Regional patterns of heavy metal exposure and contamination in the fish fauna of the Kharaa River basin (Mongolia)

Abstract

Past and present gold mining operations scattered throughout the Kharaa River basin, Mongolia, have been identified as a major source of heavy metal and metalloid contamination. However, the potential accumulation of toxic contaminates including Cr, Zn, As, Cd, Hg, Cu, Ni and Pb in the resident fish fauna and the subsequent human health risks associated with their consumption have previously not been quantified. In the current study, contaminates in water, sediment and five consumed fish species (Leuciscus baicalensis, Thymallus baicalensis, Brachymystax lenok, Lota lota and Silurus asotus) were examined. The results indicated that concentrations of As and Hg exceeded the national permissible limits for drinking water in the Gatsuurt tributary of 10 μg L-1 and 0.05 μg L-1 respectively, while Hg contents detected in the sediment of the Boroo tributary were highly elevated (0.78 μg g-1). Heavy metal and arsenic accumulation was evident in all five fish species sampled across the basin, with maximum muscle contents of Cr, As, Hg and Pb detected in several species caught in the middle and lower river reaches, while Zn was highly elevated in B. lenok collected in the upper tributaries. Elevated median contents of Cr, Cu, Hg and Pb increased with trophic level, with Hg accumulation posing the greatest threat to humans as 10.7 % of all fish sampled in the study exceeded the internationally recommended threshold for Hg in consumable fish tissue. Although recreational fishing is rapidly growing throughout Mongolia, the overall level of fish capture and consumption remains relatively low. However, increasing pollution and accumulation in resident fish species could lead to chronic heavy metal intoxication in people who consume them regularly from the most polluted regions of the basin, while additionally being exposed to other sources of contamination.