2,4-dichlorophenoxyacetic acid (2,4-D) is an herbicide used for post-emergence, selective control of broadleaf weeds in the United States since 1945. In consideration of its upcoming registration review, an effort is being made to reevaluate the state of knowledge pertaining to the range of sensitivities of terrestrial and aquatic plants to 2,4-D. In order to capture this range, a species sensitivity distribution (SSD) will be derived for relevant combinations of plants and endpoints. An SSD, which is an alternative to using a point estimate for the measure of effect (i.e., most sensitive species), is a statistical distribution derived from available toxicity data and visualized as a cumulative distribution function. SSDs have the advantage of making more use of the available toxicity data for a larger array of species, and describe the range of sensitivity rather than focusing on a single (e.g. lowest) value. The use of SSDs has been proposed for evaluating the risk of mortality to animals in pesticide endangered species assessments, and should also be scientifically appropriate for plants. As a first step in the derivation of SSDs characterizing 2,4-D toxicity to terrestrial and aquatic plants, a comprehensive literature review was conducted. Next, it was necessary to evaluate the reliability and relevance of data prior to consideration for use in the SSDs. A systematic approach was developed that includes identifying databases and other sources for locating data, developing reliability and relevance categories according to pre-determined validity criteria, and scoring the information using a tiered system to select key data for use in deriving the SSDs. This data evaluation process increases the overall transparency, clarity, and objectivity of the risk assessment process.

Characterizing the range of sensitivities of aquatic and terrestrial plants to 2,4-D: A quantitative approach to selection and evaluation of data

250th National Meeting (2015)

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