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Toward a Global Model of Methylmercury Biomagnification in Marine Food Webs: Trophic Dynamics and Implications for Human Exposure
Abstract
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.
... Methylmercury is a highly toxic environmental pollutant primarily formed through microbial methylation of inorganic mercury [1,2]. Its lipophilic nature enables bioaccumulation in aquatic organisms, such as fish and shellfish, and subsequent transfer through the food chain [3]. Upon human consumption of contaminated food, methylmercury can cross the blood-brain barrier, causing central nervous system damage and impairing language and memory functions. ...
... Under the reduction potential, CH 3 3 Hg ⋅ + H + + e − ⇒ CH 4 + Hg recombination to form metallic Hg (2, 3) or undergo further reduction to form metallic Hg (4) [33]. Subsequently, by applying a positive scan potential to the working electrode, the deposited Hg can be re-oxidized to Hg 2 ⁺, generating an oxidative peak current signal. ...
... Under the reduction potential, CH 3 3 Hg ⋅ + H + + e − ⇒ CH 4 + Hg recombination to form metallic Hg (2, 3) or undergo further reduction to form metallic Hg (4) [33]. Subsequently, by applying a positive scan potential to the working electrode, the deposited Hg can be re-oxidized to Hg 2 ⁺, generating an oxidative peak current signal. ...
Methylmercury (CH3Hg⁺), a lipophilic environmental pollutant, accumulates in fish, shellfish, and other organisms, posing significant risks to human health through the food chain. Developing a convenient and sensitive analytical method for CH3Hg⁺ detection is crucial for reducing costs and enhancing the efficiency of food safety testing. In this study, we prepared an octyl-modified silica isoporous membrane on the indium tin oxide (ITO) electrode (Octyl-SIM/ITO) via the electrochemical-assisted self-assembly (EASA) method using octyltrimethoxysilane (O-TES) as the functional organosilane. The Octyl-SIM/ITO electrode exhibits vertically-ordered nanochannels and strong hydrophobic affinity, enabling selective penetration and enrichment of weakly polar analytes. Utilizing square wave anodic stripping voltammetry (SWASV), the Octyl-SIM/ITO electrode demonstrates superior electrochemical response signals for CH3Hg⁺ detection, achieving a detection limit as low as 4 nM. This method allows for accurate and reproducible detection of CH3Hg⁺ in fish and oyster samples with minimal sample preparation, offering promising potential for portable in situ detection.
Graphical Abstract
... However, there is a significant lack of data on MeHg concentrations in Level 1 and Level 4 marine fishes, as well as other seafoods (Fig. 2). Given the significant bioaccumulation effect of MeHg in the marine food web, there is a correlation between different seafoods 27,28 . Based on this background, this study employed the random forest method to investigate their relationships with the MeHg concentrations in Level 2 and Level 3 marine fishes and utilized these relationships to impute missing values. ...
Mercury exposure poses significant threats to human health, particularly in its organic form, methylmercury (MeHg). Diet is the main pathway for human MeHg exposure, especially through seafood consumption. In this context, numerous studies have established seafood MeHg concentration datasets to assess MeHg-related health risks from seafood consumption. However, existing datasets are limited to specific regions and short-term observations, making it difficult to support continuous and dynamic assessments of global MeHg-related health risks. This study takes a bottom-up approach to construct a global seafood MeHg concentration dataset during 1995-2022. Firstly, it compiles a long-term time series marine-scale dataset of seafood MeHg concentrations, based on the reported seafood mercury concentrations from existing literature and machine learning methods. Subsequently, this study used the seafood catch volumes of each nation in different marine areas as weights to estimate the national-scale seafood MeHg concentrations. This dataset can provide essential data support for environmental impact assessment of mercury and its compounds as mentioned in Articles 12 and 19 of the Minamata Convention on Mercury.
... Yet there are many more studies of fishing impacts to be explored from purely theoretical to regionally specific approaches. FEISTY can also be applied to assess the consequences of other anthropogenic actions on the marine environment, such as the bioaccumulation and biomagnification of persistent organic pollutants in marine food webs (Wu & Zhang, 2023). Implementing the fully two-way coupling would allow for examinations of the role of the fish community on nutrient cycling and the biological carbon pump (Dupont et al., 2023;Pinti et al., 2023), both directly via exudation and indirectly through predation on mesozooplankton. ...
The FishErIes Size and functional TYpe model (FEISTY) is a mechanistic ecosystem model that fully integrates ecosystem structure across trophic levels through functional types.
We present an R package that enables users to run simulations ranging from a 0D chemostat to full global scales. The library is written in Fortran90 with an R interface and provides a web application for visual exploration.
We present and compare results from four core configurations across a range of depths, productivity and fishing levels, and we assess the convergence of solutions as the number of size classes is increased.
The model has historically been coupled to biogeochemical models of mesozooplankton and detritus production, but it can also be applied in a stand‐alone version. We demonstrate the library to set up and simulate fish communities under varying productivity of mesozooplankton and benthos, and top‐down forcing from fishing.
We outline three strategies for coupling FEISTY with biogeochemical model output and discuss future directions and open issues.
... Targeted fishing of large pelagic species and higher bioavailability of Hg at the base of the food webs results in the dominance of the tropics and subtropics as source regions for MeHg in global commercial seafood markets ( 24 ). Recent literature has noted that oligotrophic food webs tend to have more TLs and thus can exhibit the highest concentrations of MeHg in species from these regions ( 25 ). However, low productivity in the oligotrophic ocean and resulting low catch biomass means their contributions to the total MeHg fished from the ocean for the commercial seafood market is also low. ...
Global pollution has exacerbated accumulation of toxicants like methylmercury (MeHg) in seafood. Human exposure to MeHg has been associated with long-term neurodevelopmental delays and impaired cardiovascular health, while many micronutrients in seafood are beneficial to health. The largest MeHg exposure source for many general populations originates from marine fish that are harvested from the global ocean and sold in the commercial seafood market. Here, we use high-resolution catch data for global fisheries and an empirically constrained spatial model for seafood MeHg to examine the spatial origins and magnitudes of MeHg extracted from the ocean. Results suggest that tropical and subtropical fisheries account for >70% of the MeHg extracted from the ocean because they are the major fishing grounds for large pelagic fishes and the natural biogeochemistry in this region facilitates seawater MeHg production. Compounding this issue, micronutrients (selenium and omega-3 fatty acids) are lowest in seafood harvested from warm, low-latitude regions and may be further depleted by future ocean warming. Our results imply that extensive harvests of large pelagic species by industrial fisheries, particularly in the tropics, drive global public health concerns related to MeHg exposure. We estimate that 84 to 99% of subsistence fishing entities globally likely exceed MeHg exposure thresholds based on typical rates of subsistence fish consumption. Results highlight the need for both stringent controls on global pollution and better accounting for human nutrition in fishing choices.
... Numerous studies have established a link between fish consumption and mercury exposure. 5,6 This is a significant public health concern as methyl mercury can pass through the placental barrier and affect the developing fetus, leading to neurotoxic and developmental abnormalities. 7 Several large epidemiology studies have reported an inverse dose-response relationship between children's neurobehavioral performance and maternal consumption of methylmercurycontaminated seafood during pregnancy. ...
Background: Mercury pollution from industries poses health risks through bioaccumulation in fish. Women in coastal communities with high fish intakes are particularly vulnerable. However, methylmercury (MeHg) exposure has not been quantified in Pakistan. Objective: To estimate MeHg levels in the scalp hair of women from a coastal community in Sindh province and examine the relationship with fish consumption and other risk factors. Methods: A cross-sectional study was conducted among 100 women aged 15–49 years in Rehri Goth, Sindh. Detailed dietary histories were obtained through interviews. Scalp hair samples were analysed for total mercury using cold-vapour Vapor Atomic Absorption Spectrophotometry. Results: The median hair MeHg level was 7.15 μg/g, exceeding international guidelines. Higher levels were associated with fish from polluted waters (3.5 μg/g), skin whitening product use (6.5 μg/g), and traditional medicine intake (9.0 μg/g). A weak positive correlation was found between MeHg and age. Fish consumption averaged 4 times/week. Conclusion: Women in coastal Sindh have high MeHg exposure from frequent fish intake, likely exacerbated by industrial pollution. Risk mitigation is needed to protect vulnerable populations, especially during critical windows of neurodevelopment.
... Mercury is considered to be one of the top ten chemicals of major public health concerns by the World Health Organization (WHO, 2021). In fish and seafood, Hg is principally found as methylmercury (MeHg) (Lavoie et al., 2013;Wu & Zhang, 2023). MeHg levels are biomagnified through the trophic chain, resulting in serious social, environmental, and human health effects. ...
This paper reports the first record of total mercury (THg) concentrations in albacore (Thunnus alalunga), one of the main tuna species caught from the Western Equatorial Atlantic Ocean and presents a preliminary comparison with other regions and tuna species. Mean, standard deviation and range of concentrations in T. alalunga (515 ± 145 ng g− 1 ww; 294–930 ng g− 1 ww) with 92 % being of methyl-Hg, are higher than in albacore from other Atlantic Ocean subregions despite their smaller body size. These concentrations are similar to those from the Pacific and Indian oceans, but lower than in the Mediterranean. Compared to other sympatric tuna species, concentrations are higher than those in T. albacares and similar to T. obesus. These results are discussed considering the potential differences in stable isotope values (13C and 15N) of T. alalunga populations from multiple oceanic areas and compared to other tuna species worldwide.
This study presents a 35-year record of total mercury (Hg) concentrations in the detritivore fish Prochilodus nigricans (Curimatã) and the carnivore Cichla pleiozona (Tucunaré), two of the most widely distributed, ecologically important and consumed fish species in the upper Madeira River Basin in the Western Brazilian Amazon. Fish samples from the major Madeira River and marginal lakes and tributaries were compared. Irrespective of site, Hg concentrations were higher in the carnivore fish compared to the detritivore. Hg concentrations increased 5-fold in C. pleiozona in the past three decades, whereas they remained relatively constant in P. nigricans when analyzing the entire 35-year period. When analyzed separately, fish in the main river and marginal lake and tributaries presented the same pattern of Hg variation, with a significant increase in Hg concentrations in the carnivore and in the detritivore in marginal lakes and tributaries but not in the main river. This was in line with the increase in methyl-Hg production in tributaries, mostly associated with deforestation in the past decade in the basin. Although an increase in direct emissions from artisanal gold mining also occurred in the past decade, this caused virtually no impact on fish Hg concentrations, suggesting atmospheric emission and deposition in forests and further export to water systems as an intermediate link with fish Hg concentrations.
In the important coastal fishery for Atlantic cod in Norway quality-based pricing is largely absent. Thus, driven by a focus on fish quantity, not quality, a high share of downgraded fish is landed. This study identified some encouraging exceptions with actors trying to align incentives and increase revenues in both fishing and processing. More specifically, we examine two cases involving quality-enhancing fishing and find indications of substantial improvements in fish quality and importantly, that this is rewarded with higher prices. In a revenue-sharing arrangement with a focus on high quality fish delivered outside of the main season, fishers obtain approximately 50 % higher prices than comparable vessels fishing with the same gear in the same period. In the other case, fishers' "skip" the Norwegian ex-vessel market and sell their high-quality cod catches at Danish auctions at significantly higher prices than comparable vessels fishing in the same area and delivering in South Norway. The cases may guide fishers and fish buyers in increasing revenues through quality-enhancing fishing but also involve important dilemmas for policymakers which are highlighted and discussed.
High levels of methylmercury (MeHg) have been reported in Arctic marine biota, posing health risks to wildlife and human beings. Although MeHg concentrations of some Arctic species have been monitored for decades, the key environmental and ecological factors driving temporal trends of MeHg are largely unclear. We develop an ecosystem-based MeHg bioaccumulation model for the Beaufort Sea shelf (BSS) using the Ecotracer module of Ecopath with Ecosim, and apply the model to explore how MeHg toxicokinetics and food web trophodynamics affect bioaccumulation in the BSS food web. We show that a food web model with complex trophodynamics and relatively simple MeHg model parametrization can capture the observed biomagnification pattern of the BSS. While both benthic and pelagic production are important for transferring MeHg to fish and marine mammals, simulations suggest that benthic organisms are primarily responsible for driving the high trophic magnification factor in the BSS. We illustrate ways of combining empirical observations and modelling experiments to generate hypotheses about factors affecting food web bioaccumulation, including the MeHg elimination rate, trophodynamics, and species migration behavior. The results indicate that population dynamics rather than MeHg elimination may determine population-wide concentrations for fish and lower trophic level organisms, and cause large differences in concentrations between species at similar trophic levels. This research presents a new tool and lays the groundwork for future research to assess the pathways of global environmental changes in MeHg bioaccumulation in Arctic ecosystems in the past and the future.
Significance
Bluefin tuna (BFT) is an apex predatory, long-lived, migratory pelagic fish that is widely distributed throughout the world's oceans. These fish have very high concentrations of neurotoxic methylmercury (MeHg) in their tissues, which increase with age. Our study shows that Hg accumulation rates (MARs) in BFT as a global pollution index can reveal global patterns of Hg pollution and bioavailability in the oceans and further reflect both natural and anthropogenic emissions and regional environmental features. Overall, MARs provide a means to compare Hg bioavailability among geographically distinct populations of upper trophic level marine fish across ocean subbasins, to investigate trophic dynamics of Hg in marine food webs, and furthermore, to improve public health risk assessments of Hg exposure from seafood.
Mercury is a potent neurotoxic substance and accounts for 250,000 intellectual disabilities annually. Worldwide, coastal fisheries contribute the majority of human exposure to mercury through fish consumption. Recent global mercury cycling and risk models attribute all the mercury loading to the ocean to atmospheric deposition. Nevertheless, new regional research has noted that the riverine mercury export to coastal oceans may also be significant to the oceanic burden of mercury. Here we construct an unprecedented high-spatial-resolution dataset estimating global river mercury and methylmercury exports. We find that rivers annually deliver 1,000 (minimum–maximum: 893–1,224) Mg mercury to coastal oceans, threefold greater than atmospheric deposition. Furthermore, high flow events, which are becoming more common with climate change, are responsible for a disproportionately large percentage of the export. Coastal oceans constitute 0.2% of the entire ocean volume but receive 27% of the external mercury input to the ocean. We estimate that the river mercury export could be responsible for a net annual export of 350 (interquartile range: 52–640) Mg mercury across the coastal–open-ocean boundary, although there is still high uncertainty around this estimate. Our results show that river export is the largest source of mercury to coastal oceans worldwide, and continued mercury risk modelling should incorporate the impact of rivers.
Aim
Understanding how fish food webs emerge from planktonic and benthic energy pathways that sustain them is an important challenge for predicting fisheries production under climate change and quantifying the role of fish in carbon and nutrient cycling. We examine if a trait‐based fish community model using the fish traits of maximum body weight and vertical habitat strategy can meet this challenge by globally representing fish food web diversity.
Location
Global oceans.
Time period
Predictions are representative of the early 1990s.
Major taxa studied
Marine teleost fish.
Methods
We present a size‐ and trait‐based fish community model that explicitly resolves the dependence of fish on pelagic and benthic energy pathways to globally predict fish food web biogeography. The emergent food web structures are compared with regionally calibrated models in three different ecosystem types and used to estimate two fish ecosystem functions: potential fisheries production and benthic–pelagic coupling.
Results
Variations in pelagic–benthic energy pathways and seafloor depth drive the emergent biogeography of fish food webs from shelf systems to the open ocean, and across the global ocean. Most shelf regions have high benthic production, which favours demersal fish that feed on pelagic and benthic pathways. Continental slopes also show a coupling of benthic and pelagic pathways, sustained through vertically migrating and interacting mesopelagic and deep‐sea demersal fish. Open ocean fish communities are primarily structured around the pelagic pathway. Global model results compare favourably with data‐driven regional food web models, suggesting that maximum weight and vertical behaviour can capture large‐scale variations in food web structure.
Main conclusions
Mechanistically linking ocean productivity with upper trophic levels using a size‐ and trait‐based fish community model results in spatial variations in food web structure. Energy pathways vary with ocean productivity and seabed depth, thereby shaping the dominant traits and fish communities across ocean biomes.
Mercury is a potent neurotoxin that poses health risks to the global population. Anthropogenic mercury emissions to the atmosphere are projected to decrease in the future due to enhanced policy efforts such as the Minamata Convention, a legally-binding international treaty entered into force in 2017. Here, we report the development of a comprehensive climate-atmosphere-land-ocean-ecosystem and exposure-risk model framework for mercury and its application to project the health effects of future atmospheric emissions. Our results show that the accumulated health effects associated with mercury exposure during 2010–2050 are $19 (95% confidence interval: 4.7–54) trillion (2020 USD) realized to 2050 (3% discount rate) for the current policy scenario. Our results suggest a substantial increase in global human health cost if emission reduction actions are delayed. This comprehensive modeling approach provides a much-needed tool to help parties to evaluate the effectiveness of Hg emission controls as required by the Minamata Convention. Mercury is a neurotoxin and pollutant with enhanced emissions from anthropogenic activities. Here, the authors develop a global emissions, transport, and human risk model and find substantial future losses in revenue and public health if emission reductions proposed by the Minamata Convention are delayed.
Monomethylmercury (CH3Hg) is the only form of mercury (Hg) known to biomagnify in food webs. Here we investigate factors driving methylated mercury [MeHg = CH3Hg + (CH3)2Hg)] production and degradation across the global ocean and uptake and trophic transfer at the base of marine food webs. We develop a new global 3‐D simulation of MeHg in seawater and phyto/zooplankton within the Massachusetts Institute of Technology general circulation model. We find that high modeled MeHg concentrations in polar regions are driven by reduced demethylation due to lower solar radiation and colder temperatures. In the eastern tropical subsurface waters of the Atlantic and Pacific Oceans, the model results suggest that high MeHg concentrations are associated with enhanced microbial activity and atmospheric inputs of inorganic Hg. Global budget analysis indicates that upward advection/diffusion from subsurface ocean provides 17% of MeHg in the surface ocean. Modeled open ocean phytoplankton concentrations are relatively uniform because lowest modeled seawater MeHg concentrations occur in oligotrophic regions with the smallest size classes of phytoplankton, with relatively high uptake of MeHg and vice versa. Diatoms and synechococcus are the two most important phytoplankton categories for transferring MeHg from seawater to herbivorous zooplankton, contributing 35% and 25%, respectively. Modeled ratios of MeHg concentrations between herbivorous zooplankton and phytoplankton are 0.74–0.78 for picoplankton (i.e., no biomagnification) and 2.6–4.5 for eukaryotic phytoplankton. The spatial distribution of the trophic magnification factor is largely determined by the zooplankton concentrations. Changing ocean biogeochemistry resulting from climate change is expected to have a significant impact on marine MeHg formation and bioaccumulation.
More than three billion people rely on seafood for nutrition. However, fish are the predominant source of human exposure to methylmercury (MeHg), a potent neurotoxic substance. In the United States, 82% of population-wide exposure to MeHg is from the consumption of marine seafood and almost 40% is from fresh and canned tuna alone¹. Around 80% of the inorganic mercury (Hg) that is emitted to the atmosphere from natural and human sources is deposited in the ocean², where some is converted by microorganisms to MeHg. In predatory fish, environmental MeHg concentrations are amplified by a million times or more. Human exposure to MeHg has been associated with long-term neurocognitive deficits in children that persist into adulthood, with global costs to society that exceed US$20 billion³. The first global treaty on reductions in anthropogenic Hg emissions (the Minamata Convention on Mercury) entered into force in 2017. However, effects of ongoing changes in marine ecosystems on bioaccumulation of MeHg in marine predators that are frequently consumed by humans (for example, tuna, cod and swordfish) have not been considered when setting global policy targets. Here we use more than 30 years of data and ecosystem modelling to show that MeHg concentrations in Atlantic cod (Gadus morhua) increased by up to 23% between the 1970s and 2000s as a result of dietary shifts initiated by overfishing. Our model also predicts an estimated 56% increase in tissue MeHg concentrations in Atlantic bluefin tuna (Thunnus thynnus) due to increases in seawater temperature between a low point in 1969 and recent peak levels—which is consistent with 2017 observations. This estimated increase in tissue MeHg exceeds the modelled 22% reduction that was achieved in the late 1990s and 2000s as a result of decreased seawater MeHg concentrations. The recently reported plateau in global anthropogenic Hg emissions⁴ suggests that ocean warming and fisheries management programmes will be major drivers of future MeHg concentrations in marine predators.
The main chemical forms of mercury are elemental mercury, inorganic divalent mercury, and methylmercury, which are metabolized in different ways and have differing toxic effects in humans. Among the various chemical forms of mercury, methylmercury is known to be particularly neurotoxic, and was identified as the cause of Minamata disease. It bioaccumulates in fish and shellfish via aquatic food webs, and fish and sea mammals at high trophic levels exhibit high mercury concentrations. Most human methylmercury exposure occurs through seafood consumption. Methylmercury easily penetrates the blood-brain barrier and so can affect the nervous system. Fetuses are known to be at particularly high risk of methylmercury exposure. In this review, we summarize the health effects and exposure assessment of methylmercury as follows: (1) methylmercury toxicity, (2) history and background of Minamata disease, (3) methylmercury pollution in the Minamata area according to analyses of preserved umbilical cords, (4) changes in the sex ratio in Minamata area, (5) neuropathology in fetuses, (6) kinetics of methylmercury in fetuses, (7) exposure assessment in fetuses.
Human activities have increased the global circulation of mercury, a potent neurotoxin. Mercury can be converted into methylmercury, which biomagnifies along aquatic food chains and leads to high exposure in fish-eating populations. Here we quantify temporal trends in the ocean-to-land transport of total mercury and methylmercury from fisheries and we estimate potential human mercury intake through fish consumption in 175 countries. Mercury export from the ocean increased over time as a function of fishing pressure, especially on upper-trophic-level organisms. In 2014, over 13 metric tonnes of mercury were exported from the ocean. Asian countries were important contributors of mercury export in the last decades and the western Pacific Ocean was identified as the main source. Estimates of per capita mercury exposure through fish consumption showed that populations in 38% of the 175 countries assessed, mainly insular and developing nations, were exposed to doses of methylmercury above governmental thresholds. Our study shows temporal trends and spatial patterns of Hg transport by fisheries. Given the high mercury intake through seafood consumption observed in several understudied yet vulnerable coastal communities, we recommend a comprehensive assessment of the health exposure risk of those populations.
[This corrects the article DOI: https://doi.org/10.1289/EHP2644.].
Global fisheries landings data from a range of public sources was harmonised and mapped to 30-min spatial cells based on the distribution of the reported taxa and the fishing fleets involved. This data was extended to include the associated fishing gear used, as well as estimates of illegal, unregulated and unreported catch (IUU) and discards at sea. Expressed as catch rates, these results also separated small-scale fisheries from other fishing operations. The dataset covers 1950 to 2014 inclusive. Mapped catch allows study of the impacts of fisheries on habitats and fauna, on overlap with the diets of marine birds and mammals, and on the related use of fuels and release of greenhouse gases. The fine-scale spatial data can be aggregated to the exclusive economic zone claims of countries and will allow study of the value of landed marine products to their economies and food security, and to those of their trading partners.
Average total Hg concentrations measured in muscle of two species of tuna (Thunnus obesus and T. albacares) captured in the Brazilian Equatorial Atlantic Ocean varied from 95 to 1748 ng.g⁻¹ wet weight in T. obesus and 48 to 500 ng.g⁻¹ wet weight in T. albacares. Higher concentrations in T. obesus are probably related to foraging on deep water carnivorous fish. Smaller individuals of both species showed the lowest concentrations, but a significant positive relationship between fish weight and length and Hg concentrations was found for T. obesus, but not for T. albacares. Largest individuals (>30 kg) of T. obesus showed Hg concentrations ≥1000 ng.g⁻¹, surpassing the legal limits for human consumption, although the average concentration for this species was much lower (545 ng.g⁻¹). Concentrations in T. albacares from the Brazilian Equatorial were lower than those found in the African and in the North Atlantic. No comparison could be made for T. obesus due to few studies for this species in the Atlantic Ocean.
Mercury contamination in water has been an issue to the environment and human health. In this article, mercury in marine and oceanic waters has been reviewed. In the aquatic environment, mercury occurs in many forms, which depend on the oxidation-reduction conditions. These forms have been briefly described in this article. Mercury concentrations in marine waters in the different parts of the world have been presented. In the relevant literature, two models describing the fate and behavior of mercury in saltwater reservoirs have been presented, a conceptual model which treats all the oceans as one ocean and the “ocean margin” model, providing that the ocean margins manifested themselves as the convergence of continents and oceans, covering such geological features, such as estuaries, inland seas, and the continental shelf. These two conceptual models have been summarized in the text. The mercury content in benthic sediments usually reflects is level in the water reservoir, particularly in reservoirs situated in contaminated areas (mines, metallurgical plants, chemically protected crops). The concentrations of mercury and its compounds determined in the sediments in surface waters in the different parts of the world have been presented. Due to the fact that the pollution caused by mercury is a serious threat for the marine environment, the short paragraph about mercury bioaccumulation in aquatic organisms has been included. The cited data demonstrated a large scatter of mercury contents both between the fish species and the water areas. Mathematical models, valuable tools which provide information about the possible responses of ecosystems, developed to simulate mercury emissions, both at a small scale, for local water reservoirs, and at a global scale, as well as to model mercury bioaccumulation in the chain web of aquatic systems have been described.
Ecosystems exhibit surprising regularities in structure and function across terrestrial and aquatic biomes worldwide. We assembled a global data set for 2260 communities of large mammals, invertebrates, plants, and plankton. We find that predator and prey biomass follow a general scaling law with exponents consistently near 3⁄4. This pervasive pattern implies that the structure of the biomass pyramid becomes increasingly bottom-heavy at higher biomass. Similar exponents are obtained for community production-biomass relations, suggesting conserved links between ecosystem structure and function. These exponents are similar to many body mass allometries, and yet ecosystem scaling emerges independently from individual-level scaling, which is not
fully understood. These patterns suggest a greater degree of ecosystem-level organization than previously recognized and a more predictive approach to ecological theory.
The shape of the productivity-diversity relationship (PDR) for marine phytoplankton has been suggested to be unimodal, that is, diversity peaking at intermediate levels of productivity. However, there are few observations and there has been little attempt to understand the mechanisms that would lead to such a shape for planktonic organisms. Here we use a marine ecosystem model together with the community assembly theory to explain the shape of the unimodal PDR we obtain at the global scale. The positive slope from low to intermediate productivity is due to grazer control with selective feeding, which leads to the predator-mediated coexistence of prey. The negative slope at high productivity is due to seasonal blooms of opportunist species that occur before they are regulated by grazers. The negative side is only unveiled when the temporal scale of the observation captures the transient dynamics, which are especially relevant at highly seasonal latitudes. Thus selective predation explains the positive side while transient competitive exclusion explains the negative side of the unimodal PDR curve. The phytoplankton community composition of the positive and negative sides is mostly dominated by slow-growing nutrient specialists and fast-growing nutrient opportunist species, respectively.
The effects of human exposure to mercury (Hg) and its compounds in Europe have been the focus of numerous studies that differed in their design, including recruiting different population groups at different levels of exposure and by using different protocols and recruitment strategies. The objective of this work was to review current studies of Hg exposure in Europe, taking into account the potential routes of Hg exposure, actual Hg exposure levels assessed by different biomarkers and the effects of Hg to Europeans. All published studies from 2000 onwards were reviewed and exposure and effects studies were compared to known Hg levels in environmental compartments by mapping the various population groups studied and taking into account known sources of Hg. A study of the spatial distribution trends confirmed that the highest exposure levels to Hg, mostly as methyl mercury (MeHg), are found in coastal populations who consume more fish in their diet compared to inland populations. Fewer studies addressed exposure to elemental Hg through inhalation of Hg in air and inorganic Hg in food, particularly in highly contaminated areas. Overall, at the currently low exposure levels of Hg prevalently found in Europe, further studies are needed to confirm the risk to European populations taking into consideration exposure to various Hg compounds and mixtures of stressors with similar end-points, nutritional status, as well as a detailed understanding of Hg in fish present on European markets. Environ Toxicol Chem © 2013 SETAC.
The slope of the simple linear regression between Log10 transformed mercury (Hg) concentration and stable nitrogen isotope values (δ(15)N), hereafter called trophic magnification slope (TMS), from several trophic levels in a food web can represent the overall degree of Hg biomagnification. We compiled data from 69 studies that determined total Hg (THg) or methyl Hg (MeHg) TMS values in 205 aquatic food webs worldwide. Hg TMS values were compared against physico-chemical and biological factors hypothesized to affect Hg biomagnification in aquatic systems. Food webs were comprised of 1.7 ± 0.7 (mean ± SD) and 1.8 ± 0.8 trophic levels (calculated using δ(15)N from baseline to top predator) for THg and MeHg, respectively. The average trophic level (based on δ(15)N) of the upper-trophic-level organisms in the food web was 3.7 ± 0.8 and 3.8 ± 0.8 for THg and MeHg food webs, respectively. For MeHg, the mean TMS value was 0.24 ± 0.08 but varied from 0.08 to 0.53 and was, on average, 1.5 times higher than that for THg with a mean of 0.16 ± 0.11 (range: -0.19 to 0.48). Both THg and MeHg TMS values were significantly and positively correlated with latitude. TMS values in freshwater sites increased with dissolved organic carbon and decreased with total phosphorus and atmospheric Hg deposition. Results suggest that Hg biomagnification through food webs is highest in cold and low productivity systems; however, much of the among-system variability in TMS values remains unexplained. We identify critical data gaps and provide recommendations for future studies that would improve our understanding of global Hg biomagnification.
Concentrations of total mercury (T-Hg) and methylmercury (MeHg) were measured in zooplankton and 13 fish species from a coastal food web of the Gulf of Oman, an arm of the Arabian Sea between Oman and Iran. Stable isotope ratios (δ13C and δ15N) also were determined to track mercury biomagnification. The average concentration of T-Hg in zooplankton was 21 ± 8.0 ng g−1 with MeHg accounting 10% of T-Hg. Total mercury levels in fish species ranged from 3.0 ng g−1 (Sardinella longiceps) to 760 ng g−1 (Rhizoprionodon acutus) with relatively lower fraction of MeHg (72%) than that found in other studies. The average trophic difference (△13C) between zooplankton and planktivorous fish (Selar crumenopthalmus, Rastrelliger kanagurta, and S. longiceps) was higher (3.4%0) than expected, suggesting that zooplankton may not be the main diet or direct carbon source for these fish species. However, further sampling would be required to compensate for temporal changes in zooplankton and the influence of their lipid content. Trophic position inferred by δ15N and and slopes of the regression equations (log10[T-Hg] = 0.13[δ15N] — 3.57 and log10[MeHg] = 0.14[δ15N] — 3.90) as estimates of biomagnification indicate that biomagnification of T-Hg and MeHg was lower in this tropical ocean compared to what has been observed in arctic and temperate ecosystems and tropical African lakes. The calculated daily intake of methylmercury in the diet of local people through fish consumption was well below the established World Health Organization (WHO) tolerable daily intake threshold for most of the fish species except Euthynnus affinis, Epinephelus epistictus, R. acutus, and Thunnus tonggol, illustrating safe consumption of the commonly consumed fish species.
Our review of the literature showed that since the beginning of the socio-economic transformation in Poland in the 1990s, the downward trend in Hg emissions and its deposition in the southern Baltic Sea was followed by a simultaneous decrease in Hg levels in water and marine plants and animals. Hg concentrations in the biota lowered to values that pose no or low risk to wildlife and seafood consumers. However, in the first decade of the current century, a divergence between these two trends became apparent and Hg concentrations in fish, herring and cod, began to rise. Therefore, increasing emission-independent anthropogenic pressures, which affect Hg uptake and trophodynamics, remobilization of land-based and marine legacy Hg deposits, as well as the structure of the food web, can undermine the chances of reducing both the Hg pool in the marine environment and human Hg exposure from fish.
Fish consumption is the primary dietary route of human exposure to methylmercury. It has been well documented that elevated mercury concentration in fish in North America and Europe is linked to anthropogenic mercury emissions. China is the world’s largest producer, consumer, and emitter of mercury, as well as the world’s largest commercial fish producer and consumer. Although mercury pollution in fish in China is currently receiving much attention worldwide, its status remains largely unknown. Here, we conducted a meta-analysis on total mercury concentrations in marine and freshwater fish samples, covering 35,464 samples collected in China over the past 30 years. It is found that, opposite to the increasing emission and documented mercury contamination events, mercury levels in fish have gradually decreased in China over the past 30 years. The results were in sharp contrast to those found in North America and Europe. The mercury concentrations in fish were significantly anticorrelated with the fish catch, fish aquaculture, and were inverse to trophic levels. Overfishing and the short lifecycle of aquaculture fish, both reducing the trophic level and the duration of mercury accumulation, were the most likely causes leading to the decline of mercury concentrations found in fish in China.
Despite their remoteness, deep-sea species bioaccumulate mercury, mostly in the form of the neurotoxin methylmercury (MeHg). Although the concentration of MeHg in the water column is known to increase with depth down to a maximum found at the base of the permanent thermocline, the knowledge of the relationship between MeHg content in marine species and their depth of occurrence is limited. We analyzed total mercury (THg) and MeHg concentrations in 25 species of fish inhabiting the Avilés Submarine Canyon and its adjacent shelf (Cantabrian Sea, North-East Atlantic) between 50 and 1868 m depth. THg concentrations ranged from 0.03 μg g⁻¹ in wet weight (ww) in Chauliodus sloani and 4.0 μg g⁻¹ ww in Coryphaenoides guentheri. 65% of the species analyzed exceeded 0.5 μg g⁻¹ ww of MeHg, the maximum level for safe consumption recommended by FAO/WHO. THg and MeHg contents in muscle tissue increased with the depth of occurrence of fish and was influenced by their habitat so that demersal species had higher THg content than pelagic species inhabiting the same depth. MeHg accounted for an average 76 ± 3.9% of THg (mean ± SD), which is lower than that reported for other fish communities and can be explained by the high concentration of Hg present in sediments of the Nalón estuary, which discharges right off the Avilés Canyon head. The % of THg as MeHg was also strongly correlated with δ¹⁵N values, confirming that MeHg can be an indicator of the trophic identity of a species within the food web.
Mercury (Hg) is a well-known toxicant which enters the marine environment by both natural and anthropogenic sources. Consumption of fish and other seafood that contain methylmercury (MeHg) is a leading source of Hg exposure in humans. Considerable efforts have been made to mitigate the Hg presence and reduce its risks to humans. In this review the acknowledged methods of mitigation are summarized such as regulation and maximum allowable limits, and culinary treatments. In addition, selected industrial level trials are reviewed, and studies on Hg intoxication and the protective effects of the essential trace element, selenium (Se), are discussed. In view of the available literature, Hg reduction in fish and other seafood on a large industrial scale still is largely unsuccessful. Hence, more research and further attempts are necessary in order to better mitigate the Hg problem in fish and other seafood products.
Climate change-driven alterations to marine biogeochemistry will impact the formation and trophic transfer of the bioaccumulative neurotoxin methylmercury (MeHg) in the global ocean. We use a 3D model to examine how MeHg might respond to changes in primary production and plankton community driven by ocean acidification and alterations in physical factors (e.g., ocean temperature, circulation). Productivity changes lead to significant increases in seawater MeHg in the polar oceans and a decrease in the North Atlantic Ocean. Phytoplankton MeHg may increase at high latitudes and decrease in lower latitudes due to shifts in community structure. Ocean acidification might enhance phytoplankton MeHg uptake by promoting the growth of a small species that efficiently accumulate MeHg. Non-linearities in the food web structure lead to differing magnitudes of zooplankton MeHg changes relative to those for phytoplankton. Climate-driven shifts in marine biogeochemistry thus need to be considered when evaluating future trajectories in biological MeHg concentrations.
Data concerning the monomethylmercury (MeHg) bioaccumulation in marine biota from Southeast Atlantic Ocean are scarce. This study purchased large specimens of demersal fishes from an upwelling region: Warsaw grouper (Epinephelus nigritus), Dusky grouper (Epinephelus marginatus) and Namorado sandperch (Pseudopercis numida). The authors addressed the bioaccumulation and toxicokinetic of mercury in fish organs, and the toxicological risk for human consumption of this metal in the muscle tissues accessed. Additionally, the present study discussed the possible implications of shifts in key variables of the environment related to a climate-changing predicted scenario, to the mercury biomagnification in a tropical upwelling system. The muscle was the main stock of MeHg, although the highest THg concentrations have been found in liver tissue. Regarding the acceptable maximum level (ML = 1 mg kg⁻¹), E. nigritus and E. marginatus showed 22% of the samples above this limit. Concerning P. numida, 77% were above 0.5 mg kg⁻¹, but below the ML. The %MeHg in liver and muscle showed no significative correlations, which suggest independent biochemical pathways to the toxicokinetic of MeHg, and constrains the indirect assessment of the mercury contamination in the edible tissue by the liver analyses. The present study highlights the food web features of a tropical upwelling ecosystem that promote mercury biomagnification. Additionally, recent studies endorse the enhancement of upwelling phenomenon due to the climate global changes which boost the pumping of mercury enriched water to the oceanic upper layer. Therefore, the upwelling areas might be hot spots for MeHg monitoring in marine biota.
Diet, age, and growth rate influences on fish mercury concentrations were investigated for Arctic char (Salvelinus alpinus) and brook trout (Salvelinus fontinalis) in lakes of the eastern Canadian Arctic. We hypothesized that faster-growing fish have lower mercury concentrations because of growth dilution, a process whereby more efficient growth dilutes a fish’s mercury burden. Using datasets of 57 brook trout and 133 Arctic char, linear regression modelling showed fish age and diet indices were the dominant explanatory variables of muscle mercury concentrations for both species. Faster-growing fish (based on length-at-age) fed at a higher trophic position, and as a result, their mercury concentrations were not lower than slower-growing fish. Muscle RNA/DNA ratios were used as a physiological indicator of short-term growth rate (days to weeks). Slower growth of Arctic char, inferred from RNA/DNA ratios, was found in winter versus summer and in polar desert versus tundra lakes, but RNA/DNA ratio was (at best) a weak predictor of fish mercury concentration. Net effects of diet and age on mercury concentration were greater than any potential offset by biomass dilution in faster-growing fish. In these resource-poor Arctic lakes, faster growth was associated with feeding at a higher trophic position, likely due to greater caloric (and mercury) intake, rather than growth efficiency.
Due to growing commercial interest as a fishing resource and its intermediate position in the marine trophic chains as both prey and predator, cephalopods can play an important role in mercury (Hg) transfer along the marine food webs, since they can bioaccumulate this metal in its tissues.
Our study aims to analyze Hg accumulation in Loligo forbesi caught in the Azores Archipelago (Portugal) quantifying Hg in different tissues (mantle and stomach), as well in the squid stomach content, in order to evaluate the efficiency of Hg transfer from prey to predator. Hg data from the tissues was used to estimate the weekly tolerable Hg intake due to squid consumption.
Overall data indicate that Hg measured in the stomach tissue (0.1 ± 0.01 μg g⁻¹) was significantly higher than Hg levels found in the mantle (0.04 ± 0.001 μg g⁻¹) and stomach contents (0.01 ± 0.001 μg g⁻¹). BMF (bioaccumulation factor) was >1 for all the samples, indicating a biomagnification process from prey to predator. Hg concentration in the mantle tissue was correlated with mantle size; although females present higher Hg levels than males, the difference was found to be not related to gender but rather to the fact that females had larger bodies.
Finally, considering the Hg concentration found in the mantle and the permitted Hg levels, it is advisable to consume up to 1050–1890g of squid per week, according to the regulatory agencies. Thus, our results indicate that, since these doses are respected, consumption of squids from the Azorean waters do not pose a risk to humans.
Methylmercury is greatly bioconcentrated and biomagnified in marine plankton ecosystems, and these communities form the basis of marine food webs. Therefore, evaluating the potential exposure of methylmercury to higher trophic levels, including humans, requires a better understanding of its distribution in the ocean and the factors that control its biomagnification. In this study, a coupled physical/ecological model is used to simulate the trophic transfer of monomethylmercury (MMHg) in a marine plankton ecosystem. The model includes phytoplankton, a microbial community, herbivorous zooplankton (HZ), and carnivorous zooplankton (CZ). The model captures both shorter food chains in oligotrophic regions, with small HZ feeding on small phytoplankton, and longer chains in higher nutrient conditions, with larger HZ feeding on larger phytoplankton and larger CZ feeding on larger HZ. In the model, trophic dilution occurs in the food webs that involve small zooplankton, as the grazing fluxes of small zooplankton are insufficient to accumulate more MMHg in themselves than in their prey. The model suggests that biomagnification is more prominent in large zooplankton and that the microbial community plays an important role in the trophic transfer of MMHg. Sensitivity analyses show that with increasing body size, the sensitivity of the trophic magnification ratio to grazing, mortality rates, and food assimilation efficiency (AEC) increases, while the sensitivity to excretion rates decreases. More predation or a longer zooplankton lifespan may lead to more prominent biomagnification, especially for large species. Because lower AEC results in more predation, modeled ratios of MMHg concentrations between large plankton are doubled or even tripled when the AEC decreases from 50% to 10%. This suggests that the biomagnification of large zooplankton is particularly sensitive to food assimilation efficiency.
Marine animals often accumulate various harmful substances through the foods they ingest. The bioaccumulation levels of these harmful substances are affected by the degrees of pollution in the food and of biomagnification; however, which of these sources is more important is not well-investigated for mercury (Hg) bioaccumulation. Here we addressed this issue in fishes that inhabit the waters around Minamata Bay, located off the west coast of Kyushu Island in Kumamoto Prefecture, Japan. The total Hg concentration (hereafter [THg]) and carbon and nitrogen stable isotope ratios (δ¹³C and δ¹⁵N) were analyzed in the muscle tissue of 10 fish species, of which more than five individuals were caught by gillnet. Except one species, each was separated into two trophic groups with respective lower and higher δ¹³C values ranging from −17‰ to −16‰ and −15‰ to −14‰, which suggested that the fishes depended more on either phytoplankton- and microphytobenthos-derived foods (i.e., pelagic and benthic trophic pathways), respectively. Linear mixed effects models showed that the Hg levels were significantly associated with both δ¹⁵N and the differences in the trophic groups. [THg] increased with δ¹⁵N (i.e., indicative of higher trophic levels), but the slopes did not differ between the two trophic groups. [THg] was significantly higher in the group with higher δ¹³C values than in those with lower δ¹³C values. The effect size from marginal R squared (R²) values showed that the variation in [THg] was strongly ascribed to the trophic group difference rather than δ¹⁵N. These results suggest that the substantial Hg bioaccumulation in the fishes of Minamata Bay is mainly an effect of ingesting the microphytobenthos-derived foods that contain Hg, and that the subsequent biomagnification is secondary.
he concentrations of total and proportions of organic mercury were measured in tissues of 355 in- dividuals of 8 species of Southern Ocean squid (Alluroteuthis antarcticus, Bathyteuthis abyssicola, Filippovia knipovitchi, Galiteuthis glacialis, Gonatus antarcticus, Kondakovia longimana, Psychroteuthis glacialis and Slosarczykovia circumantarctica). Squid were caught around South Georgia (Scotia Sea) during 5 cruises, between the austral summers of 2006/07 to 2016/17 to evaluate temporal changes in bio- accumulation and tissue partitioning. Total mercury concentrations varied between 4 ng g�1 and 804ngg�1 among all tissues. Net accumulation of mercury in muscle with size was observed in A. antarcticus, B. abyssicola and P. glacialis, but no relationship was found for S. circumantarctica and lower concentrations were observed in larger individuals of G. glacialis. Muscle tissues had the highest mercury concentrations in the majority of species, except for F. knipovitchi for which the digestive gland contained highest concentrations. In terms of the percentage of organic mercury in the tissues, muscle always contained the highest values (67%e97%), followed by the digestive gland (22%e38%). Lowest organic mercury percentages were found consistently in the gills (9%e19%), suggesting only low levels of incorporation through the dissolved pathway and/or a limited redistribution of dietary organic mercury towards this tissue. Overall, results are indicative of a decreasing trend of mercury concentrations in the majority of analysed species over the last decade. As cephalopods are an important Southern Ocean trophic link between primary consumers and top predators, these changes suggest decreasing mercury levels in lower trophic levels and an alleviation of the mercury burden on higher predators that consume squid.
Large-scale spatial heterogeneity in fisheries production is predominantly controlled by the availability of zooplankton and benthic organisms, which have a complex relationship with primary production. To investigate how cross-ecosystem differences in these drivers determine fish assemblages and productivity, we constructed a spatially explicit mechanistic model of three fish functional types: forage, large pelagic, and demersal fishes. The model is based on allometric scaling principles, includes basic life cycle transitions, and has trophic interactions between the fishes and with their pelagic and benthic food resources. The model was applied to the global ocean, with plankton food web estimates and ocean conditions from a high-resolution earth system model. Further, a simple representation of fishing was included, and led to moderate matches with total, large pelagic, and demersal catches, including re-creation of observed variations in fish catch spanning two orders of magnitude. Our results highlight several ecologically meaningful model sensitivities. First, coexistence between forage and large pelagic fish in productive regions occurred when forage fish survival is promoted via both favorable metabolic allometry and enhanced predator avoidance in adult forage fish. Second, the prominence of demersal fish is highly sensitive to the efficiency of energy transfer to benthic invertebrates. Third, the latitudinal distribution of the total catch is modulated by the temperature dependence of metabolic rates, with increased sensitivity pushing fish biomass toward the poles. Fourth, forage fish biomass is suppressed by strong top-down controls on temperate and subpolar shelves, where mixed assemblages of large pelagic and demersal fishes exerted high predation rates. Last, spatial differences in the dominance of large pelagics vs. demersals is strongly related to the ratio of pelagic zooplankton production to benthic production. We discuss the potential linkages between model misfits and unresolved processes including movement, spawning phenology, seabird and marine mammal predators, and socioeconomically driven fishing pressure, which are identified as priorities for future model development. Ultimately, the model and analyses herein are intended as a baseline for a robust, mechanistic tool to understand, quantify, and predict global fish biomass and yield, now and in a future dominated by climate change and improved fishing technology.
Abstract
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.
Mercury (Hg) bioaccumulation in fish poses well-known health risks to wildlife and humans through fish consumption. Yet fish Hg concentrations are highly variable, and key factors driving this variability remain unclear. One little studied source of variation is the influence of habitat-specific feeding on Hg accumulation in lake fish. However, this is likely important because most lake fish feed in multiple habitats during their lives, and the Hg and caloric content of prey from different habitats can differ. This study used a three-pronged approach to investigate the extent to which habitat-specific prey determine differences in Hg bioaccumulation in fish. This study first compared Hg concentrations in common nearshore benthic invertebrates and pelagic zooplankton across five lakes and over the summer season in one lake, and found that pelagic zooplankton generally had higher Hg concentrations than most benthic taxa across lakes, and over a season in one lake. Second, using a bioenergetics model, the effects of prey caloric content from habitat-specific diets on fish growth and Hg accumulation were calculated. This model predicted that the consumption of benthic prey results in lower fish Hg concentrations due to higher prey caloric content and growth dilution (high weight gain relative to Hg from food), in addition to lower prey Hg levels. Third, using data from the literature, links between fish Hg content and the degree of benthivory, were examined, and showed that benthivory was associated with reduced Hg concentrations in lake fish. Taken together, these findings support the hypothesis that higher Hg content and lower caloric content make pelagic zooplankton prey greater sources of Hg for fish than nearshore benthic prey in lakes. Hence, habitat-specific foraging is likely to be a strong driver of variation in Hg levels within and between fish species.
Methylmercury is the most toxic form of mercury for the effects it produces on human health when exposed to it, and fish is the food that contributes most to the intake of this contaminant. Predatory species (swordfish, shark or tuna) have higher levels of mercury, swordfish being the species that showed the highest content, while cephalopods and bivalves had the lowest concentrations. Exposure data and risk, taken from different studies, are variable and indicate that fish consumption may represent a risk only in certain geographic areas and in certain sectors of the population, and it warns of the potential risk in pregnant women, nursing women, women of childbearing age and children. The keys to reducing exposure and minimize risk of fish consumption would be: changes in eating habits at local level, including a varied consumption of fish in the diet; replace the consumption of species with high mercury levels by other species with lower levels; and implement programs of ongoing information from health authorities aimed at the general population and specific risk groups.
Open ocean samples of phytoplankton and zooplankton were collected from the central Pacific on board the R/V Kilo Moana in October of 2011. The cruise traveled from Hawaii to Samoa, progressing through a High Nutrient Low Chlorophyll (HNLC) zone, and an equatorial upwelling region. Phytoplankton samples were size fractioned into 0.2–5 μm, 5–20 μm, and N20 μm samples. Methylmercury concentrations were 2.91 ± 2.58 pmol g−1 (wet weight) for the overall b200 μm size fractions, and highest around the HNLC region. Phytoplankton bioconcentration factors (logBCFs) averaged to 5.69±0.98 and were higher than the values found for coastal regions. Both %MeHg ([MeHg]/[Hg]) and logBCF values indicated that the lowest size fraction had the largest fraction of the HgT as MeHg, signifying enhanced accumulation of MeHg into smaller organisms. Zooplankton vertical net tows were completed from depths of 200 m up to ~10 m. Zooplankton samples were analyzed for carbon, nitrogen and sulfur in addition to Hg and MeHg at size fractionations of 0.2–0.5 mm, 0.5–1.0 mm, 1.0–2.0 mm and occasionally >2.0 mm. Zooplankton abundance and MeHg concentrations both peaked at Stations 3 and 5 (upwelling region). The %MeHg in the organisms was highest in the >2.0 mm size class, displaying MeHg bioaccumulation for increasing zooplankton sizes. Separate day and night net tows were collected at Stations 3 and 5 in order to investigate differences due to diurnal migration of zooplankton. There were higher concentrations of MeHg for all sizes in night collections of zooplankton at Station 5, but no discrepancy for Station 3. These results represent some of the few measurements of Hg and MeHg at the base of the open ocean food chain, and are significant as they represent the instigation of bioconcentration into the base of marine food webs.
Rivers discharge 28±13 Mmol a−1 of mercury (Hg) to ocean margins, an amount comparable to atmospheric deposition to the global oceans. Most of the Hg discharged by rivers is sequestered by burial of benthic sediment in estuaries or the coastal zone, but some is evaded to the atmosphere and some is exported to the open ocean. We investigate the fate of riverine Hg by developing a new global 3-D simulation for Hg in the MIT ocean general circulation model (MITgcm). The model includes plankton dynamics and carbon respiration (DARWIN project model) coupled to inorganic Hg chemistry. Results are consistent with observed spatial patterns and magnitudes of surface ocean Hg concentrations. We use observational constraints on seawater Hg concentrations and evasion to infer that most Hg from rivers is sorbed to refractory organic carbon and preferentially buried. Only 6% of Hg discharged by rivers (1.8 Mmol a−1) is transported to the open ocean on a global basis. This fraction varies from a low of 2.6% in East Asia due to the barrier imposed by the Korean Peninsula and Japanese Archipelago, up to 25% in eastern North America facilitated by the Gulf Stream. In the Arctic Ocean, low tributary particle loads and efficient degradation of particulate organic carbon by deltaic microbial communities favors a more labile riverine Hg pool. Evasion of Hg to the Arctic atmosphere is indirectly enhanced by heat transport during spring freshet that accelerates sea-ice melt and ice rafting. Discharges of 0.23 Mmol Hg a −1 from Arctic rivers can explain the observed summer maximum in the Arctic atmosphere and this magnitude of releases is consistent with recent observations. Our work indicates that rivers are major contributors to Hg loads in the Arctic Ocean.
This study is the first comprehensive evaluation of total Hg and methylmercury (MeHg) concentrations in wild marine fish from an estuarine and a coastal ecosystem in southern China. A total of 571 fish from 54 different species were examined. Our results showed that the Hg levels were generally low in the fish, and the Hg levels were below 30 ng g(-1) (wet weight) for 82% of the samples, which may be related to the reduced size of the fish and altered food web structure due to overfishing. Decreased coastal wetland coverage and different carbon sources may be responsible for the habitat-specific Hg concentrations. The degree of biomagnification was relatively low in the two systems.
Inorganic and methylmercury in copepods collected from 9 stations in the Antarctic Sea in December 1985 and February 1986 was measured. There was considerable variation of inorganic mercury in copepods at all stations while inorganic mercury in copepods from deeper (bottom) waters was higher than that from surface waters. This result indicates that the inorganic mercury concentrated in the copepods might have been derived from bottom sediments and/or bottom waters. On the contrary, there is little regional or vertical difference in methyl- mercury content of copepods which was generally low. Its value is considered to be standard value in sea areas expected to be non-polluted from human activities. The mercury content (mean value) in zooplankton collected from various sea areas was compared with each other. The value of total mercury in the Antarctic Sea (recorded in the present study) was about the same as that in Yatsushiro-kai adjacent to polluted area and was higher than those in the other non-polluted sea areas, except the East Indian Ocean (off Java) affected by active submarine volcanos.
Previous research has documented that total mercury concentrations ([THg]) are lower in anadromous Arctic charr than in non-anadromous conspecifics, but the two life-history forms have rarely been studied together. Here, data from nine pairs of closely-located anadromous and non-anadromous Arctic charr populations were used to explore the impact of biological and life-history factors on individual [THg] across a range of latitudes (49-81° N) in eastern Canada. Unadjusted mean [THg] ranged from 20 to 114ng/g wet weight (ww) in anadromous populations, and was significantly higher in non-anadromous populations, ranging from 111 to 227ng/g ww. Within-population variations in [THg] were best explained by fish age, and were often positively related to fork-length and δN-inferred trophic level. Differences in [THg] were not related to differences in length-at-age (i.e., average somatic growth rate) among populations of either life-history type. Mercury concentrations were not related to site latitude in either the anadromous or non-anadromous fish. We conclude that the difference in Arctic charr [THg] with life-history type could not be explained by differences in fish age, fork-length, trophic position, or length-at-age, and discuss possible factors contributing to low mercury concentrations in anadromous, relative to freshwater, fish.
Patterns in primary production and carbon export from the euphotic zone suggest that the relative contribution of planktonic heterotrophs to community biomass should decline along gradients of phytoplankton biomass and primary production. Here, we use an extensive literature data survey to test the hypothesis that the ratio of total heterotrophic (bacteria + protozoa + mesozooplankton) biomass to total autotrophic biomass (H:A ratio) is not constant in marine plankton communities but rather tends to decline with increasing phytoplankton biomass and primary production. Our results show that the plankton of unproductive regions are characterized by very high relative heterotrophic biomasses resulting in inverted biomass pyramids, whereas the plankton of productive areas are characterized by a smaller contribution of heterotrophs to community biomass and a normal biomass pyramid with a broad autotrophic base. Moreover, open-ocean communities support significantly more heterotrophic biomass in the upper layers than do coastal communities for a given autotrophic biomass. These differences in the biomass structure of the community could be explained by the changes in the biomass-specific rates of phytoplankton production that seem to occur from ultraoligotrophic to eutrophic marine regions, but other factors could also generate them. The patterns described suggest a rather systematic shift from consumer control of primary production and phytoplankton biomass in open ocean to resource control in upwelling and coastal areas.
Mass balance models can be used to predict mercury accumulation in fish. However, factors influencing mercury elimination, an essential parameter of the mass balance model, are poorly understood. We developed a general model of mercury elimination from fish using literature data. Our analysis showed that short-term experiments (<90 days) overestimated the elimination rate of mercury and that inorganic mercury was excreted 3-fold faster than methylmercury. Both inorganic mercury and methylmercury excretion were negatively correlated to body size, but only methylmercury elimination was significantly correlated to water temperature.A general model of methylmercury excretion was developed using temperature, body size, and a dummy variable representing exposure time (acute vs chronic) as independent variables (r 2 = 0.77). Methylmercury depuration rate was independent of mercury burden and concentration, indicating that it is a first-order process. Methylmercury elimination tended to be overestimated by a factor of 2−6 by empirical models that were published prior to this study. A field test showed that our model adequately estimated the elimination rate of methylmercury under natural conditions.
Standardized diet compositions were derived for 97 species of marine mammals from published accounts of stomach contents as well as from morphological, behavioural and other information. Diet was apportioned among eight categories of prey types (benthic invertebrates, large zooplankton, small squids, large squids, small pelagic fishes, mesopelagic fishes, miscellaneous fishes and higher invertebrates). Trophic levels were estimated for each species of marine mammals and compared with published estimates derived using stable isotope ratios. Trophic levels ranged from 3.2–3.4 in baleen whales and sea otters, to 3.8–4.4 in most pinnipeds and odontocete whales, to 4.5–4.6 in killer whales. Such information can be used for ecosystem modelling and related studies.