Potentially harmful elements in rice paddy fields in mercury hot spots in Guizhou, China

Abstract

► Levels of Hg, Pb, Cd, Cu, Zn and As in soils from rice paddy fields were assessed. ► The two different regions were assessed, one impacted by mercury mining, one in a heavy industry area. ► In the mercury impacted regions soils had elevated levels of Zn and Cd in addition to Hg. ► In the coal impacted area soils had elevated levels of As and Hg. Levels of the chalcophile metals Hg, Pb, Cd, Cu and Zn and the metalloid As in soils from rice paddy fields were assessed in two regions impacted by different industrial activities in Guizhou province, China. The two study areas (Wanshan and Qingzhen) have previously received attention in the international literature due to heavy Hg pollution, though levels of other potentially harmful elements have not previously been reported. The regions were selected as representing two important, but categorically different metal(loid) contaminated areas in China: Wanshan has been a major region for Hg production while Qingzhen is an important region for a large range of various heavy industries based on coal as an energy source. Within a limited distance of the Hg mine tailings in Wanshan the rice paddy fields are heavily contaminated by Hg (median concentration 25 μg g −1 , maximum 119 μg g −1 ) and moderately contaminated by Zn and Cd (median concentrations of 86 and 0.9 μg g −1 , respectively). Zinc and Cd levels correlate well with Hg contamination, which indicates a similar source and mechanism of transport and accumulation. Other studies have concluded that the main sources of Hg contamination in Wanshan are the numerous Hg mine tailings. This is likely as these metals are all geochemically associated with the mineral cinnabar (HgS). The other chalcophile elements (Pb, Cu and As) are nevertheless found at background levels only. In Qingzhen the soils were found to contain elevated levels of As and Hg (median concentrations of 38 and 0.3 μg g −1 , respectively). These are elements that are known to be more associated with coal and released during coal combustion.