Levels of mercury in muscle and liver of star-spotted dogfish (Mustelus manazo) from the northern region of Japan: a comparison with spiny dogfish (Squalus acanthias)

Mercury bioaccumulation and its relationship with trophic biomarkers in a Mediterranean elasmobranch mesopredator

Human activity has led to increased concentrations of mercury (Hg) in the world's oceans. Mercury can bioaccumulate and biomagnify in animal tissues via trophic transfer, thus, becoming most pronounced in larger and older predators. Here, we measured Hg concentrations and their relationship with stable isotopes-based proxies of trophic level (δ13C and δ15N values) in multiple tissues of Mustelus spp. from the Mediterranean Sea. We found higher Hg concentrations in muscle than in liver and fin tissues. The relationship between Hg concentrations and δ15N values in muscle suggested repeated foraging for low trophic level and Hg-poor prey, and biomagnification of Hg at higher trophic levels. Seasonal variations in δ13C values could indicate shifts in primary production sources and/or in local prey availability. The HBVSe index suggested no risk to human health, however the safe meal limit recommendations are 4.5 and 2.2 portions per month for adults and children, respectively.

Bioaccumulation and biomagnification in elasmobranchs: A concurrent assessment of trophic transfer of trace elements in 12 species from the Indian Ocean

We provided the first multi-species study investigating the presence and organotropism of trace elements in three tissues of 12 elasmobranch species. Shark species showed comparable TE loads, although milk sharks and juvenile scalloped hammerhead sharks exhibited the highest Cd and Hg levels, respectively. Fins accumulated higher levels of Pb, Co, and Cr; muscles higher V, As, and Hg; livers higher Se and Cd levels. The organotropism of TEs calls for cautious when choosing a tissue to be sampled since certain tissues, like fin clips, do not provide reliable surrogate for the internal loads of some TEs. Strong correlations between essential and toxic TEs indicated detoxification mechanisms, while the TMF provided evidence for Hg, As and Se biomagnification along the food-web. Considering the difficulties in assessing elasmobranchs contamination from different areas, the proposed multi-species approach represents a valuable way to estimate the species-specific accumulation and transfer of pollutants in sharks.

Elevated accumulation of the toxic metal mercury in the Critically Endangered oceanic whitetip shark Carcharhinus longimanus from the northwestern Atlantic Ocean

The oceanic whitetip shark Carcharhinus longimanus is a widely distributed large pelagic shark species once considered abundant in tropical and warm temperate waters, but recently listed as Critically Endangered by the IUCN due to drastic population declines associated with overfishing. In addition to risks posed to its populations due to overexploitation, oceanic whitetip sharks are also capable of accumulating elevated quantities of harmful environmental toxicants, placing them at special risk from anthropogenic pollution. Herein, we provide the first data on accumulation of the toxic, non-essential metal mercury (Hg) in northwest Atlantic (NWA) oceanic whitetip sharks, focusing on aggregations occurring at Cat Island, The Bahamas. Total Hg (THg) concentrations were measured in muscle of 26 oceanic whitetip sharks and compared with animal length and muscle δ15N to evaluate potential drivers of Hg accumulation. THg concentrations were also measured in fin and blood subcomponents (red blood cells and plasma) to determine their value as surrogates for assessing Hg burden. Muscle THg concentrations were among the highest ever reported for a shark species and correlated significantly with animal length, but not muscle δ15N. Fin, red blood cell, and plasma THg concentrations were significantly correlated with muscle THg. Fin THg content was best suited for use as a surrogate for estimating internal Hg burden because of its strong relationship with muscle THg levels, whereas blood THg levels may be better suited for characterizing recent Hg exposure. We conclude that Hg poses health risks to NWA oceanic whitetip sharks and human consumers of this species.

Mercury (Hg) and selenium (Se) content in the shark Mustelus henlei (Triakidae) in the northern Mexican Pacific

Mercury and selenium were assessed in Mustelus henlei, which is a carnivorous predatory shark that is important for the coastal communities of the northern Mexican Pacific (NMP). Sixty-two individuals were sampled; muscle and liver were isolated and analyzed by atomic absorption spectrophotometry. The mean Hg concentrations (wet weight) obtained for muscle (0.08 ± 0.10 μg g^-1) and liver (0.09 ± 0.26 μg g^-1) were below the allowed limits (< 1.0 μg g^-1 Hg). The average Se concentration was 0.03 ± 0.01 μg g^-1 in muscle and 0.13 ± 0.05 μg g^-1 in liver. The Se/Hg molar ratio of muscle was 1.83; however, the selenium health benefit value (HBV_Se) was of 0.08. We calculated that an adult man (70 kg), an adult woman (60 kg), and a child (16 kg) could consume 1595, 838, and 223 g/week of M. henlei muscle, respectively, without risks to health. In conclusion, the concentrations and molar ratio of Hg and Se in M. henlei muscle mean that consumption of this shark's meat does not represent neither a benefit nor a public health risk.

Blood plasma levels of heavy metals and trace elements in white sharks (Carcharodon carcharias) and potential health consequences

Heavy metals may adversely affect health in marine organisms. As top predators, sharks may be especially vulnerable to exposure over long lifespans. Here we evaluate plasma levels of 14 heavy metals and 12 trace elements in white sharks, Carcharodon carcharias, in South Africa to determine whether they are related to sex, body size, and/or body condition and other health parameters. High levels of mercury and arsenic were found in shark blood at levels considered toxic in other vertebrates. Heavy metal concentrations were not related to body size or sex. Metal concentrations were not related to body condition with exception of copper, which was positively correlated. Protective effects of elements such as selenium, zinc, and iron were not detected. No negative effects on health parameters, such as total leukocytes or granulocyte to lymphocyte ratios were observed. Results suggest that sharks may have protective mechanisms that mitigate harmful effects of heavy metal exposure, providing new opportunities for future studies.

Mercury concentrations in three ray species from the Pacific coast of Baja California Sur, Mexico: Variations by tissue type, sex and length

Total mercury concentrations ([THg]) were determined in muscle and liver of the bat ray (Myliobatis californica), shovelnose guitarfish (Pseudobatos productus) and banded guitarfish (Zapteryx exasperata). Generalized linear models (GLM) were used to determine the effects of size and sex in [THg] and showed that both are determinants of [THg] in these species. The [THg] in both tissues significantly increased with length especially in sexually mature organisms with a steeper slope for mature male than mature female. This may relate to elasmobranchs sexual dimorphism driven variation in growth rates. Median muscle [THg] was significantly greater than liver in each ray species but there were some individuals with higher liver [THg] than muscle. There were individuals with muscle [THg] higher than the advisory thresholds of 0.2 and 0.5mgkg^-1ww (2.4 and 11% of the bat ray; 2.1 and 10% of the shovelnose guitarfish; 12.6 and 45% of the banded guitarfish, respectively).

Growth-related changes in non-essential and essential metals in the liver of star-spotted smooth-hounds (dogfish) Mustelus manazo from the northern region of Japan

We analyzed Cd, Hg, Zn, Cu, Mn and Fe concentrations in liver samples from male and female star-spotted smooth-hounds at various life stages. Male sharks of this species are known to reach their maximum body length (BL) more quickly than females, while females are known to mature later and live longer than males. Hepatic Cd and Hg concentrations in males and females markedly increased after maturation, but these increases proceeded earlier in males than in females. Hepatic Zn and Cu concentrations decreased during the growth stage of males and females, and thereafter increased concomitantly with increases of Cd and Hg burdens, forming a U-shaped curve over their lifespan, and the BL at which the lowest concentrations of Zn and Cu were observed was smaller in males than in females. These gender-related differences in those metals could reflect the faster growth and earlier cessation of growth in males.

Heavy metal concentrations in edible muscle of whitecheek shark, Carcharhinus dussumieri (elasmobranchii, chondrichthyes) from the Persian Gulf: A food safety issue

Together with several health benefits, fish meat could lead to heavy metal intoxication of consumers. In this study, we discuss Zn, Cu, Pb, Hg and Cd concentrations in fillets of forty specimens of Carcharhinus dussumieri, analyzed with atomic adsorption spectroscopy (AAS). The potential human health risks due to consumption of C. dussumieri was assessed by estimating average daily intake (EDI) and target hazard quotient (THQ) of metals. The average concentrations of metals measured in this study were (ppm dry weight): Cu 7.49 ± 0.25; Zn 3.47 ± 0.26; Pb 0.12 ± 0.03; Hg 0.028 ± 0.02; Cd 0.11 ± 0.03. Our results showed that no metal exceeded the EC and FAO limits. Cu and Cd accumulate in muscles with a body length (age)-dependent manner. The exposure daily intake of all toxic metals analyzed was found lower than the PTDI provided by WHO and the THQ resulted lower than 1, suggesting no risk for human health derived from consumption.

Trace elements (Cu, Zn, and Hg) and δ13C/δ15N in seabird subfossils from three islands of the South China Sea and its implications

Seabird subfossils were collected on three islands of the Xisha Archipelago, South China Sea. Via elemental analysis, we identified that bird guano was a significant source for heavy metals Cu, Zn, and Hg. Cu and Zn levels in these guano samples are comparable to their levels in wildbird feces, but guano Hg was lower than previously reported. Trophic positions significantly impacted transfer efficiency of heavy metals by seabirds. Despite of a common source, trace elements, as well as stable isotopes (i.e., guano δ(13)C and collagen δ(15)N), showed island-specific characteristics. Bird subfossils on larger island had relatively greater metal concentrations and revealed higher trophic positions. Partition of element and isotope levels among the islands suggested that transfer efficacy of seabirds on different islands was different, and bird species were probably unevenly distributed among the islets. Island area is possibly a driving factor for distributions of seabird species.

Metal Concentrations in the Liver and Stable Isotope Ratios of Carbon and Nitrogen in the Muscle of Silvertip Shark (Carcharhinus albimarginatus) Culled off Ishigaki Island, Japan: Changes with Growth

We analyzed Hg, Cd, Zn, Cu and Fe concentrations in liver samples as well as the Hg concentration and stable isotope ratios of carbon and nitrogen (δ13C and δ15N) in muscle samples from silvertip sharks (Carcharhinus albimarginatus) in Japan. Muscular and hepatic Hg concentrations increased with increased body length. However, these increases were more prominent in the liver than in the muscle samples, and appeared to occur after maturation. Hepatic Zn and Cu concentrations decreased during the growth stage, and then increased concomitantly thereafter with increases in Cd burden. Hepatic Fe concentration from males increased proportionally with increases in body length, whereas no increase was observed in samples from females, probably due to the mother-to-embryo transfer of Fe. The δ13C values tended to decrease with increases in body length, whereas no decrease in the δ15N values was observed.

Species-specific accumulation of methyl and total mercury in sharks from offshore and coastal waters of Korea

Limited information is available on mercury (Hg) levels in various shark species consumed in Korea. The methyl-Hg (Me-Hg) and total Hg concentrations in all shark species ranged from 0.08 to 4.5 (mean: 1.2) mg/kg wet weight and from 0.1 to 7.0 (mean: 1.4) mg/kg wet weight, respectively. Inter-species differences in Hg accumulation were found among the species; however, Hg accumulation was homogenous between dorsal and pectoral fins within species. The highest Hg levels were found in aggressive carnivore shark species. Trophic position was important in determining Hg accumulation for aggressive carnivore sharks. Approximately 80% of shark species exceeded the safety limits for Me-Hg established by domestic and international authorities. The mean estimated daily intake of Me-Hg (1.3 μg/kg body weight/day) for Korean populations consuming various sharks was higher than the guidelines proposed by international regulatory authorities, suggesting that excessive shark fin consumption may pose potential health risks for Koreans.

Stable isotope ratios of carbon, nitrogen and oxygen in killer whales (Orcinus orca) stranded on the coast of Hokkaido, Japan

We analyzed δ(13)C, δ(15)N and δ(18)O in the muscle and liver from killer whales stranded on the coast of Japan. The δ(15)N values in the muscle samples from calves were apparently higher than those in their lactating mothers, suggesting that nursing may result in the higher δ(15)N values in the muscle samples of calves. The δ(15)N value in the muscle samples of male and female whales, except for the calves, were positively correlated with the δ(13)C values and body length, suggesting that the increases in δ(15)N were due to the growth of the whales and increase in their trophic level. In contrast, the δ(18)O values in the muscle samples of female whales except for the calves were negatively correlated with the δ(13)C and δ(15)N values. The δ(18)O may be lower in whales occupying higher trophic positions (δ(15)N), although it might also be affected by geographic and climatic conditions.

Mercury bioaccumulation in cartilaginous fishes from Southern New England coastal waters: contamination from a trophic ecology and human health perspective

This study examined total mercury (Hg) concentrations in cartilaginous fishes from Southern New England coastal waters, including smooth dogfish (Mustelus canis), spiny dogfish (Squalus acanthias), little skate (Leucoraja erinacea), and winter skate (Leucoraja ocellata). Total Hg in dogfish and skates were positively related to their respective body size and age, indicating Hg bioaccumulation in muscle tissue. There were also significant inter-species differences in Hg levels (mean ± 1 SD, mg Hg/kg dry weight, ppm): smooth dogfish (3.3 ± 2.1 ppm; n = 54) > spiny dogfish (1.1 ± 0.7 ppm; n = 124) > little skate (0.4 ± 0.3 ppm; n = 173) ∼ winter skate (0.3 ± 0.2 ppm; n = 148). The increased Hg content of smooth dogfish was attributed to its upper trophic level status, determined by stable nitrogen (δ(15)N) isotope analysis (mean δ(15)N = 13.2 ± 0.7‰), and the consumption of high Hg prey, most notably cancer crabs (0.10 ppm). Spiny dogfish had depleted δ(15)N signatures (11.6 ± 0.8‰), yet demonstrated a moderate level of contamination by foraging on pelagic prey with a range of Hg concentrations, e.g., in order of dietary importance, butterfish (Hg = 0.06 ppm), longfin squid (0.17 ppm), and scup (0.11 ppm). Skates were low trophic level consumers (δ(15)N = 11.9-12.0‰) and fed mainly on amphipods, small decapods, and polychaetes with low Hg concentrations (0.05-0.09 ppm). Intra-specific Hg concentrations were directly related to δ(15)N and carbon (δ(13)C) isotope signatures, suggesting that Hg biomagnifies across successive trophic levels and foraging in the benthic trophic pathway increases Hg exposure. From a human health perspective, 87% of smooth dogfish, 32% of spiny dogfish, and <2% of skates had Hg concentrations exceeding the US Environmental Protection Agency threshold level (0.3 ppm wet weight). These results indicate that frequent consumption of smooth dogfish and spiny dogfish may adversely affect human health, whereas skates present minimal risk.

Carbon and nitrogen stable isotope ratios and mercury concentration in the scalp hair of residents from Taiji, a whaling town

We analyzed stable isotope ratios of carbon (δ(13)C) and nitrogen (δ(15)N) as well as mercury (Hg) concentration in the scalp hair of Japanese who consumed whale meat and those who did not, and investigated the relationships among the δ(13)C and δ(15)N values and Hg concentration. The average δ(15)N and δ(13)C values of whale meat-eaters (10.11‰ and -18.5‰) were significantly higher than those of non-eaters (9.28‰ and -18.9‰), respectively. The average Hg concentration of whale meat-eaters (20.6 μg/g) was significantly higher than that of non-eaters (2.20 μg/g). Significant positive correlations were found between the δ(13)C and δ(15)N values and between the δ(15)N value and Hg concentration in the hair of whale meat-eaters, while the correlation between the δ(15)N value and Hg concentration was not statistically significant in the non-eaters. The consumption of whale meat may increase Hg concentration as well as δ(15)N and δ(13)C values in scalp hair.