Mercury concentrations in a contaminated river system in Kazakhstan and biomonitoring of the local population

Abstract

The River Nura in central Kazakhstan has been heavily contaminated by mercury (Hg). […] Humans are exposed to Hg primarily via the consumption of contaminated fish from the river. A survey was undertaken in June/July 2005 to investigate Hg concentrations in river water, drinking water, sediments and fish. To estimate the risk posed to the local population, approximately 300 hair samples were collected from people living in villages near the most contaminated section of the river, at a distance of between 5 and 30 km downstream of the acetaldehyde plant, and their dietary habits were recorded. Mercury concentrations in river water ranged from 2-3 ng/L upstream of the source of the pollution to 348 ng/L downstream of the factory outfall pipe. Some drinking water wells close to the river were contaminated, but deeper wells had Hg concentrations below the detection limit. An earlier investigation conducted by us in 2002 found that average Hg concentrations in fish are between 0.4 and 0.5 mg/kg within 30 km from the outfall. Fish collected in 2005 also contained up to 0.5 mg/kg of Hg in their tissue. Mercury concentrations in human hair samples were found to be strongly linked with fish consumption. Overall, Hg concentrations in human hair ranged from 0.01 to 5.18 mg/kg, with a mean of 0.58 mg/kg (compared to 0.03-0.9 mg/kg for samples taken from a control group in an uncontaminated area). Mean Hg concentrations in hair were found to be twice as high for males (0.84 mg/kg, n=115) compared to females (0.41 mg/kg, n=175). Most significantly, people living in a village ~30 km downstream had a higher Hg bodyburden (as estimated from hair samples) than people living in villages in the most contaminated section of the river. This could be due to higher rates of MeHg production in less contaminated areas and has important implications for planned remediation work.