Anthropogenic mercury sequestration in different soil types on the southeast coast of China

Abstract

Soil is a major pool of anthropogenically emitted mercury (Hg) and will in turn be a source of atmospheric Hg contamination. It was hypothesized that accumulation of anthropogenic Hg in the soil at a regional scale is associated with the amount of Hg emitted to the atmosphere and soil type. A total of 448 horizon samples were collected from the typical soil types of the Yangtze River Delta and Pearl River Delta. Titanium (Ti) was selected as a reference element to discriminate anthropogenic Hg from the Hg associated with pedogenic processes. Soil pools of anthropogenic Hg were quantified to show the difference in Hg sequestration among soil types and regions. Soil pools of anthropogenic Hg ranged from 0.70 to 6971 g/ha in the Yangtze River Delta (YRD) and from 35.81 to 13098.71 g/ha in the Pearl River Delta (PRD). The estimated soil Hg pools were well correlated with the amounts of Hg emitted in these two regions. Soil properties, namely organic matter content, amorphous iron oxides, and cation exchange capacity, were significantly (p < 0.01) and positively correlated with soil Hg accumulation. Meanwhile, soil organic matter was the most important factor to determine the depth distribution of Hg in soil profile of the majority of soils. Perudic Cambisols and Stagnic Anthrosols which contained higher content of amorphous iron oxides had the highest soil Hg pools, indicating the importance of amorphous iron oxides other than organic matter to the Hg retention in soil. Soil and soil horizons with low pH and high salinity did show a low accumulation of Hg probably due to the remobilization of Hg under such conditions. In addition to the amount of Hg emitted, soil types may be a major factor in controlling the sequestration of anthropogenic Hg in both regions. Stagnic Anthrosols are an important pool for retention of anthropogenic Hg.