Skip to main content

The Whole Effluent Toxicity (WET) Program

Whole effluent toxicity (WET) tests are used, in addition to chemical-specific testing, to measure, predict and control the discharge of materials that may be harmful to aquatic life. Recognizing that no single test or organism can be expected to satisfy a comprehensive approach to environmental protection, the DNR requires a battery of toxicity tests that are broadly accepted and that measure toxic effects using organisms representing different trophic levels and taxonomic groups.

The organisms most commonly used in WET tests in Wisconsin are the fathead minnow (Pimephales promelas), a waterflea (Ceriodaphnia dubia), and a green algae (Selenastrum capricornutum). These organisms are exposed to effluent samples for a specific time period. Acute tests last 48 to 96 hours and are used to determine the concentration of effluent that causes death during a short-term exposure. Chronic tests last about seven days and estimate the effluent concentration that interferes with growth or reproductive potential.

State of Wisconsin Aquatic Life Toxicity Testing Methods Manual (Methods Manual)

In Wisconsin, laboratories must be certified to perform WET tests to be used for permit compliance according to s. NR 149.20, Wis. Adm Code. The Methods Manual provides the test methods and laboratory procedures that must be followed in order to maintain laboratory certification. All WET tests submitted for compliance with a WPDES permit must be done according to the Methods Manual, according to NR 219.04, Wis. Adm. Code. The information given in the Methods Manual [PDF] includes testing and sampling procedures, types of tests, definitions, quality control/quality assurance procedures, etc. All site-specific conditions such as sampling types or instream waste concentrations, which are different for each permittee, are specified in the WPDES permit.

The "WET Test Report Form" (available as an Excel file for acute only [XLS], chronic only [XLS] or acute and chronic [XLS] tests) is required to be submitted for demonstrating test completion and compliance with a WPDES permit. (See Section 6 of the Methods Manual [PDF] for instructions and submittal requirements.) The original, complete, signed version of the report form must be sent to the department´s Biomonitoring Coordinator by the date specified in the WPDES permit. Reports must contain a description and justification of any abnormal procedures, conditions or manipulations used in the test(s). The permittee and/or laboratory should also provide any attachments or additional information they believe to be relevant to the test. All other test documentation (e.g., bench sheets, record books, etc.) needed to fulfill manual or QA requirements must be maintained at the laboratory for laboratory certification purposes.

DNR Whole Effluent Toxicity (WET) Program Guidance Document

The WET Guidance Document provides examples, clarification, and explanation of existing rule and Methods Manual requirements. It is intended to help DNR staff, permittees and others make decisions regarding WET testing. The guidance given covers sampling procedures, monitoring and limits decisions, WET enforcement, lab selection, toxicity reduction investigations and other topics. Part I of the guidance document contains guidance that was written primarily for DNR staff (though others may find it useful, too). Part II is intended as guidance and clarification of existing requirements for permittees, consultants and others. The Guidance Document is revised as program needs dictate. Users should call or email Kari Fleming to suggest any issues they feel need to be addressed in future revisions.

Whole Effluent Toxicity testing