Geochemical characteristics of copper in soil of Qintang district, Guigang city, Guangxi and its ecological health research

This paper is the result of environmental geological survey engineering.

Objective Copper (Cu) is an essential trace element for humans, while moderate intake of Cu is important, deficiency or overdose of Cu can also be harmful to human health. Therefore, it is important to determine the optimal range of Cu content in agricultural products and soil by knowing the range of daily Cu intake for each person to safeguard human health.

Methods In this paper, taking the Qintang District of the Guigang City of Guangxi as the study area, based on the investigation results of the dietary structure survey of the residents in Guangxi and the Cu content in the soil, crops, and root soil obtained from the 1∶50000 land quality geochemical survey, the characteristics and spatial distribution of Cu content in the soil and rice were studied, the influencing factors of Cu absorption by rice are analyzed. A prediction model for the Cu content of rice was proposed and derived the optimal range of soil Cu content was for the safe development and cultivation of rice in the study area.

Results The results showed that the soil Cu content in the study area ranged from 6~74 mg/kg, with mean and median values of 28 mg/kg and 26 mg/kg, respectively. Only 1.6% exceeded the risk screening value of Cu content specified in GB15618, and it is mainly distributed in the carbonate rock outcropping area. Fe-Mn nodules are widely distributed in this area, and the soil's biological activity of heavy metals such as Cu is relatively low. The range of rice Cu content in the study area is 0.790~4.440 mg/kg; the mean and median values are 2.452 mg/kg and 2.718 mg/kg, and 60 rice samples do not exceed the limit value of Cu specified in NY861- 2004.

Conclusions To protect human health and reduce ecological risks, the optimal range of copper intake in rice is 0.615~8.204 mg/kg. The prediction model of Cu content in rice is established, and it is concluded that the optimal range of safe development of copper in soil and rice cultivation is 6~84 mg/kg.