Spatial distribution and risk assessments of mercury in topsoils of Central Asia

Central Asia is one of the largest arid areas on earth, yet little is known about the concentration levels and risks of mercury (Hg) in the soils of this region. In this study, extensive sampling of topsoils (0-10 cm) from representative landscapes was carried out over Central Asia (i.e., Tajikistan, Uzbekistan, and Kyrgyzstan). The total mercury (THg) concentrations in topsoils varied widely from 1.6 to 908.0 ng/g, with high values observed in samples collected in the capital cities and urban areas. Topsoil THg concentrations among different landscapes showed a decreasing order of urban (79.8±184.0 ng/g) > woodland (27.3±28.9 ng/g) > grassland (20.6±15.9 ng/g) > farmland (18.3±9.5 ng/g) > desert (12.3±8.0 ng/g). High THg concentrations were found in the capital cities/urban clusters, followed by a gradual decrease towards the peripheries. THg concentrations were found to be negatively correlated with the distance from the sampling sites to their nearest cities, indicating that anthropogenic emissions significantly influenced the spatial distribution of topsoil Hg. A significant correlation between THg concentrations and topsoil total organic carbon (TOC) contents was also observed, suggesting that TOC played an essential role in the spatial distribution of topsoil Hg. The assessments of pollution and potential ecological risk suggested that topsoils in highly densely-populated areas were contaminated by Hg and had higher degrees of potential ecological risks. The health risk assessment results showed that the exposure risk of topsoil Hg to children was higher than that to adults. Fortunately, there was no unacceptable human health risk of topsoil Hg. This study clarified the spatial distribution and risks of Hg in the Central Asian topsoils, offering new insight into the risk prevention and control of soil Hg.