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Water: Whole Effluent Toxicity

Proposed Rule for Whole Effluent Toxicity Test Methods

Note: EPA no longer updates this information, but it may be useful as a reference or resource.


 Fact Sheet; September 2001

In 1995, we amended the "Guidelines Establishing Test Procedures for the Analysis of Pollutants," to add a series of standardized whole effluent toxicity (WET) test methods to the list of methods approved at 40 CFR Part 136 (60 FR53529; October 16, 1995) (WET final rule). The WET final rule approved 17 methods for measuring the acute and short-term chronictoxicity of effluents and receiving waters to fresh water, marine, and estuarine organisms.

After promulgation, a variety of parties filed suit challenging our rulemaking. To resolve that litigation, we entered into settlement agreements with the various parties. This proposed rule, inpart, fulfills the requirements of two settlement agreements between EPA and stakeholders (Edison Electric Institute et al. v. EPA, Settlement Agreement, July 24, 1998; Lone Star Steel v. EPA, Settlement Agreement, March 4, 1998).

Proposed Rule

This proposed rule would revise WET test methods to update the methods, to provide minor corrections and clarifications, and to address specific stakeholder concerns. Proposed updates to the methods include revising method precision statements to reflect recent variability studies, incorporating all previous addenda and errata, and correcting additional technical errors not noted in previous errata. Proposed revisions also address the following specific stakeholder concerns: blocking by known parent age, pH drift, concentration-response relationships, nominal error rate adjustments, confidence intervals, dilution series selection, dilution water acceptability, and pathogen interference. Lastly, this proposed rule presents the final results of an interlaboratory variability study of WET test methods and proposes to ratify the previous approval of those methods evaluated in the study.

Additional Information

The complete text of the proposed rule was published in the Federal Register.

Supporting Documents

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