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

A level IV fugacity model is described and illustrated by application to the fate of alpha-, beta-, gamma-, and delta-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.