) and polycyclic aromatic hydrocarbons (PAHs), in addition to estimate potential human health risk of PTEs (As, Cd, Co, Cr, Cu, Hg, Mn, Ni, Pb, Se, V, and Zn) through the consumption of three edible fish species (Leuciscus vorax, Liza abu, and Coptodon zillii) and two prawn species (Metapenaeus affinis and Penaeus semisulcatus) collected from Arvand River and Musa Estuary in the Persian Gulf. The concentration of As in prawn species exceeded permissible limit set by international organizations. PAHs were dominated by low molecular weight species such as naphthalene, phenanthrene, and, fluorene but generally exhibited low mean concentrations in fish and prawn samples. The human health hazard posed by PTEs was assessed using methods that consider estimated daily intake (EDI), estimated weekly intake (EWI), target hazard quotients (THQ), and combined THQ. The results suggested that elevated As concentrations in almost all prawn samples may pose a probable health hazard to local inhabitants.

A Model of Mercury Distribution in Tuna from the Western and Central Pacific Ocean: Influence of Physiology, Ecology and Environmental Factors

Information on ocean scale drivers of methylmercury levels and variability in tuna is scarce, yet crucial in the context of anthropogenic mercury (Hg) inputs and potential threats to human health. Here we assess Hg concentrations in three commercial tuna species (bigeye, yellowfin, and albacore, n = 1000) from the Western and Central Pacific Ocean (WCPO). Models were developed to map regional Hg variance and understand the main drivers. Mercury concentrations are enriched in southern latitudes (10°S-20°S) relative to the equator (0°-10°S) for each species, with bigeye exhibiting the strongest spatial gradients. Fish size is the primary factor explaining Hg variance but physical oceanography also contributes, with higher Hg concentrations in regions exhibiting deeper thermoclines. Tuna trophic position and oceanic primary productivity were of weaker importance. Predictive models perform well in the Central Equatorial Pacific and Hawaii, but underestimate Hg concentrations in the Eastern Pacific. A literature review from the global ocean indicates that size tends to govern tuna Hg concentrations, however regional information on vertical habitats, methylmercury production, and/or Hg inputs are needed to understand Hg distribution at a broader scale. Finally, this study establishes a geographical context of Hg levels to weigh the risks and benefits of tuna consumption in the WCPO.

Effect of body length, trophic position and habitat use on mercury concentrations of sharks from contrasted ecosystems in the southwestern Indian Ocean

The non-essential metal mercury (Hg) can have deleterious effects on health of organisms, and tends to bioaccumulate with age in long-lived organisms and to biomagnify along food webs. Because elasmobranchs are fished for human consumption and their Hg levels are frequently above the maximum Hg concentration recommended for fish consumption, understanding the drivers of Hg concentration is of considerable interest. Total Hg concentrations were analysed in muscle tissues of 14 shark and 2 batoid species (n = 339 individuals) sampled across multiple habitats (coastal, open ocean and bathyal) in the southwestern Indian Ocean. Stable isotope ratios of carbon (δ¹³C) and nitrogen (δ¹⁵N) were analysed to assess whether relative trophic position and foraging habitats affected Hg concentrations. Hg concentrations increased with δ¹⁵N and body length, highlighting the mechanisms of bioaccumulation and biomagnification in relation with the trophic position and size of the individuals. Habitats where elasmobranchs were collected also affected their Hg concentrations. Bathyal sharks had high Hg concentrations that were almost similar to those of oceanic species, despite their lower relative trophic position. Higher bioavailability of Hg due to its enhanced methylation in deeper waters was considered as the most likely explanation for this result. These results highlight that multiple factors contribute to mercury accumulation in elasmobranchs.

Limited effects of changing prey fish communities on food quality for aquatic predators in the eastern Canadian Arctic in terms of essential fatty acids, methylmercury and selenium

We determined concentrations of eicosapentaenoic and docosahexaenoic acids (EPA + DHA), Σomega-3, polyunsaturated fatty acids (ΣPUFA), selenium, methylmercury, and selenium:methylmercury (Se:Hg) ratios in native and northward-redistributing sub-Arctic marine fish and invertebrates from low, mid-, and high Canadian Arctic latitudes. There was no clear latitudinal trend in nutrient or contaminant concentrations. Among species, EPA + DHA concentrations in native Arctic cod (Boreogadus saida) were similar to concentrations in sub-Arctic capelin (Mallotus villosus) and sand lance (Ammodytes spp.) (444-658 mg.100 g^-1), and higher than in most other species. Concentrations of EPA + DHA were related to lipid content, but to a greater extent for higher trophic position species (R² = 0.83) than for species at lower trophic positions (R² = 0.61). Selenium concentrations were higher in sand lance (1.15 ± 0.16 μg g^-1) than in all other species (0.30-0.69 μg g^-1), which was significantly, but weakly, explained by more pelagic feeding in sand lance. Methylmercury concentrations were similar (and Se:Hg ratios were higher) in capelin, sand lance, and Arctic cod (0.01-0.03 μg g^-1 wet weight (ww)) and lower than in other prey (0.12-0.26 μg g^-1 ww), which was significantly explained by the smaller size of these species and more pelagic feeding habits than other fish. These results suggested that a shift in prey fish composition from Arctic cod to capelin and/or sand lance is unlikely to reduce the food quality of the prey available to marine predators at least with respect to concentrations of essential fatty acids, selenium, and Se:Hg ratios.

Selenium, Mercury, and Their Molar Ratio in Sportfish from Drinking Water Reservoirs

Mercury (Hg) bioaccumulates in aquatic ecosystems and may pose a risk to humans who consume fish. Selenium (Se) has the ability to reduce Hg toxicity, but the current guidance for human consumption of fish is based on Hg concentration alone. The purpose of the present study was to examine the relationship between Se and Hg in freshwater sportfish, for which there is a paucity of existing data. We collected three species of fish from different trophic positions from two drinking water reservoirs in central North Carolina, USA, to assess Hg and Se concentrations in relation to fish total length and to compare two measures of the protective ability of Se, the Se:Hg molar ratio and Se health benefit value (HBV_Se), to current guidance for Hg. According to the Se:Hg molar ratio, all of the low trophic position fish sampled and the middle trophic position fish sampled from one of the reservoirs were safe for consumption. The same number of fish were considered safe using the HBV_Se. More fish were deemed unsafe when using the Se:Hg molar ratio and HBV_Se than were considered unsafe when using the U.S. Environmental Protection Agency (USEPA) Hg threshold. These findings suggest that the measures of Se protection may be unnecessarily conservative or that the USEPA Hg threshold may not be sufficiently protective of human health, especially the health of sensitive populations like pregnant or nursing mothers and young children. Future examination of the Se:Hg molar ratio and HBV_Se from a variety of fish tissue samples would help refine the accuracy of these measures so that they may be appropriately utilized in ecological and human health risk assessment.

Revised fish aging techniques improve fish contaminant trend analyses in the face of changing Great Lakes food webs

Incorporation of fish age into the assessment of status and trends for persistent, bioaccumulative and toxic chemicals in the Great Lakes has become an important step for the U.S. EPA's Great Lakes Fish Monitoring and Surveillance Program (GLFMSP). A slowing in the rate of decline for total PCBs in Lake Huron beginning in 2000, led the Program to complete a retrospective analysis to assess how chemical contamination may be influenced by fish age. Analytical results suggest that fish age is an important variable when assessing contaminant trends and that the Program needed to revise its compositing scheme to group fish according to age, rather than by length, prior to homogenization and chemical analysis. An Interlaboratory comparison study of multiple age structures was performed to identify the most appropriate age estimation structure for the Program. The lake trout (Salvelinus namaycush) maxillae was selected, over the otolith, as the most precise, accurate, and rapidly assessed structure for the Program when compared between laboratories and against the known age from the coded wire tag (CWT). Age-normalization practices can now be implemented when assessing contaminant concentrations and trends for the GLFMSP.

Species- and habitat-specific bioaccumulation of total mercury and methylmercury in the food web of a deep oligotrophic lake

Niche segregation between introduced and native fish in Lake Nahuel Huapi, a deep oligotrophic lake in Northwest Patagonia (Argentina), occurs through the consumption of different prey. Therefore, in this work we analyzed total mercury [THg] and methylmercury [MeHg] concentrations in top predator fish and in their main prey to test whether their feeding habits influence [Hg]. Results indicate that [THg] and [MeHg] varied by foraging habitat and they increased with greater percentage of benthic diet and decreased with pelagic diet in Lake Nahuel Huapi. This is consistent with the fact that the native creole perch, a mostly benthivorous feeder, which shares the highest trophic level of the food web with introduced salmonids, had higher [THg] and [MeHg] than the more pelagic feeder rainbow trout and bentho-pelagic feeder brown trout. This differential THg and MeHg bioaccumulation observed in native and introduced fish provides evidence to the hypothesis that there are two main Hg transfer pathways from the base of the food web to top predators: a pelagic pathway where Hg is transferred from water, through plankton (with Hg in inorganic species mostly), forage fish to salmonids, and a benthic pathway, as Hg is transferred from the sediments (where Hg methylation occurs mostly), through crayfish (with higher [MeHg] than plankton), to native fish, leading to one fold higher [Hg].

Mercury and persistent organic pollutants in native and invading forage species of the Canadian Arctic: Consequences for food web dynamics

Contaminant dynamics within Arctic marine food webs may be altered through the climate-driven northward invasions of temperate/boreal species. Here, we compare tissue concentrations of total mercury (THg) and legacy and emerging persistent organic pollutants (POPs) in native versus invading forage species sampled from 2012 to 2014 near Arviat, Clyde River, and Resolute Bay, NU, representing, low, mid- and high eastern Canadian Arctic regions, respectively. Concentrations of THg, legacy Σ-polychlorinated biphenyls (ΣPCB) and Σ-organochlorine (ΣOC) pesticides were detected in all forage species, whereas emerging halogenated flame retardants were detected in only a few individuals. Concentrations of major contaminant groups among regions did not vary for Arctic cod (Boreogadus saida), while for sculpin (Cottoidea) there was no clear latitudinal trend. Thus, considering interspecific variation, native sculpin and northern shrimp (Pandalus borealis) had the highest overall concentrations of THg (0.17 ± 0.02 and 0.21 ± 0.01 μg g^-1 wet weight, respectively), ΣPCB (322 ± 35 and 245 ± 25 ng g^-1 lipid weight (lw), respectively), and ΣOC (413 ± 38 and 734 ± 64 ng g^-1 lw, respectively). Comparing the keystone native species, Arctic cod, to its 'replacement' species, capelin (Mallotus villosus) and sandlance (Ammodytes spp.), THg concentrations were higher in Arctic cod compared to capelin (p < 0.001), which was partly explained by differences in fish length. Conversely, capelin and sandlance had higher concentrations of most POPs than Arctic cod (p < 0.02). Neither feeding habitat (based on δ¹³C), trophic position (based on δ¹⁵N), nor fish length significantly explained these differences in POPs between Arctic cod, capelin and sandlance. Higher POPs concentrations, as well as variation in congener/compound patterns, in capelin and sandlance relative to Arctic cod seem, therefore, more likely related to a more "temperate"-type contaminant signature in the invaders. Nevertheless, the relatively small (up to two-fold) magnitude of these differences suggested limited effects of these ecological changes on contaminant uptake by Arctic piscivores.

Mercury concentration trend as a possible result of changes in cod population demography

Mercury (Hg) in Atlantic cod (Gadus morhua) is one of many parameters that are monitored through OSPAR's Joint Assessment and Monitoring Programme. Time series for cod in the Inner Oslofjord (Norway) go back to 1984. Until 2014, annual median Hg-concentrations in cod from the Inner Oslofjord showed both significant upward long-term (whole time series) and short-term (recent 10 years) trends (when 2015 was included, the short-term trend was not significant). However, the median length of the cod sampled also showed upward trends. This may have been caused by low cod recruitment in the area since the start of the 2000s, as indicated by beach seine surveys. To investigate how length would impact the trend analysis, the Hg-concentrations in the cod were normalised to 50 cm. No significant short-term trend in Hg-concentrations could be detected for length-normalised concentrations. The results indicated that most of the upward trend in Hg-concentrations could be attributed to the sampling of larger fish. The reasons for the apparent change in the cod population demography are not conclusive, however, sampling bias must also be considered.

Evaluation of Trace Element and Metal Accumulation and Edibility Risk Associated with Consumption of Labeo umbratus from the Vaal Dam, South Africa

With the occurrence of recreational and small scale subsistence fishing activities at the Vaal Dam, South Africa, consumption of fish from this dam may result in health risks associated with trace elements and metals. The Vaal Dam is one of the largest dams in South Africa, located between the Gauteng Province and Orange Free State, and supplies water to approximately 11.6 million people. A total of 38 specimens of the benthic cyprinid fish Labeo umbratus were collected from the Vaal Dam during two surveys, in 2011 and 2016. Samples of muscle, liver, kidney, gill and spinal cord were analysed, along with sediment samples collected during the same surveys. Thirteen trace elements were analysed in the samples by Inductively Coupled Plasma–Optical Emission Spectrometry, Inductively Coupled Plasma–Mass Spectrometry, Atomic Absorption Spectroscopy and Total Reflection X-ray Fluorescence spectroscopy. This is the first survey on trace element and Hg accumulation in this fish species from the Vaal Dam and target hazard quotients (THQ) indicated that there is a risk for consumers of fish for As and Hg (THQ = 1.43 and 1.14 respectively). Although levels of trace elements in this impoundment have shown little change for a number of years and are lower than global background levels, studies detailing the accumulation of metals by fish inhabiting the Vaal Dam have indicated that trace elements in muscle tissue are above food safety guidelines. Trace element levels in L. umbratus are lower compared to other species inhabiting the Vaal Dam and further indicate that risks for consumers can be decreased if humans relying on fish from the Vaal Dam preferentially consume this species over others.

Semiquantitative determination of total mercury in Pygocentrus nattereri Kner, 1858 and sediment at the plateau of Upper Paraguai River, Brazil

In this study an environmental assessment of contamination by total mercury (THg) was carried out at the Plateau of the Upper Paraguai River. Total mercury was evaluated in sediment and muscle of the red piranha Pygocentrus nattereri Kner, 1858, a piscivorous species at the top of the food chain consumed for subsistence and commercially. THg concentrations were below national guidelines established by WHO for sediments (100 ng g^-1) and fish (100-600 ng g^-1) for most of the sampled sites. Two sites located downstream of artisanal diamond and gold mines had THg concentrations in fish equal or greater than 600 ng g^-1.

Mercury contamination in Southern New England coastal fisheries and dietary habits of recreational anglers and their families: Implications to human health and issuance of consumption advisories

Total mercury (Hg) was measured in coastal fishes from Southern New England (RI, USA), and Hg exposure was estimated for anglers and family members that consumed these resources. Fish Hg was positively related to total length (n = 2028 across 7 fish species), and interspecies differences were evident among legally harvestable fish. Many recreational anglers and their families experienced excessively high Hg exposure rates, which was attributed to the enriched Hg content of frequently consumed fishes. Specifically, 51.5% of participants in this study had Hg exposures exceeding the US EPA reference dose, including 50.0% of women of childbearing years. These results are noteworthy given that Hg neurotoxicity occurs in adults and children from direct and prenatal low-dose exposure. Moreover, this study underscores the need for geographic-specific research that accounts for small-scale spatial variations in fish Hg and dietary habits of at-risk human populations.

Mercury concentration in muscle, bellyfat and liver from Oreochromis niloticus and Lates niloticus consumed in Lake Albert fishing communities in Uganda

Without surveillance studies on mercury (Hg) levels in predominant fish species and parts eaten in a fishing community, the FAO/WHO guidelines might be surpassed, hence health risk. A monitoring study in a developing country with 29 Oreochromis niloticus (Nile tilapia) and 34 Lates niloticus (Nile perch) from landing sites provided muscle, bellyfat and liver samples for Mercury detection using Inductive Couple Plasma-optical emission spectroscopy. The study shows that fish eaten in the fishing community are small with fewer risks from mercury. Tilapia accumulated more mercury in muscle and liver than Nile perch. Fish consumed has mercury levels higher than FAO/WHO guidelines, and the bellyfat of Nile perch bioaccumulated more mercury than Tilapia. Based on the above, it is clear that some fish species should not be eaten by the vulnerable groups due to levels of Hg found in the muscle and bellyfat. This research will serve as a base for future studies, sensitization campaigns and policy design on mercury uptake through fish in fishing communities of developing countries.

Assessing potential health risks to fish and humans using mercury concentrations in inland fish from across western Canada and the United States

Fish represent high quality protein and nutrient sources, but Hg contamination is ubiquitous in aquatic ecosystems and can pose health risks to fish and their consumers. Potential health risks posed to fish and humans by Hg contamination in fish were assessed in western Canada and the United States. A large compilation of inland fish Hg concentrations was evaluated in terms of potential health risk to the fish themselves, health risk to predatory fish that consume Hg contaminated fish, and to humans that consume Hg contaminated fish. The probability that a fish collected from a given location would exceed a Hg concentration benchmark relevant to a health risk was calculated. These exceedance probabilities and their associated uncertainties were characterized for fish of multiple size classes at multiple health-relevant benchmarks. The approach was novel and allowed for the assessment of the potential for deleterious health effects in fish and humans associated with Hg contamination in fish across this broad study area. Exceedance probabilities were relatively common at low Hg concentration benchmarks, particularly for fish in larger size classes. Specifically, median exceedances for the largest size classes of fish evaluated at the lowest Hg concentration benchmarks were 0.73 (potential health risks to fish themselves), 0.90 (potential health risk to predatory fish that consume Hg contaminated fish), and 0.97 (potential for restricted fish consumption by humans), but diminished to essentially zero at the highest benchmarks and smallest fish size classes. Exceedances of benchmarks are likely to have deleterious health effects on fish and limit recommended amounts of fish humans consume in western Canada and the United States. Results presented here are not intended to subvert or replace local fish Hg data or consumption advice, but provide a basis for identifying areas of potential health risk and developing more focused future research and monitoring efforts.

Total Mercury in Mugil spp and Eugerres axillaris of a Subtropical Lagoon of NW Mexico

The mercury content of mullets and black mojarras of Urías lagoon (NW Mexico) were determined every second month from November 2012 to September 2013, to determine differences related to season or to trophic levels. The Hg contents of the muscle were significantly higher in mojarras, confirming that Hg contents tend to increase along the food chain, while the levels in liver were higher in mullets, suggesting different Hg storage strategies of these species. In mullets, the content of muscles did not vary seasonally and was significantly lower than in the liver. In black mojarras there were no significant differences between muscle and liver, and the lowest mean values were in May in both tissues. Given the low Hg contents, both species are safe for human consumption, but care should be taken in traditional fishing communities.

Mercury sources and trophic ecology for Hawaiian bottomfish

In Hawaii, some of the most important commercial and recreational fishes comprise an assemblage of lutjanids and carangids called bottomfish. Despite their importance, we know little about their trophic ecology or where the mercury (Hg) that ultimately resides in their tissue originates. Here we investigated these topics, by analyzing muscle samples for mercury content, nitrogen, carbon, and amino acid specific nitrogen isotope ratios in six species distributed across different depths from the Northwestern Hawaiian Islands (NWHI) and the Main Hawaiian Islands (MHI). Fishes had different sources of nitrogen and carbon, with isotopic values suggesting benthic food sources for shallow nearshore species. High trophic position lutjanids that foraged in deeper water, benthic environments generally had higher Hg levels. Model results also suggested that benthic Hg methylation was an important source of Hg for shallow benthic feeders, while deepwater sources of mercury may be important for those with a diet that derives, at least in part, from the pelagic environment. Further, despite the lack of freshwater sources of Hg in the NWHI, statistical models explaining the variation in tissue Hg in the MHI and NWHI were nearly identical, suggesting freshwater Hg inputs were not a major source of Hg in fish tissue.

Seafood substitutions obscure patterns of mercury contamination in Patagonian toothfish (Dissostichus eleginoides) or "Chilean sea bass"

Seafood mislabeling distorts the true abundance of fish in the sea, defrauds consumers, and can also cause unwanted exposure to harmful pollutants. By combining genetic data with analyses of total mercury content, we have investigated how species substitutions and fishery-stock substitutions obscure mercury contamination in Patagonian toothfish (Dissostichus eleginoides), also known as “Chilean sea bass”. Patagonian toothfish show wide variation in mercury concentrations such that consumers may be exposed to either acceptable or unacceptable levels of mercury depending on the geographic origins of the fish and the allowable limits of different countries. Most notably, stocks of Patagonian toothfish in Chile accumulate significantly more mercury than stocks closer to the South Pole, including the South Georgia/Shag Rocks stock, a fishery certified by the Marine Stewardship Council (MSC) as sustainably fished. Consistent with the documented geography of mercury contamination, our analysis showed that, on average, retail fish labeled as MSC-certified Patagonian toothfish had only half the mercury of uncertified fish. However, consideration of genetic data that were informative about seafood substitutions revealed a complex pattern of contamination hidden from consumers: species substitutions artificially inflated the expected difference in mercury levels between MSC-certified and uncertified fish whereas fishery stock substitutions artificially reduced the expected difference in mercury content between MSC-certified and uncertified fish that were actually D. eleginoides. Among MSC-certified fish that were actually D. eleginoides, several with exogenous mtDNA haplotypes (i.e., not known from the certified fishery) had mercury concentrations on par with uncertified fish from Chile. Overall, our analysis of mercury was consistent with inferences from the genetic data about the geographic origins of the fish, demonstrated the potential negative impact of seafood mislabeling on unwanted mercury exposure for consumers, and showed that fishery-stock substitutions may expose consumers to significantly greater mercury concentrations in retail-acquired fish than species substitutions.

Maternally transferred mercury in wild largemouth bass, Micropterus salmoides

Maternal transfer of mercury in fish represents a potential route of elimination for adult females and a risk to developing embryos. To better quantify maternal transfer, we measured Hg in female largemouth bass (Micropterus salmoides) muscle and eggs from six waterbodies. Mercury in eggs from two waterbodies exceeded a US federal screening level (0.3 μg g(-1)) and was likely high enough to cause adverse reproductive effects. We found a curvilinear relationship between female and egg Hg. Fish with <0.37 μg g(-1) Hg had low levels of Hg in eggs; those with Hg >0.37 μg g(-1) showed a direct relationship between egg and muscle Hg (Log10 egg Hg = -1.03 + 1.18 * log10 muscle tissue Hg + 2.15 * (log10 muscle tissue Hg + 0.35)(2)). We also report higher maternal transfer (0.2-13.2%) and higher ratios of egg to muscle tissue Hg (4-52%) and egg to whole body Hg concentrations (7-116%) than previously observed for teleost fish.