Long-term fate of three hexachlorocyclohexanes in the lower reach of Liao River basin: dynamic mass budgets and pathways.

The Liao River Basin Multimedia Fate and Transport Model (LRBMFTM), a non-steady state multiple-segment river fugacity-based model, for describing the long-term fate of persistent organic pollutants (POPs) in Liao River basin environment, is used to illustrate a quantitative understanding of the behavior of alpha-, beta-, and gamma-hexachlorocyclohexane (HCH) in more detail in the lower reach of Liao River basin from 1952 to 2001. The major pathway of the three HCHs from the basin to the surrounding environment is the atmospheric advection. One of the major removing of HCHs from the basin is degradation, where 2388.5 ton of alpha-HCH, 405.6 ton of beta-HCH, 382.7 ton of gamma-HCH emitted into the basin have been degraded, especially in the soil of application regions. The main reservoir of the HCHs is the soil in the basin, where there is a positive correlation between the accumulated amount and emission. The model suggests that the mass fluxes of all processes show an obviously seasonal trend. After the use ban, HCHs evaporate from water bodies, soils, and vegetation, and are advected away in the atmosphere. It is believed that the model can provide a valuable understanding of the processes that determine the overall fate of HCHs in the basin.