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Interpretation of the Ecological Significance of Atrazine Stream-Water Concentrations Using a Statistically-Designed Monitoring Program
Citation:
Interpretation of the Ecological Significance of Atrazine Stream-Water Concentrations Using a Statistically-Designed Monitoring Program.
Impact/Purpose:
Key questions being addressed by this FIFRA Scientific Advisory Panel meeting are as follows: 1. Based on available experimental microcosm and mesocosm studies and ecosystem response models were the relationships between atrazine exposure profiles and aquatic community responses determined in a reasonable and transparent manner to establish and thresholds of concern for atrazine? 2. Based on the monitoring design, is the approach to estimating the extent of watersheds in corn and sorghum producing areas that exceed atrazine thresholds of concern for aquatic community effects appropriate? 3. Based on results of the monitoring study, are the hypotheses and related methods and data sets being employed to identifiy potential watershed attributes associated with higher atrazine exposures appropriate?
Description:
A risk assessment was conducted by the US Environmental Protection Agency (EPA) as part of the 2003 Interim Registration Eligibility Document (IRED) on atrazine. The assessment indicated potential community- and population-level risk to sensitive aquatic ecosystems at prolonged concentrations of atrazine from 10 – 20 parts per billion. As a condition of re-registration, atrazine registrants were required to develop a monitoring program to determine the extent to which atrazine concentrations in streams associated with corn and sorghum production may be exceeding levels that could cause effects to aquatic communities. If the threshold were exceeded, then a watershed-based mitigation program could be required. The atrazine exposure threshold was developed based on an analysis of the magnitude and duration of atrazine exposure that caused significant effects as reported in experimental microcosm and mesocosm studies. The primary endpoint of concern focused on impacts to the primary producers in the aquatic plant community and the subsequent impacts to community structure. The monitoring program design was based on a population of 1,172 watersheds whose streams were identified as highly vulnerable to atrazine exposure based on factors such as atrazine use intensity in corn and sorghum production and run-off vulnerability. A sub-set of 40 sites was selected for monitoring using a stratified, random statistical survey design. Streams were monitored for a minimum of two years with samples collected at least once every four days. Data from each stream were evaluated on a yearly basis to determine if atrazine concentrations were detected at sufficient levels over sufficiently long time durations to exceed the exporse threshold of concern. Based on the sampling design, the results from the streams in the 40 waterheds allow statistically-based inferences to the larger population of 1,172 watersheds vulnerable to atrazine runoff.