PARENT SESSION
PM25 - Agrochemicals
Monday, 18 November 2002
8:00 AM to 6:30 PM
Exhibit Hall

(P430) Evaluating fate and effects of atrazine and -cyhalothrin in vegetated and unvegetated ditch mesocosms.

Bouldin, Jennifer^*,1, ¹ Arkansas State University, State University, AR, USA

ABSTRACT- Beneficial uses of agricultural drainage ditches have included the transport and transformation of pesticides associated with runoff during storm events and conventional flooding for specific crops. Our research has shown that ditch ecosystems can vary structurally and functionally by the presence or absence of vegetation, which help to mitigate contaminants from adjacent agricultural fields. Eight mesocosms, including four vegetated and four unvegetated, were used to measure the fate and effects of atrazine (triazine herbicide) and -cyhalothrin (pyrethroid insecticide). Concentrations for exposures were determined by suggested application rates for each pesticide, as well as combinations of both atrazine and cyhalothrin. Sequential sampling of aqueous, sediment and plant materials followed amendment of the mesocosms with each pesticide and a combination of the pesticides. Water from all treatments with atrazine significantly reduced Ceriodaphnia dubia survival to 5% through 24h following application and Pimephales promelas to 0% survival through 3h following application. Toxicity was no longer measured in water samples from mesocosms following 14 days. Toxicity to C. dubia was present through the 3h sampling of -cyhalothrin-amended mesocosms and showed no significant toxicity to P. promelas throughout the 28d sampling. Decreased survival of Chironomus tentans in sediments collected 3h post amendment was noted in unvegetated mesocosms exposed to the combination of pesticides as well as unvegetated mesocosms with atrazine alone. Chironomus larvae exhibited decreased survival (<43%) in sediments from atrazine-amended mesocosms at 24h sampling and also in sediments from unvegetated mesocosms exposed to the pesticide combination. Survival patterns of test organisms were similar in water from mesocosms amended with pesticide mixtures and atrazine alone. These data suggest that organism response to pesticide application is specific for functional characteristics found in laboratory mesocosms, while both sediment and aqueous fates of these

Key words: -cyhalothrin, atrazine, toxicity, agricultural ditch mesocosms