| A global multicompartment model which is based on a 3-D atmospheric general
circulation model (ECHAM5) coupled to 2-D soil, vegetation and sea surface
mixed layer reservoirs, is used to simulate the atmospheric transports and
total environmental fate of dichlorodiphenyltrichloroethane (DDT) and
γ-hexachlorocyclohexane (γ-HCH, lindane).
Emissions into the model world reflect the substance's agricultural usage in
1980 and 1990 and same amounts in sequential years are applied. Four
scenarios of DDT usage and atmospheric decay and one scenario of
γ-HCH are studied over a decade.
The global environment is predicted to be contaminated by the substances
within ca. 2a (years). DDT reaches quasi-steady state within 3-4a in the
atmosphere and vegetation compartments, ca. 6a in the sea surface mixed
layer and near to or slightly more than 10a in soil. Lindane reaches
quasi-steady state in the atmosphere and vegetation within 2a, in soils
within 8 years and near to or slightly more than 10a and in the sea surface
mixed layer. The substances' differences in environmental behaviour translate
into differences in the compartmental distribution and total environmental
residence time, τoverall. τoverall≈0.8a for
γ-HCH's and ≈1.0-1.3 a for the various DDT
scenarios. Both substances' distributions are predicted to migrate in
northerly direction, 5-12° for DDT and 6.7° for lindane
between the first and the tenth year in the environment. Cycling in various
receptor regions is a complex superposition of influences of regional
climate, advection, and the substance's physico-chemical properties. As a
result of these processes the model simulations show that remote boreal
regions are not necessarily less contaminated than tropical receptor regions.
Although the atmosphere accounts for only 1% of the total contaminant
burden, transport and transformation in the atmosphere is key for the
distribution in other compartments. Hence, besides the physico-chemical
properties of pollutants the location of application (entry) affects
persistence and accumulation emphasizing the need for georeferenced exposure
models. |