Simulation of the transfer and fate of HCHs since the 1950s in Lanzhou, China

Abstract

A level IV fugacity model is described and illustrated by application to the fate of α-, β-, γ-, and δ-hexachlorocyclohexane (HCH) in the Lanzhou area over a 60-year period from their introduction into the agricultural field until 2019. The established model is successfully applied to simulate the transfer processes and the concentration distribution of HCHs under non-steady-state assumptions in four environmental compartments in the Lanzhou area: soil, air, water, and sediment. Furthermore, the calculated results agree well with monitoring data from the literature in the same period of time. We assume that 40% of the total use of HCHs isomers enters into the air and 60% enters the soil. The results indicate that the main source of HCHs in the area is agricultural applications; the biggest bulk sink is soil (accounting for 99.6% of total amount in the environment). Among all the transfer processes, the deposition and the diffusion at the air–soil and air–water interfaces are the primary processes, and degradation in soil and air is the key process of HCH disappearance.