[en] Little is known about differences among trace elements in patterns of bioaccumulation in freshwater food webs. Our goal was to identify patterns in bioaccumulation of different elements that are large and consistent enough to discern despite variation across lakes. We measured methylmercury (MeHg) and trace element (As, Cd, Hg, Pb, and Zn) concentrations in food web components of seven New England lakes on 3–5 dates per lake, and contrasted patterns of bioaccumulation across lakes, metals and seasons. In each lake, trace element concentrations were compared across trophic levels, including three size fractions of zooplankton, planktivorous fish, and piscivorous fish. The trophic position of each food web component was estimated from N isotope analysis. Trace element concentrations varied widely among taxa, lakes and sampling dates. Yet, we identified four consistent patterns of bioaccumulation that were consistent across lakes: (1) MeHg concentration increased (i.e., was biomagnified) and Pb concentration decreased (i.e., was biodiminished) with increased trophic position. (2) Zinc concentration (as with MeHg) was higher in fish than in zooplankton, but overall variation in Zn concentration (unlike MeHg) was low. (3) Arsenic and Cd concentrations (as with Pb) were lower in fish than in zooplankton, but (unlike Pb) were not significantly correlated with trophic position within zooplankton or fish groups. (4) Average summer concentrations of As, Pb, Hg, and MeHg in zooplankton significantly predicted their concentrations in either planktivorous or piscivorous fish. Our secondary goal was to review sampling approaches in forty-five published studies to determine the extent to which current sampling programs facilitate cross-lake and cross-study comparisons of bioaccumulation. We found that studies include different components of the food web and sample too infrequently to enable strong cross-lake and cross-study comparisons. We discuss sampling strategies that would improve our capacity to identify consistent patterns of bioaccumulation and drivers of elevated trace element concentrations under naturally high levels of variability. - Highlights: ► We assessed bioaccumulation of MeHg and 5 trace elements across trophic levels ► Patterns were compared across multiple sample dates in 7 New England lakes ► Each element had a unique pattern of bioaccumulation, consistent across lakes ► Characterizing such patterns requires spatial and temporal replication in sampling

[en] Highlights: • Lionfish Hg concentrations fell below World Health Organization safety limits. • Lionfish Hg concentration increased with body size and body condition. • A petroleum refinery is not a significant source of metal contaminants in lionfish. • Consuming lionfish does not pose a risk of exposure to metal contaminants. - Abstract: A wide range of ecological and environmental factors influence metal bioaccumulation in fish. Studies of mercury and other metal contaminants in invasive Indo-Pacific lionfish are limited, yet consumption of the invasive predator is increasingly utilized as a management strategy. In this study, we examined the effects of body size, body condition, sex, trophic level, carbon source, diet, depth and capture location on mercury concentrations in lionfish collected from Curaçao. In addition, we examined whether or not a local petroleum refinery is the source of metal contamination in lionfish. Mercury concentrations ranged from 0.008 to 0.106 mg/kg and we found no effect of the petroleum refinery on metal bioaccumulation in lionfish. Low concentrations of metal contaminants indicate lionfish from Curaçao are safe for human consumption.

[en] There is a well documented accumulation of mercury in fish to concentrations of concern for human consumption. Variation in fish Hg burden between lakes is often high and may result from differences in Hg transfer through lower levels of the food web where mercury is bioconcentrated to phytoplankton and transferred to herbivorous zooplankton. Prior research derived patterns of mercury accumulation in freshwater invertebrates from field collected animals. This study provides results from controlled mesocosm experiments comparing the effects of zooplankton composition, algal abundance, and the chemical speciation of mercury on the ability of zooplankton to accumulate mercury from phytoplankton and transfer that mercury to planktivores. Experiments were conducted in 550-L mesocosms across a gradient of algal densities manipulated by inorganic nutrient additions. Enriched, stable isotopes of organic (CH₃²⁰⁰HgCl) and inorganic (²⁰¹HgCl₂) mercury were added to mesocosms and their concentrations measured in water, seston, and three common zooplankton species. After 2 weeks, monomethylmercury (MMHg) concentrations were two to three times lower in the two copepod species, Leptodiaptomus minutus and Mesocyclops edax than in the cladoceran, Daphnia mendotae. All three zooplankton species had higher MMHg concentrations in mesocosms with low versus high initial algal abundance. However, despite higher concentrations of inorganic mercury (Hg_I) in seston from low nutrient mesocosms, there were no significant differences in the Hg_I accumulated by zooplankton across nutrient treatments. Bioaccumulation factors for MMHg in the plankton were similar to those calculated for plankton in natural lakes and a four-compartment (aqueous, seston, macrozooplankton, and periphyton/sediments) mass balance model after 21 days accounted for ∼18% of the CH₃²⁰⁰Hg and ∼33% of the ²⁰¹Hg added. Results from our experiments corroborate results from field studies and suggest the importance of particular zooplankton herbivores (e.g., Daphnia) in the transfer of Hg to higher trophic levels in aquatic food webs

[en] Highlights: • Water column mercury largely associated with the particulate fraction. • Particulate Hg highly enriched relative to sediments. • Evidence of biomass dilution of mercury with increasing productivity. • Fish mercury bioaccumulation determined by feeding strategy. • Nutrient loading increases trophic transfer efficiency of mercury to fish. Estuaries provide critical habitat for food webs supporting fish and shellfish consumed by humans, but estuarine ecosystem health has been threatened by increases in nitrogen loading as well as inputs of the neurotoxin, mercury (Hg), which biomagnifies in food webs and poses risk to humans and wildlife. In this study, the effects of nutrient loading on the fate of Hg in shallow coastal estuaries were examined to evaluate if their interaction enhances or reduces Hg bioavailability in sediments, the water column, and concentrations in lower trophic level fish (Fundulus heteroclitus and Menidia menidia). Multiple sites were sampled within two human impacted coastal lagoons, Great South Bay (GSB) and Jamaica Bay (JB), on the southern coast of Long Island, NY, United States of America (U.S.A.). Carbon (C), nitrogen (N), sulfur (S), Hg, and methylmercury (MeHg) were measured in surface sediments and the water column, and total Hg (THg) was measured in two species of forage fish. Minimal differences were found in dissolved and particulate Hg, dissolved organic carbon (DOC), and salinity between the two bays. Across lagoons, concentrations of chlorophyll-a were correlated with total suspended solids (TSS), and water column THg and MeHg was largely associated with the particulate fraction. Methylmercury concentrations in particulates decreased with increasing TSS and chlorophyll-a, evidence of biomass dilution of MeHg with increasing productivity at the base of the food chain. Water column Hg was associated with THg concentrations in Atlantic silversides, while mummichog THg concentrations were related to sediment concentrations, reflecting their different feeding strategies. Finally, higher nutrient loading (lower C:N in sediments) while related to lower particulate concentrations coincided with higher bioaccumulation factors (BAF) for Hg in both fish species. Thus, in shallow coastal lagoons, increased nutrient loading resulted in decreased Hg concentrations at the base of the food web but resulted in greater bioaccumulation of Hg to fish relative to its availability in algal food.

[en] Biogeochemical conditions and landscape can have strong influences on mercury bioaccumulation in fish, but these effects across regional scales and between sites with and without point sources of contamination are not well understood. Normal means clustering, a type of unsupervised machine learning, was used to analyze relationships between forage fish (Fundulus heteroclitus and Menidia menidia) mercury (Hg) concentrations and sediment and water column Hg and methylmercury (MeHg) concentrations, ancillary variables, and land classifications within the sub-watershed. The analysis utilized data from 38 sites in 8 estuarine systems in the Northeast US, collected over five years. A large range of mercury concentrations and land use proportions were observed across sites. The cluster correlations indicated that for Fundulus, benthic and pelagic Hg and MeHg concentrations were most related to tissue concentrations, while Menidia Hg was most related to water column MeHg, reflecting differing feeding modes between the species. For both species, dissolved MeHg was most related to tissue concentrations, with sediment Hg concentrations influential at contaminated sites. The models considering only uncontaminated sites showed reduced influence of bulk sediment MeHg for both species, but Fundulus retained sediment drivers at some sites, with dissolved MeHg still highly correlated for both. Dissolved organic carbon (DOC), chlorophyll, land use, and other ancillary variables were of lesser importance in driving bioaccumulation, though DOC was strongly related within some clusters, likely in relation to dissolved Hg. Land use, though not of primary importance, showed relationships opposite to those observed in freshwater, with development positively correlated and forests and agriculture negatively correlated with tissue concentrations across clusters and species. Clusters were composed of sites from geographically distinct systems, indicating the greater importance of small scale drivers of MeHg formation and uptake into the food web over system or region-wide influences.