PARENT SESSION
19 - Pesticide Ecotoxicology
8:00 AM to 6:30 PM, Monday, 13 May 2002
Exhibition Area

(19-33) Methyl-parathion effects on macroinvertebrates in vegetated and unvegetated wetland mesocosms.

Schulz, Ralf^*,1, Moore, Matt², Bennett, Erin³, Milam, Cristin⁴, Bouldin, Jennifer⁴, Farris, Jerry⁴, Smith, Sammie², Cooper, Charles², ¹ Technical University Braunschweig, Braunschweig, Germany² United States Dept. of Agriculture, Oxford, Mississippi³ Great Lakes Institute for Environmental Research, Windsor, Canada⁴ Arkansas State University, Jonesboro, Arkansas

ABSTRACT- Methyl-parathion was amended into constructed wetlands for the purpose of assessing the influence of emergent vegetation on transport and toxicity of the pesticide. Two vegetated (90% cover, mainly Juncus sp.) and two unvegetated wetland cells (each 50 m x 5.5 m x 0.2 m) were dosed each with 6.5 m₃ of water containing 6.6 mg/L a.i. Methyl-Parathion associated with 400 mg/L suspended sediment to simulate a typical Mississippi storm runoff event. Acute toxicity was assessed by sampling benthic macroinvertebrates at 5, 10, 20 and 40 m distance from the inlet before and 96 h after contamination and by in situ exposure of Chironomus tentans (Diptera) at the same sites up to 24 h after contamination. Methyl parathion was detectable throughout the unvegetated wetlands (700 g/L at 20 m, 8 g/L at 40 m), while the pesticide was not transported through the vegetated wetlands (25 g/L at 20 m, not detectable at 40 m). Factorial analysis of variance (ANOVA) using contamination (repeated measure variable), location and vegetation as factors indicated significant negative effects of contamination on various insect taxa, such as mayfly and caddisfly larvae. Seven out of the total of 15 species revealed a significant contamination x vegetation effect with individuals in the vegetated wetlands being less affected. Four species showed a significant contamination x location effect confirming a higher toxicity in the inlet area of the wetlands. A significant three-way interaction of contamination x vegetation x location was detected in Chironomus sp. and Telebasis sp. (Odonata), with both species mostly affected at the inlet area of the unvegetated wetlands. In situ exposure bioassays confirmed the positive effect of wetland vegetation on the reduction of methyl-parathion toxicity.

Key words: risk, mitigation, management, insecticides