Evaluating a Model of the Historical Behavior 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 evaluated
for its capability to simulate the behavior of a- and
g-hexachlorocyclohexane isomers from 1970 to 2000. The
model predicts HCH concentrations in air, seawater,
marine sediments, and needles well within an order of
magnitude, often within a factor of 2, and reproduces major
features of the observed differences in space and time.
The spatial and temporal patterns of HCHs in the Baltic Sea
environment are found to be controlled mostly by chemical
input, both through direct emissions within the drainage
basin and through advective inflow from adjacent areas, but
variable environmental conditions can significantly modify the spatial distribution patterns. Simulations with different boundary conditions, i.e., variable assumptions
concerning advective atmospheric inflow, suggest
that sources within the drainage basin alone are not
capable of explaining the observed HCH levels and that
significant transport into the region must occur. Deviations
between predicted and measured HCH concentrations can often be explained by uncertain estimates of usage and advective import, illustrating the usefulness of the model
for evaluating the reasonability of emission estimates
and boundary conditions.