Overview

The NAWQA Pesticide National Synthesis Project, which began in 1992, is a national-scale assessment of the occurrence and behavior of pesticides in streams and ground water of the United States and the potential for pesticides to adversely affect drinking-water supplies or aquatic ecosystems.

Features

• Prediction of Atrazine Concentrations: Estimate atrazine concentrations in your stream with this interactive model and mapping tool.
  Watershed Regressions for Pesticides (WARP) Atrazine Model (BETA demonstration)
• The Quality of Our Nation's Waters
  Pesticides in the Nation's Streams and Ground Water, 1992-2001
  Released March 2, 2006

• Full Report
• Fact Sheet
• Frequently Asked Questions
• Supporting Information

• Recent Publications

• Comparison of pesticide concentrations in streams at low flow in six metropolitan areas of the United States: Environmental Toxicology and Chemistry, Vol. 27, No. 2, pp. 288–298
  
• Relative toxicity and occurrence patterns of pesticide mixtures in streams draining agricultural watersheds dominated by corn and soybean production: Integrated Environmental Assessment and Management, v.3, n.1, pp. 90-100 (2007)
• Response of stream chemistry during base flow to gradients of urbanization in selected locations across the conterminous United States: USGS SIR 2007-5083 (2007)
• Pesticides in the Nation's Streams and Ground Water; Environmental Science and Technology, v. 41, n.10, pp. 3408–3414 (2007)
• The geochemistry of pesticides. In: Environmental Geochemistry (ed. B. S. Lollar), Volume 9 of Treatise on Geochemistry (eds. H.D.Holland and K.K. Turekian), Elsevier—Pergamon, Oxford, UK, on-line edition, 43 p. (2007)
• How well can we predict the toxicity of pesticide mixtures to aquatic life? Integrated Environmental Assessment and Management, v. 3, n.3, pp. 364-372 (2007)
• Development and application of health-based screening levels for use in water-quality assessments: USGS SIR 2007-5106, 12 p. (2007)

Additive Toxicity Model Predicts the Toxicities of Pesticide Mixtures to Aquatic Organisms

This graph shows how an additive toxicity model performs for predicting the toxicities of pesticide mixtures to aquatic organisms. The additive model specifies that the toxicity of a mixture of co-occurring pesticides results from the sum of their individual concentrations, each normalized for potency. Mixtures may also exhibit toxicities that are greater than or less than additive. The model deviation ratio (MDR) is the ratio of the predicted toxic concentration (additive model) to the toxic concentration observed from a laboratory toxicity test, such as an LC50 value. Each symbol on the graph is the result of a toxicity test in which an aquatic plant or animal was exposed to a pesticide mixture. An MDR of 1 indicates agreement of observed toxicity with the prediction from the additive model, an MDR less than 1 indicates less toxicity than predicted, and an MDR greater than 1 indicates greater toxicity than predicted. Toxicities of mixtures with the same mode of toxic action were most closely estimated by the additive model (most are near MDR=1). Predicted toxicities of mixtures of pesticides with different modes of toxic action were more variable, both within the same group (insecticide or herbicide) and in different groups. Overall, however, almost 90 percent of tested mixtures had observed toxicities within a factor of 2 of the additive model prediction (MDR of 0.5 to 2). Findings support the use of the additive model as a slightly conservative, but broadly applicable model for preliminary predictions of the toxicities of pesticide mixtures.

For further details, see: How well can we predict the toxicity of pesticide mixtures to aquatic life?

Posted on June 5, 2008