THE ENVIRONMENT DIVISION
COMMISSION ON AGROCHEMICALS AND THE ENVIRONMENT
Significance of the Long Range Transport
of Pesticides in the Atmosphere
IUPAC Reports on Pesticides (41)
J. B. Unsworth,
R. D. Wauchope,
A-W. Klein, E.
Dorn, B. Zeeh, S.M.
Yeh, M. Akerblom, K.D.
Synopsis: Since the 1960s there has been a growing
body of data regarding the presence of pesticides in the atmosphere.
The monitoring results obtained show that traces of pesticides may undergo
long range transport and be deposited considerable distances away from
the treatment areas, including remote areas such as the Arctic and Antarctic
regions. Pesticides have been found in air, rain, cloud water, fog and
snow. The appearance and subsequent behaviour of pesticides in the atmosphere
are complex processes and the concentrations found depend on several
variables such as their volatility, photostability, method of application
and extent of use. Whilst volatility of pesticides can be linked to
their Henrys Law constant this is very much a simplification since
it is also influenced by the surfaces treated, e.g. soil or leaves,
and by the extent to which aerosols are formed during the application.
The disappearance of pesticides from the atmosphere is due to hydrolysis,
indirect photolysis via OH. radicals and to deposition
in rain. Pesticides which are resistant to hydrolysis and photolysis
can be transported over great distances, for example, organochlorine
insecticides have been detected in the Arctic regions. In general, concentrations
in rainwater are, when detected, in the low or sub mg/l
range and highest concentrations are found during the time of application.
The use of fugacity models has been shown to be a useful approach to
predict concentrations in air. Under most conditions the presence of
pesticides in air, or rainwater, has no significant effects on non-target
systems, including direct and indirect effects. Exceptions to this are
damage by auxin-type herbicides to sensitive plants which has resulted
on restrictions in their use in certain areas and transient chlorotic
spotting thought to be caused by drift of aerosols from application
of low rate sulfonyl urea herbicides. For animal species one possible
exception has been postulated. This is for persistent organochlorine
pesticides in Arctic regions where, due to the very oligotrophic nature
of the Arctic ocean, they are more liable to bioaccumulate and be transported
in the food web giving enhanced levels in mothers milk.
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