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 5.184µg/g with a mean of 0.577µg/g. Nearly 17% of the population exceeded 1µg/g for hair Hg, which corresponds to the reference of dose (RfD) 0.1µg/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.

Burdens of mercury in residents of Temirtau, Kazakhstan: II: verification of methodologies for estimating human exposure to high levels of Hg pollution in the environment.

A considerable amount of work has been conducted developing exposure estimate models for quantitative evaluation of mercury (Hg) intake and human health risks, but few have assessed the applicability and the validity for evaluating the risks posed by Hg in the environment and have achieved very mixed results. The present study focused on verifying estimated daily Hg intake using exposure equations with either the deterministic or probabilistic (the Monte Carlo) approaches. The simulated daily Hg intake doses were compared with those established from measured Hg concentrations in the hair of 289 participants. The results showed that the single-value deterministic method for simulating Hg exposure levels overestimated the level of risk by a factor of 1.5 when compared with the highest concentration of Hg observed in the hair of the study population. Contrarily, the average daily Hg intake doses simulated using the probabilistic simulation were similar in distribution to the biomarker data. When the reference dose (RfD) of 0.1 microg/kg body weight/day was adopted as the acceptable dose for daily intake rate, there were approximately 19 percent estimated to have potential Hg exposure risks based on the Monte Carlo simulation. This percentage was favourably similar to the 17 percent determined from Hg concentrations in the hair samples. The difference between the probabilistic simulation and the data derived from hair Hg levels was considered mainly due to the uncertainties in unconfirmed questionnaire-based survey data, small sampling sizes and the surrogates used in the exposure models. The findings implied that the existing exposure models together with the probabilistic approach were appropriate for research of human exposure to Hg.

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.

Mercury contamination in the vicinity of a derelict chlor-alkali plant Part II: contamination of the aquatic and terrestrial food chain and potential risks to the local population.

This study investigated the environmental impact and level of risk associated with mercury (Hg) contamination near a derelict chlor-alkali plant in Pavlodar, Northern Kazakhstan. Several species of fish were sampled from the highly polluted Lake Balkyldak and the nearby river Irtysh, to assess the extent of Hg bioaccumulation in the aquatic food chain and potential human health risks. A small number of bovine tissue samples, water samples, soil and plant samples from a nearby village were also investigated in order to make a preliminary assessment of potential impacts on the terrestrial food chain. Mercury levels in fish caught from Lake Balkyldak ranged from 0.16 to 2.2 mg kg(-1) and the majority of fish exceeded current human health criteria for Hg. Interspecies comparisons indicated that Hg is accumulated in the order dace>carp>tench. Site-specific bioaccumulation factors (BAF) were calculated for THg, and were estimated for MeHg. Fish from the river Irtysh and floodplain oxbow lakes contained between 0.075 and 0.159 mg kg(-1) of Hg and can be regarded as uncontaminated. Soils were found to be impacted by past atmospheric emissions of Hg. Cattle grazing in the surroundings of the factory are exposed to Hg from contaminated soils, plants and surface water, but the consumption of contaminated fish from the lake appears to be the main route of exposure for humans.