Mercury and selenium in blue shark (Prionace glauca, L. 1758) and swordfish (Xiphias gladius, L. 1758) from two areas of the Atlantic Ocean

Inhibition of the thioredoxin system in the brain and liver of zebra-seabreams exposed to waterborne methylmercury

Mercury compounds were recently found to interact in vitro with the thioredoxin system, inhibiting both Thioredoxin (Trx) and Thioredoxin reductase (TrxR). In order to evaluate if Trx and TrxR are affected in vivo by methylmercury (MeHg), we exposed juvenile zebra-seabreams to different concentrations of this toxicant in water for 28days followed by a 14-day depuration period. Methylmercury accumulated to a larger extent in the kidney and liver of fishes, but decreased significantly during the depuration. During the exposure, MeHg percentage in the liver reached levels above 90% of total mercury (HgT) decreasing to 60% of HgT by the end of the depuration period. In the kidney, MeHg accounted for 50-70% of HgT. In the brain and muscle, mercury accumulated throughout the exposure with all mercury being MeHg. The total mercury kept increasing in these organs during the depuration period. However, in the brain, this increase in HgT was accompanied by a decrease in the MeHg percentage (~10%). In the liver, both Trx and TrxR activities were significantly reduced (TrxR--40%; Trx--70%) by the end of the exposure, but recovered to control levels (100%) during the depuration. In the brain, both enzymes where inhibited during the depuration period (TrxR--75%; Trx--70%) when some production of inorganic mercury was detected. Activity of glutathione reductase showed increased levels when TrxR activity was low, suggesting complementarity between both systems. These results indicate that in vivo the thioredoxin system is a toxicological target for MeHg with TrxR being particularly affected.

Mercury bioaccumulation in the spotted dogfish (Scyliorhinus canicula) from the Atlantic Ocean

The annual and life-cycle mercury bioaccumulation pattern in selected tissues of the economically relevant Elasmobranchii species Scyliorhinus canicula was studied, and the risks associated with its consumption evaluated. Preferential mercury bioaccumulation occurred in muscle tissue, and followed the order muscle>heart>liver>gills>pancreas. Total mercury in muscle tissue ranged from 0.13mgkg(-1) (wwt) in 1+year old males to 0.8mgkg(-1) (wwt) in 8+ year old mature females, with no significant differences found between genders, and no clear lifespan bioaccumulation pattern observed, except for mature females. Organic mercury in the muscle ranged from 0.05mgkg(-1) (wwt) to 0.52mgkg(-1) (wwt), corresponding to an average of 70% of total mercury content. In mature females, a significant correlation (R=0.99, P=0.01) was found between size and organic mercury fraction, suggesting reproduction as an important factor controlling organic mercury bioaccumulation in the spotted dogfish.

Estimation of risk assessment of some heavy metals intake through black scabbardfish (Aphanopus carbo) consumption in Portugal

The intake of Cd, methyl-Hg, and Pb through consumption of black scabbardfish (BSF) (Aphanopus carbo) in Portugal as well as the associated probability of exceeding the respective provisional tolerable weekly intakes (PTWIs) was estimated. For this purpose, the contamination levels of heavy metals in this fish species were combined with constructed consumption scenarios or with a hypothesized consumption distribution. Whereas Cd and Pb posed no serious risk, the consumption of at least one portion of BSF per month as well as the hypothetical study in the Portuguese population produced nonnegligible probabilities of surpassing the PTWI for Me-Hg. Risk assessment for Portuguese consumers revealed a higher risk regarding Me-Hg, 1.19% and 1.81% with the plug-in (PI) and the tail estimation (TE) estimators, respectively. On the other hand, the risk for Cd and Pb was less than 1 in 100,000. TE was more realistic and accurate for Cd and Pb. Concerning Me-Hg, TE and PI estimators produced similar results. Furthermore, the limitations of a deterministic approach were shown.

Nonessential metals in striped marlin and Indo-Pacific sailfish in the southeast Gulf of California, Mexico: concentration and assessment of human health risk

Seventeen sailfish (Istiophorus platypterus; 166-246 cm long) and 13 striped marlin (Tetrapturus audax; 159-254 cm long) specimens from the southern Gulf of California were analyzed for As, Cd, Hg, and Pb concentrations. More than 20% of the As and Cd levels exceeded the guideline levels of the World Health Organization (WHO), the U.S. Food and Drug Administration, and the European Union. About 65-90% of the specimens exceeded the limit value for Hg. Pb levels in billfish were significantly lower than guideline values. The intakes of As and Cd through billfish consumption by the population represented 20-40% of the provisional tolerable weekly intake (PTWI) values as recommended by the WHO. Levels of Hg exceeded the PTWI value. Pb intake represented <5% of the PTWI through these species in all age and gender groups. The target hazard quotients (THQs) for Cd and Pb were <1 in each group of interest. In contrast, THQ values based on As and Hg showed large variations, with the highest values for children, then pregnant women, and, finally, adults. Values of THQ >1 indicate risk for As and Hg; the risk from As was estimated assuming that 20% of the total As was inorganic. These metals can affect the nervous system and intellectual and physical development of unborn children and infants. A national moratorium on billfish consumption in México is recommended for children (0-6 years old), pregnant women, and women planning pregnancy.

Effects of diet composition and trophic structure on mercury bioaccumulation in temperate flatfishes

The summer flounder Paralichthys dentatus and winter flounder Pseudopleuronectes americanus support valuable fisheries along the northeastern United States. The importance of these flatfish as a human dietary resource indicates they are potential sources of mercury (Hg) to fish-consuming citizens. In this study, summer flounder (SF) and winter flounder (WF) were collected from the Narragansett Bay (Rhode Island, USA) and were measured for total Hg burden in whole-body or dorsal muscle tissue. Interspecies differences in Hg contamination were analyzed relative to flounder body size, age, and Hg content of preferred prey. Stable isotope signatures were also used to elucidate the effect of trophic processes on Hg accumulation in the estuarine food web. The mean Hg content of SF exceeded concentrations measured in WF across multiple life-history stages (0.039-0.100 and 0.016-0.029 mg Hg/kg wet weight for SF and WF, respectively), and observed values for both species were lower than the US Environmental Protection Agency regulatory threshold of 0.3 mg Hg/kg wet weight. Total Hg concentrations were also positively correlated with flounder age and length, verifying that both flatfish bioaccumulate Hg. SF accumulate Hg at an accelerated rate, however, owing to this species consuming Hg-enriched prey (teleosts, squid, and macrocrustaceans; mean Hg content = 0.023 mg Hg/kg wet weight), whereas WF feed on prey with low Hg levels (amphipods and polychaetes; mean Hg content = 0.013 mg Hg/kg wet weight). The positive correlation observed between mean biota Hg content and stable nitrogen (delta(15)N) isotope signatures further indicates that Hg is trophically transferred through the food web, and higher trophic level organisms (i.e., enriched delta(15)N) have increased Hg concentrations. Therefore, results from this study suggest that dietary preference and trophic structure are the main factors affecting Hg bioaccumulation in the estuary. Total Hg concentrations of flatfish from the Narragansett Bay, however, do not necessarily reflect coastwide contamination patterns. This reinforces the importance of having research conducted at sufficiently small spatial scales, including the local assessment of Hg contamination for the purpose of issuing state consumption advisories.

Contamination levels of mercury in the muscle of female and male spiny dogfishes (Squalus acanthias) caught off the coast of Japan

We analyzed the total mercury (T-Hg) and stable isotopes of (13)C and (15)N in the muscle of spiny dogfish (Squalus acanthias) caught off the coast of Japan. The average body length of the female spiny dogfish sampled (94.9+/-20.2 cm, 50.5-131.0 cm, n=40) was significantly larger than that of the males sampled (77.8+/-10.8 cm, 55.5-94.0 cm, n=35), although the ages of the samples were unknown. The T-Hg concentration in the muscle samples rapidly increased after maturity in the females (larger than about 120 cm) and males (larger than about 90 cm), followed by a continued gradual increase. Contamination level of T-Hg in female muscle samples (0.387+/-0.378 microg(wet g)(-1), n=40) was slightly higher than that in male muscle samples (0.316+/-0.202 microg(wet g)(-1), n=35), probably due to the greater longevity of females. In contrast, the contamination level of T-Hg in females smaller than 94.0 cm in length (0.204+/-0.098 microg(wet g)(-1), n=20) was slightly lower than that in the males, probably due to the faster growth rate of females. Although the partial differential(13)C and partial differential(15)N values in the muscle samples increased with an increase in body length, there were no significant differences between the females (-17.2+/-0.4 per thousand and 12.4+/-0.9 per thousand, respectively) and males (-17.3+/-0.4 per thousand and 12.4+/-0.8 per thousand, respectively). A positive correlation was found between partial differential(13)C and partial differential(15)N values, suggesting trophic enrichment due to the growth.

Integrated mercury monitoring program for temperate estuarine and marine ecosystems on the North American Atlantic coast

During the past century, anthropogenic activities have altered the distribution of mercury (Hg) on the earth's surface. The impacts of such alterations to the natural cycle of Hg can be minimized through coordinated management, policy decisions, and legislative regulations. An ability to quantitatively measure environmental Hg loadings and spatiotemporal trends of their fate in the environment is critical for science-based decision making. Here, we outline a Hg monitoring program for temperate estuarine and marine ecosystems on the Atlantic Coast of North America. This framework follows a similar, previously developed plan for freshwater and terrestrial ecosystems in the U.S. Methylmercury (MeHg) is the toxicologically relevant form of Hg, and its ability to bioaccumulate in organisms and biomagnify in food webs depends on numerous biological and physicochemical factors that affect its production, transport, and fate. Therefore, multiple indicators are needed to fully characterize potential changes of Hg loadings in the environment and MeHg bioaccumulation through the different marine food webs. In addition to a description of how to monitor environmental Hg loads for air, sediment, and water, we outline a species-specific matrix of biotic indicators that include shellfish and other invertebrates, fish, birds and mammals. Such a Hg monitoring template is applicable to coastal areas across the Northern Hemisphere and is transferable to arctic and tropical marine ecosystems. We believe that a comprehensive approach provides an ability to best detect spatiotemporal Hg trends for both human and ecological health, and concurrently identify food webs and species at greatest risk to MeHg toxicity.

Hg, Zn and Cu levels in the muscle and liver of tiger sharks (Galeocerdo cuvier) from the coast of Ishigaki Island, Japan: relationship between metal concentrations and body length

We analyzed Hg, Zn and Cu concentrations in the liver and muscle of tiger sharks (Galeocerdo cuvier) from the coast of Ishigaki Island, Japan. The Hg concentration in the muscle increased proportionally with body length in the tiger sharks, whereas that in the liver increased rapidly after maturity (defined by a length of over 2.7 m). Muscle Hg levels were higher than liver concentrations in immature sharks, with the inverse trend observed in mature sharks. Notably, the Zn and Cu concentrations in the liver tended to decrease with increasing body length. This rapid increase in hepatic Hg concentration concurrent with the onset of maturity in sharks may result from the continuous intake of Hg via food and the slower growth of mature sharks. The high concentrations of the essential metals Zn and Cu in immature sharks may be explained by the physiological demands related to rapid growth.