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ATRAZINE ECOLOGICAL EFFECTS ASSESSMENT FOR OPP LEVEL OF CONCERN AND OW WATER QUALITY CRITERION FOR AQUATIC LIFE
Citation:
Erickson, R J. ATRAZINE ECOLOGICAL EFFECTS ASSESSMENT FOR OPP LEVEL OF CONCERN AND OW WATER QUALITY CRITERION FOR AQUATIC LIFE. Presented at Surface Water Monitoring and Standards Meeting, Chicago, IL, February 4, 2004.
Description:
Atrazine is a relatively water-soluble and persistent herbicide that can reach concentrations of possible ecological concern for aquatic plants in vulnerable watersheds in regions with high agricultural usage of atrazine. As a consequence, the U.S. EPA Office of Water is currently developing an aquatic life water quality criterion for atrazine and the Office of Pesticide Programs is developing an ecological level of concern for use in an atrazine monitoring program. Toxic effects concentrations for atrazine generally are much lower for aquatic plants than animals, and effects in plants typically involve a rapid reduction in photosynthetic rates, followed by quick recovery when exposures are ended. Exposure concentrations in surface waters are highly dependent on episodic runoff events, and thus tend to be highly variable. Therefore, key issues in ecological effects assessments for atrazine are (1) what levels of effect across multiple plant species are of significance to aquatic communities and (2) how to quantify effects for such variable exposures. The first of these issues is addressed in current OW and OPP efforts by using a large set of aquatic community microcosm and mesocosm tests with atrazine to establish what exposure conditions elicit significant effects. However, these data are not sufficient to quantify the time-dependence of these effects. To do this, mathematical simulation models for aquatic communities are being used. Models are parameterized with available single-species atrazine toxicity data, and multiple computer simulations are conducted to assess likely effects relative to parameter variability and uncertainty. An integrated response variable from the simulation outputs is selected that is well correlated with the level of effects in the micro/mesocosm data, and a reference value for this model output variable is selected that best discriminates the effects of concern in these data. It should be emphasized that it is not assumed that such simulation models provide an accurate representation of absolute responses of aquatic communities. Rather, the principal assumption is that the models have good enough representations of the time-dependence of important community processes to support useful extrapolations among different exposure situations, provided that the levels of concern for model output variables are referenced to effects in actual micro/mesocosm tests. Current efforts are further testing and refining important aspects of this methodology.
IMPACT STATEMENT:
This presentation summarizes joint efforts by NHEERL/MED, OPP/EFED, and OW/HECD addressing the definition of concentrations of concern for impact of atrazine on aquatic plants. Atrazine is a relatively water-soluble and persistent herbicide that can reach concentrations of possible ecological concern for aquatic plants in vulnerable watersheds in regions with high agricultural usage of atrazine. As a consequence, the U.S. EPA Office of Water is currently developing an aquatic life water quality criterion for atrazine and the Office of Pesticide Programs is developing an ecological level of concern for use in an atrazine monitoring program. The methodology resulting from these efforts is noteworthy for such applications because it combines extensive data from microcosm/mesocosm tests with mathematical simulation models for aquatic communities to set acceptable effect levels for variable exposure scenarios.