Hg Levels In Fish Research Articles

Gut microbiome play a crucial role in geographical and interspecies variations in mercury accumulation by fish

Mercury (Hg) contamination in fish has raised global concerns for decades. The Hg biotransformation can be manipulated by gut microbiome and it is found to have a substantial impact on the speciation and final fate of Hg in fish. However, the contribution of intestinal microbiota in geographical and interspecies variations in fish Hg levels has not been thoroughly understood. The present study compared the Hg levels in wild marine fish captured from two distinct regions in South China sea. We observed a quite “ironic” phenomenon that MeHg levels in carnivorous fish from a region with minimal human impacts (Xisha Islands, 92 ± 7.2 ng g−1 FW) were much higher than those from a region with severe human impacts (Daya Bay, 19 ± 0.41 ng g−1 FW). Furthermore, the results showed that gut microbiome determined Hg biotransformation and played a crucial role in the variances in fish Hg levels across different geographical locations and species. The intestinal methylators, rather than demethylators, were more significant in affecting Hg biotransformation in fish. The carnivorous species in Xisha Islands exhibited a higher abundance of intestinal methylators, leading to higher MeHg accumulation. Besides, the gut microbiome could be shaped in response to the elevated Hg levels in these fish, which may benefit their adaptation to Hg toxicity and overall health preservation. However, anthropogenic activities (particularly overfishing) in Daya Bay have severely affected the fish population, disrupting the reciprocal relationships between fish and intestinal microbiota and rendering them more susceptible to pathogenic microbes. Overall, this study provided a comprehensive understanding of the role of gut microbiome in Hg bioaccumulation in fish and offered valuable insights into the co-evolutionary dynamics between fish and gut microbiome in the presence of Hg exposure.

Causes of low mercury levels in fish from the Three Gorges Reservoir, China

Previous studies have suggested that growth dilution may be an important factor contributing to the low fish Hg levels in China. To evaluate the impact of growth rate to MeHg bioaccumulation in fish in the Three Gorges Reservoir (TGR), this study used two fish species, Aristichthys nobilis (A. nobilis) and Coilia nasus (C. nasus), which differ significantly in their growth rates. A combined bioenergetic-toxicokinetic model was used to simulate methylmercury (MeHg) concentrations in these two species. The model simulations were compared with the field data and showed good fits. It explained 44.0% and 46.5% of the variation in MeHg concentrations in A. nobilis and C. nasus, respectively. Sensitivity analysis revealed that growth rate accounted for 50.9% and 16.0% of MeHg concentrations in A. nobilis and C. nasus, respectively. This indicated that growth rate was the most critical factor affecting MeHg concentrations in fast-growing fish, such as A. nobilis. However, in species with low growth rate, such as C. nasus, the effect of growth rate was not as prominent as that in fast-growing fish. As a result, MeHg elimination rates and diet MeHg levels could offset the effect of growth, and become the decisive factors for MeHg concentrations in slow-growing fish.

Total Hg levels distribution in fish and fish products and their relationships with fish types, weights, and protein and lipid contents: A multivariate analysis.

This study investigates the mercury (Hg) levels distribution in fish and fish products and their relationships with fish types, weights, protein, and lipid contents in Qatar. Principal component analysis (PCA) was employed to analyze the influence of lipids and protein content on Hg accumulation in the fish tissues. Additionally, the impact of Hg concentration and fish consumption on the estimated weekly intake (EWI). The PCA results showed that Hg contamination levels are primarily affected by protein-lipid content in predatory species. The results showed that high lipid content reflected lower Hg levels and that high Hg levels in fish with high lipid content indicated a polluted environment. The finding of the PCA of EWI, consumption, and Mercury concentration indicate that EWI is highly correlated to Mercury concentration except in the case of low Mercury concentration.

Local intensity of artisanal gold mining drives mercury accumulation in neotropical oxbow lake fishes

Driven by surges in global gold prices and additional socio-economic factors, artisanal small-scale gold mining (ASGM) in the Global South is increasing and driving emissions of significant quantities of mercury (Hg) into the air and freshwater. Hg can be toxic to animal and human populations and exacerbate the degradation of neotropical freshwater ecosystems. We examined drivers of Hg accumulation in fish that inhabit oxbow lakes of Peru's Madre de Dios, a region with high biodiversity value and increasing human populations that depend on ASGM. We hypothesized that fish Hg levels would be driven by local ASGM activities, by environmental Hg exposure, by water quality, and by fish trophic level. We sampled fish in 20 oxbow lakes spanning protected areas and areas subject to ASGM during the dry season. Consistent with previous findings, Hg levels were positively associated with ASGM activities, and were higher in larger, carnivorous fish and where water had lower dissolved oxygen levels. In addition, we found a negative relationship between fish mercury levels associated with ASGM and the occurrence of the piscivorous giant otter. The link between fine-scale quantification of spatial ASGM activity and Hg accumulation, as indicated by the result that in the lotic environment, localized effects of gold mining activities are stronger drivers (77 % model support) of Hg accumulation than environmental exposure (23 %) constitutes a novel contribution to a growing body of literature on Hg contamination. Our findings provide additional evidence of high Hg exposure risks to neotropical human and top carnivore populations subject to the impacts of ASGM, which depend on freshwater ecosystems undergoing gradual degradation. The documented spatial variation in Hg accumulation and increased Hg levels in carnivorous fish should serve as a warning to human communities in Madre de Dios to avoid the proximity of high-intensity gold mining areas and minimize local carnivorous fish consumption.

Understanding drivers of mercury in lake trout (Salvelinus namaycush), a top-predator fish in southwest Alaska's parklands

Mercury (Hg) is a widespread element and persistent pollutant, harmful to fish, wildlife, and humans in its organic, methylated form. The risk of Hg contamination is driven by factors that regulate Hg loading, methylation, bioaccumulation, and biomagnification. In remote locations, with infrequent access and limited data, understanding the relative importance of these factors can pose a challenge. Here, we assessed Hg concentrations in an apex predator fish species, lake trout (Salvelinus namaycush), collected from 14 lakes spanning two National Parks in southwest Alaska, U.S.A. We then examined factors associated with the variation in fish Hg concentrations using a Bayesian hierarchical model. We found that total Hg concentrations in water were consistently low among lakes (0.11–0.50 ng L−1). Conversely, total Hg concentrations in lake trout spanned a thirty-fold range (101–3046 ng g−1 dry weight), with median values at 7 lakes exceeding Alaska's human consumption threshold. Model results showed that fish age and, to a lesser extent, body condition best explained variation in Hg concentration among fish within a lake, with Hg elevated in older, thinner lake trout. Other factors, including plankton methyl Hg content, fish species richness, volcano proximity, and glacier loss, best explained variation in lake trout Hg concentration among lakes. Collectively, these results provide evidence that multiple, hierarchically nested factors control fish Hg levels in these lakes.

Ultrasensitive green spectrofluorimetric approach for quantification of Hg(II) in environmental samples (water and fish samples) using cysteine@MnO2 dots.

Mercury (Hg2+ ) is a natural element present in foods such as fish, water and soil. Exposure to mercury leads to severe toxic effects on the nervous, digestive, and immune systems. Here, a novel, green, and environmentally friendly fluorescent probe decorated with cysteine/MnO2 quantum dots (Cys@MnO2 QDs) was synthesized. This synthesis was carried out using a simple ultrasound technique with the aid of cysteine for fabricating Cys@MnO2 QDs to estimate Hg levels in fish and water samples. In this morphological study, Cys@MnO2 QDs were fully characterized using high-resolution transmission electron microscopy, zeta potential analysis, fluorescence, ultraviolet-visible and infrared spectroscopy. The fluorescence of the synthesized Cys@MnO2 QDs was significantly quenched by gradually increasing the Hg(II) concentration. The quenching mechanism based on the Hg-S bonds strengthened the utility of the Cys@MnO2 QDs as a novel luminescent nanoprobe. The estimation of Hg was linear in the concentration range 0.7-100.0 ng mL-1 with a limit of quantitation equal to 0.30 ng mL-1 . The Cys@MnO2 QDs are fluorescent probes with various benefits such as speed, ease of use, cost- effective, and being environmentally friendly; they are easily applied in food manufacturing and for public health improvement.

Mercury in tuna from the western equatorial Atlantic Ocean and health risk assessment

This study analyses the mercury (Hg) concentration in the meat of Thunnus albacares and Thunnus obesus caught from the western equatorial Atlantic Ocean. The objective was to estimate the Hg intake via tuna ingestion and presents the possible health risk assessment. For T. albacares and T. obesus, the median concentration was 212 ng·g-1 and 475.1 ng·g-1 wet weight, respectively. The Hg concentrations were below the maximum tolerable limit established by international and Brazilian regulations for fishery products. The consumption would pose a risk for human populations that ingest more than 80 g·day-1. Regular monitoring of both human consumption rates and Hg levels in fish are recommended.

Estimates, spatial variability, and environmental drivers of mercury biomagnification rates through lake food webs in the Canadian subarctic

Biomagnification of mercury (Hg) through lake food webs is understudied in rapidly changing northern regions, where wild-caught subsistence fish are critical to food security. We investigated estimates and among-lake variability of Hg biomagnification rates (BMR), relationships between Hg BMR and Hg levels in subsistence fish, and environmental drivers of Hg BMR in ten remote subarctic lakes in Northwest Territories, Canada. Lake-specific linear regressions between Hg concentrations (total Hg ([THg]) in fish and methyl Hg ([MeHg]) in primary consumers) and baseline-adjusted δ15N ratios were significant (p < 0.001, r2 = 0.58–0.88), indicating biomagnification of Hg through food webs of all studied lakes. Quantified using the slope of Hg-δ15N regressions, Hg BMR ranged from 0.16 to 0.25, with mean ± standard deviation of 0.20 ± 0.03). Using fish [MeHg] rather than [THg] lowered estimates of Hg BMR by ∼10%, suggesting that the use of [THg] as a proxy for [MeHg] in fish can influence estimates of Hg BMR. Among-lake variability of size-standardized [THg] in resident fish species from different trophic guilds, namely Lake Whitefish (Coregonus clupeaformis) and Northern Pike (Esox lucius), was not significantly explained by among-lake variability in Hg BMR. Stepwise multiple regressions indicated that among-lake variability of Hg BMR was best explained by a positive relationship with catchment forest cover (p = 0.009, r2 = 0.59), likely reflecting effects of forest cover on water chemistry of downstream lakes and ultimately, concentrations of biomagnifying MeHg (and percent MeHg of total Hg) in resident biota. These findings improve our understanding of Hg biomagnification in remote subarctic lakes.

Mercury in Kansas Fish: Levels, Patterns, and Risk-Based Safe Consumption Limits for Mercury Sensitive Individuals

In wet environments a portion of ambient inorganic mercury (Hg) is transformed to methylmercury (MeHg); a neurotoxin that readily concentrates in fish. Public health entities monitor Hg levels in fish to inform consumers of the types and amounts of fish that are safe to eat. In this study, monitoring data collected from stream and lakes across Kansas were used to summarize fillet tissue total mercury (THg = MeHg + Hg) levels in 36 fish species and hybrids. Data associated with eleven food fish taxa (genus and species) were presented in detail and statewide risk-based monthly safe consumption limits (SCLs) protective of Hg sensitive individuals were calculated, including two size categories (< or ≥ 508 mm) for larger growing taxa. Linear mixed effects models (LMEMs) were used to generate least squares (LS) mean fish THg values for between habitat (lakes and streams) and within habitat (waterbody size, ecoregion, and major river basin) categorical variables, and for individual sample sites. Sample site LS means were used to identify potential fish THg hotspots among lakes (LS means ≥ 90th percentile) and streams (Getis-Ord Gi* statistic). Across all samples (n = 2,106) a more than 200-fold difference existed between the highest (2.1 mg/kg) and lowest THg (0.01 mg/kg) concentrations, but most samples were below the Kansas Department of Health and Environment's (KDHE) human health screening level (HSL) (0.23 mg/kg). Statewide safe consumption limits ranged from 1 meal/month in ≥ 508 mm flathead catfish to 8 meals/mo. in crappie spp. Least squares mean fish THg was significantly higher in streams than lakes, and significantly higher in small lakes (< 10 surface acres) than larger lakes. Stream size did not affect fish THg levels. In both lakes and streams, ecoregion and major river basin significantly affected fish THg levels with higher levels more prevalent in eastern geographic areas. Lakes identified as potential fish THg hotspots were widely distributed throughout the study area, but all stream hotspot sites were clustered in the southeast portion of the state.

An examination of mercury levels in the coastal environment and fish of Cote d’Ivoire

Artisanal and small-scale gold mining (ASGM), energy production and other industrial inputs are a major source of anthropogenic mercury (Hg) to the aquatic environment globally, and these inputs have led to environmental contamination and human exposure. While studies have documented the effects of Hg inputs to rivers and marine waters of the West African region, estuarine waters of Cote d’Ivoire have been understudied, besides the waters surrounding Abidjan. To fill this gap, and to examine the potential for human exposure to methylmercury (MeHg), we measured the concentrations of total Hg, MeHg, and ancillary parameters in water (dissolved and particulate phases), sediment and fish to determine the extent of environmental impact and the potential for MeHg exposure for people consuming these fish. Levels of Hg and MeHg in sediment were elevated in the vicinity of the urban environment (up to 0.3 ng/g dry weight (dw) MeHg and 623 ng/g dw total Hg) and lowest in the more remote estuarine environments. Measurements of Hg in tuna and other larger pelagic coastal species indicated that levels were elevated but comparable to other North Atlantic regions. However, levels of Hg in fish, even smaller estuarine species, were such that the rural and urban populations are potentially being exposed to unsafe levels of MeHg, primarily as a result of the relatively high fish consumption in Cote d’Ivoire compared to other countries. Overall, both local point sources and the transport of Hg used in interior ASGM activities are the sources for Hg contamination to these coastal waters.

Understanding Food Web Mercury Accumulation Through Trophic Transfer and Carbon Processing along a River Affected by Recent Run-of-river Dams.

Unlike large dams which favor methylation of Hg in flooded soils over long periods, run-of-river dams are designed to flood a limited area of soils and are therefore not expected to significantly affect mercury (Hg) cycling or carbon processing. We studied the Hg and carbon cycles within food webs from several sectors along the Saint-Maurice River, Quebec, Canada, that differ in how they are influenced by two run-of-river dams and other watershed disturbances. We observed peak Hg concentrations in fish five-year postimpoundment, but these levels were reduced three years after this peak. Methylmercury concentrations in low trophic level fish and invertebrates were related to their carbon source (δ13C) rather than their trophic positions (δ15N). Biomagnification, measured by trophic magnification slopes, was driven mainly by methylmercury concentrations in low-trophic level organisms and environmental factors related to organic matter degradation and Hg-methylation. River sectors, δ13C and δ15N, predicted up to 80% of the variability in food web methylmercury concentrations. The installation of run-of-river dams and the related pondages, in association with other watershed disturbances, altered carbon processing, promoted Hg-methylation and its accumulation at the base of the food web, and led to a temporary increase in Hg levels in fish.

South Africa's Minamata, an Analysis of the Thor Chemicals Saga 1989 – 2020

This study analysed historical data collected over thirty years to evaluate the extent of environmental contamination and health risk associated with mercury (Hg) pollution attributed to Thor Chemicals, South Africa. Data from several sources were pooled to describe pollution trends over time. Total Hg levels directly below the plant remain extremely high and a cause for concern. Mercury levels in fish have increased significantly from 1999 to 2009 (p=0.0001) and the consumption of Catfish poses a risk to local communities with median values of 1.15 μg/g, it is very likely that Hg levels in fish have increased over the last decade as no recent data are available. In 1999 all human and animal hair samples were below 0.5 μg/g. However, by 2010 levels had increased significantly (p=0.016) among people living near the Inanda Dam (median 2.46 μg/g), as well as near the plant (median 2.62 μg/g in 2020). Immediate environmental remediation is required, and the remaining stockpile of Hg needs to be disposed of. Current fish Hg levels need to be established to develop fish consumption guidelines. A comprehensive environmental epidemiological study with a focus on pregnant women and children is needed to develop appropriate health protection interventions. Funding Statement: This research received no external funding. Declaration of Interests: The authors declare no conflict of interest.

Mercury Exposure and Toxicological Consequences in Fish and Fish-Eating Wildlife from Anthropogenic Activity in Latin America.

ABSTRACTDespite the risk of significant adverse toxicological effects of Hg to humans and wildlife, Hg use in anthropogenic activities, and artisanal small‐scale gold mining (ASGM) in particular, is widespread throughout Latin America. However, there are few research and monitoring studies of Hg toxicity in fish and fish‐eating wildlife in Latin America compared to North America. In the present paper, we reviewed the literature from published articles and reports and summarized and assessed data on Hg in fish from 10 391 individuals and 192 species sampled across Latin America. We compared fish Hg levels with toxicity reference values (TRVs) for fish and dietary TRVs for fish‐eating wildlife. We determined that fish, piscivorous birds, and other wildlife are at risk of Hg toxicity. We observed a large disparity in data quantity between North and Latin America, and identified regions requiring further investigation. In particular, future biomonitoring and research should focus on exposure of wildlife to Hg in Peru, Chile, Uruguay, the eastern and northern regions of Brazil, Venezuela, Ecuador, and Colombia. We also discuss Hg risk assessment methodological issues and recommend that future evaluations of Hg risk to wildlife must collect key physiological variables, including age, body size, and ideally Hg‐to‐Se molar ratios. Integr Environ Assess Manag 2021;17:13–26. © 2020 Environment and Climate Change Canada. Integrated Environmental Assessment and Management published by Wiley Periodicals LLC on behalf of Society of Environmental Toxicology & Chemistry (SETAC)

Critical review of mercury contamination in Sri Lankan fish and aquatic products.

Mercury (Hg) in fish and aquatic products is a potential threat to human health and international trade, and guidelines of international advisory bodies are established for assessing Hg in these foods. As fish are the most consumed animal protein in Sri Lanka, this assessment summarises for the first-time total mercury concentrations in Sri Lankan marine and freshwater fish, invertebrates, aquatic plants, and fisheries products. It reveals that Hg levels in fish and other edible aquatic species are mostly below the published safety limits, except for certain top trophic level fish (swordfish, tuna, marlin). The review also highlights gaps in Sri Lankan Hg assessments such as a total lack of data for methyl‑mercury in these aquatic species and food products. This data compilation and assessment will serve as an initial baseline for comparison with results from future monitoring and research studies in Sri Lanka while adding to the world-wide Hg database.

Influence of the flood pulse on mercury accumulation in detritivorous, herbivorous and omnivorous fish in Brazilian Amazonia.

Hg accumulation in fish is influenced by several factors including seasonality. In the Amazon, ecosystems are marked by strong seasonal variation in precipitation, which leads to drastic changes in the water level of lakes and rivers. The aim of this study was to evaluate Hg levels in muscle of detritivorous, herbivorous and omnivorous fish from an Amazon lake (Madeira River Basin, Amazonas, Brazil) over four seasons (rising water, high water, falling water and low water). We hypothesized that total Hg concentration varies during the seasons. The results indicate that total Hg levels in detritivorous fish were higher in rising and low water seasons while in herbivorous and omnivorous fish the total Hg concentration was higher during the rising water season. The hypothesis was supported by the results. Additionally, the study provides evidence that Hg levels in fish with different feeding habits are influenced by the flood pulse of the Amazon region.

Mercury, silver, selenium and other trace elements in three cyprinid fish species from the Vaal Dam, South Africa, including implications for fish consumers

The levels of Cr, Cu, Zn, Se, Ag, Cd, Hg, and Pb were determined in muscle and liver samples from 30 specimens of fish belonging to the species Labeobarbus aeneus, Labeobarbus kimberleyensis, and Labeo umbratus from the Vaal Dam. Health risks for human fish consumers were estimated using the target hazard quotient (THQ), the Se:Hg-ratio, and Se health benefit value (Se HBV). This is the first comprehensive report on Hg levels in fish from this lake. Mean concentrations ranging from 0.247–0.481 mg/kg dw in muscle and from 0.170–0.363 mg/kg dw in liver clearly show a contamination with this element. Although levels in muscle did not exceed maximum allowances for human consumption, a calculated THQ of 0.12 and 0.14 for the two Labeobarbus species, respectively, showed a potential risk due to additive effects. All Se:Hg-ratios as well as Se HBVs clearly suggested positive effects for fish consumers. Levels of Cu were remarkably high in the liver of L. umbratus, calling for further investigation on this species. Cadmium levels were above the maximum allowances for fish consumption in the liver of all three species (means between 0.190 and 0.460 mg/kg dw), but below the LOD in all muscle and intestine samples. This is also the first report of Ag in fish from South Africa. Levels were below the LOD in muscle, but well detectable in liver; they varied significantly between the two Labeobarbus species (0.054 ± 0.030 and 0.037 ± 0.016 mg/kg dw) compared to L. umbratus (1.92 ± 0.83 mg/kg dw) and showed a positive correlation with Cu levels (63.7 ± 17.0; 70.3 ± 9.0 and 1300 ± 823 mg/kg dw), possibly due to similar chemical affinities to metallothioneins. The detected Ag levels can serve as a basis to monitor the development of this new pollutant in aquatic environments in South Africa and worldwide.

Mercury contents in relation to biometrics and proximal composition and nutritional levels of fish eaten from the Western Mediterranean Sea (Almería bay)

Total liver and muscle mercury, and muscular composition, biometrics and trophic levels, were determined in four species (Mullus surmuletus, Merluccius merluccius, Auxis rochei and Scomber japonicus) of the Mediterranean Sea (Almería Bay, Spain). Mercury levels did not exceed the maximum residue limit, and M. merluccius obtained the highest level in muscle. Considerable variations in Hg content among individuals were observed in non-gregarious species. A positive correlation between Hg and trophic level or length was found in muscle, but not in liver. Organs (liver or muscle) with major Hg accumulation depend on species; muscle in M. merluccius and liver in S. japonicus. The results indicate that Hg levels in fish depend on intra- and interspecies factors that should be taken into account in systems to monitor Hg levels.

Mercury concentrations in seafood and the associated risk in women with high fish consumption from coastal villages of Sonora, Mexico

Mercury concentrations in the ocean have increased considerably since the industrial revolution and will continue to increase in the next 50 years. Therefore, it is important to monitor Hg levels in fish and to evaluate the health risks in populations with high fish consumption. In the present study, a total of 238 samples of commercial fish and shellfish, were analyzed from the Central Gulf of California, Mexico. Concentrations of total Hg in fish ranged from < DL (detection limit) up to 1.22 μg g-1, with a mean of 0.15 ± 0.19 μg g-1, the majority of the samples were lower than the maximum permissible level. To evaluate the risk, a total of 110 food frequency questionnaires were applied to women (16–68 years old) from 15 coastal fishing villages of Sonora. Results indicated a high seafood consumption at these communities (mean = 307 g day-1), and a high hazard risk (HQ = 6.2) due to methyl mercury ingestion. It is recommended to limit seafood consumption in pregnant women to 4 portions of fish per week, preferably of low mercury concentrations so that all the benefits of seafood consumption are obtained without the negative health effects of methyl mercury.

Mercury in fish from Norwegian lakes: The complex influence of aqueous organic carbon

Mercury (Hg) concentrations in water and biota are often positively correlated to organic matter (OM), typically measured as total or dissolved organic carbon (TOC/DOC). However, recent evidence suggests that higher OM concentrations inhibit bioaccumulation of Hg. Here, we test how TOC impacts the Hg accumulation in fish in a synoptic study of Methyl-Hg (MeHg) in water and total Hg (THg) in perch (Perca fluviatilis) in 34 boreal lakes in southern Norway. We found that aqueous MeHg (r2 = 0.49, p < 0.0001) and THg (r2 = 0.69, p < 0.0001), and fish THg (r2 = 0.26, p < 0.01) were all positively related with TOC. However, we found declining MeHg bioaccumulation factors (BAFMeHg) for fish with increasing TOC concentrations. The significant correlation between fish THg concentrations and aqueous TOC suggests that elevated fish Hg levels in boreal regions are associated with humic lakes. The declining BAFMeHg with increasing TOC suggest that increased OM promotes increased aqueous Hg concentrations, but lowers relative MeHg bioaccumulation. A mechanistic understanding of the response from OM on BAFMeHg might be found in the metal-complexation properties of OM, where OM complexation of metals reduces their bioavailability. Hence, suggesting that MeHg bioaccumulation becomes less effective at higher TOC, which is particularly relevant when assessing potential responses of fish Hg to predicted future changes in OM inputs to boreal ecosystems. Increased browning of waters may affect fish Hg in opposite directions: an increase of food web exposure to aqueous Hg, and reduced bioavailability of Hg species. However, the negative relationship between BAFMeHg and TOC is challenging to interpret, and carries a great deal of uncertainty, since this relationship may be driven by the underlying correlation between TOC and MeHg (i.e. spurious correlations). Our results suggest that the trade-off between Hg exposure and accumulation will have important implications for the effects of lake browning on Hg transport, bioavailability, and trophodynamics.

What’s hot about mercury? Examining the influence of climate on mercury levels in Ontario top predator fishes

Mercury (Hg) levels in Ontario top predator fishes have been increasing in recent decades. These increases may be a result of many additive factors, including global climate change. Only recently has research been conducted on how climate change may impact Hg levels in freshwater fishes at large-scales. We examined the relationship between Hg trends and (1) local weather, (2) large-scale climate drivers, and (3) anthropogenic Hg emissions, in native cool water (walleye and northern pike) and warm water (smallmouth bass and largemouth bass) predatory fishes in Ontario, Canada, for historical (1970–1992) and recent (1993–2014) time periods. For each fish species studied, > 25% of Ontario's secondary watersheds shifted from historically declining to recently increasing fish Hg trends, and ≥ 50% of watersheds experienced increasing trends between 1993 and 2014. Recent fish Hg increased at up to 0.20µg/g/decade; which were significant (p < 0.05) for walleye, northern pike and smallmouth bass. Multiple linear regressions revealed a complex interplay of local weather, large-scale climate drivers, and anthropogenic Hg emissions influencing fish Hg levels. Recent Hg levels for walleye and largemouth bass increased with changes in global climate drivers, while higher precipitation influenced smallmouth bass Hg levels the most. Walleye Hg levels increased during the positive phases of global climate drivers, reflecting the local influence of local temperatures and precipitation indirectly. Differentiating the effects of climate-related parameters and emissions is increasingly crucial to assess how changing multiple environmental stressors may impact health of wildlife and humans consuming fish.