V. Laabs et al., Leaching and degradation of corn and soybean pesticides in an Oxisol of the Brazilian Cerrados, CHEMOSPHERE, 41(9), 2000, pp. 1441-1449
Pesticide pollution of ground and surface water is of growing concern in tr
opical countries. The objective of this pilot study was to evaluate the lea
ching potential of eight pesticides in a Brazilian Oxisol. In a field exper
iment near Cuiaba, Mate Grosso, atrazine, chlorpyrifos, lambda-cyhalothrin,
endosulfane alpha, metolachlor, monocrotofos, simazine, and trifluraline w
ere applied onto a Typic Haplustox. Dissipation in the topsoil, mobility wi
thin the soil profile and leaching of pesticides were studied for a period
of 28 days after application. The dissipation half-life of pesticides in th
e topsoil ranged from 0.9 to 14 d for trifluraline and metolachlor, respect
ively. Dissipation curves were described by exponential functions for polar
pesticides (atrazine, metolachlor, monocrotofos, simazine) and bi-exponent
ial ones for apolar substances (chlorpyrifos, lambda-cyhalothrin, endosulfa
ne alpha, trifluraline). Atrazine, simazine and metolachlor were moderately
leached beyond 15 cm soil depth, whereas all other compounds remained with
in the top 15 cm of the soil. In lysimeter percolates (at 35 cm soil depth)
, 0.8-2.0% of the applied amounts of atrazine, simazine, and metolachlor we
re measured within 28 days after application. Of the other compounds less t
han 0.03% of the applied amounts was detected in the soil water percolates.
The relative contamination potentials of pesticides, according to the lysi
meter study, were ranked as follows: metolachlor > atrazine = simazine much
greater than monocrotofos > endsulfane alpha > chlorpyrifos > trifluraline
> lambda-cyhalothrin. This order of the pesticides was also achieved by ra
nking them according to their effective sorption coefficient K-e, which is
the ratio of K-oc to field-dissipation half-life. (C) 2000 Elsevier Science
Ltd. All rights reserved.