A preliminary study on mercury contamination to the environment from artisanal zinc smelting using indigenous methods in Hezhang County, Guizhou, China: Part 2. Mercury contaminations to soil and crop.

Artisanal zinc smelting using indigenous method in Hezhang County, Guizhou, China has posed seriously environmental pollution to the local environment. Within less than 150 km2 area in Hezhang, a few metric tons of mercury were released into the atmosphere each year since 1989 due to artisanal zinc smelting, and the surface waters were seriously contaminated with mercury. For the first time, we investigated the mercury contamination to the local soil and crop compartments due to mercury emissions from artisanal zinc smelting activities in this area. Mercury distribution patterns in 5 soil profiles collected in artisanal zinc smelting area showed that the top soils were seriously contaminated with mercury. The soils from agriculture land close to the zinc smelting areas were also contaminated with mercury due to the deposition of mercury species that emitted from artisanal zinc smelting processes. Total mercury concentrations in top soils decrease exponentially with distance from the zinc smelting area. Corn plants that were cultivated in agriculture land close to the zinc smelting area were also contaminated with mercury. Mercury concentration in corn plant tissue increased in the order of grains<stalks<roots<leaves. The average total mercury concentration in grain tissue was 0.011 mg kg-1, and the highest concentration reached 0.026 mg kg-1, exceeding the national guidance limit for foodstuff other than fish. Uptake of gaseous mercury was the predominant pathway by which Hg accumulated in the foliage, and mercury in root tissue is mainly derived from soil.