PARENT SESSION
SP9 - Field Studies: Causal Relationships Between Exposure & Effects
Chair: Lewis, Mike1, 1 U.S. EPA, Gulf Breeze, FL
2:10 PM to 5:30 PM - Sunday, 17 November 2002
Room Ballroom E
(156) Use of the modular estuarine mesocosm to assess effects of a field-simulated atrazine exposure.
Pennington, Paul*,1,2, DeLorenzo, Marie1,2, Lawton, Jennifer1, Fulton, Michael1, Scott, Geoffrey1, 1 NOAA National Ocean Service, Center for Coastal Environmental Health and Biomolecular Research, Charleston, SC, USA2 Environmental Health Sciences, Norman J. Arnold School of Public Health, University of South Carolina, Columbia, SC, USA
ABSTRACT- As part of a tiered toxicological approach, modular estuarine mesocosms were developed to assess the effects of anthropogenic NPS runoff on sensitive estuarine flora and fauna from small tidal creeks. The objective of this study was to test the effectiveness and utility of the replicated modular estuarine mesocosm in determining direct and indirect effects of pesticide exposure to estuarine organisms during a realistic exposure scenario. Twelve replicated mesocosms were designed to allow for semi-diurnal tidal flux. Sediments, flora, fauna, and seawater were collected and established in the mesocosms prior to the experiment. In a long-term exposure (7 weeks) that was modeled after monitoring data from the mid-Texas coast, direct effects of atrazine on microbial communities and indirect effects on tidal creek fauna were assessed. The replicated modular estuarine mesocosm identified structural changes in the microbial community similar to previous laboratory and mesocosm studies as a result of atrazine exposure. Also, the system was effective in the elucidation of indirect effects of atrazine on estuarine consumers. Within the mesocosm, organismal-level reductions in growth were found in oysters and clams as a result of atrazine exposure. Microalgal communities did not recover from low-level atrazine exposure during a 14-day recovery period. Microalgal communities that were pre-exposed to a long-term low-level (mean = 5 to 6 
g/L) of atrazine (with and without recovery) were greatly reduced by a subsequent high-level (mean = 261 g/L) atrazine exposure. Microalgal communities that received no pre-exposure were largely unaffected by the high-level atrazine exposure. Using time-weighted averages for atrazine concentrations, the 7 week EC50 for inhibition of microalgal density was 11 g/L.
Key words: atrazine, mesocosm, field residues, microbial communities