Mean Total Mercury Concentration Research Articles

Mercury monitoring in the coastal areas of the Republic of Korea using the black-tailed gull egg as an indicator

In the southeast and east coasts of the Republic of Korea, it is essential to monitor mercury accumulation in coastal organisms in view of the higher mercury distribution in sediments and human samples. However, mercury pollution monitoring in organisms, especially higher trophic-level organisms that can exhibit high mercury accumulation, is limited. Here, we examined the applicability of the eggs of the black-tailed gull (Larus crassirostris), which belongs to a high trophic level, for mercury monitoring in coastal areas. Breeding sites were selected in West, Southeast, and East Seas with different mercury concentrations in other matrices (sediment and biological samples of residents). The 5-year mean total mercury concentration in eggs collected during the breeding seasons from 2016 to 2020 was lower in Baengnyeongdo (705 ± 81 ng/g dry weight (dry), West Sea) than in Hongdo (1,207 ± 214 ng/g dry, Southeast Sea) and Ulleungdo (1,095 ± 95 ng/g dry, East Sea). The different patterns of mercury concentration in gull eggs among the breeding sites was consistent with those in the other matrices among the coastal areas. These results support the applicability of the black-tailed gull egg as an indicator for establishing a monitoring framework in the coastal areas of the Republic of Korea.

Enhanced Mercury Accumulation in Riparian Spiders: An Evidence of Insects' Emergence Effect in Aquatic and Upland Terrestrial Crossed Habitat.

Many studies have focused on mercury (Hg) accumulation in both aquatic and terrestrial organisms, but the effects of aquatic Hg on terrestrial organisms have rarely been documented. Here we report the accumulation of Hg in two species of spiders, Argiope bruennichi, inhabiting paddy fields, and Nephila clavata, inhabiting small forests in the riparian zones of two hydroelectric reservoirs in Guiyang, southwest China. The mean concentration of total mercury (THg) was higher in N. clavata (0.38mgkg-1) than in A. bruennichi (0.20mgkg-1). The monthly average THg in N. clavata, collected consecutively from May to October, and the highest values for THg in June (1.2mgkg-1) could be related to the emergence of aquatic insects during early summer, suggesting that emerging insects play a crucial role in the accumulation of Hg in riparian spiders. The high values could also be attributable to the different times of spider sampling or individual differences.

Atmospheric wet deposition of mercury in urban Jinan, eastern China: Speciation, scavenging process and potential sources

Understanding the speciation and related influence factors of Hg in wet deposition is important to predict the fate and transport of mercury in the atmosphere. In this study, event-based samples of rainwater were collected for one year in Jinan, a northern city in eastern China. The volume-weighted mean concentration of total mercury (THg) in rainwater was 34.8 ng L−1, comparable to levels in some inland cities in China and were significantly higher than those in North America, Korea and Japan. Most of the Hg in rainwater was associated with particulates, accounted for 15.2–92.9% of THg with a mean of 66.9%, which might be attributed to the scavenging effects of high particulate-bound mercury concentrations in ambient air in urban Jinan. Dissolved mercury (DHg) accounted for 33.1% of THg, in which Hg(OH)2, HgClOH, HgCl2 and Hg(NH3)22+ are the dominant species based on the chemical equilibrium modeling simulations. THg concentrations in rainwater decreased as the rainfall amount increased owing to the dilution effect and 5 mm rainfall might be a threshold for the full wash-out capability of atmospheric Hg. For a continuous rain event, the proportion of DHg in THg could increase from 7.1% to 84.8% with the rainfall processing, especially for the species of HgClOH and HgCl2 under the influence of rainwater pH. Positive matrix factorization (PMF) analysis suggested that the major sources of Hg in rainwater were combustion emissions, marine sources, industrial emissions, as well as complexation process, which contributed to 51.4%, 24.7%, 12.2%, and 11.7% of the THg, respectively. For the specific species, the main sources varied with different Hg species, in which combustion emissions contributed one third to one half of each species sum to particulate mercury (PHg), HgClOH, HgCl2, HgBrOH and HgBrCl followed by marine sources and industrial emissions. Cluster analysis of backward trajectories revealed that polluted air masses, transported from southeast Shandong, Anhui and Jiangsu Provinces, as well as Beijing-Tianjin-Hebei region, contributed to high Hg concentration in rainwater in Jinan.

High mercury concentrations in steelhead/rainbow trout, sculpin, and terrestrial invertebrates in a stream-riparian food web in coastal California.

Stream and riparian food webs are connected by cross-habitat exchanges of invertebrate prey that can transfer contaminants including mercury. Marine fog has been identified as a source of methylmercury (MeHg) to some terrestrial food webs in coastal California, suggesting that terrestrial invertebrates might have elevated MeHg relative to stream invertebrates and might lead to higher mercury exposure in fish that consume terrestrial subsidies. As an initial step to examine this possibility, we analyzed mercury concentrations in terrestrial and aquatic invertebrates and two fish species, steelhead/rainbow trout (Oncorhynchus mykiss) and coastrange sculpin (Cottus aleuticus), in a small watershed. Mean MeHg and total mercury (THg) concentrations in terrestrial invertebrates were three to four times higher than in aquatic invertebrates of the same trophic level. MeHg was >1000 ng/g dw in some individual centipede and scorpion samples, and also relatively high (100-300 ng/g dw) in some terrestrial detritivores, including non-native isopods. Mean THg in age 0 trout was 400 ng/g dw compared to 1200-1300 ng/g dw in age 1+ trout and sculpin, and the largest trout sampled had THg >3500 ng/g dw. However, the similar mercury concentrations between age 1+ trout and sculpin, despite different diet types, indicated that Hg concentrations in fish were not related simply to differences in consumption of terrestrial invertebrates. The high mercury concentrations we found in terrestrial invertebrates and fish suggest that further research on the sources and bioaccumulation of mercury is warranted in this region where O. mykiss populations are threatened.

Participation of water deer (Hydropotes inermis argyropus) in mercury transport in the ecosystem of Southern Primorye

Abstract. We present the first opportunity to study mercury in the fur of a water deer that recently entered Russia.13 samples from 7 animals (fur was taken from the back and belly) were collected similarly to the World Health Organization recommendations for humans. The mean concentration of total mercury in the fur of water deer was 0.01 0.003 mg/kg, which roughly coincides with the mercury in the fur of other herbivorous animals. For a more accurate assessment, it is necessary to obtain data for other deers in the study region.

Impacts of Indian summer monsoon and stratospheric intrusion on air pollutants in the inland Tibetan Plateau

Air pollutants can be transported to the pristine regions such as the Tibetan Plateau, by monsoon and stratospheric intrusion. The Tibetan Plateau region has limited local anthropogenic emissions, while this region is influenced strongly by transport of heavy emissions mainly from South Asia. We conducted a comprehensive study on various air pollutants (PM2.5, total gaseous mercury, and surface ozone) at Nam Co Station in the inland Tibetan Plateau. Monthly mean PM2.5 concentration at Nam Co peaked in April before monsoon season, and decreased during the whole monsoon season (June–September). Monthly mean total gaseous mercury concentrations at Nam Co peaked in July and were in high levels during monsoon season. The Indian summer monsoon acted as a facilitator for transporting gaseous pollutants (total gaseous mercury) but a suppressor for particulate pollutants (PM2.5) during the monsoon season. Different from both PM2.5 and total gaseous mercury variabilities, surface ozone concentrations at Nam Co are primarily attributed to stratospheric intrusion of ozone and peaked in May. The effects of the Indian summer monsoon and stratospheric intrusion on air pollutants in the inland Tibetan Plateau are complex and require further studies.

Total mercury and methylmercury in human hair and food: Implications for the exposure and health risk to residents in the Three Gorges Reservoir Region, China

Three Gorges Dam (TGD) is the largest hydroelectric construction in the world, and its potential impacts on the ecological environment and human health risks have invoked considerable global concern. However, as a mercury (Hg) sensitive system, limited work was conducted on the Hg exposure level of local residents around the Three Gorges Reservoir (TGR). Thus, 540 human hair samples and 22 species of local food samples were collected to assess the Hg exposure and human health risk to the residents located in the Three Gorges Reservoir Region (TGRR) and to investigate their dietary exposure to Hg. The results showed that the geometric mean concentrations of total mercury (THg) and methylmercury (MeHg) in hair were 0.42 ± 0.43 μg g−1 and 0.23 ± 0.32 μg g−1, respectively, lower than the reference level (1.0 μg g−1) recommended by the United States Environmental Protection Agency (US EPA), indicating a low level Hg exposure for residents around the TGR. No significant difference in the accumulation of Hg in hair between the gender subgroups was observed, whereas age difference, smoking and alcohol drinking behavior, and fish consumption frequency were significant predictors of hair Hg level. Besides, THg and MeHg of all the investigated food samples did not exceed the corresponding Chinese national standard. The average probable daily intakes (PDIs) of THg and MeHg were 0.032 μg kg−1 day−1 and 0.007 μg kg−1 day−1, which were obviously below the recommended values of 0.57 μg kg−1 day−1 and 0.1 μg kg−1 day−1, respectively. The cereal (mainly rice) contribution of THg (76.0%) and MeHg (74.4%) intakes to the local residents around the TGR was much higher than that of fish (10.7% and 22.9%, respectively) due to the considerable rice consumption. Overall, residents around the TGR were at a low Hg exposure and rice consumption was the major pathway for Hg exposure.

Mercury and neurochemical biomarkers in multiple brain regions of five Arctic marine mammals

Mercury is a neurotoxic chemical that represents one of the greatest pollution threats to Arctic ecosystem health. Evaluating the direct neurotoxic effects of mercury in free ranging wildlife is challenging, necessitating the use of neurochemical biomarkers to assess potential sub-clinical neurological changes. The objective of this study was to characterize the distribution and speciation of mercury, as well as exposure-associated changes in neurochemistry, across multiple brain regions (n = 10) and marine mammal species (n = 5) that each occupy a trophic niche in the Arctic ecosystem. We found consistent species differences in mean brain and brain region-specific concentrations of total mercury (THg) and methyl mercury (MeHg), with higher concentrations in toothed whales (narwhal, pilot whales and harbour porpoise) compared to fur-bearing mammals (polar bear and ringed seal). Mean THg (μg/g dw) in decreasing rank order was: pilot whale (11.9) > narwhal (7.7) > harbour porpoise (3.6) > polar bear (0.6) > ringed seal (0.2). The higher THg concentrations in toothed whales was associated with a marked reduction in the percentage of MeHg (<40 %) compared to polar bears (>70 %) that had lower brain THg concentrations. This pattern in mercury concentration and speciation corresponded broadly to an overall higher number of mercury-associated neurochemical biomarker correlations in toothed whales. Of the 226 correlations between mercury and neurochemical biomarkers across brain regions, we found 60 (27 %) meaningful relationships (r>0.60 or p < 0.10). We add to the growing weight of evidence that wildlife accumulate mercury in their brains and demonstrate that there is variance in accumulation across species as well as across distinct brain regions, and that some of these exposures may be associated with sub-clinical changes in neurochemistry.

Mercury exposure in mammalian mesopredators inhabiting a brackish marsh.

Bioaccumulation of environmental contaminants in mammalian predators can serve as an indicator of ecosystem health. We examined mercury concentrations of raccoons (Procyon lotor; n=37 individuals) and striped skunks (Mephitis mephitis; n=87 individuals) in Suisun Marsh, California, a large brackish marsh that is characterized by contiguous tracts of tidal marsh and seasonally impounded wetlands. Mean (standard error; range) total mercury concentrations in adult hair grown from 2015 to 2018 were 28.50μg/g dw (3.05μg/g dw; range: 4.46-81.01μg/g dw) in raccoons and 4.85μg/g dw (0.54μg/g dw; range: 1.53-27.02μg/g dw) in striped skunks. We reviewed mammalian hair mercury concentrations in the literature and raccoon mercury concentrations in Suisun Marsh were among the highest observed for wild mammals. Although striped skunk hair mercury concentrations were 83% lower than raccoons, they were higher than proposed background levels for mercury in mesopredator hair (1-5μg/g). Hair mercury concentrations in skunks and raccoons were not related to animal size, but mercury concentrations were higher in skunks in poorer body condition. Large inter-annual differences in hair mercury concentrations suggest that methylmercury exposure to mammalian predators varied among years. Mercury concentrations of raccoon hair grown in 2017 were 2.7 times greater than hair grown in 2015, 1.7 times greater than hair grown in 2016, and 1.6 times greater than hair grown in 2018. Annual mean raccoon and skunk hair mercury concentrations increased with wetland habitat area. Furthermore, during 2017, raccoon hair mercury concentrations increased with the proportion of raccoon home ranges that was wetted habitat, as quantified using global positioning system (GPS) collars. The elevated mercury concentrations we observed in raccoons and skunks suggest that other wildlife at similar or higher trophic positions may also be exposed to elevated methylmercury bioaccumulation in brackish marshes.

Utilization of black-tailed gull (Larus crassirostris) eggs for monitoring of mercury levels in coastal areas of South Korea: Preliminary study

Studies on the monitoring of mercury accumulation using high trophic-level predators of the marine ecosystem have been scarce in South Korea. In this study, we compared the mercury concentrations of the eggs of the black-tailed gulls, a higher-order predator, breeding in two coastal areas. Breeding sites with varying mercury concentrations in land-origin freshwater fish and freshwater and marine sediments were selected in the southeastern (Hongdo Island) and western (Baengnyeongdo Island) seas. The 5-year mean total mercury concentration in eggs collected during the breeding seasons from 2012 to 2016 was higher in those collected from Hongdo than in those collected from Baengnyeongdo. This difference in mercury concentration in eggs was observed for each year. In addition, the total mercury concentration in eggs was consistently higher on Hongdo, which also had higher mercury pollution, than on Baengnyeongdo Island. These results support the suitability of black-tailed gull eggs for monitoring of mercury pollution.

Levels of mercury found in hair and fish consumption of riverine communities in the Tapajós region of the Brazilian Amazon

Riverine communities are exposed to mercury due to the high ingestion of fish in their diet. In order to evaluate the levels of exposure in the Tapajós region, also assessing the fish ingestion frequency, a study was conducted in adults living in riverine communities in the municipality of Itaituba in the State of Pará. Hair samples were collected for the determination of total mercury and the weekly frequency data of fish ingestion was recorded. The mean concentration of total mercury varied from 7.25μg/g (in 2013) to 10.80μg/g (in 2014), with no significant difference being observed (p = 0.1436). As for fish ingestion frequency, the majority of the individuals evaluated revealed high consumption both in 2013 and in 2014. High levels of total mercury were observed only in those with high consumption of fish in both years. The importance of ongoing monitoring of exposure levels in humans should be stressed, basing itself on indices of tolerance of 6μg/g recommended by the World Health Organization, and investigation about the consumption of fish such that strategies for control and prevention are improved.

Spatial variation of mercury bioaccumulation in bats of Canada linked to atmospheric mercury deposition

Wildlife are exposed to neurotoxic mercury at locations distant from anthropogenic emission sources because of long-range atmospheric transport of this metal. In this study, mercury bioaccumulation in insectivorous bat species (Mammalia: Chiroptera) was investigated on a broad geographic scale in Canada. Fur was analyzed (n=1178) for total mercury from 43 locations spanning 20° latitude and 77° longitude. Total mercury and methylmercury concentrations in fur were positively correlated with concentrations in internal tissues (brain, liver, kidney) for a small subset (n=21) of little brown bats (Myotis lucifugus) and big brown bats (Eptesicus fuscus), validating the use of fur to indicate internal mercury exposure. Brain methylmercury concentrations were approximately 10% of total mercury concentrations in fur. Three bat species were mainly collected (little brown bats, big brown bats, and northern long-eared bats [M. septentrionalis]), with little brown bats having lower total mercury concentrations in their fur than the other two species at sites where both species were sampled. On average, juvenile bats had lower total mercury concentrations than adults but no differences were found between males and females of a species. Combining our dataset with previously published data for eastern Canada, median total mercury concentrations in fur of little brown bats ranged from 0.88–12.78μg/g among 11 provinces and territories. Highest concentrations were found in eastern Canada where bats are most endangered from introduced disease. Model estimates of atmospheric mercury deposition indicated that eastern Canada was exposed to greater mercury deposition than central and western sites. Further, mean total mercury concentrations in fur of adult little brown bats were positively correlated with site-specific estimates of atmospheric mercury deposition. This study provides the largest geographic coverage of mercury measurements in bats to date and indicates that atmospheric mercury deposition is important in determining spatial patterns of mercury accumulation in a mammalian species.

Methyl mercury, but not inorganic mercury, associated with higher blood pressure during pregnancy

Prior studies addressing associations between mercury and blood pressure have produced inconsistent findings; some of this may result from measuring total instead of speciated mercury. This cross-sectional study of 263 pregnant women assessed total mercury, speciated mercury, selenium, and n-3 polyunsaturated fatty acids in umbilical cord blood and blood pressure during labor and delivery. Models with a) total mercury or b) methyl and inorganic mercury were evaluated. Regression models adjusted for maternal age, race/ethnicity, prepregnancy body mass index, neighborhood income, parity, smoking, n-3 fatty acids and selenium. Geometric mean total, methyl, and inorganic mercury concentrations were 1.40µg/L (95% confidence interval: 1.29, 1.52); 0.95µg/L (0.84, 1.07); and 0.13µg/L (0.10, 0.17), respectively. Elevated systolic BP, diastolic BP, and pulse pressure were found, respectively, in 11.4%, 6.8%, and 19.8% of mothers. In adjusted multivariable models, a one-tertile increase of methyl mercury was associated with 2.83mmHg (0.17, 5.50) higher systolic blood pressure and 2.99mmHg (0.91, 5.08) higher pulse pressure. In the same models, an increase of one tertile of inorganic mercury was associated with −1.18mmHg (−3.72, 1.35) lower systolic blood pressure and −2.51mmHg (−4.49, −0.53) lower pulse pressure. No associations were observed with diastolic pressure. There was a non-significant trend of higher total mercury with higher systolic blood pressure. We observed a significant association of higher methyl mercury with higher systolic and pulse pressure, yet higher inorganic mercury was significantly associated with lower pulse pressure. These results should be confirmed with larger, longitudinal studies.

Mercury and hydroquinone content of skin toning creams and cosmetic soaps, and the potential risks to the health of Ghanaian women.

In this study, sixty-two (62) skin-lightening creams and soaps were analysed for total mercury and hydroquinone levels. Total mercury was determined by the Cold Vapour Atomic Absorption Spectrophotometry using an automatic mercury analyser and hydroquinone by High Performance Liquid Chromatography. The mean concentration of total mercury in skin toning creams and cosmetic soaps were 0.098 ± 0.082 and 0.152 ± 0.126 μg/g, respectively. The mean concentration of hydroquinone was 0.243 ± 0.385 and 0.035 ± 0.021 % in skin toning creams and cosmetic soaps, respectively. All the creams and soaps analysed had mercury and hydroquinone levels below the US Food and Drug Administration’s acceptable limit of 1 μg/g and 2 %, respectively. The low levels of mercury and hydroquinone in the creams and soaps analysed in this study therefore do not pose any potential risk to consumers who are mostly women in Ghana.

Mercury and selenium concentrations in skeletal muscle, liver, and regions of the heart and kidney in bearded seals from Alaska, USA.

Mean concentrations of total mercury ([THg]) and selenium ([TSe]) (mass and molar-based) were determined for 5 regions of the heart and 2 regions of the kidney of bearded seals (Erignathus barbatus) harvested in Alaska, USA, in 2010 and 2011. Mean [THg] and [TSe] of bearded seal liver and skeletal muscle tissues were used for intertissular comparison. The Se:Hg molar ratios were used to investigate elemental associations and potential antioxidant protection against Hg toxicosis. Age was an important factor in [THg] and Se:Hg molar ratios in heart and kidney. Small but statistically significant differences in mean [THg] occurred among some of the 5 heart regions (p < 0.05). Mean [THg] was highest in liver, 3.057 µg/g, and lowest in heart left ventricle, 0.017 µg/g. Mean [THg] ranked: liver > kidney cortex > kidney medulla > skeletal muscle > heart left ventricle (p < 0.001). Mean [TSe] was highest in liver, 3.848 µg/g, and lowest in heart left ventricle, 0.632 µg/g. Mean [TSe] ranked: liver > kidney cortex > kidney medulla > skeletal muscle > heart left ventricle (p < 0.001). The Se:Hg molar ratios were significantly greater than 1.0 in all tissues (p < 0.001) and represented baselines for normal [TSe] under relatively low [THg]. Mean Se:Hg molar ratios ranked: heart left ventricle > kidney medulla > kidney cortex (p < 0.001).

Mercury contamination in Khramulia (Capoeta capoeta) from the Cheshme Kile and Zarrin Gol Rivers in Iran and human health risk assessment.

Total mercury concentrations were determined in muscle tissue of Khramulia (Capoeta capoeta) captured in the Cheshme Kile and Zarrin Gol Rivers, Iran. In Cheshme Kile River, 49 fish samples were collected. The mean total mercury concentration in the muscles of C. capoeta from this area was 249 ng g(-1) dw. In Zarrin Gol River, where 62 fish samples were collected, the total mercury in muscles averaged 164 ng g(-1) dw. A significant difference was found between means of mercury in the rivers (p < 0.001). All samples from the two rivers had mean mercury concentrations below the maximum allowable limits for mercury set by the Food and Agriculture Organization, World Health Organization, Standardization Administration of China and Environmental Protection Agency. The results of this study indicate that the values of hazard target quotient and estimated weekly intake are low and represent a negligible risk for human health.

Does mercury contamination reduce body condition of endangered California clapper rails?

We examined mercury exposure in 133 endangered California clapper rails ( Rallus longirostris obsoletus) within tidal marsh habitats of San Francisco Bay, California from 2006 to 2010. Mean total mercury concentrations were 0.56 μg/g ww in blood (range: 0.15–1.43), 9.87 μg/g fw in head feathers (3.37–22.0), 9.04 μg/g fw in breast feathers (3.68–20.2), and 0.57 μg/g fww in abandoned eggs (0.15–2.70). We recaptured 21 clapper rails and most had low within-individual variation in mercury. Differences in mercury concentrations were largely attributed to tidal marsh site, with some evidence for year and quadratic date effects. Mercury concentrations in feathers were correlated with blood, and slopes differed between sexes ( R 2 = 0.58–0.76). Body condition was negatively related to mercury concentrations. Model averaged estimates indicated a potential decrease in body mass of 20–22 g (5–7%) over the observed range of mercury concentrations. Our results indicate the potential for detrimental effects of mercury contamination on endangered California clapper rails in tidal marsh habitats.

Assessment of environmental mercury discharge at a four-year-old artisanal gold mining area on Lombok Island, Indonesia

Indonesian artisanal and small-scale gold mining activities (ASGM) have been described for the islands of Borneo (Kalimantan) and Sulawesi. But the increased gold price over recent years has seen operations extend to the islands of Lombok and Sumbawa. For the current research, an environmental assessment was conducted across three new ASGM locations. Gold is recovered by miners through a two-stage process of whole-ore amalgamation and cyanidation. Waste (tailings) is discharged to land or sea with no concern for contaminants in the tailings. The gold grade of ore is up to 5000 mg kg(-1). The mean gold grade of the amalgamation tailings is 7 mg kg(-1), dropping to 1.2 mg kg(-1) for the cyanidation tailings. The mean mercury concentration of the amalgamation tailings is about 3000 mg kg(-1) and greater than 1600 mg kg(-1) for the cyanidation tailings. Samples of paddy rice grain collected adjacent to cyanidation tailings ponds showed methyl mercury concentrations greater than 100 ng g(-1). This is five times above the Chinese permissible level for total mercury in food crops. The mean total mercury concentration in hair of Lombok ASGM workers was greater than that in a non-exposed population; however there was no difference in methyl mercury concentration. This indicates the primary pathway of mercury exposure is inhalation of volatile mercury in the atmosphere. Future exposure may come from ingestion of methyl mercury contaminated rice where discharge of cyanide tailings to paddies continues. To protect the environment and to enhance the sustainability of ASGM, appropriate tailings management must be implemented. The gold grade of the tailings indicates that the residual value might be recoverable with appropriate technology. Ongoing research is investigating systems such as phytoextraction that might assist ASGM operators in Lombok and Sumbawa to improve their environmental performance.

Distribution of mercury in water, sediment and fish from the Volta lake and its major tributaries

Concentrations of total mercury and methyl mercury were determined in fish and sediment from the waters of the Volta Lake and its main tributaries to understand their distribution in the ecosystem. Total mercury concentrations in fish ranged from 2.11to 355.16 (mean: 75.64) ng/g wet wt. Methyl mercury concentration ranged from 1.77 to 319.48 (mean: 68.44) ng/g wet wt and accounted for, on the average 90% of the total mercury in the muscles of the fish. Methyl mercury concentrations in fish were directly proportional to total mercury concentrations with average correlation coefficient of r = 0.98. The relationship of total mercury and methyl mercury concentrations in fish to those of sediments from corresponding locations was fish-species dependent. Concentrations of total mercury in sediment ranged from 0.96 to 700.25 ng/g dry wt. which is lower than the IAEA threshold of 810ng/g. Water samples from the main tributaries of the Volta and the Volta Lake showed total mercury concentrations of 0.0027 to 0.0862 ng/L and methylmercury concentrations of 0.0004 to 0.0259 ng/L. The methylmercury concentrations accounted for 13.2 to 35.0% of total mercury in the water samples. The results of this study indicate that mean total mercury and methylmercury concentrations in fish increase with increase in trophic level of fish. All the fish samples obtained from the Volta and its major tributaries had mercury concentrations below the WHO/FAO recommended limit of 500 ng/g wet weight. The low levels of mercury in the fish analyzed in this study suggest a comparatively clean aquatic environment which has not yet been impacted by mercury contamination.

Mercury and selenium content of Taiwanese seafood

Fish consumption is avid in Taiwan (and other Asian nations), but little is known about the mercury and selenium content in local seafood. This paper reports on total mercury, methylmercury and selenium levels from 14 commonly consumed seafood items obtained from Taichung, Taiwan. Mean total mercury concentrations varied nearly 100-fold across species. Fifty per cent of the marlins sampled and 35% of the sharks exceeded the 0.3 µg g−1 US Environmental Protection Agency (USEPA) guideline. Methylmercury comprised a majority of the total mercury in all species. In all species studied there was a molar excess of selenium over mercury. The rank order of mean selenium–mercury molar ratios was red tilapia (166.8) > abura (87.9) > river prawn (82.4) > whiteleg shrimp (64.2) > butterfish (44.6) > milkfish (37.0) > tuna (15.6) > grouper (13.9) > ayu (13.4) > coral hind (13.0) > weever (11.8) > saury (9.0) > shark (7.8) > marlin (4.2).