Migration of Heavy Metal Elements in Reclaimed Irrigation Water-Soil-Plant System and Potential Risk to Human Health

[Objectives] To study the impact of heavy metal pollution of soil and plants during the process of reclaimed water for irrigation of green land in arid areas and the potential health risks to humans during use. [Methods] Taking Zhongwei City in Ningxia, a typical arid area, as the research area, the irrigation water, soil and green grass in the reclaimed water irrigation region and the original green water irrigation region were sampled, the heavy elements Hg, As, Zn, Pb, Cd, Cr were detected, and the Nemerow method, biological absorption coefficient, and health risk assessment were employed to evaluate the degree of soil pollution, plant absorption capacity, and human health risks. [Results] Compared with the original green water, the Hg, Cd, and Cr pollution of the reclaimed water irrigated green land was higher, the As, Zn, Pb pollution was lower, and the content of Hg and Cd was higher than the environmental background values of soil in Ningxia; the Cr content exceeded the risk intervention values of the first type of land in the Soil Environmental Quality -- Risk Control Standard for Soil Contamination of Development Land (GB36600-2018). Compared with the original green water irrigation region, it is found that the reclaimed water irrigation reduced the heavy metal pollution of the soil to a certain extent. The heavy metal content of tall fescue grass (Festuca arundinacea) in the reclaimed water irrigation region was Zn, Cr, Pb, As, Cd, and Hg from high to low; the order of the biological absorption coefficient was Cd>As>Zn>Pb>Hg>Cr; irrigation water exerted a certain effect on the content of heavy metals in plants and the biological absorption coefficient through the soil. Using the health risk assessment method recommended by Environmental Protection Agency of the United States of America (USEPA), it was found that the reclaimed water has the highest risk through the inhalation route, and the occupational population has a higher risk of skin contact with soil and plants. [Conclusions] This study is intended to provide data support and theoretical basis for the environmental safety risk research of the application of reclaimed water in arid areas to urban greening.