Characteristics and sources of Cd and As trace elements in soil-irrigationrainwater-atmospheric dust-fall in Huishui County, Guizhou Province

This paper is the result of ecological geological survey engineering.

Objective The origin and enrichment of trace elements such as Cd and As in soil- water- atmosphere dust fall are the focus of environmental geology research. The quantitative research on migration and enrichment of trace elements such as Cd and As in soilirrigation-rain-atmosphere dust fall system was carried out in Huishui. It is of great significance for agricultural production and agricultural products planting in this region.

Methods Taking the samples of surface soil, irrigation water, rainwater and atmospheric dust- fall from Huishui County of Guizhou Province as research objects, this paper analyzes the geochemical characteristics of trace elements such as Cd and As.

Results The results show that the study area is dominated by acid soil. Cd is positively correlated with As, Cr, Hg, Mn, Ni, Pb, Zn and pH while it is negatively correlated with Cu and Se in the 147 topsoil elements. The 34 irrigation water samples are mainly As, B, F^-, Se and Zn. The single factor pollution index and Nemero composite index of heavy metal elements from irrigation water are Level 1, belonging to the clean range, which indicates that the water quality of irrigation water is up to the standard. Among the 5 rainwater and atmospheric dust-fall samples, the atmospheric dust-fall mainly includes As, Cd, Cr, Hg and Pb and the main components of rainwater are As, B, Cd, Cr⁶⁺, F^-, Ge, Hg, Pb, Se and Zn.

Conclusions The evaluation results show that the Cd single factor pollution index is the highest, and the Nemero composite pollution index is arranged as followed: Hongqi Village, Xiantang Town>Yangma Village, Lushan Town>Lianjiang Street, Dapo Village>Haohuahong Village, Haohuahong Town>Lixin Village, Baijin Town. The irrigation water quality reaches the standard without heavy metal pollution. The order of the average annual flux density of atmospheric dust- fall is B>Se>Pb>Zn>Cr>As>F>Cd>Ge>Hg. The average total amount of atmospheric dust-fall in the study area is 89 g·m^-2·a^-1, which is slightly lower than that of some cities and provinces in China. The comparison between surface soil and atmospheric dust-fall shows that Cd, Cr, Pb, Zn are rich and Se is poor in terms of the comparison between surface soil and annual rainwater flux, indicating that rainwater contributes largely to Se. Compared with rainwater, elements in the atmospheric dust-fall are higher except Hg. Compared the atmospheric dust-fall annual flux to the average surface soil, all elements are in deficit except Se. And compared the atmospheric dust-fall annual flux to the irrigation water contents, As, Hg, Se are enriched while Cr is depleted. So it can be concluded that the heavy metal element Cd pollution in surface soil comes from geological background, industrial wastes and coal burning while the atmospheric dust- fall mainly comes from coal burning dust and traffic dust.