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

(BEL-1117-809450) Occurrence of pesticide mixtures in corn-belt surface water.

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

ABSTRACT- Monitoring of surface water has indicated that pesticides, usually occurring as mixtures, are ubiquitous contaminants throughout agricultural regions of the United States. Thus, it can be assumed that the majority of aquatic organisms are exposed to pesticide mixtures during their lifetime. Understanding the hazards posed by mixtures is a complicated task because a large number of different pesticides may occur as co-contaminants. Testing all of the possible mixtures is not feasible for even simple systems. Although toxicity-modeling techniques have improved recently, there is still a great deal of uncertainty in regard to modeling, especially for chronic endpoints. Therefore, techniques are needed for determining priority mixtures that are most likely to have an environmental impact. In our approach, occurrence of pesticide mixtures were determined by defining a pesticide-usage landscape (corn/soybean row-crops) and toxicologically censoring the monitoring data collected in the landscape. To sensor the data, toxicological endpoints for duckweed, green algae, water fleas, and bluegill were used to generate levels of interest for each species. Pesticide concentrations below the level of interests were not included in further analyses. Thus, species-dependent sub-sets of the monitoring database were generated that only included pesticide concentrations that are likely to be important toxicologically for a given reference species. Through this approach, the prevalence and types of mixtures that are important were determined. The composition of pesticide mixtures as determined by this approach was much simpler than would have been predicted statistically, with only a few specific mixtures accounting for most contamination patterns. Nearly all of the problematic mixtures identified in this study were composed of herbicides from one of two classes, triazine and chloroacetanilide, and were identified using duckweed or green algae biological endpoints in the censoring process.

Key words: mixture, pesticide, surface water, occurrence