Pesticides used in banana production may enter watercourses and pose ecological risks
for aquatic ecosystems. The occurrence and effects of pesticides in a stream draining
a banana plantation was evaluated using chemical characterization, toxicity testing
and macrobenthic community composition. All nematicides studied were detected in the
surface waters of the banana plantation during application periods, with peak concentrations
following applications. Toxicity tests were limited to the carbofuran application
and no toxicity was observed with the acute tests used. However, since pesticide concentrations
were generally below the lowest LC50 value for crustaceans but above calculated aquatic
quality criteria, there remains a risk of chronic toxicity. Accurate ecological assessments
of pesticide use in banana plantations are currently limited by the lack of local
short-term chronic toxicity tests and tests using sensitive native species. Relatively
constant levels of four pesticides (imazalil, thiabendazole, chlorpyrifos and propiconazole),
which had toxic effects according to the 96h hydra and 21d daphnia chronic test, were
recorded in the effluent of the packing plant throughout the study, indicating that
the solid waste trap used in this facility was not effective in eliminating toxic
chemicals. Certain taxa, such as Heterelmis sp. (Elmidae), Heteragrion sp. (Megapodagrionidae,
Odonata), Caenis sp. (Caenidae, Ephemerotera), and Smicridea sp. (Hidropsychidae,
Trichoptera), were more abundant at reference sites than in the banana farm waters,
and may be good candidates for toxicity testing. Multivariate analyses of the macroinvertebrate
communities clearly showed that the banana plantation sites were significantly different
from the reference sites. Moreover, following the pesticide applications, all the
banana plantation sites showed significant changes in community composition, with
the same genera being affected at all sites and for all pesticides (terbufos, cadusafos
and carbofuran). Consequently, the results presented here show that multivariate analysis
of community composition was more sensitive in distinguishing pesticide effects than
the toxicity tests and richness and composition measures used. We conclude that monitoring
macroinvertebrate communities can be a powerful tool in the assessment of ecological
effects of banana production.