Quantification of the risk associated with high levels of mercury pollution at Temirtau, Kazakhstan

Abstract

This research aims to establish the risks of human exposure to high environmental mercury levels, based on a quantitative risk modelling approach. The study site was located on the River Nura in central Kazakhstan. From the 1950s until its closure in the mid 1990s, an acetaldehyde production plant located in the industrial city of Temirtau released Hg-containing wastewater into the river. River sediments are highly contaminated with Hg up to a distance of 25 km and beyond. In additon, a local power station released an estimated 6 million tonnes of fly-ash into the water and the Hg has become quite tightly associated with the ash deposits. River water, fish and agricultural land in the floodplain are also contaminated with mercury, yet the risks posed to the local population have not been evaluated to date. In June and July 2005, we took samples of soil, interior and exterior dust, drinking water, and food from individual households, communal areas and markets. Additionally, water and sediment samples and fish were taken from the river. Interviews were conducted with householders to establish their age and body weight, general living conditions and sources of irrigation and drinking water. A food frequency questionnaire (FFQ) was designed to investigate the frequencies of consumption of several common regional food items, including fish from the river and/or local market. Human hair samples were also collected to estimate the Hg bioburden and to enable the validity of the modelling approach to be established. The paper expands on the main pathways of contamination and looks at linkages between exposure pathways and Hg concentrations found in peoples’ hair. Uncertainties inherent in risk analysis as well as their influence on the relative importance of different exposure routes are also discussed. The analysis showed that the risk was less than originally expected, the most likely cause being the ability of the fly-ash to reduce the bioavailability of the mercury.