Methylmercury Biomagnification Research Articles

Toward a Global Model of Methylmercury Biomagnification in Marine Food Webs: Trophic Dynamics and Implications for Human Exposure.

Marine fish is an excellent source of nutrition but also contributes the most to human exposure to methylmercury (MMHg), a neurotoxicant that poses significant risks to human health on a global scale and is regulated by the Minamata Convention. To better predict human exposure to MMHg, it is important to understand the trophic transfer of MMHg in the global marine food webs, which remains largely unknown, especially in the upper trophic level (TL) biota that is more directly relevant to human exposure. In this study, we couple a fish ecological model and an ocean methylmercury model to explore the influencing factors and mechanisms of MMHg transfer in marine fish food webs. Our results show that available MMHg in the zooplankton strongly determines the MMHg in fish. Medium-sized fish are critical intermediaries that transfer more than 70% of the MMHg circulating in food webs. Grazing is the main factor to control MMHg concentrations in different size categories of fish. Feeding interactions affected by ecosystem structures determine the degree of MMHg biomagnification. We estimate a total of 6.1 metric tons of MMHg potentially digested by the global population per year through marine fish consumption. The model provides a useful tool to quantify human exposure to MMHg through marine fish consumption and thus fills a critical gap in the effectiveness evaluation of the convention.

Evaluating total mercury and methylmercury biomagnification using stable isotopes of carbon and nitrogen in fish from the Madeira River basin, Brazilian Amazon.

The isotopic signatures of carbon in primary consumer fish species in the Madeira River basin (Western Amazon) follow a pattern, with basal species feeding mainly on C3 (e.g., vascular plants and phytoplankton). In this study with 196 specimens of 19 fish species and six trophic guilds, significant differences were found between the two main groups of primary consumers (herbivores and detritivores) in the Madeira River basin. The mercury and δ15N data indicated that the fish specimens collected in Puruzinho and Cuniã Lakes provided greater trophic magnification factors (TMFs) for this metal than those found in the corresponding rivers. In relation to total mercury (0.09-2.07μgg-1) and methylmercury (0.05-1.91μgg-1) concentrations, the piscivorous/carnivorous species exceeded the values recommended by the World Health Organization, with a [MeHg:THg] ratio of about 80%. Preventive and educational practices should be adopted to reduce the possible toxic effects of Hg in the riverside population, for whom fish constitutes the main protein source. Also, biomonitoring of the fish species in the Madeira River should be conducted on an ongoing basis to detect possible alterations in mercury concentrations.

Selective organomercury determination by ICP-MS made easy

A fast and cost-effective procedure based on Inductively Coupled Plasma – Mass Spectrometry (ICP-MS) for the selective determination of methylmercury (MeHg) is proposed and validated for fish tissue analysis. Selectivity for MeHg is achieved by simply inserting a strong anion exchange resin to block inorganic mercury as negatively charged chloride species, leaving MeHg unretained. The procedure features a 15 min extraction time followed by a 100 s analysis time achieving a limit of detection of 1.6 μg kg−1 on solid samples. The effect of the solution composition and inorganic mercury concentration were extensively studied to fully assess the selectivity of the procedure: Hg(II):MeHg ratios up to 50 are tolerated and cause systematic errors lower than 15%. The entire procedure was successfully validated by standard reference material from the marine food web, namely fish muscle and liver plus zooplankton. The method was finally applied to the detection of MeHg in the marine trophic web of Djibouti (Gulf of Aden): a trophic magnification factor of 13.5 proved the high risk associated with the biomagnification of methylmercury.

Enhanced Susceptibility of Methylmercury Bioaccumulation into Seston of the Laurentian Great Lakes.

Mercury concentrations in the Laurentian Great Lakes waters are among the lowest reported in the literature, while game fish concentrations approach consumption advisory limits, particularly in Lakes Superior, Huron, and Michigan, indicating efficient methylmercury transfer from water to game fish. To determine if increased transfer efficiency is evident within the lower food web, we measured (2010-2018) mercury and dissolved organic carbon (DOC) in water, and in size-sieved seston, dietary tracers (carbon and nitrogen isotope ratios), phytoplankton methylmercury bioaccumulation, and methylmercury biomagnification between increasing seston size fractions. We observed consistently low filter-passing methylmercury (<0.010 ng L-1) and comparatively variable DOC (1.1 to 3.4 mg L-1) concentrations. Methylmercury biomagnification factors between size-sieved seston were similar between lakes. Bioaccumulation factors in phytoplankton were among the highest in the literature (log 5.5 to 6.1), exceeding those in oceans, smaller lakes, and streams, and was influenced by DOC. Higher bioaccumulation rates increase the susceptibility of methylmercury accumulation into the food web. Because mercury is dominantly delivered to the Great Lakes through the atmosphere and the biota therein is highly susceptible to methylmercury uptake, we propose that the Laurentian Great Lakes are excellent sentinels to trace the success of efforts to decrease global mercury emissions (e.g., Minamata Treaty) in the future.

Exposure to methylmercury and inorganic mercury in the food does not lead to trophic magnification in the sea star Asterias rubens

Methylmercury accumulated at the top of aquatic food chains constitutes a toxicological risk to humans and other top predators. Biomagnification of methylmercury takes place among vertebrates at the higher trophic levels, but this process is less elucidated in benthic invertebrates at the lower trophic levels. Therefore, we investigated the accumulation from food and elimination of methylmercury and inorganic mercury in the benthic sea star Asterias rubens (L.) - a representative of trophic level ~3 - in laboratory experiments. Sea stars fed over 49 days with contaminated mussels (Mytilus edulis) accumulate methylmercury and inorganic mercury to the highest concentrations in the digestive glands, the pyloric caeca, less in stomach, gonad, tube feet, aboral body wall and not to detectable levels in the coelomic fluid. Concerning whole body contents, steady states were reached for both methylmercury and inorganic mercury during the 7-week feeding period and the sea stars reached approximately ½ and ¼ of the concentrations in the mussel food for the two mercury forms, respectively. Half-lives for the elimination of the two mercury forms varied between 45 and 173 days in a 140-d elimination period following the feeding period; inorganic mercury was eliminated faster than methylmercury. Examination of total mercury concentrations in field-collected sea stars confirmed this lack of trophic magnification in relation to the major food items, soft parts of molluscs. We suggest that mercury is not trophically magnified in sea stars 1) because they eliminate methylmercury faster than larger fish and decapod crustaceans and 2) maybe more importantly, because inorganic mercury with its faster elimination constitutes a larger fraction of the total mercury in the food at the lower trophic levels - as opposed to methylmercury which dominates at the higher trophic levels.

Drivers of variability in mercury and methylmercury bioaccumulation and biomagnification in temperate freshwater lakes

The four largest freshwater lakes in southwestern France are of both ecological and economic importance. However, some of them are subjected to mercury (Hg) contamination, resulting in the ban of human consumption of piscivorous fish. Moreover, beyond predatory fish, little information exist regarding Hg levels in other species of these ecosystems. In this context, we used a food web analytical approach to investigate Hg bioaccumulation and biomagnification in relation to the trophic structure of these four lakes. More specifically, various organisms (macrophytes, epiphyton, invertebrates and fish) were collected at the four lakes and analysed for carbon and nitrogen stable isotopes as well as for total Hg (THg) and methylmercury (MeHg). A spatial variability of bioaccumulation in organisms was observed, particularly in carnivorous fish, with higher Hg levels being found in the two more northern lakes (median±SE: 3491 ± 474 and 1113 ± 209 ng THg.g−1 dw in lakes HC and L, respectively) than in the southern pair (600 ± 117 and 911 ± 117 ng THg.g−1 dw in lakes CS and PB, respectively). Methylmercury biomagnification was observed through the food webs of all four lakes, with different trophic magnification slopes (HC = 0.16; L = 0.33; CS = 0.27; PB = 0.27), even though the length of the food chains was similar between the lakes. Our results suggest that rather than the food web structure, anthropogenic inputs (sulfate in northern lakes and phosphorus inputs in southern ones) may have a strong impact, more or less directly, on Hg methylation in freshwater environments, and lead to concentrations exceeding environmental recommendations despite low Hg backgrounds in sediment and water.

Methylmercury biomagnification in coastal aquatic food webs from western Patagonia and western Antarctic Peninsula

Mercury (Hg) is a global pollutant of concern because its organic and more toxic form, methylHg (MeHg), bioaccumulates and biomagnifies through aquatic food webs to levels that affect the health of fish and fish consumers, including humans. Although much is known about trophic transfer of MeHg in aquatic food webs at temperate latitudes in the northern hemisphere, it is unclear whether its fate is similar in biota from coastal zones of the southeastern Pacific. To assess this gap, MeHg, total Hg and food web structure (using δ13C and δ15N) were measured in marine macroinvertebrates, fishes, birds, and mammals from Patagonian fjords and the Antarctic Peninsula. Trophic magnification slopes (TMS; log MeHg versus δ15N) for coastal food webs of Patagonia were high when compared with studies in the northern hemisphere, and significantly higher near freshwater inputs as compared to offshore sites (0.244 vs 0.192). Similarly, in Antarctica, the site closer to glacial inputs had a significantly higher TMS than the one in the Southern Shetland Islands (0.132 vs 0.073). Composition of the food web also had an influence, as the TMS increased when mammals and seabirds were excluded (0.132–0.221) at a coastal site. This study found that both the composition of the food web and the proximity to freshwater outflows are key factors influencing the TMS for MeHg in Patagonian and Antarctic food webs.

Methylmercury biomagnification in aquatic food webs of Poyang Lake, China: Insights from amino acid signatures

As the dominant mercury species in fish, methylmercury (MeHg) biomagnifies during its trophic transfer through aquatic food webs. MeHg is known to bind to cysteine, forming the complex of MeHg-cysteine. However, relationship between MeHg and cysteine in large-scale food webs has not been explored and contrasted with MeHg biomagnification models. Here, we quantified the compound-specific nitrogen isotopic analysis of amino acids (CSIA-AA), MeHg, and amino acid composition in aquatic organisms of Poyang Lake, the largest freshwater lake in China. The trophic positions (TPAA) of organisms ranged from 1.0 ± 0.1–3.7 ± 0.2 based on CSIA-AA approach. The trophic magnification factor (TMF) of MeHg, derived from the regression slope of Log-transformed MeHg in organisms upon their TPAA for the entire food web was 9.5 ± 0.5. Significantly positive regression between MeHg and cysteine (R2 = 0.64, p < 0.01) was documented, suggesting MeHg-cysteine complex may potentially play a critical role in the bioaccumulation of MeHg. Furthermore, TMFs of MeHg calculated with and without cysteine normalization compared well (7.7–8.7) when excluding primary producers. Our results implied that MeHg may biomagnify as the complex of MeHg-cysteine and contribute to our understanding of MeHg trophic transfer at the molecular level.

Biomagnification of methylmercury in a marine food web in Laizhou Bay (North China) and associated potential risks to public health

The concentrations of total mercury (THg) and methylmercury (MeHg) were assessed in water, sediment and biota (54 species) samples from the coast of Laizhou Bay, to evaluate MeHg biomagnification in Laizhou Bay food web. The trophic web structure was determined with stable isotope ratios. The MeHg concentrations were highly variable among species ranged from 4.8 ng g−1 in primary producers to 411.2 ng g−1 in spotted sea bass. Weight and ecotype were the principal parameters related to the mercury concentrations for most species. The trophic magnification factors (TMFs) for MeHg and THg were 2.09 and 1.69, respectively, indicating that mercury biomagnification is occurring in this marine food web. The estimated weekly intake (EWI) and target hazard quotient (THQ) values demonstrated that consuming predatory fishes from the bay could cause potential health risks to humans.

Mercury pollution in modern times and its socio-medical consequences

Mercury plays a critical role in serious health problems due to environmental or occupational exposures. Aquatic ecosystems are an essential component of the global biogeochemical cycle of mercury, as inorganic mercury can be converted to toxic methyl mercury in these environments and reemissions of elemental mercury rival anthropogenic mercury releases on a global scale.The history of the Minamata disease, a typical example of industrial pollution, has shown how corporate secrecy and ignorance on part of the health authorities may influence the devastating spread of environmental contamination and the progress of disease. While the Minamata Convention, in place since 2017, is aiming to lower mercury exposure and to prevent adverse effects, there are still knowledge gaps in the areas of global environmental mercury exposure. Areas of uncertainty in the global biogeochemical cycle of mercury include oxidation processes in the atmosphere, land-atmosphere and ocean-atmosphere cycling, and methylation processes in the ocean. Pollution related to climate change (especially in boreal and arctic regions), bioaccumulation and biomagnification of methyl mercury in the food chain, especially in fish and marine mammals, needs to be addressed in more detail. Information is lacking on numerous hidden contaminant exposures i.e. from globally applied traditional medicine, mercury containing skin creams and soaps, dental amalgam, ethyl mercury containing vaccines and latex paint additives, as well as on mercury releases from power plants, e-waste/fluorescent lamps, wildfire emissions, and global artisanal small-scale gold mining activities.Mercury occurs in various forms with different levels of toxicity. While much is already known and documented on the health effects of mercury, present knowledge and translation into preventive actions is still incomplete. Risks for long term health effects trough prolonged low dose exposure and trough cumulative exposures of various mercury forms should be further addressed. Preventive actions should include adequate human biomonitoring programs. Research data should be translated swiftly into management tools for local policy makers and health professionals, also paying attention at the major differences in mercury contamination across the globe.

Differential bioaccumulation of mercury by zooplankton taxa in a mercury-contaminated reservoir Guizhou China

Mercury (Hg) contamination in aquatic systems remains a global concern with the biomagnification of methylmercury (MeHg) through primary consumers (zooplankton) to fish and humans. In this study, total mercury (THg) and MeHg concentrations were analyzed in zooplankton collected from Baihua reservoir (Guizhou Province, China). Our results demonstrated that THg and MeHg concentrations were strongly correlated to zooplankton community and biomass composition. The THg concentration was significantly higher in micro-zooplankton compared to meso-zooplankton and macro-zooplankton, and MeHg concentration increased significantly as body size increased. Hg increases in zooplankton were influenced by the numbers of calanoid copepods and Daphnia present relative to phytoplankton and zooplankton biomass. Many zooplankton taxa in the three size-fractions were affected by THg exposure. The biomasses of Bosmina longirostris, Thermocyclops brevifurcatus, Asplanchna priodonta and Cyclops vicinus vicinus were positively correlated with Hg accumulation, while Daphnia hyalina, and Phyllodiaptomus tunguidus had a negative association. THg and MeHg bioaccumulation factors were correlated with phosphorus and total nitrogen concentration, zooplankton biomass, and chlorophyll-a concentration. Phosphorus loading was associated with increased THg and MeHg accumulation in the zooplankton highlighting biomagification with eutrophication. Chlorophyll-a levels were not correlated to THg and MeHg accumulation in zooplankton when phytoplankton densities were >107 cells L−1 and chlorophyll-a concentrations <9 μgL−1. This finding contradicts the idea of MeHg biodilution with increased algae biomass. However, changes in the phytoplankton species and biomass altered the availability of food for zooplankton, particularly micro-zooplankton and macro-zooplankton. Ultimately, the bioaccumulation of MeHg and THg across lower trophic levels was based more on the availability of preferred food resources than on total biological productivity.

Fracked ecology: Response of aquatic trophic structure and mercury biomagnification dynamics in the Marcellus Shale Formation.

Unconventional natural gas development and hydraulic fracturing practices (fracking) are increasing worldwide due to global energy demands. Research has only recently begun to assess fracking impacts to surrounding environments, and very little research is aimed at determining effects on aquatic biodiversity and contaminant biomagnification. Twenty-seven remotely-located streams in Pennsylvania's Marcellus Shale basin were sampled during June and July of 2012 and 2013. At each stream, stream physiochemical properties, trophic biodiversity, and structure and mercury levels were assessed. We used δ15N, δ13C, and methyl mercury to determine whether changes in methyl mercury biomagnification were related to the fracking occurring within the streams' watersheds. While we observed no difference in rates of biomagnificaion related to within-watershed fracking activities, we did observe elevated methyl mercury concentrations that were influenced by decreased stream pH, elevated dissolved stream water Hg values, decreased macroinvertebrate Index for Biotic Integrity scores, and lower Ephemeroptera, Plecoptera, and Trichoptera macroinvertebrate richness at stream sites where fracking had occurred within their watershed. We documented the loss of scrapers from streams with the highest well densities, and no fish or no fish diversity at streams with documented frackwater fluid spills. Our results suggest fracking has the potential to alter aquatic biodiversity and methyl mercury concentrations at the base of food webs.

Effects of Maternally-Transferred Methylmercury on Stress Physiology in Northern Water Snake (Nerodia sipedon) Neonates.

Biomagnification of methylmercury in aquatic systems can cause elevated tissue mercury (Hg) and physiological stress in top predators. Mercury is known to affect stress hormone levels in mammals, birds and fish. In this study, the effects of maternally-transferred methylmercury on the stress physiology of Northern Water Snake (Nerodia sipedon) neonates were tested. Gravid females were dosed via force-fed capsules during late gestation with 0, 0.01, or 10µg methylmercury per gram of body mass. Plasma corticosterone levels and leukocyte differentials were analyzed in baseline and confinement-stressed neonates from all dose levels. Neither Hg nor confinement stress had a significant effect on leukocyte differentials nor was Hg related to corticosterone levels. However, stress group neonates showed lower heterophil/lymphocyte ratios and this study was the first to show that neonate N. sipedon can upregulate CORT in response to stress. These results indicate that N. sipedon may be somewhat tolerant to Hg contamination.

Simple metal model for predicting uptake and chemical processes in sewage-fed aquaculture ecosystem

This paper shows how a model can be used as an experimental tool to assess the processes in aqua chemistry that should be included in the model. The STELLA software was used to study the uptake of Cd, Pb, Cr, Cu and Hg from sewage-fed aquaculture. Model calibration revealed that feeding rate of 15% was the best, which is also in accordance to the fish growth. The ratio of fish food was also calibrated to be 70% due to a food chain in the water and 30% due to a food chain in the sediment. This gave the lowest uncertainty of the model. The simple metal model was working acceptably well for Pb, Cu and Cd but not working properly for chromium and mercury. Additional processes, including precipitation of chromium and bio-magnification of methylmercury were introduced to explain concentration of chromium and mercury in fish. Comparison of measured and predicted metal concentration used for validation gave a linear regression with an R2 value of 0.9 indicating that a good agreement between the model predictions and the experimental measurements. The finding suggests that the simple metal model is an accurate and useful for predicting uptake and chemical processes in ecosystem.

Methylmercury biomagnification in an Arctic pelagic food web.

Mercury (Hg) is a toxic element that enters the biosphere from natural and anthropogenic sources, and emitted gaseous Hg enters the Arctic from lower latitudes by long-range transport. In aquatic systems, anoxic conditions favor the bacterial transformation of inorganic Hg to methylmercury (MeHg), which has a greater potential for bioaccumulation than inorganic Hg and is the most toxic form of Hg. The main objective of the present study was to quantify the biomagnification of MeHg in a marine pelagic food web, comprising species of zooplankton, fish, and seabirds, from the Kongsfjorden system (Svalbard, Norway), by use of trophic magnification factors. As expected, tissue concentrations of MeHg increased with increasing trophic level in the food web, though at greater rates than observed in several earlier studies, especially at lower latitudes. There was strong correlation between MeHg and total Hg concentrations through the food web as a whole. The concentration of MeHg in kittiwake decreased from May to October, contributing to seasonal differences in trophic magnification factors. The ecology and physiology of the species comprising the food web in question may have a large influence on the magnitude of the biomagnification. A significant linear relationship was also observed between concentrations of selenium and total Hg in birds but not in zooplankton, suggesting the importance of selenium in Hg detoxification for individuals with high Hg concentrations.

Rapidly increasing methyl mercury in endangered ivory gull (Pagophila eburnea) feathers over a 130 year record.

Mercury (Hg) is increasing in marine food webs, especially at high latitudes. The bioaccumulation and biomagnification of methyl mercury (MeHg) has serious effects on wildlife, and is most evident in apex predators. The MeHg body burden in birds is the balance of ingestion and excretion, and MeHg in feathers is an effective indicator of overall MeHg burden. Ivory gulls (Pagophila eburnea), which consume ice-associated prey and scavenge marine mammal carcasses, have the highest egg Hg concentrations of any Arctic bird, and the species has declined by more than 80% since the 1980s in Canada. We used feathers from museum specimens from the Canadian Arctic and western Greenland to assess whether exposure to MeHg by ivory gulls increased from 1877 to 2007. Based on constant feather stable-isotope (δ(13)C, δ(15)N) values, there was no significant change in ivory gulls' diet over this period, but feather MeHg concentrations increased 45× (from 0.09 to 4.11 µg g(-1) in adults). This dramatic change in the absence of a dietary shift is clear evidence of the impact of anthropogenic Hg on this high-latitude threatened species. Bioavailable Hg is expected to increase in the Arctic, raising concern for continued population declines in high-latitude species that are far from sources of environmental contaminants.

Biomagnification of mercury in mollusks from coastal areas of the Chinese Bohai Sea

Biomagnification of methylmercury and growth dilution of inorganic mercury were found during the trophic transfer of mercury in different mollusk species.

Bioaccumulation of Methylmercury in Neovison vison (Schreber, 1777) Populations of the Susquehanna River Valley

ABSTRACT Being the longest non-navigable river on the eastern coast of the United States, the Susquehanna River and the surrounding areas support a vast number of plants, animals, and other organisms, creating a vast and complex food web within a large and biodiverse ecosystem. One of the most prominent and essential organisms within this food web is the American mink (Neovison vison). In recent years, studies have been conducted to determine the level of biomagnification of methylmercury in terrestrial organisms that reside at higher trophic levels. This particular study has found that American mink populations residing in the Susquehanna River Valley of Pennsylvania are reliable indicators of bioaccumulation of methylmercury due to their role as piscivorous carnivores residing at a high trophic level of the terrestrial food web. Analysis of methylmercury concentrations of 166 hair samples from collected mink specimens yielded 111 samples with concentrations in excess of the toxicity threshold of 1 mg kg-1 body weight. Furthermore, our data suggest that although mercury contamination is a global concern, geographical location of mercury producers, such as coal-burning power plants, and the relationship to the location of mink populations may be a large factor in bioaccumulation of mercury. In particular, samples taken from mink specimens within habitats in the northeastern region of Pennsylvania contained higher concentrations of methylmercury as well as a larger quantity of samples containing concentrations higher than the toxicity threshold than in samples from other regions of the state.

Higher and more variable methylmercury biomagnification factors for floodplain than the contiguous river (South River, Virginia USA)

Extending previous trophic transfer studies of the mercury-contaminated South River watershed, predictive models were built for mercury biomagnification in floodplain food webs at two more locations (North Park and Grand Cavern). Four of five models built to date based on methylmercury and δ15N met the a priori requirement for useful prediction (prediction r2≈0.80). An additional factor included in models was organism thermoregulatory strategy (poikilothermy or homeothermy). The methylmercury food web biomagnification factors (FWMFs, fold increase per trophic level) for the North Park and Grand Cavern locations were 17.4 (95% CI of 9.5–31.6) and 6.2 (95% CI of 3.5–11.0) respectively. FWMF calculated in 2009 were 9.3 (95% CI of 5.4–16.2) for the Augusta Forestry Center and 25.1 (95% CI of 12.6–50.1) for Grottoes Town Park. The overall South River floodplain FWMF generated by meta-analysis of the four locations was 12.4 (95% CI of 6.8–22.3). These results supported previous findings that the South River floodplain food webs had higher biomagnification factors than the contiguous aquatic food web (4.6, 95% CI of 3.6–5.7). Floodplain FWMFs were also more variable than those of the river.

Mercury environmental quality standard for biota in Europe: Opportunities and challenges

The European Union sets Environmental Quality Standards (EQS) for 33 + 8 “priority or priority hazardous substances”; Hg being included in the latter group. Directive 2008/105/EC fixes EQS for total Hg concentration in filtered water (0.45 µm) and allows Member States to opt for an alternative EQS for biota. However, proposal COM 2011/876, currently under discussion, sets to reverse this approach by requiring the application of a biota-based EQS of 20 ng g−1 total Hg wet weight and specifying, at the time of writing, that this EQS is intended for fish. The biota EQS is meant for the protection of piscivorous wildlife against secondary poisoning and should protect the aquatic ecosystems and human health. Adopting a biota-based EQS for Hg reflects current scientific understanding, with most Hg-related environmental issues arising from the biomagnification of methylmercury (meHg) rather than direct Hg (or meHg) toxicity via water exposure. An EQS for biota also automatically accounts for Hg bioavailability issues, thus greatly increasing the possibility to identify situations requiring risk management during routine monitoring programs. Depew et al. (2012) derived a threshold concentration of 40 ng g−1 wet weight for reproductive effects in fish following dietary exposure to meHg. Besides protecting piscivorous organisms, the proposed EQS is therefore amenable to application for the protection of prey fish. However, adoption of the EQS for biota is likely to pose enormous pressure on regulatory agencies. Looking at fish collected from some European lakes and rivers during 2005–2010, Hg concentrations exceed the proposed EQS by 2- to 16-fold (Table 1). Table 1, albeit far from exhaustive, includes representative water bodies and should reflect the range of Hg contamination in fish from European surface waters. How to reconcile the scientific superiority of the EQS for biota with regulatory compliance, therefore, represents a major conundrum. Guilizzoni (2011) Pessina (2010) Pola (2011) Pola (2011) Ortelli et al. (2009) Babut et al. (2011) ICPR (2011) In this respect, proposal COM 2011/876 makes specific provision for substances behaving as ubiquitous persistent bioaccumulative and toxic (UPBT) substances. If there is a robust statistical monitoring baseline, Member States can justify failure in meeting the EQS for an UPBT by presenting separate classification maps showing that the “bad” status is caused by an UPBT for which all possible measures have been taken. The same proposal allows Member States to apply an EQS for different matrices, provided they demonstrate that it achieves the same level of protection as the EQS for biota. Other arguments, not stated in the proposal, include the application of the EQS for biota to invertebrate groups (expected to have lower Hg concentrations) or, in a purely pragmatic way, a revision of the numerical EQS value to make it less stringent. Reverting to a water-based EQS is not advisable because of the scientific superiority of the standard for biota and, similarly, revision of the EQS numerical value is difficult to justify on a scientific basis. As to the other possibilities, application of the EQS to invertebrates will protect forage fish against dietary Hg exposure (Depew et al. 2012), but EQS for piscivorous wildlife and forage fish may not be interchangeable. Finally, the choice of including Hg in the list of UPBT would shift focus from the national to the global scale, thus reducing efforts to target important local issues. For example, lakes Maggiore and Lugano have contiguous catchments, but current Hg concentrations in fish (Table 1) reflect the long history of Hg contamination of Lake Maggiore through the 20th century and require specific basin-scale measures for remediation. Overall, the impact of Hg on European waters may be much more serious than previously thought. The practical problems of such situations are obvious, but most recent scientific evidence confirms rather than questions the solidity of the proposed numerical value. Regulatory agencies must therefore expand Hg monitoring of biota to fully appreciate the gap between the targeted and the current situation. With more information, specific cases possibly allowing for the use of less stringent EQS for the same level of protection may be identified. Further research on global and local Hg biogeochemical cycles along with ecologically meaningful investigation of Hg ecotoxicology, rather than shortcuts to reduce noncompliance, therefore appear as the correct way to reinforce the successful marriage of science and policy exemplified by the Hg EQS for biota.