Influence of fipronil compounds and rice-cultivation land-use intensity on macroinvertebrate communities in streams of southwestern Louisiana, USA

Authors

Scott V. Mize, U.S. Geological SurveyFollow
Stephen D. Porter, U.S. Geological Survey
Dennis K. Demcheck, U.S. Geological Survey

Document Type

Article

Date of this Version

2008

Comments

Published in Environmental Pollution 152 (2008) 491e503

Abstract

Laboratory tests of fipronil and its degradation products have revealed acute lethal toxicity at very low concentrations (LC₅₀) of <0.5 μg/L to selected aquatic macroinvertebrates. In streams draining basins with intensive rice cultivation in southwestern Louisiana, USA, concentrations of fipronil compounds were an order of magnitude larger than the LC₅₀. The abundance (p=-0.64; p=0.015) and taxa richness (r²=0.515, p<0.005) of macroinvertebrate communities declined significantly with increases in concentrations of fipronil compounds and rice-cultivation land-use intensity. Macroinvertebrate community tolerance scores increased linearly (r²=0.442, p < 0.005) with increases in the percentage of rice cultivation in the basins, indicating increasingly degraded stream conditions. Similarly, macroinvertebrate community-tolerance scores increased rapidly as fipronil concentrations approached about 1 μg/L. Pesticide toxicity index determinations indicated that aquatic macroinvertebrates respond to a gradient of fipronil compounds in water although stream size and habitat cannot be ruled out as contributing influences.