Mass Budgets, Pathways, and Equilibrium States of Two Hexachlorocyclohexanes in the Baltic Sea Environment

The POPCYCLING-Baltic model, a non-steady-state
multicompartmental mass balance model of long-term
chemical fate in the Baltic Sea environment, is used to
derive a quantitative understanding of the behavior of a- and g-hexachlorocyclohexane (HCH) from 1970 to 2000. The
atmosphere is found to effectively distribute the HCHs
within the Baltic Sea environment and beyond, resulting
in relatively uniform concentrations in environmental
compartments that do not directly receive emissions. This
uniformity is the result of a large-scale redistribution of
a relatively small fraction of the emitted HCHs from the
agricultural systems in source areas to all other environmental compartments throughout the Baltic Sea region. The major fraction of the HCHs is degraded in the soils receiving the pesticide application. In areas where HCH-containing pesticides are used, HCHs evaporate from soils and water bodies and are advected away in the atmosphere. They are deposited to forests and water bodies when they reach remote regions. This redistribution is driven by the inclination of the HCHs to equalize their chemical potential within the environment, which is illustrated through the use of fugacity fractions. The model is believed to provide useful insight into the complex set of interactions that determine the overall fate of an environmental contaminant but which are inaccessible to measurements.