Runoff-related endosulfan contamination and aquatic macroinvertebrate response in rural basins near Buenos Aires, Argentina.

JERGENTZ, S.; MUGNI, H; BONETTO, C.; SCHULZ, R.

ARCHIVES OF ENVIRONMENTAL CONTAMINATION AND TOXICOLOGY

Springer Verlag

Lugar: New York; Año: 2004 vol. 46 p. 345 - 353

0090-4341

Abstract. Information in the open literature about the fate and effects of pesticides in small streams in the main agricultural area of Argentina is very rare. The objective of the present work was to study the pesticide contamination and potential biological effects in basins which have undergone intense agricultural activity, mainly related to the cultivation of soybeans. Three streams (Maguire, Helves, and Horqueta) with a low-flow discharge in March, between 0.1 and 0.2 m3/s, close to the city of Arrecifes were  studied during the period of maximum insecticide application, between February and April 2001. Various sampling devices were installed to trap suspended particles, runoff and flood-water plus sediment throughout the study period. The suspended-particle samples were analysed for the insecticides endosulfan (END), chlorpyrifos and cypermethrin. Water chemistry and the macroinvertebrate communities were assessed on four occasions and the organismic drift was measured continously. During a runoff event related to a 184-mm rainfall on March 1, 2001, b-endosulfan concentrations up to 318 µg/kg and 43 µg/kg were detected in suspended particles in flood samplers in Horqueta and in suspended-particle samples in Helves, respectively, while no END contamination was detected in Maguire. Chlorpyrifos and cypermethrin were not detected in any of the streams. A significant decrease of the average species density was observed in Horqueta (from 12.8±0.5 to 9±0.7 species; ANOVA; p < 0.05) and Helves (from 10.8±1.7 to 3.3±1.3 species; p < 0.001) following the same rainfall event at the beginning of March, while the species density in Maguire remained constant at 7.9±0.3 species. The runoff primarily affected insect species belonging to the Odonata and Ephemeroptera, the abundances of which were significantly (p < 0.01) reduced in Horqueta and Helves but were not affected in Maguire. A greater drift of Smicridae (Trichoptera) and Ephemeroptera occurred in Helves and Horqueta during this runoff event, while no changes in the macroinvertebrate drift were detectable in Maguire. This study highlights the potential pesticide effects on macroinvertebrate communities in Argentinian rural streams. It is assumed that a small wetland area formed by Maguire between the agriculturally used catchment and the sampling site contributes to the absence of contamination and effects at this site.