R8 PM Pesticide Mixtures
Thursday, 17 November 2005: 1:50 PM - 5:30 PM in 331-332

(LYD-1117-808488) Hazard of Pesticide Mixtures in Corn-Belt Surface Water.

Lydy, M¹, Belden, J¹, ¹ Southern Illinois University, Carbondale, IL, USA

ABSTRACT- Although numerous studies have shown that mixtures of toxicants generally result in greater toxicity than would be expected from any of the single components, little work has been conducted quantifying the increased hazard posed in actual environmental samples. In the current study, a database containing pesticide-monitoring data was evaluated using a toxic unit approach. Four model species including duckweed, green algae, water fleas, and bluegill were used as indicators of toxicity. Toxic unit values (TU) calculated based on all pesticides and pesticide classes were used to evaluate the risk posed by each sample. In each case, the toxic unit value of the mixture was compared to the individual pesticide that occurred at the highest concentration. Few samples had a mixture TU value of greater than 0.1 for water fleas and bluegill, while many samples had TU values above 0.1 for duckweed and green algae. For duckweed and green algae, only a few pesticides, and only two classes of herbicides, the triazines and chloroacetanilides generally dominated the magnitudes of the toxic unit values. Although consideration of mixtures increased the toxic unit value, and thus the potential hazard, the increase was always less than 2-fold. The small increase in TU value indicates that in this pesticide-usage landscape consideration of mixtures may have minimal impact on the overall risk assessment of pesticides.

Key words: pesticides, mixtures, aquatic organisms, risk assessment