The Pesticide Toxicity Index (PTI) is a screening tool to assess potential aquatic toxicity of complex pesticide mixtures by combining measures of pesticide exposure and acute toxicity in an additive model. The PTI incorporates 492 pesticides and degradates and is determined separately for fish, cladocerans, and benthic invertebrates. The Median-PTI is calculated from the median of reported toxicity values, so is robust to outliers. The Sensitive-PTI uses the 5th percentile of toxicity values, and is a more sensitive indicator of potential toxicity. The PTI's predictive ability was tested using data from published field studies that measured pesticide concentrations and toxicity to Ceriodaphnia dubia in ambient stream water. C. dubia mortality was =50% in 97% of samples with Median-PTI>1, 44% of samples with Median-PTI of 0.1�1, and 10% of samples with Median-PTI<0.1. Applications of the PTI tool include screening-level assessment of pesticide mixtures and interpretation of invertebrate community condition in streams.

Pesticide Toxicity Index for freshwater aquatic organisms: A screening-level tool for assessing complex mixtures of pesticides in streams

248th National Meeting (2014)

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