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Abstract

The global environmental fate of two modern pesticides was studied using a multimedia model based on a three-
dimensional atmosphere general circulation model. The emissions are predicted dynamically based on
agricultural application inventories.
The insecticide methyl parathion, when assuming properties at the high mobility end of the respective data
uncertainties, was found to be distributed on continental and even global scales. This finding implies that based
on present knowledge one cannot exclude that methyl parathion reaches regions as far from the sources as e.g.
the Arctic. Two scenarios of the environmental cycling of the herbicide atrazine were studied which reflect a
lower and an upper estimate of the substance’ mobility. Atrazine largely remains in the source (application)
regions and the neighbouring seas. But also atrazine seems to have an albeit limited potential for long-range
transport. The findings on substance mobilities are quantified by indicators which address spatial range in the
zonal direction in individual media. The seasonal variability of the total environmental burden of both pesticides
is governed by the degradation in soil and vegetation which together host 73 % of methyl parathion and 90-99 %
of atrazine. Also, the cycling between compartments was studied. Methyl parathion undergoes more deposition
and re-emission cycles than atrazine, a characteristics of the environmental fate of semivolatile substances.
Persistence is addressed by determination of global total environmental decay times during periods without
introduction of new substance into the environment. These are in the range 4-7 months. It is found that the
seasonal variability of persistence is pronounced.