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 PARENT SESSION
12 - Predicting Pollution Effects in the Field
2:10 PM to 5:20 PM, Monday, 13 May 2002
Session Chair: Liess, Mathias 1, Schulz, Ralf2, 1 2 .
Lanner
(12-03) A combined microcosm and field approach to evaluate the aquatic toxicity of azinphos-methyl to stream communities.
Dabrowski, James*,1, Thiere, Geraldine2, Schulz, Ralf1, 1 University of Stellenbosch, Stellenbosch, Western Province2 Institute of Zoology, Braunschweig
ABSTRACT- Potential ecotoxicological effects of the orchard insecticide azinphos-methyl (AZP) were evaluated in a combined microcosm and field approach. The upper regions of the Lourens River, South Africa are free of contamination (control site), while the subsequent stretches flowing through a 400-ha orchard area receive transient insecticide pollution (e.g. 0.82  g/L AZP, 344 g/kg chlorpyrifos) following spray drift and runoff (contaminated site). Stones taken from the control site were transferred to outdoor microcosms (1.5 x 0.2 x 0.2 m) resulting in 12 core species and approximately 350 individuals per microcosm. Microcosms were contaminated for 1 h with AZP (control, 0.2; 1, 5 and 20 g/L; three replicates each) and acute effects on survival were evaluated 6 days following exposure. The two highest treatments led to a significant (ANOVA, Fisher's PLSD) reduction in abundance of various insect groups, such as Demoreptus sp., Castanophlebia sp., Simuliidae and Chironomidae. In contrast, Aeshna sp., Dugesia sp., Ceratopogonidae and Cheumatopsyche sp. were not affected. In parallel, a quantitative macroinvertebrate survey was conducted at the control site and the contaminated site of the Lourens River. Both sites contained a similar number of species but differed considerably in their species composition. Six out of the eight species that reacted sensitively to AZP in the microcosm study occurred in the field at significantly lower densities or were absent at the contaminated site in comparison to the control site. All of the four species that were tolerant in the microcosm occurred at significantly higher densities at the contaminated field site. Two out of the twelve species reacted differently in the microcosm and the field study. It can be concluded that microcosm studies employing a field relevant design could be linked successfully to field studies and that transient pesticide contamination affects the aquatic communities of the Lourens River.
Key words: azinphos-methyl, microcosm, field, communities
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