Relation between trophic position and mercury accumulation among fishes from the Tongue River Reservoir,Montana

Concentrations of total mercury were determined in muscle tissue from northern pike (Esox lucius), sauger (Stizostedion canadense), walleye (S. vitreum), black crappie (Pomoxis nigromaculatus), and white crappie (P. annularis) collected from the Tongue River Reservoir, Montana, prior to extensive surface coal-mine development in the region. Mercury concentrations in fish flesh increased with fish size and age; larger individuals of all five species exceeded the U.S. Food and Drug Administration's mercury concentration guideline of 0.5 μg/g. The rate of mercury accumulation was faster in the piscivorous species (northern pike, saugers, and walleyes) than in the planktivores (black crappies and white crappies). Differences in mercury uptake rates among the various species appeared to be directly related to the quantity of mercury eaten: results are discussed in relation to published models of mercury accumulation by fishes.     

Joint toxicity of mercury and selenium in salmonid eggs

Toxic interactions between mercury and selenium in fertilized eggs of rainbow trout (Salmo gairdneri) and lake trout (Salvelinus namaycush) were investigated and compared to the pronounced synergistic effect previously reported in carp (Cyprinus carpio) eggs. Mercury produced concentration-dependent decreases in median survival times and caused decreases in median hatch times. Selenium, at concentrations up to 10 mg Se/L, had no effect on hatching times, and did not produce mortality, and had no effect on mercury toxicity. At concentrations of 100 mg Se/L and higher, an apparent protective effect of selenium on mercury toxicity was observed in lake trout eggs. Requirements for additional research are discussed with emphasis on predictions of region-wide damage to freshwater fish populations due to atmospheric deposition of these chemical elements.     

Determination of Bioaccumulation of Heavy Metals and Selenium in Tissues of Brown Trout Salmo trutta macrostigma (Duméril, 1858) from Munzur Stream, Tunceli, Turkey

The objective of the present work was to determine the bioaccumulation of arsenic (As), cadmium (Cd), copper (Cu), lead (Pb), mercury (Hg), uranium (U) and selenium (Se) in gill, liver, and muscle tissues of the fresh water fish Salmo trutta macrostigma (Duméril, 1858) in Munzur Stream, Tunceli, Turkey. The highest concentrations of U (1.83?μg?kg^?1), Pb (119.84?μg?kg^?1) and Se (1.31?μg?kg^?1) were recorded in the gills of S. t. macrostigma. Concentrations of As (46.27?μg?kg^?1), Cd (109.19?μg?kg^?1), Hg (16.40?μg?kg^?1), Cu (18.19?μg?kg^?1) were recorded at highest levels in the liver. The results showed that there were significant differences in concentrations of As, Cd, Cu, Pb, Se, U and Hg in gill, liver and muscle tissue (p?<?0.05). Heavy metals were within the edible parts of the investigated fish were in the permissible safety levels for human uses.     

Low-Level Experimental Selenite Additions Decrease Mercury in Aquatic Food Chains and Fish Muscle but Increase Selenium in Fish Gonads

We investigated whether low-level addition of selenium (Se) could decrease mercury (Hg) in freshwater fish without imposing Se toxicity. Using a regression design, selenite was added to large mesocosms in a lake to achieve target concentrations ≤1.6 μg/L. ¹⁹⁸Hg (spike Hg) was added to mesocosms to determine changes in Hg bioaccumulation. Adding Se decreased spike total Hg (THg) in fish muscle, ambient THg in fish liver, and bioaccumulation of spike THg in muscle and spike methylmercury (MeHg) in zooplankton and Chironomid larvae relative to controls. Se decreased Hg in the food web but not in water, indicating that the dominant effect of Se on Hg cycling occurs in the food web. Concentrations of Se in gonads of fish were positively correlated with Se concentrations in water but did not exceed reproductive toxicity thresholds after 8 weeks. We conclude that low-level addition of Se decreases MeHg bioaccumulation and increases Se in gonads of fish; however, additions of Se to freshwater systems to decrease Hg in fish should be treated with caution because Se in fish gonads were likely to exceed toxic concentrations if exposed to increased Se for a longer period of time.     

Biomarkers of Contaminant Exposure in Northern Pike (<Emphasis Type="Italic">Esox lucius</Emphasis>) from the Yukon River Basin,Alaska

As part of a larger investigation, northern pike (n = 158; Esox lucius) were collected from ten sites in the Yukon River Basin (YRB), Alaska, to document biomarkers and their correlations with organochlorine pesticide (total p,p’-DDT, total chlordane, dieldrin, and toxaphene), total polychlorinated biphenyls (PCBs), and elemental contaminant (arsenic, cadmium, copper, lead, total mercury, selenium, and zinc) concentrations. A suite of biomarkers including somatic indices, hepatic 7-ethoxyresorufin O-deethylase (EROD) activity, vitellogenin concentrations, steroid hormone (17B- ustradiol and 16-kebtestosteront) concentrations, splenic macrophage aggregates (MAs), oocyte atresia, and other microscopic anomalies in various tissues were documented in YRB pike. Mean condition factor (0.50 to 0.68), hepatosomatic index (1.00% to 3.56%), and splenosomatic index (0.09% to 0.18%) were not anomalous at any site nor correlated with any contaminant concentration. Mean EROD activity (0.71 to 17.51 pmol/min/mg protein) was similar to basal activity levels previously measured in pike and was positively correlated with selenium concentrations (r = 0.88, P < 0.01). Vitellogenin concentrations in female (0.09 to 5.32 mg/mL) and male (<0.0005 to 0.097 mg/mL) pike were not correlated with any contaminant, but vitellogenin concentrations >0.01 mg/mL in male pike from multiple sites indicated exposure to estrogenic compounds. Mean steroid hormone concentrations and percent oocyte atresia were not anomalous in pike from any YRB site. Few site differences were significant for mean MA density (1.86 to 6.42 MA/mm²), size (812 to 1481 μm²), and tissue occupied (MA-%; 0.24% to 0.75%). A linear regression between MA-% and total PCBs was significant, although PCB concentrations were generally low in YRB pike (≤63 ng/g), and MA-% values in female pike (0.24% to 0.54%) were lower than in male pike (0.32% to 0.75%) at similar PCB concentrations. Greater numbers of MAs were found as zinc concentrations increased in YRB female pike, but it is unlikely that this is a causative relationship. Histological abnormalities observed in gill, liver, spleen, and kidney tissues were not likely a result of contaminant exposure but provide information on the general health of YRB pike. The most common histologic anomalies were parasitic infestations in various organs and developing nephrons and nephrocalcinosis in posterior kidney tissues. Overall, few biomarker responses in YRB pike were correlated with chemical contaminant concentrations, and YRB pike generally appeared to be healthy with no site having multiple anomalous biomarker responses.     

Tissue levels of mercury determined in a deceased worker after occupational exposure

Objectives: To examine mercury (Hg) and selenium (Se) levels in autopsy samples from a thermometer worker who had been exposed over a long period to, and monitored for, mercury vapor. Case report: Hg and Se levels were determined using radiochemical neutron activation analysis in a worker who had commited suicide 4 weeks after the end of 14 years of exposure and in an unexposed age-matched referent. Histochemical staining of cerebellum was performed according to the method of Danscher and Schrøder. Results: The Hg concentrations (wet weight) were 25?μg/g in the kidney cortex, 1.2?μg/g in the liver, 0.72?μg/g in the lung, 0.025?μg/g in the testis, and 0.014–0.018?μg/g in the cerebellum (gray matter, dentate nucleus, and white matter). The Se level in the kidney cortex was high, 4.6?μg/g, whereas the concentration detected in the other tissue samples was normal. Light microscopy of the cerebellum was normal, and no histochemical staining for mercury was observed. Autopsy samples from the referent showed low Hg and Se levels consistent with other reports. Conclusions: The observed kidney-Hg, which was 50–100 times higher than that occurring in the general population, is in agreement with previous sparse data from ongoing occupational exposure. The high Se level detected in the kidney indicates coaccumulation with mercury. The low Hg concentration found in the cerebellum was unexpected, since some reports have shown much higher brain-Hg long after the cessation of exposure.     

Mercury Contamination in Idaho Bald Eagles, <Emphasis Type="Italic">Haliaeetus leucocephalus</Emphasis>

Because mercury contamination is potentially threatening to bald eagle (Haliaeetus leucocephalus) populations, we collected molted feathers at nests to determine the level of contamination in bald eagles in the state of Idaho, USA. Eagle feathers contained measurable amounts of cadmium (Cd), chromium (Cr), selenium (Se), lead (Pb), as well as mercury (Hg). Cadmium, Cr, Se, and Pb levels averaged 0.17, 4.68, 2.02, and 1.29 mg/kg dry weight, respectively, and were at or below concentrations indicated as causing reproductive failure in bald eagles. Mercury contamination was found to be the highest averaging 18.74 mg/kg dry weight. Although a concentration of only 7.5 mg/kg dry weight Hg in bird feathers can cause reduced productivity and even sterility, all of the eagles we sampled bred successfully and the population of bald eagles continues to grow annually throughout the state.     

Zinc Distribution in the Organs of Adult Fundulus heteroclitus After Waterborne Zinc Exposure in Freshwater and Saltwater

Zinc (Zn) is an essential micronutrient to aquatic organisms, but increased concentrations may result in accumulation and toxic effects. Water chemistry is known to influence the uptake of Zn in aquatic biota; therefore, organisms inhabiting environments with variable salinities may exhibit different patterns of Zn accumulation. Likewise, metal uptake can vary in fish as a consequence of ionoregulatory status (acclimated to freshwater or saltwater). The euryhaline fish, Fundulus heteroclitus, was exposed to a control and two increased Zn concentrations (15 and 75?μg/L in moderately hard freshwater and 100 and 1,000?μg/L in 35?g/L saltwater) for 7?days. The ionic Zn concentrations were equivalent in the 75?μg/L Zn treatment in freshwater and the 100?μg/L Zn treatment in saltwater. Throughout the 7-day experiments, fish were dissected, and organ Zn distribution was quantified in the gill, intestine, liver, gall bladder, heart, and carcass. Different patterns of Zn accumulation were observed in F. heteroclitus dependent on exposure medium. Despite lower exposure concentrations, F. heteroclitus accumulated more Zn in freshwater than in saltwater in all of the organs analyzed with the exception of the carcass. In addition, there were correlations between Zn distribution and known physiological mechanisms related to osmoregulation in F. heteroclitus. Furthermore, this research suggests that F. heteroclitus are more susceptible to Zn accumulation in freshwater environments.     

Comparative acute toxicity and bioconcentration of selenium by the midge Chironomus decorus exposed to selenate,selenite, and seleno-DL-methionine

The increased flux of selenium into aquatic ecosystems due to anthropogenic activities has resulted in the degradation of several systems. Initial experiments examined the comparative acute toxicity of waterborne selenate, selenite, and seleno-DL-methionine to fourth instar Chironomus decorus larvae resulting in 48-h LC₅₀ concentrations of 23.7, 48.2, and 194 mg Se/L, respectively. The relative toxicities of the selenium forms are reversed compared to previous studies on other species and demonstrate that relative waterborne selenium toxicity is species specific. Studies examining the kinetics of selenate and selenite (the dominant waterborne forms) accumulation by C. decorus larvae exposed to the 48-h LC₅₀ selenium concentrations showed initial rapid uptake and subsequent plateauing with maximum concentrations attained by 16 h. The final whole body selenium levels were approximately 63 mg Se/kg for selenate and 85 mg Se/kg for selenite. Comparative bioconcentration experiments demonstrated that after 48 h selenium accumulation was greater in larval C. decorus exposed to 25 mg Se/L as seleno-DL-methionine than in those exposed to 25 mg Se/L as selenate and selenite.     

Concentrations of selenium,barium, and radium in Brazil nuts

The concentrations of selenium, barium, and radium were determined in Brazil nuts grown in four regions: Brazil, Bolivia, Peru, and an unknown locality assigned to northern South America. Results indicated that, regardless of geographic origin, all nuts contained measurable amounts of selenium, barium, and radium. The concentration range of Se (2–20 μg/g) and that of Ba (96–1990 μg/g) each varied by more than an order of magnitude in the nuts, while ²²⁶Ra (17–27 mBq/g) and ²²⁸Ra (18–31 mBq/g) activities were comparable and within a factor of two of one another. The greatest concentrations of the elements were measured in nuts from Bolivia, for Ba; Brazil, for Ra; and northern South America, for Se. Only the northern South American nuts contained ¹³⁷Cs.     

Detoxification Mechanism of Heavy Metals in Marine Mammals and Seabirds: Interaction of Selenium with Mercury,Silver, Copper,Zinc, and Cadmium in Liver

Subcellular distribution of mercury, selenium, silver, copper, zinc, and cadmium was determined in the liver of northern fur seals (Callorhinus ursinus), black-footed albatrosses (Diomedea nigripes), and Dalls porpoises (Phocoenoides dalli). Mercury, selenium, and silver were preferentially accumulated in nuclear, lysosomal, and mitochondrial fraction with an increase in their hepatic concentrations, whereas copper, zinc, and cadmium were accumulated mainly in cytosol with an increase in the hepatic concentrations for all three species. To gain insight into the existing state of the metals, they were extracted with four extractants—sodium dodecylsulfate (SDS); 2-mercaptoethanol; 2-mercaptoethanol + guanidinium thiocyanate; and copper sulfate (CuSO₄)—at several concentrations from nuclear, lysosomal, and mitochondrial fraction in liver from a specimen of northern fur seal. Extraction efficiencies of the metals for 2-mercaptoethanol + guanidinium thiocyanate and CuSO₄ were much higher than those for SDS and 2-mercaptoethanol. Also, for all individuals of the three species, metals were extracted by the three extractants—2% SDS; 0.25 mol/L 2-mercaptoethanol + 5 mol/L guanidinium thiocyanate; and 0.1 mol/L CuSO₄—from nuclear, lysosomal, and mitochondrial fraction of liver. In the northern fur seals with higher concentration of mercury, the molar ratio of selenium to mercury approached unity in the nonextractable fraction of 0.25 mol/L 2-mercaptoethanol + 5 mol/L guanidinium thiocyanate, suggesting the possible formation of mercuric selenide (HgSe) with increasing hepatic concentration. Because the nonextractable content of mercury and its distribution were larger for black-footed albatross than those for the other two species, it was suggested that the black-footed albatross has a stronger ability to form a stable compound(s) of mercury in the liver. It is notable that the existing state of silver was similar to that of mercury as judged by their subcellular distribution and the extraction tests, suggesting that silver also interacted with selenium in the liver of marine animals used in this study.     

Mercury Elimination Rates for Adult Northern Pike Esox lucius: Evidence for a Sex Effect

We examined the effect of sex on mercury elimination in fish by monitoring isotope-enriched mercury concentrations in the muscle tissue of three adult female and three adult male northern pike Esox lucius, which had accumulated the isotope-enriched mercury via a whole-lake manipulation and were subsequently moved to a clean lake. Mercury elimination rates for female and male northern pike were estimated to be 0.00034 and 0.00073 day^?1, respectively. Thus, males were capable of eliminating mercury at more than double the rate than that of females. To the best of our knowledge, our study represents the first documentation of mercury elimination rates varying between the sexes of fish. This sex difference in elimination rates should be taken into account when comparing mercury accumulation between the sexes of fish from the same population. Further, our findings should eventually lead to an improved understanding of mechanisms responsible for mercury elimination in vertebrates.     

SLC30A3 and SEP15 gene polymorphisms influence the serum concentrations of zinc and selenium in mature adults

Because of their numerous roles in several biological processes, zinc and selenium are the most commonly studied micronutrients in the elderly. Therefore, we hypothesized that the polymorphisms in the genes that are responsible for the transport of zinc and selenium may have a genotype-dependent effect on the serum concentration of these micronutrients. The objective of this study was to determine the effects of solute carrier family 30 member 3 (SLC30A3) and 15-kd selenoprotein (SEP15) polymorphisms on zinc and selenium concentrations, respectively, in the serum. This cross-sectional study included 110 individuals who were aged 50 years or older. Serum micronutrient concentrations were determined by flame atomic absorption spectrophotometry (for zinc) and by atomic absorption spectrophotometry with a graphite furnace (for selenium). The single-nucleotide polymorphisms, rs73924411 and rs11126936 of the SLC30A3 gene and rs5859, rs5854, and rs561104 of the SEP15 gene, were examined by real-time polymerase chain reaction. Regarding rs11126936, the serum zinc concentration was lower in CC homozygotes (0.75 ± 0.31 mg/L) than in A carriers (0.89 ± 0.28 mg/L, P = .016). Concerning rs561104, the serum selenium concentration was higher in CC homozygotes (5.65 ± 1.11 μg/dL) compared with T carriers (4.88 ± 1.25 μg/dL, P = .044). Our results demonstrate the influence of SLC30A3 and SEP15 gene polymorphisms on the serum concentrations of zinc and selenium, respectively. The effects of these associations should be further investigated to help elucidate the modes of action of trace elements and to identify biomarkers, which could ultimately define the optimal intake of these micronutrients at the molecular level. More research must be performed before the roles of these polymorphisms in the serum concentrations of zinc and selenium can be fully understood.     

The antagonism between selenium and cadmium in a freshwater mollusc

The protective effect of selenium against cadmium toxicity in rats is well documented. Data concerning such protection are lacking in invertebrates. The object of this study was to check whether such an antagonism between Se and Cd can be found in the freshwater molluscLymnaea stagnalis L. In the presence of sublethal amounts of selenium, sensitivity with respect to cadmium is nearly halved. Sublethal amounts of cadmium give additional protection against the toxic effects of selenium, since this concentration completely prevented mortality due to high doses of selenite (3 mg/L Se) and selenate (15 mg/L Se).     

Selenium Bioaccumulation by the Water Boatman Trichocorixa reticulata (Guerin-Meneville)

The input of selenium from subsurface agricultural drainage into surface water systems can result in the accumulation of toxic concentrations of selenium in aquatic food chains. Elevated selenium concentrations in aquatic systems is a significant environmental problem in many areas of the United States. A laboratory investigation was conducted to determine the dominant route of selenium bioaccumulation by the corixid Trichocorixa reticulata, an important food chain organism. The roles of waterborne and foodborne exposure in selenium bioaccumulation were examined using 48-h bioassays. Waterborne selenium concentrations ranged from 0 to 1,000 μg Se/L as selenate. A mixture of two species of blue-green algae cultured in media with selenium concentrations ranging from 0 to 1,000 μg Se/L as selenate was used as a corixid diet in the foodborne treatments. Corixids exposed to waterborne selenate did not accumulate selenium above control concentrations. Corixids fed algae exposed to ≥100 μg Se/L as selenate had significantly higher selenium concentrations than control organisms. These data suggest that corixids may be effectively isolated from the water and selenium accumulation is solely through dietary exposure. Received: 8 July 1998/Accepted: 21 October 1998     

Selenium bioaccumulation in aquatic ecosystems: 1. Effects of sulfate on the uptake and toxicity of selenate in Daphnia magna

Selenium contamination and toxicity have been reported for aquatic ecosystems across the United States. Because waterborne selenium concentrations in natural systems are seldom high enough to be directly toxic, it has been concluded that bioaccumulation of selenium is causing observed toxicity problems. As a result, information regarding the bioaccumulation processes of selenium in aquatic organisms is necessary for appropriate management and remediation of selenium in aquatic ecosystems. Studies of selenium bioaccumulation in bacteria, fungi, and algae have indicated that selenate and sulfate compete for uptake via a common mechanism. However, such competitive interactions have not been examined in higher, multi-cellular organisms. To address this, we conducted experiments to determine how changes in ambient sulfate concentrations affect the uptake of selenate in the freshwater crustacean Daphnia magna. D. magna were exposed to waterborne selenate concentrations ranging from control to 500 g/L Se with varying concentrations of sulfate ranging from 0 mg/L to concentrations equivalent to EPA very hard water. At the higher concentrations of selenate, selenium uptake increased significantly as sulfate concentrations decreased. No toxicity was observed except at the 500 g/L Se and no sulfate treatment, where virtually all of the daphnids died within 72 h.     

The effect of sulfate on the bioconcentration of selenate by Chironomus decorus and Daphnia magna

Agricultural drainage containing high concentrations of selenium (Se) poses a continuing threat to wildlife in California's San Joaquin Valley. Drainage water from this area frequently contains high concentrations of sulfate, which are known to have mediating effects on the bioaccumulation and toxicity of Se in some organisms. It has been proposed that sulfate concentration should be a consideration in determining water quality criteria for Se. As a step toward analyzing the viability of such a plan, this study evaluated the effect of varying sulfate concentration on Se bioconcentration by two aquatic invertebrates. Fourth instar Chironomus decorus and neonate Daphnia magna were exposed, for a 48 h period, to 5.92 and 0.71 mg Se/L, as selenate, respectively. The selenium:sulfur (Se:S) ratio in the dilution waters ranged from 1:0 to 1:480 for C. decorus and 1:3 to 1:240 for D. magna. Increasing sulfate concentrations significantly reduced the accumulation of Se by both organisms. However, D. magna and C. decorus bioconcentrate Se differently at low sulfate concentrations. This difference can be explained by a two permease model for selenate/sulfate absorption. Although this experiment showed that sulfate may reduce selenate bioavailability to aquatic invertebrates, there is no indication that sulfate may completely eliminate selenate absorption. Thus, further research should be performed before sulfate concentration becomes a factor in the determination of water quality standards for selenium.     

Environmental Contaminants in Fish and Their Associated Risk to Piscivorous Wildlife in the Yukon River Basin, Alaska

Organochlorine chemical residues and elemental contaminants were measured in northern pike (Esox lucius), longnose sucker (Catostomus catostomus), and burbot (Lota lota) from 10 sites in the Yukon River Basin (YRB) during 2002. Contaminant concentrations were compared to historical YRB data and to toxicity thresholds for fish and piscivorous wildlife from the scientific literature. A risk analysis was conducted to screen for potential hazards to piscivorous wildlife for contaminants that exceeded literature-based toxicity thresholds. Concentrations of total DDT (sum of p,p′-homologs; 1.09–13.6 ng/g), total chlordane (0.67–7.5 ng/g), dieldrin (<0.16–0.6 ng/g), toxaphene (<11–34 ng/g), total PCBs (<20–87 ng/g), TCDD-EQ (≤1.7 pg/g), arsenic (0.03–1.95 μg/g), cadmium (<0.02–0.12 μg/g), copper (0.41–1.49 μg/g), and lead (<0.21–0.27 μg/g) did not exceed toxicity thresholds for growth and reproduction in YRB fish. Concentrations of mercury (0.08–0.65 μg/g), selenium (0.23–0.85 μg/g), and zinc (11–56 μg/g) exceeded toxicity thresholds in one or more samples and were included in the risk analysis for piscivorous wildlife. No effect hazard concentrations (NEHCs) and low effect hazard concentrations (LEHCs), derived from literature-based toxicity reference values and avian and mammalian life history parameters, were calculated for mercury, selenium, and zinc. Mercury concentrations in YRB fish exceeded the NEHCs for all bird and small mammal models, which indicated that mercury concentrations in fish may represent a risk to piscivorous wildlife throughout the YRB. Low risk to piscivorous wildlife was associated with selenium and zinc concentrations in YRB fish. Selenium and zinc concentrations exceeded the NEHCs and LEHCs for only the small bird model. These results indicate that mercury should continue to be monitored and assessed in Alaskan fish and wildlife.     

Accumulation,sublethal effects,and safe concentration of a refined oil as evaluated with cutthroat trout

Cutthroat trout (Salmo clarki) were exposed for 90 days in the laboratory to a refined oil collected from the North Platte River at a seepage site below the American Oil Company refinery at Casper, Wyoming. Fish were exposed to five concentrations and a control, and seven biological responses (survival, growth, gill pathology, liver pathology, caudal fin erosion, caudal fin pathology and swimming performance) were correlated with water concentration and tissue accumulation of petroleum hydrocarbons. Fish in the highest water concentration, 183μg/L total oil, accumulated tissue concentrations of 4.6μg/g total naphthalenes and responded adversely to all seven biological measurements. Cutthroat trout in the lowest water concentration, 24μg/L total oil, had a mean tissue concentration of 1.2μg/g total naphthalenes, but their response was similar to that of the control fish to all seven biological responses. Fish exposed to 39μg/L water concentration accumulated tissue concentrations of 2.7μg/g and responded negatively to 2 of the 7 biological measurements. Therefore, the maximum safe limit for this oil and cutthroat trout is between 24 and 39μg/L.     

Mercury Contamination of Fish and Shrimp Samples Available in Markets of Mashhad, Iran

Fish and shrimp are common healthy sources of protein to a large percentage of the world’s population. Hence, it is vital to evaluate the content of possible contamination of these marine-foods. Six species of fishes and two species of shrimps were collected from the local markets of Mashhad, Iran. The mercury (Hg) concentration of samples was determined by atomic absorption spectrophotometry using a mercuric hydride system (MHS 10). High concentration of total Hg was found in Clupeonella cultriventris caspia (0.93 ± 0.14 μg/g) while the lowest level was detected in Penaeus indicus (0.37 ± 0.03 μg/g). Mean Hg levels in fish and shrimp samples were 0.77 ± 0.08 μg/g and 0.51 ± 0.05 μg/g, respectively. Farmed species (except for P. indicus) and all samples from Persian Gulf and the Caspian Sea had mean mercury concentrations above 0.5 μg/g, which is the maximum standard level recommended by Joint FAO/WHO/Expert Committee on Food Additives (JECFA). All samples had also mean Hg concentrations that exceeded EPA’s established safety level of 0.3 μg/g. A little more extensive analysis of data showed that weekly intake of mercury for the proportion of the Iranian population consuming Hg contaminated fish and shrimp is not predicted to exceed the respective provisional tolerable weekly intakes recommended by JECFA. However, the Iranian health and environmental authorities should monitor Hg contamination of the fishes and shrimps before marketing.