Hg Concentrations In Muscle Research Articles

Mercury accumulation, speciation, and temporal trends in Atlantic Stingrays (Hypanus sabinus)

Mercury (Hg) deposited into aquatic sediments can be converted into the more toxic methylmercury (MeHg) by microbial activity. Atlantic stingrays (Hypanus sabinus) are an estuarine and nearshore species found in coastal regions of the western North Atlantic, occurring in multiple habitat types, and feeding mainly on benthic invertebrates. Mercury dynamics and speciation in stingrays have not been well examined. This study quantified total Hg and Hg species (Hg (II) and MeHg) in Atlantic stingrays sampled from Florida's Indian River Lagoon (IRL) from 2012 to 2013. Tissues (muscle and liver) collected from 29 stingrays were lyophilized and homogenized before being analyzed using a direct mercury analyzer. Concentrations of total Hg in muscle were positively related to stingray disk width, but concentrations in liver were not. Mean (±SD) total Hg in muscle (0.56 ± 0.30 mg/kg dw) was significantly higher than mean total Hg in liver (0.23 ± 0.19 mg/kg dw). Within liver tissue, percent MeHg (of total Hg) ranged from 31 to 99%. The ratio between total Hg in liver and total Hg in muscle was <1 for nearly all individuals, suggesting a lack of active hepatic demethylation and sequestration mechanisms. Concentrations of Hg in IRL Atlantic stingrays fall below concentrations known to result in direct toxicity to fishes; however, effects thresholds are not well understood for elasmobranchs. Comparisons of Hg concentrations in IRL Atlantic stingrays sampled previously (37 individuals in 1994) indicate that total Hg concentrations in muscle of Atlantic stingrays have decreased over the past two decades, suggesting a reduction in the bioavailable Hg in the IRL ecosystem.

Screening-level risk assessment of methylmercury for non-anadromous Arctic char (Salvelinus alpinus).

Non-anadromous forms of Arctic char (Salvelinus alpinus), those that are restricted to lakes and rivers, typically have higher mercury (Hg) concentrations than anadromous forms, which migrate to and from the sea. Using tissue burden data from the literature and our own analyses, we performed a screening-level risk assessment of methylmercury (MeHg) for non-anadromous Arctic char. Our assessment included 1569 fish distributed across 83 sites. Site-specific mean total Hg concentrations in non-anadromous Arctic char muscle varied considerably from 0.01 to 1.13 µg/g wet weight, with 21% (17 of 83 sites) meeting or exceeding a threshold-effect level in fish of 0.33 µg/g wet weight, and 13% (11 of 83 sites) meeting or exceeding a threshold-effect level in fish of 0.5 µg/g wet weight. Of the sites in exceedance of the 0.33-µg/g threshold, 7 were located in Greenland and 10 in Canada (Labrador, Nunavut, and Yukon). All but one of these sites were located in interfrost or permafrost biomes. Maximum total Hg concentrations exceeded 0.33 µg/g wet weight at 53% of sites (40 of the 75 sites with available maximum Hg values), and exceeded 0.5 µg/g wet weight at 27% (20 of 75 sites). Collectively, these results indicate that certain populations of non-anadromous Arctic char located mainly in interfrost and permafrost regions may be at risk for MeHg toxicity. This approach provides a simple statistical assessment of MeHg risk to non-anadromous Arctic char, and does not indicate actual effects. We highlight the need for studies that evaluate the potential toxic effects of MeHg in non-anadromous Arctic char, as well as those that aid in the development of a MeHg toxic-effect threshold specific to this species of fish. Environ Toxicol Chem 2019;38:489-502. © 2018 SETAC.

Tracing Mercury Pollution along the Norwegian Coast via Elemental, Speciation, and Isotopic Analysis of Liver and Muscle Tissue of Deep-Water Marine Fish ( Brosme brosme).

Liver and muscle tissue of tusks ( Brosme brosme) have been analyzed for their THg and MeHg concentrations and Hg isotopic signatures for tracing Hg pollution along the Norwegian coast. Clear differences between tissue types and locations were established. At five of the eight locations, the Hg concentration in muscle exceeded the maximum allowable level of 0.5 mg kg-1 wet weight. δ202Hg values in both tissue types indicated that Hg speciation affects the bulk Hg isotopic signature. Tusk liver seems to be more sensitive to immediate changes and to anthropogenic inorganic Hg, while the muscle rather reflects the Hg accumulated over a longer period of exposure. The δ202Hg values of liver and muscle also enabled different sources of Hg and exposure pathways to be distinguished. δ202Hgmuscle-δ202Hgliver showed a clear correlation with the % MeHg in tusk liver for the coastal waters, but not for the fjords. The absence of significant differences in Δ199Hg values between both tissues of tusk from the same location suggests that in vivo metabolic processes are the underlying reason for the differences in Hg speciation and in δ202Hg values. This work highlights the importance of selecting different tissues of marine fish in future Hg monitoring programs.

Stable isotope analyses revealed the influence of foraging habitat on mercury accumulation in tropical coastal marine fish

Bioaccumulation of toxic metal elements including mercury (Hg) can be highly variable in marine fish species. Metal concentration is influenced by various species-specific physiological and ecological traits, including individual diet composition and foraging habitat. The impact of trophic ecology and habitat preference on Hg accumulation was analyzed through total Hg concentration and stable isotope ratios of carbon (δ13C) and nitrogen (δ15N) in the muscle of 132 fish belonging to 23 different species from the Senegalese coast (West Africa), where the marine ecosystem is submitted to nutrient inputs from various sources such as upwelling or rivers. Species-specific ecological traits were first investigated and results showed that vertical (i.e. water column distribution) and horizontal habitat (i.e. distance from the coast) led to differential Hg accumulation among species. Coastal and demersal fish were more contaminated than offshore and pelagic species. Individual characteristics therefore revealed an increase of Hg concentration in muscle that paralleled trophic level for some locations. Considering all individuals, the main carbon source was significantly correlated with Hg concentration, again revealing a higher accumulation for fish foraging in nearshore and benthic habitats. The large intraspecific variability observed in stable isotope signatures highlights the need to conduct ecotoxicological studies at the individual level to ensure a thorough understanding of mechanisms driving metal accumulation in marine fish. For individuals from a same species and site, Hg variation was mainly explained by fish length, in accordance with the bioaccumulation of Hg over time. Finally, Hg concentrations in fish muscle are discussed regarding their human health impact. No individual exceeded the current maximum acceptable limit for seafood consumption set by both the European Union and the Food and Agriculture Organization of the United Nations. However, overconsumption of some coastal demersal species analyzed here could be of concern regarding human exposure to mercury.

Spatial and temporal trends of mercury in the aquatic food web of the lower Penobscot River, Maine, USA, affected by a chlor-alkali plant

Mercury (Hg) concentrations in aquatic biota, including fish and shellfish, were measured over the period 2006–2012 in the lower Penobscot River and upper estuary (Maine, USA). The Penobscot is a system contaminated with Hg by a chlor-alkali plant that operated from 1967 to 2000, discharging 6–12 tons of mercury into the river. Mercury levels in aquatic biota were highest at sites downstream of the chlor-alkali plant and spatial trends were similar to those of sediments. Mean total Hg concentrations in fish muscle (adjusted for size or age) in the most affected areas were 521 (480, 566; 95% CI) ng/g ww in American eels, 321 (261,395) in mummichog, 121 (104, 140) in rainbow smelt, 155 (142,169) in tomcod, 55.2 (42.7,71.4) in winter flounder, and 328 (259,413) in American lobster tail and 522 (488,557) ng/g dw in blue mussel. Levels exceeded the 50 ng/g ww considered protective for piscivorous predators and were of concern for human health, with American eels and American lobster exceeding Maine's mercury action level of 200 ng/g ww. Calculations of trophic position (using nitrogen isotopes) suggested that the spatial patterns observed in total Hg concentrations were not due to changes in feeding habits of the species. Fish feeding in benthic food webs, as defined by stomach content and stable carbon isotope analyses, showed no change in Hg concentrations over time. In contrast, declining trends in Hg were found in two species dependent on pelagic food webs. The absence of declines in Hg concentrations in the benthically-based food webs, despite the fact that most Hg was discharged into the system >40 years ago, is consistent with the long recovery predicted from dated sediment cores and from similar studies elsewhere.

Hg Concentrations in Muscles and Gills of Fish from Shallow Lakes of Different Trophic Status (Eastern Poland)

Hg Concentrations in Muscles and Gills of Fish from Shallow Lakes of Different Trophic Status (Eastern Poland)

Mercury Concentrations and Se:Hg Molar Ratios in Flyingfish (Exocoetus volitans) and Squid (Uroteuthis chinensis).

We measured total mercury (Hg) and selenium (Se) concentrations as well as stable nitrogen (N) isotopic composition in flyingfish and squid muscle tissues from the eastern Indian Ocean and western South China Sea. The results showed that the mean Hg concentration in squid muscle from the western South China Sea was lower than that in the eastern Indian Ocean. The Hg concentrations in flyingfish and squid muscle samples were positively correlated with organism size (length and weight) and δ15N in all the study areas. Furthermore, we found a negative correlation between Se and Hg in molar content of flyingfish and squid muscle from the western South China Sea. The Se:Hg molar ratio was significantly negative correlated with fish weight and δ15N, suggesting that the Se:Hg molar ratio decreases with the increase of fish size and trophic level in the food web.

High status of mercury and selenium in false killer whales (Pseudorca crassidens, Owen 1846) stranded on Southern South America: A possible toxicological concern?

The study was carried out to determine Hg and Se concentrations in false killer whales stranded on the Estrecho de Magallanes, Chile, South America. Tissue samples of five mature specimens were analyzed (two females and three males). Mean Hg concentration in liver 1068 (234) μg g−1 dry weight (DW) (standard deviation in parenthesis) was markedly higher than those in kidney 272 (152) μg g−1 DW, lung 423 (325) μg g−1 DW, spleen 725 (696) μg g−1 DW, muscle 118 (94) μg g−1 DW and testicle 18.0 (2.8) μg g−1 DW. Mean Se concentration in liver, 398 (75) μg g−1 DW, was higher than those in kidney 162 (69) μg g−1 DW, lung 128 (84) μg g−1 DW, spleen 268 (245) μg g−1 DW, muscle 47 (38) μg g−1 DW and testicle 25.4 (2.1) μg g−1 DW. Positive correlations were found between Hg and Se molar concentrations in muscle, lung, spleen and kidney. Molar ratio of Se/Hg in liver, lung and muscle were <1, but those in kidney and testicle were markedly >1 suggesting a Se protection against Hg toxicity. In all the examined specimens Hg values exceeded the toxic thresholds defined for hepatic damage in marine mammals, with Se/Hg molar ratios below 1 implying limited protective action of Se. Generally, our results showed that individuals are carrying a significant burden, reflecting a high exposure to this toxic metal. This constitutes the first report on Hg and Se levels for a large subantarctic odontocete in South America region, providing insights into their contamination status and with information to the understanding of possible impacts on wild populations.

Mercury in blue shark (Prionace glauca) and shortfin mako (Isurus oxyrinchus) from north-eastern Atlantic: Implication for fishery management

Pelagic sharks (blue shark Prionace glauca and shortfin mako Isurus oxyrinchus) caught by long-line Spanish and Portuguese fleets in the NE Atlantic, were sampled at Vigo fish market (Spain) for total mercury (Hg) analysis. Hg concentration in white muscle increased with size and weight in both species, but at a higher rate in shortfin mako than in the blue shark. No difference was found with sex, year and season. Spatial variation was observed in the blue shark with higher Hg values in the North of the Azorean archipelago, but not in the shortfin mako. These high-level predators are particularly susceptible to bioaccumulate contaminants (Hg) in their tissues (muscle). However, a significant positive relationship between Hg concentration and trophic level (δ15N) of individuals was observed only in the shortfin mako. Most sharks landed were juveniles which presented Hg concentration lower than the maximum limit allowed by the European Union (1mgkg−1 wet weight) for marketing. However, concentrations above this threshold were most recorded in blue sharks larger than 250cm total length (TL) and in shortfin makos larger than 190cm TL, raising the question of the commercialization of large-sized individuals.

Mercury content of blue crabs (Callinectes sapidus) from southern New England coastal habitats: Contamination in an emergent fishery and risks to human consumers

Total mercury (Hg; ppm dry weight) was measured in blue crabs, Callinectes sapidus, collected from Narraganset Bay and adjacent coastal lagoons and tidal rivers (Rhode Island/Massachusetts, USA) from May to August 2006–2016. For juvenile crabs (21–79mm carapace width, CW), total Hg was significantly greater in chelae muscle tissue (mean±1 SD=0.32±0.21ppm; n=65) relative to whole bodies (0.21±0.16ppm; n=19), and irrespective of tissue-type, crab Hg was positively related to CW indicating bioaccumulation of the toxicant. Across a broader range of crab sizes (43–185mm CW; n=465), muscle Hg concentrations were significantly higher in crabs from the Taunton River relative to other locations (0.71±0.35ppm and 0.20±0.10ppm, respectively). Spatial variations in crab Hg dynamics were attributed to habitat-specific Hg burdens of their prey, including bivalves, gastropods, polychaetes, and shrimp. Prey Hg, in turn, was directly related to localized sediment Hg and methylmercury conditions. Biota-sediment accumulation factors for crabs and prey were negatively correlated with sediment organic content, verifying that organically-enriched substrates reduce Hg bioavailability. From a human health perspective, frequent consumption of crabs from the Taunton River may pose a human health risk (23% of legal-size crabs exceeded US EPA threshold level); thus justifying spatially-explicit Hg advisories for this species.

Mercury in wintering American black ducks (Anas rubripes) downstream from a point-source on the lower Penobscot River, Maine, USA

Waterfowl wintering along the lower Penobscot River, Maine continue to be exposed to elevated Hg concentrations from the HoltraChem chlor-alkali plant that operated along the river between 1967 and 2000. In American black ducks (Anas rubripes) total Hg in duck breast muscle increased with residence time on contaminated marshes, reaching means of 0.82±0.21μg/g ww (wet weight) by the end of the fall hunting season, and prompting Maine to issue a human consumption advisory on duck breast muscle. Methyl Hg comprised over 99% of the total Hg in breast muscle. The ratio of Hg concentrations in blood and muscle were strongly correlated and approached 1:1 after extended residence times. Primary feather (P1) total Hg concentrations averaged 2.2±1.3μg/g fw (fresh weight), verifying low Hg exposure during feather growth on distant breeding grounds the preceding summer. Mercury concentrations in black ducks, following winter residence along the lower Penobscot exceeded levels associated with reproductive toxicity. Carry-over of Hg to summer breeding grounds may limit the subsequent reproductive success of black ducks.

Genotoxic Assessment of Some Inorganic Compounds in Desert Pupfish (Cyprinodon macularius) in the Evaporation Pond from a Geothermal Plant.

The frequency of micro nucleated erythrocytes in peripheral blood of the desert pupfish (Cyprinodon macularius) from a geothermal effluent pond is determined and compared to organisms kept in an aquarium. The frequency of micronucleated erythrocytes found in pupfish from the geothermal pond is 2.75 (±2.09) and only 0.44 (±0.52) in captivity organisms. Dissolved As in the ponds doubles the 340µgL-1 US-EPA acute quality criteria for aquatic life and Hg equals the 1.77µgL-1 chronic criteria. The organisms with high MNE also have significantly high Se, As and Hg concentrations in muscle and liver. Compared to international maximum allowable limits for fish consumption, there is 81× enrichment for Se, 6× for As and 5× for Hg. Although Se is not significantly enriched in water, it is likely that its bioaccumulation occurs via feeding of detritus. The desert pupfish has a significant resistance to extreme metal accumulations and to recover under unpolluted conditions.

Comparison of trace metals in different fish tissues of Scomberomorus spp. (“sierra”) and Lutjanus synagris (“arrayado”) from Jobos Bay and La Parguera coastal areas in Southern Puerto Rico

Metal pollution in aquatic systems are a health concern worldwide. This study compared the distribution As, Cd, Cu, Pb, Se, and Zn, in liver, gonad, gill and muscle of S. cavallaand L. synagris from Jobos Bay to levels in S. regalisand L. synagrisfrom La Parguera (reference site). Levels of Hg were only determined in fish muscle. Arsenic, Se, and Hg (only for S. cavalla) were significantly higher in tissues of fish species from Jobos Bay when compared to fish from La Parguera. Liver displayed higher metal concentrations, while muscle tended to accumulate less metals. In all tissues, Zn exhibited the highest concentrations, while Cd and Pb were limited to liver and gill of L. synagris from both sampling areas. Most metal content in different tissues of S. cavalla and L. synagris from the Jobos Bay area fell in the range of metal concentrations that were associated to low aquatic metal pollution, although As and Hg concentrations in fish muscle represent a human health concern based on health criteria values.

Concentrations of trace metals in tissues of Chionoecetes crabs (Chionoecetes japonicus and Chionoecetes opilio) caught from the East/Japan Sea waters and potential risk assessment.

The concentrations of trace metals (As, Cd, Co, Cu, Fe, Hg, Pb, and Zn) were measured in muscle and hepatopancreas of two Chionoecetes crabs (Chionoecetes japonicus and C. opilio) caught from the East/Japan Sea (EJS) in order to assess the potential health risk by the consumption of deep sea crabs. The highest metal concentrations in muscle and hepatopancreas were As and Fe, respectively, while the lowest metal concentration in two tissues was Pb. The mean concentrations of Cd, Co, Cu, Fe, and Pb in Chionoecetes crabs were one or two orders of magnitude higher in hepatopancreas than in muscles. The mean concentrations of As, Cu, and Hg in muscle and hepatopancreas were relatively higher in C. japonicus than in C. opilio. The estimated daily intakes (EDI) of all metals in muscle were below 0.1% of the provisional tolerable daily intake (PTDI) adopted by the Joint FAO/WHO Expert Committee on Food Additives. Similarly, the target hazard quotient (THQ) of all trace metals in muscle was less than 1.0. These results imply that Chionoecetes crabs caught from EJS do not have an adverse impact on the Korean health. Based on the mean metal concentrations, PTDI, and THQ, the daily maximum permissible intakes of C. japonicus and C. opilio were estimated to be approximately 240 and 410g/day, respectively.

DISTRIBUTION OF ARSENIC AND MERCURY IN THE AQUATIC ECOSYSTEM OF THE FIVE CHILEAN RESERVOIRS

Arsenic and mercury are among the metals and metalloids more toxic to the ecosystem. A quantification method by atomic absorption spectroscopy with hydride generator (AAS-HG) to determine total As and cold steam to determine Hg was optimized and validated in various matrices: superficial water, interstitial or pore water, sediments and in gill, liver and muscle of two fish species, a silverside ( Basilichthys microlepidotus ) and a catfish ( Trichomycterus areolatus ). The quality of the results was tested using certified reference materials (Water: ERM-CA615; Fish: DOLT-4; Sediment: BCR-320R). Samples were collected in the affluent and effluent of five reservoirs: Cogoti (31o00’S, 71o05’W); Corrales (31o54oS, 70o54’W); La Paloma (30o44’S, 71o00’W); Rapel (34o08’S, 71o29’O); Recoleta (30o28’S, 71o06’W). ), in two campaigns during high flow (winter 2010) and low flow (summer 2011). The results show a clear difference in the distribution of As and Hg in the different matrices; higher concentrations were found in the order sediment ˃ interstitial water ˃ surface water. Catfish showed higher accumulation of both metals, and metal concentrations generally decreased in the order liver > gill > muscle. No significant effect of reservoirs and zones was observed in As and Hg content. However, Arsenic (As) was found in higher concentration in the different matrices of the five reservoirs and zones. The concentrations of As and Hg in all samples did not exceed international standards in the case of sediment and the Chilean norm in the case of water, while in both fish species concentrations of As and Hg in muscle exceeded international standards.

Mercury in the Blue Marlin (Makaira nigricans) from the Southern Gulf of California: Tissue Distribution and Inter-Annual Variation (2005-2012).

With the aim of knowing annual variations of Hg concentrations in muscle and liver of blue marlin (Makaira nigricans) from the southern Gulf of California, fish were collected between 2005 and 2012 in three areas. In general, Hg levels were more elevated in liver than in muscle. Variations of Hg concentrations in muscle and liver among the studied years were not significant. Hg levels in muscle and liver increased significantly with length and weight of fish. In comparison to other studies, Hg levels in muscle and liver were lower. With respect to maximum permissible limits (1.0µgg-1 wet weight) of Hg in Mexico, the average concentration (1.91µgg-1 wet weight) in the edible portion (muscle) of blue marlin was over the legal limit; this issue is worth research efforts in relation to the rate of ingestion of this species and the co-occurrence of selenium in the edible portion.

Relationships for mercury and selenium in muscle and ova of gravid freshwater fish.

At high concentrations, mercury (Hg) is toxic to vertebrates, causing neurological, behavioral, and teratological dysfunction. Selenium (Se) not only is an essential element but also has a high affinity for Hg, binding to organic methyl mercury at a molar ratio of Se/Hg of 1:1. Ratios of <1 increase risk of Hg toxicity. For gravid fish, low concentrations of Se in ova could increase potential for Hg toxicity, compromising embryonic development and fitness of fry. Mercury and selenium concentrations and ratios were investigated in the muscle and ovaries of six species from five families of fish to assess potential for risk to ecological fitness. Molar ratios of Se/Hg in muscle were typically >18 for lower trophic level species but ≤2 for piscivores. For all species combined, the concentrations of Hg in ova were significantly related to concentrations of Hg in muscle. Concentrations of Se in ova versus muscle showed a similar significant relationship that was independent of muscle Hg concentration. Mean ova molar Se/Hg ratios were high, ranging from 69 to 955 for the 6 species. However, a declining relationship between the ova Se/Hg molar ratio and the muscle concentration of Hg for all species combined suggests that development of ova and fry might be compromised for those piscivores with the highest muscle Hg concentrations because of Hg-related Se deficiency.

Cyanobacterial Neurotoxin BMAA and Mercury in Sharks.

Sharks have greater risk for bioaccumulation of marine toxins and mercury (Hg), because they are long-lived predators. Shark fins and cartilage also contain β-N-methylamino-l-alanine (BMAA), a ubiquitous cyanobacterial toxin linked to neurodegenerative diseases. Today, a significant number of shark species have found their way onto the International Union for Conservation of Nature (IUCN) Red List of Threatened Species. Many species of large sharks are threatened with extinction due in part to the growing high demand for shark fin soup and, to a lesser extent, for shark meat and cartilage products. Recent studies suggest that the consumption of shark parts may be a route to human exposure of marine toxins. Here, we investigated BMAA and Hg concentrations in fins and muscles sampled in ten species of sharks from the South Atlantic and Pacific Oceans. BMAA was detected in all shark species with only seven of the 55 samples analyzed testing below the limit of detection of the assay. Hg concentrations measured in fins and muscle samples from the 10 species ranged from 0.05 to 13.23 ng/mg. These analytical test results suggest restricting human consumption of shark meat and fins due to the high frequency and co-occurrence of two synergistic environmental neurotoxic compounds.

Biomagnification of mercury and selenium in two lakes in southern Norway

We have investigated bioaccumulation and trophic transfer of both mercury (Hg) and selenium (Se) in two lakes in southern Norway to reveal a suggested mitigating effect of Se on Hg biota accumulation. The study included analysis of total Se (Se), total Hg (Hg), and methyl-mercury (MeHg) in water, littoral and pelagic invertebrates and perch (Perca fluviatilis), together with stable isotope analysis (δ15N and δ13C) in biota. Mean dissolved Se ranged from 22 to 59ngL−1, while Hg and MeHg in lake water ranged from 1 to 3ngL−1 and 0.01 to 0.06ngL−1. Biota Se and Hg concentrations (dry weight) ranged from 0.41mgSekg−1 and 0.06mgHgkg−1 in primary littoral invertebrates and up to 2.9mg Sekg−1 and 3.6mgHgkg−1 in perch. Both Hg and Se biomagnified in the food web, with a trophic magnification factor (TMF) of 4.64 for Hg and 1.29 for Se. The reported positive transfer of Se in the food web, despite the low measured dissolved Se, suggest that a major proportion of the Se in these lakes are both highly bioavailable and bioaccumulative. However, we did not find support for a Se-facilitated inhibition in the accumulation of Hg in perch, as Se and Hg concentrations in perch muscle correlated positively and Se did not explain any variations in Hg after we controlled for the effects of other important covariates. We postulate that this may be a result of insufficient concentrations of dissolved Se and subsequently in biota in our studied lakes for an efficient Hg sequestration up the food web.

Mercury species, selenium, metallothioneins and glutathione in two dolphins from the southeastern Brazilian coast: Mercury detoxification and physiological differences in diving capacity

In the present study, the concentration of trace elements, total mercury (Hg) and selenium (Se) and mercury forms (MeHg, Hginorg and HgSe) in the vulnerable coastal dolphins Pontoporia blainvillei and Sotalia guianensis were appraised and compared, using metallothioneins (MT) and glutathione (GSH) as biomarkers for trace element exposure. The trace element concentrations varied between muscle and liver tissues, with liver of all dolphin specimens showing higher Hg and Se concentrations than those found in muscle. Hg, MeHg and Hginorg molar concentrations showed a clear increase with Se molar concentrations in the liver of both dolphins, and Se concentrations were higher than those of Hg on a molar basis. Se plays a relevant role in the detoxification of MeHg in the hepatic tissue of both dolphins, forming Hg-Se amorphous crystals in liver. In contrast, MT were involved in the detoxification process of Hginorg in liver. GSH levels in P. blainvillei and S. guianensis muscle tissue suggest that these dolphins have different diving capacities. Muscle Hg concentrations were associated to this tripeptide, which protects dolphin cells against Hg stress.