Mercury contamination in the vicinity of a derelict chlor-alkali plant. Part I: sediment and water contamination of Lake Balkyldak and the River Irtysh

A mercury-cell chlor-alkali plant operated in Pavlodar, Northern Kazakhstan, for 18 years and caused widespread contamination of the surrounding environment. Untreated wastewater from the plant was discharged to Lake Balkyldak, a shallow impounded lake without an outlet. The nearby River Irtysh was also suspected to be impacted by mercury (Hg) via the transport of contaminated groundwater. We took sediment and water samples from both aquatic systems, and also sampled soils along the shoreline of the lake and in the Irtysh flood plain. Sediments from Lake Balkyldak were found to be very heavily contaminated, with Hg concentrations in the surface layer reaching up to approximately 1500 mg kg(-1) near the wastewater outfall pipe. The contaminated lake sediments are prone to wind-driven resuspension and are acting as a strong source of Hg to the water column. Unfiltered lake water samples taken in shallow areas within 10-15 m from the shoreline contained from 0.11 microg Hg L(-1) in the less contaminated northern part of the lake to 1.39 microg L(-1) near the pollutant outfall in the south (up to 7.3 microg L(-1) on windy days). Sediments from the River Irtysh were only slightly impacted, with maximum Hg concentrations of 0.046 mg kg(-1) in the old river channel and 0.36 mg kg(-1) in floodplain oxbow lakes. In water samples from the River Irtysh, Hg was generally not detected, although trace concentrations (3 to 9 ng L(-1)) were found in some samples taken from oxbow lakes. We conclude that the river is not significantly impacted by Hg, but the highly contaminated Lake Balkyldak poses a threat and is in need of remediation. Potential remediation options for the lake are reviewed and are discussed in the context of experiences made at other Hg-contaminated sites.     

Environmental assessment of mercury contamination from the Rwamagasa artisanal gold mining centre, Geita District, Tanzania

This study presents the results of an environmental assessment of mercury (Hg) contamination in the Rwamagasa artisanal gold mining area, northwest Tanzania, and the potential downstream dispersion along the River Malagarasi to Lake Tanganyika. At the time of sampling, generally low concentrations of Hg (<0.05 mg/kg) occurred in most cultivated soils although higher Hg (0.05-9.2 mg/kg) was recorded in urban soils and vegetable plot soils where these are impacted by Hg-contaminated water and sediment derived from mineral processing activities. Hg in vegetable and grain samples is mostly below the detection limit of 0.004 mg/kg Hg, apart from 0.007 and 0.092 mg/kg Hg in two yam samples and 0.011 to 0.013 mg/kg Hg in three rice samples. The standardized (i.e., standardized to 10 cm length) Hg concentrations in Clarias spp. increase from about 0.01 mg Hg/kg for the River Malagarasi delta to 0.07, 0.2, and 1.6 mg/kg, respectively, for the Rwamagasa 'background', moderately and most contaminated sites. For piscivorous (Lates, Brycinus, and Hydrocynus spp.), insectivorous (Barbus spp.), and planktivorous (Haplochromis spp.) fish species, the 10-cm standardized Hg concentrations increase from about 0.006 mg/kg for the River Malagarasi-Lake Tanganyika area to 0.5 and 3.5 mg/kg, respectively, for the Rwamagasa moderately and most contaminated sites. The low concentrations of Hg in fish from the Malagarasi River delta and Lake Tanganyika indicate that Hg contamination from the Rwamagasa area does not have a readily discernible impact on the biota of Lake Tanganyika. Many of the fish samples from Rwamagasa exceed guidelines for human consumption (0.5 mg/kg) as well as the WHO recommended limit for vulnerable groups (0.2 mg/kg). Tissue total Hg (THg) of all fish collected from the River Malagarasi-Lake Tanganyika subarea is well below these guidelines. Potential human exposure through consumption of 300 g/day of rice grown on Hg-contaminated soils is 5.5 microg/week. Consumption of 250 g Nile perch (Lates spp.), 500 g tilapia (Oreochromis spp.), and 250 g of catfish (Clarias spp.) each week would result in an intake of 65 microg Hg/week for people consuming only fish from the Mara and Mwanza regions of Lake Victoria and 116 microg Hg/week for people in the Rwamagasa area consuming tilapia and Nile perch from Lake Victoria and catfish from mining-impacted streams. This is lower than the Provisional Tolerable Weekly Intake (PTWI) of 300 microg for Hg in the diet set by the WHO and the FAO. Inadvertent ingestion of soil containing 9 mg Hg/kg at a rate of 80 mg/day would give an additional estimated weekly intake of 5 microg THg, whereas the persistent and purposeful consumption of soil (geophagia) at a rate of 26 g soil/day would produce an additional chemical exposure of 230 microg Hg/day.     

Mercury contamination in the vicinity of a chlor-alkali plant and potential risks to local population

A mercury-cell chlor-alkali plant operated in Estarreja (North-western Portugal) for 50 years causing widespread environmental contamination. Although production by this process ceased in 2002, mercury contamination from the plant remains significant. The main objective of this study was to investigate mercury impact on the nearby environment and potential risks to local population. To assess the level of contamination soil samples were collected from agricultural fields in the vicinity of the plant, extending the study by taking samples of the predominant vegetation suitable for animal and human consumption, water samples, and fish species from a nearby coastal lagoon, to gain a preliminary insight into the potential for contamination of the terrestrial and aquatic food web. To determine population exposure to mercury, hair samples were collected from local residents. Total mercury concentration in the 0-15 cm layer of soil was found to be highly variable, ranging between 0.010 and 91 mg kg^− 1, although mercury contamination of soils was found to be restricted to a confined area. Lolium perenne roots contained between 0.0070 and 2.0 mg kg^− 1, and there is evidence that root systems uptake mercury from the soil. Levels of mercury in the aerial parts of plants ranged between 0.018 and 0.98 mg kg^− 1. It appears that plants with higher mercury concentration in soils and roots also display higher mercury concentration in leaves.Total mercury concentration in water samples ranged between 12 and 846 ng L^− 1, all samples presenting concentrations below the maximum level allowable for drinking water defined in the Portuguese law (1.0 μg L^− 1).Mercury levels in fish samples were below the maximum limit defined in the Portuguese law (0.5 mg kg^− 1), ranging from 0.0040 to 0.24 mg kg^− 1. Vegetables collected presented maximum mercury concentration of 0.17 mg kg^− 1. In general, food is not contaminated and should not be responsible for major human exposure to the metal.Mercury determined in human hair samples (0.090-4.2 mg kg^− 1; mean 1.5 mg kg^− 1) can be considered within normal limits, according to WHO guidelines suggesting that it is not affecting the local population. Despite being subject to decades of mercury emissions, nowadays this pollutant is only found in limited small areas and must not constitute a risk for human health, should these areas be restricted and monitored.Considering the present data, it appears that the population from Estarreja is currently not being affected by mercury levels that still remain in the environment.     

Mercury in fishes of Alaska, with emphasis on subsistence species

In the north, the presence of mercury (Hg) in food leading to chronic exposure is a scientific, economic and political issue. Guidelines have been established for the safe consumption of fish containing Hg, however, adherence to these guidelines must be weighed against the health benefits of consuming fish, such as from the omega-3 polyunsaturated fatty acids, vitamins and minerals. Alaskan Natives generally consume much more fish than the national average. This review summarizes and synthesizes the significant amount of data that has been generated on Hg in Alaska fish, particularly those consumed by Alaskans. Also included are a review of the benefits of eating fish, human health concerns relating to Hg toxicity and various risk assessment guidelines for food consumption. Emphasis was placed on methylmercury (MeHg), the most toxic form to humans. Hg concentrations were examined in 17 freshwater fish species and 24 anadromous and marine fish species, for a total of 2,692 specimens. For freshwater fish the greatest database was on northern pike (Esox lucius). For anadromous and marine fish the greatest database was on Pacific halibut (Hippoglossus stenolepis) and the five species of Pacific salmon (Oncorhynchus spp.). Overall, most fish had muscle Hg concentrations of < or =1 mg kg(-1) (wet wt.), within the USFDA's Action Level and Alaska's guideline for safe concentrations of MeHg in edible fish. Pacific salmon, the most commonly consumed fish group, had exceptionally low (< or =0.1 mg kg(-1)) Hg concentrations. Pacific halibut muscle Hg content was less than 0.3 mg kg(-1). Northern pike, a piscivorous (fish-eating) and long-lived fish, contained the highest muscle Hg values, often exceeding the state's guidelines for food consumption. A discussion of the safe consumption level for pike is included.     

Mercury levels in Oryza sativa cultivated in Philippine small-scale mining villages

Soil physico-chemical parameters and total mercury concentrations were measured in soil and rice plant samples collected over a cropping period grown in areas near mine tailings ponds in two Philippine small-scale mining (SSM) communities. Step-wise regression analysis relating environmental parameters to Hg uptake showed that pH has a highly significant effect on Hg content in the samples (p < 0.001) while temperature, contrary to previous studies, had no significant effect. The mean total Hg concentrations appeared to be significantly lower in rice plant parts sampled in control sites than in the contaminated sites in both SSM communities: 0.020 and 2.832 mg/kg, respectively in Aroroy, Masbate and 0.004 and 0.016 mg/kg, respectively in Fidelisan, Sagada. Harvested rice grains from the Masbate sampling sites further revealed total Hg concentration at 0.1331 mg/kg, exceeding the maximum permissible limit of 0.02 mg/kg Hg contamination. The study shows that Hg use in SSM activities and the cumulative effects of prolonged exposure to the metal through regular consumption of the village-cultivated rice may put the local residents at risk of health problems related to mercury.     

Anthropogenic impacts on mercury concentrations and nitrogen and carbon isotope ratios in fish muscle tissue of the Truckee River watershed, Nevada, USA

The lower Truckee River originates at Lake Tahoe, California/Nevada (NV), USA and ends in the terminal water body, Pyramid Lake, NV. The river has minimal anthropogenic inputs of contaminants until it encounters the cities of Reno and Sparks, NV, and receives inflows from Steamboat Creek (SBC). SBC originates at Washoe Lake, NV, where there were approximately six mills that used mercury for gold and silver amalgamation in the late 1800s. Since then, mercury has been distributed down the creek to the Truckee River. In addition, SBC receives agricultural and urban nonpoint source pollution, and treated effluent from the Reno-Sparks water reclamation facility. Fish muscle tissue was collected from different species in SBC and the Truckee River and analyzed for mercury and stable isotopes. Nitrogen (delta(15)N) and carbon (delta(13)C) isotopic values in these tissues provide insight as to fish food resources and help to explain their relative Hg concentrations. Mercury concentrations, and delta(15)N and delta(13)C values in fish muscle from the Truckee River, collected below the SBC confluence, were significantly different than that found in fish collected upstream. Mercury concentrations in fish tissue collected below the confluence for all but three fish sampled were significantly greater (0.1 to 0.65 microg/g wet wt.) than that measured in the tissue collected above the confluence (0.02 to 0.1 microg/g). Delta(15)N and delta(13)C isotopic values of fish muscle collected from the river below the confluence were higher and lower, respectively, than that measured in fish collected up river, most likely reflecting wastewater inputs. The impact of SBC inputs on muscle tissue isotope values declined down river whereas the impact due to Hg inputs showed the opposite trend.     

Metal contamination in water and bioaccumulation of metals in the planktons,molluscs and fishes in Jamshedpur stretch of Subarnarekha River of Chotanagpur plateau,India

Subarnarekha River is a rain‐fed peninsular river passing through industrial city Jamshedpur, an important industrial centre of Jharkhand, India. Heavy metal concentrations like Zn, Pb, Cr, Cd, Ni and Cu in water, sediment and in different food webs were determined using inductively coupled plasma‐mass spectrophotometer for two sampling sites that are found stressed with high contamination due to urbanization and anthropogenic activities. Present study mainly focuses on the metal concentration in water, sediment, plankton with bioaccumulation factor (BAF) in body parts of molluscs and fishes. The study revealed that Zn and Pb were found in highest concentration in plankton (Zn: 20.6 g/kg, Pb: 6.0 g/kg), molluscs (Zn: 4.6 g/kg, Pb: 0.6 g/kg) and in fish (Zn: 6.1 g/kg, Pb: 3.0 g/kg) as biomagnification. Calculated BAF indicated that in fish species Zn has highest BAF value followed by Pb, which may be harmful for human consumption.     

Factors affecting enhanced mercury bioaccumulation in inland lakes of Isle Royale National Park,USA

We investigated factors causing mercury (Hg) concentrations in northern pike to exceed the consumption advisory level (>500 ng/g) in some inland lakes of Isle Royale National Park. Using Hg-clean techniques, we collected water, zooplankton, macro invertebrates, and fishes in 1998 and 1999 from one advisory lake, Sargent Lake, for analysis of total mercury (Hg(T)) and methylmercury (MeHg). For comparison, samples were also collected from a non-advisory lake, Lake Richie. Concentrations of Hg(T) in northern pike were significantly higher in Sargent Lake (P<0.01). Counter to expectations, mean concentrations of both Hg(T) and MeHg in open water samples were slightly higher in Lake Richie. However, zooplankton in Sargent Lake contained higher average concentrations of Hg(T) and MeHg than in Lake Richie. Mercury concentrations in macro invertebrates were similar between lakes, but different between taxa. The two lakes exhibited similar Hg(T) concentrations in age-1 yellow perch and adult perch but concentrations in large adult perch (>160 mm) in Sargent Lake were twice the concentrations in Lake Richie. Analysis of stable isotopes (delta(13)C and delta(15)N) in biota showed that pike from the two lakes are positioned at the same trophic level (4.2 and 4.3), but that the food web is more pelagic-based in Sargent and benthic-based in Richie. Factors causing concentrations in large pike to be higher in Sargent Lake may include higher bioavailability of methylmercury and a food web that enhances bioaccumulation.     

A comparison of the non-essential elements cadmium, mercury, and lead found in fish and sediment from Alaska and California

Concentrations of three non-essential elements (cadmium (Cd), mercury (Hg), and lead (Pb)) were determined in sediment and fish from several locations in Alaska (AK) and California (CA) and used to examine differences in bioaccumulation within and between geographic locations. We analyzed tissue (liver, muscle, gill, and stomach contents) from white croaker (Genyonemus lineatus) and English sole (Pleuronectes vetulus) in California and flathead sole (Hippoglossoides elassodon) in Alaska, in addition to several species of invertebrates (mercury only). As found in previous work on arsenic (As) [Meador et al., 2004], Cd in fish liver exhibited a negative correlation with sediment concentrations. No such correlations were found for Hg and Pb when fish liver and sediment were compared; however, these metals did exhibit a positive relationship between liver and organic carbon normalized sediment concentrations, but only for the CA sites. Sediment concentrations of Hg at the AK sites were lower than those for the CA sites; however, AK invertebrates generally bioaccumulated more Hg than CA invertebrates. Conversely, Hg bioaccumulation was higher in CA fish. Even though ratios of total metal/acid volatile sulfides (AVS) in sediment were one to two orders of magnitude higher for the AK sites, bioaccumulation of these elements was much higher in fish from the CA sites. Bioaccumulation factors ([liver]/[sediment]) (BAFs) were highest at relatively clean sites (Bodega Bay and Monterey), indicating that elements were more bioavailable at these sites than from more contaminated locations. The observation of high BAFs for As in fish from Alaska and low BAFs for the California fish, but reversed for Cd, Hg, and Pb in this study, implies that differences in fish species are less important than the unique geochemical features at each site that control bioavailability and bioaccumulation and the potential sources for each element. Additionally, these data were also used to examine the metal depletion hypothesis, which describes the inverse relationship between elements and organic contaminants documented in some monitoring studies. Our results suggest that the enhanced bioavailability of the metals at some uncontaminated sites is the main determinant for the inverse correlation between metal and organic contaminants in tissue.     

Age and trophic position dominate bioaccumulation of mercury and organochlorines in the food web of Lake Washington

Understanding the mechanisms of bioaccumulation in food webs is critical to predicting which food webs are at risk for higher rates of bioaccumulation that endanger the health of upper-trophic predators, including humans. Mercury and organochlorines were measured concurrently with stable isotopes of nitrogen and carbon in key fishes and invertebrates of Lake Washington to explore important pathways of bioaccumulation in this food web. Across the food web, age and trophic position together were highly significant predictors of bioaccumulation. Trophic position was more important than age for predicting accumulation of mercury, sigmaDDT, and sigma-chlordane, whereas age was more important than trophic position for predicting sigmaPCB. Excluding age from the analysis inflated the apparent importance of trophic position to bioaccumulation for all contaminants. Benthic and pelagic habitats had similar potential to bioaccumulate contaminants, although higher sigma-chlordane concentrations in organisms were weakly associated with more benthic carbon signals. In individual fish species, contaminant concentrations increased with age, size, and trophic position (delta15N), whereas relationships with carbon source (delta13C) were not consistent. Lipid concentrations were correlated with contaminant concentrations in some but not all fishes, suggesting that lipids were not involved mechanistically in bioaccumulation. Contaminant concentrations in biota did not vary among littoral sites. Collectively, these results suggest that age may be an important determinant of bioaccumulation in many food webs and could help explain a significant amount of the variability in apparent biomagnification rates among food webs. As such, effort should be made when possible to collect information on organism age in addition to stable isotopes when assessing food webs for rates of biomagnification.     

Total mercury,methylmercury and selenium in mercury polluted areas in the province Guizhou,China

The province of Guizhou in Southwestern China is currently one of the world's most important mercury production areas. Emissions of mercury from the province to the global atmosphere have been estimated to be approximately 12% of the world total anthropogenic emissions. The main objective of this study was to assess the level of contamination with Hg in two geographical areas of Guizhou province. Mercury pollution in the areas concerned originates from mercury mining and ore processing in the area of Wanshan, while in the area of Quingzhen mercury pollution originates from the chemical industry discharging Hg through wastewaters and emissions to the atmosphere due to coal burning for electricity production. The results of this study confirmed high contamination with Hg in soil, sediments and rice in the Hg mining area in Wanshan. High levels of Hg in soil and rice were also found in the vicinity of the chemical plant in Quingzhen. The concentrations of Hg decreased with distance from the main sources of pollution considerably. The general conclusion is that Hg contamination in Wanshan is geographically more widespread, due to deposition and scavenging of Hg from contaminated air and deposition on land. In Quingzhen Hg contamination of soil is very high close to the chemical plant but the levels reach background concentrations at a distance of several km. Even though the major source of Hg in both areas is inorganic Hg, it was observed that active transformation of inorganic Hg to organic Hg species (MeHg) takes place in water, sediments and soils. The concentration of Hg in rice grains can reach up to 569 microg/kg of total Hg of which 145 microg/kg was in MeHg form. The percentage of Hg as MeHg varied from 5 to 83%. The concentrations of selenium can reach up to 16 mg/kg in soil and up to 1 mg/g in rice. A correlation exists between the concentration of Se in soil and rice, indicating that a portion of Se is bioavailable to plants. No correlation between Hg and Se in rice was found. Exposure of the local population to Hg may occur due to inhalation of Hg present in air (in particular in Hg mining area) and consumption of Hg contaminated food (in particular rice and fish) and water. Comparison of intake through these different routes showed that the values of Hg considerably exceed the USA EPA Reference Concentration (RfC) for chronic Hg exposure (RfC is 0.0004 mg/m(3)) close to the emission sources. Intake of Hg through food consumption, particularly rice and fish, is also an important route of Hg exposure in study area. In general, it can be concluded that the population mostly at risk is located in the vicinity of smelting facilities, mining activities and close to the waste disposal sites in the wider area of Wanshan. In order to assess the real level of contamination in the local population, it is recommended that biomonitoring should be performed, including Hg and MeHg measurements in hair, blood and urine samples.     

Recent declines in mercury concentration in a freshwater fishery: isolating the effects of de-acidification and decreased atmospheric mercury deposition in Little Rock Lake

The atmospheric deposition of H+, SO4, and Hg to Little Rock Lake in northern Wisconsin has declined substantially during the past decade. Parallel decreases have been observed in the surface waters of the lake. Here we extend the observations to the fish community and we present evidence of a contemporaneous decline in levels of Hg in fish tissue. By comparing data from two separated basins of the lake, we then make an initial effort to isolate and quantify the relative importance of de-acidification and reduced Hg deposition on mercury contamination in fish. Statistical modeling indicates that fish Hg in both basins decreased by roughly 30% between 1994 and 2000 (-5%/y) due to decreased atmospheric Hg loading. De-acidification could account for an additional 5% decrease in one basin (-0.8%/y) and a further 30% decrease in the other basin (-5%/y), since the basins de-acidified at very different rates. These results are consistent with the hypothesis that depositional inputs of SO4 and Hg(II) co-mediate the biosynthesis of methyl mercury and thereby co-limit bioaccumulation. And they suggest that modest changes in acid rain or mercury deposition can significantly affect mercury bioaccumulation over short-time scales.     

Lower than expected mercury concentration in piscivorous African sharptooth catfish Clarias gariepinus (Burchell)

The concentrations of total mercury (THg), stable isotopes of nitrogen (delta(15)N) and carbon (delta(13)C), and the diet of the African sharptooth catfish Clarias gariepinus in Lake Awassa, Ethiopia, were studied from January 2003 to February 2004. Values of the delta(15)N were used as an index of trophic position in four length groups and compared to actual stomach contents. The diet of C. gariepinus within the length range of 201-600 mm L(T) mainly consisted of the small barb Barbus paludinosus, aquatic insects, and mollusks. The proportion of fish prey in the diet was 60% by volume, irrespective of fish size. The differences in delta(15)N values of individuals within and between length classes were less than 3 per thousand, and were not significantly related to total length, showing the similarity in trophic niche of the different sizes, which corresponded to recorded stomach contents. Mercury concentrations were in the range of 0.002-0.154 mg kg(-1) ww, and had no significant relationship to total length. Hence, even large specimens of C. gariepinus have Hg values below the WHO threshold of 0.2 mg kg(-1) ww. The slope of the regression line between log [Hg] and delta(15)N was small, 0.06, indicating the absence of trophic shifts and biomagnification of Hg in larger specimens in our samples. The low Hg concentrations in C. gariepinus compared to the Hg concentrations in other piscivorous fish species in Lake Awassa, such as Barbus intermedius and B. paludinosus, may be due to its dependence on invertebrate preys at small size, diet switching towards low Hg prey fish at larger size, and growth biodilution owing to higher growth rate.     

90Sr in fish: a review of data and possible model approach

Data on the relationship between the equilibrium concentration factor of (90)Sr in fish and concentration of Ca in water have been collected and analyzed. The dataset contains 115 values of the concentration factors at different environmental concentrations of Ca. The data included in the dataset are based primarily on publications in Russian and relate to the whole-body concentration factors. An empirical formula was derived to estimate the equilibrium concentration factor of (90)Sr in fish as a inverse relationship of Ca: CF((90)Sr, Bq/kg w.w.)=3940/[Ca, mg/l](water). The derived relationship adequately accounts for the equilibrium concentration factor of (90)Sr in freshwater and marine fish species. A dynamic model was proposed to calculate the (90)Sr bioaccumulation of fish for non-equilibrium situations, for instance, immediately after accidental contamination of water bodies. The model was applied to reconstruct the dynamics of (90)Sr in fish from highly contaminated lake in the Southern Ural (Lake Uruskul). A comparison with data of observations showed that the model is well suited for estimating the dynamic characteristics of (90)Sr bioaccumulation by fish.     

A preliminary study of mercury contamination in the surface soil and river sediment of the Roscio District, Bolivar State, Venezuela

The present study constitutes a comparison of mercury in surface soil and river sediments of a contaminated and an uncontaminated area of Venezuela. In the contaminated area, gold prospectors have been using mercury to separate gold from auriferous sand and rock powders for many years. The baseline level of mercury in the river sediments of the uncontaminated area (Manzanares River, Sucre State) was 0.06 micrograms g-1, while in the contaminated area in the Roscio District of Bolivar State the concentration varied from 0.12 to 129 micrograms g-1. In the river sediments the average level of mercury was 0.71 micrograms g-1 and in the surface soil of the working areas 37 micrograms g-1, which shows a significant increase in the mercury level in the contaminated areas. This high level of mercury in the soil and sediments constitutes a serious risk to public health in the contaminated area, where the local people use the water for drinking and other domestic purposes; moreover, they also consume fish from these rivers.     

Mercury in the open Mediterranean: evidence of contamination?

In relation to the previously observed higher Hg concentrations in the tissues of certain Mediterranean fish (e.g. mackerel and tuna) compared with the same species in the Atlantic, the evidence for anomolously high Hg contamination of the Mediterranean has been examined. Four aspects have been addressed: the reliability of analytical measurements; the paucity of data on Hg in the Mediterranean and other oceanic areas; the actual levels of Hg in truly open-ocean waters; and ecological factors which may play a role in the enrichment of Hg in Mediterranean fish. Recent evidence suggests that former measurements of Hg in sea water are inadequate, and overestimate the concentrations of Hg in oceanic waters. Even today, intercalibration studies suggest that there are serious problems in the determination of Hg at the levels present in open oceans. A comparison of the most recent reliable data indicates that Mediterranean open-ocean waters are not enriched in Hg relative to the North Atlantic or other open-ocean areas. Similarly, no evidence exists for Hg anomalies in deep-ocean sediments in the Mediterranean, although it is apparent that localised coastal anomalies do occur as a result of natural and anthropogenic Hg sources. Generally, there is a severe lack of data on total Hg concentrations in truly open-ocean environments, and virtually no data on alkyl forms of Hg. Geographic comparisons of Hg in plankton and small pelagic fish do not indicate the presence of higher Hg concentrations in the Mediterranean Sea compared with oceanic regimes. Since these lower trophic species serve as a source of food for larger predaceous fish, e.g. tuna, the origin of the high Hg content in top-level predators is difficult to explain by evoking solely food chain relationships. In trying to resolve the question of why high Hg concentrations are found in certain Mediterranean fish, future studies should include an examination of the alkyl as well as inorganic forms of Hg, and ecological factors such as growth rates and feeding regime.     

Total and methyl mercury transformations and mass loadings within a wastewater treatment plant and the impact of the effluent discharge to an alkaline hypereutrophic lake

Concerns over the fate and bioaccumulation of mercury (Hg) inputs to Onondaga Lake, a hypereutrophic lake in central New York, prompted an investigation into the concentrations and fluxes of Hg discharge from the Onondaga County Metropolitan Wastewater Treatment Plant (METRO WWTP). Discharge of methyl Hg (MeHg) is of concern because it is the form of Hg that readily bioaccumulates along the aquatic food chain. This study incorporated clean protocols for sampling and Hg analysis to evaluate: seasonal patterns in the concentrations of total Hg (THg) and MeHg in the WWTP unit processes; the production of MeHg within the unit processes of the WWTP; the overall fate of THg and MeHg within the WWTP; and the relative impact of the Hg discharged from the WWTP to Onondaga Lake. Concentrations of THg (range: 80-860 ng/L) and MeHg (0.7-17 ng/L) in raw sewage were highly variable, with higher concentrations observed in the summer months. The dynamics of THg though the WWTP were correlated with total suspended solids (TSS). As a result, the majority of the THg removal (55%) occurred during primary treatment. Overall, about 92% of the THg entering the plant was removed as sludge, with volatilization likely a minor component of the overall Hg budget. The transformation of MeHg through the plant differed from THg in that MeHg was not correlated with TSS, and displayed strong seasonal differences between winter (November to April) and summer (May-October) months. During the summer months, substantial net methylation occurred in the activated sludge secondary treatment, resulting in higher MeHg concentrations in secondary effluent. Net demethylation was the dominant mechanism during tertiary treatment, resulting in removal of substantial MeHg from the secondary effluent. The overall MeHg removal efficiency through the plant was about 70% with more efficient removal during summer months. Sediment trap collections made below the epilimnion of Onondaga Lake indicated average deposition rates of 12 μg/m²-day for THg and 0.33 μg/m²-day for MeHg. These deposition rates are more than an order of magnitude higher than the thermocline area normalized external loads from METRO effluent (0.85 μg/m²-day for THg, 0.05 μg/m²-day for MeHg). Our findings indicate that the impact of the discharge from METRO is relatively small, contributing about 10-15% of Hg to the total gross Hg input to the hypolimnion of the lake.     

Burdens of mercury in residents of Temirtau, Kazakhstan: I: Hair mercury concentrations and factors of elevated hair mercury levels

Mercury (Hg) is released either naturally in the environment or by anthropogenic activities. During its global circulation, Hg presents in a diversity of chemical forms and transforms between each other. Among Hg species, methylmercury (MeHg) is readily absorbed by humans via the aquatic food chain and thus it is very neurotoxic to exposed populations including fetuses due to perinatal exposure. In 2005, a survey was carried out in Temirtau, an Hg-contaminated site in North Central Kazakhstan, to investigate Hg concentrations in the hair samples of the residents and the relationship between Hg exposure levels and the related factors. Among the 289 hair samples, Hg concentrations ranged from 0.009 to 5.184 µg/g with a mean of 0.577 µg/g. Nearly 17% of the population exceeded 1 µg/g for hair Hg, which corresponds to the reference of dose (RfD) 0.1 µg/kg body weight/day developed by the United States Environmental Protection Agency (USEPA). Subgroups of males, people aged over 45 and fishermen or anglers were found to have elevated Hg exposure levels in their hair. A positive correlation was found between Hg concentrations in hair and frequencies of river fish consumption. As a result, the finding that people were exposed to high levels of Hg was expected due to the frequent consumption of fish caught from the polluted River Nura or the neighbouring lakes. A regression model showed that approximately 41% of variance of Hg concentrations in the study population's hair was attributed to the variables of gender, residential location, age and fishery occupation. The model implied that demographic characteristics together with dietary behaviour should be taken into account in studies associated with Hg exposure risk, in order to clearly define the group potentially sensitive to Hg exposure.     

Prediction of the bioaccumulation factors and body burden of natural and synthetic estrogens in aquatic organisms in the river systems

This study undertakes an initial prediction of the bioaccumulation factors and body burden of the steroid estrogens, estrone, estradiol, estriol and ethinylestradiol in a range of aquatic organisms (plankton, benthic and free-living invertebrates and fish) in river systems using a food-web model. These data are compared to that derived from less complex predictions based on octanol-water partition coefficient and molecular connectivity index. The model predicted that bioaccumulation of steroid estrogens occurred in all organisms, however, the values were small, and the maximum and minimum bioaccumulation factors in this study were found in the fish at the lowest trophic level with ethinylestradiol (332) and the fish at the highest trophic level with estriol (1.8), respectively. Moreover, the bioaccumulation factors were sensitive to the metabolic rates of the estrogens in the free living organisms, while the concentration of estrogens in sediment was a significant factor in determining these values in benthic invertebrates. Biomagnification contributed little to the overall bioaccumulation, but the importance increased in fish exposed to ethinylestradiol. The predicted bioaccumulation factors from the food web model were generally smaller than the calculated bioconcentration factors from the simpler octanol-water partition coefficient/molecular connectivity index based estimates. Compared to literature measured data, the predicted values for fish were approximately 1000 times less than the values observed in laboratory tests, while for invertebrates, the modeled values were less than two orders of magnitude below laboratory results. However, the model predicted a similar bioconcentration factor for plankton in relation to experimental data for Chlorella vulgaris for estrone and estriol.     

Critical review of mercury fates and contamination in the arctic tundra ecosystem

Mercury (Hg) contamination in tundra region has raised substantial concerns, especially since the first report of atmospheric mercury depletion events (AMDEs) in the Polar Regions. During the past decade, steady progress has been made in the research of Hg cycling in the Polar Regions. This has generated a unique opportunity to survey the whole Arctic in respect to Hg issue and to find out new discoveries. However, there are still considerable knowledge gaps and debates on the fate of Hg in the Arctic and Antarctica, especially regarding the importance and significance of AMDEs vs. net Hg loadings and other processes that burden Hg in the Arctic. Some studies argued that climate warming since the last century has exerted profound effects on the limnology of High Arctic lakes, including substantial increases in autochthonous primary productivity which increased in sedimentary Hg, whereas some others pointed out the importance of the formation and postdeposition crystallographic history of the snow and ice crystals in determining the fate and concentration of mercury in the cryosphere in addition to AMDEs. Is mercury re-emitted back to the atmosphere after AMDEs? Is Hg methylation effective in the Arctic tundra? Where the sources of MeHg are? What is its fate? Is this stimulated by human made? This paper presents a critical review about the fate of Hg in the Arctic tundra, such as pathways and process of Hg delivery into the Arctic ecosystem; Hg concentrations in freshwater and marine ecosystems; Hg concentrations in terrestrial biota; trophic transfer of Hg and bioaccumulation of Hg through food chain. This critical review of mercury fates and contamination in the Arctic tundra ecosystem is assessing the impacts and potential risks of Hg contamination on the health of Arctic people and the global northern environment by highlighting and “perspectiving” the various mercury processes and concentrations found in the Arctic tundra.