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Water: Whole Effluent Toxicity

Whole Effluent Toxicity

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Whole Effluent Toxicity (WET) refers to the aggregate toxic effect to aquatic organisms from all pollutants contained in a facility's wastewater (effluent). It is one way we implement the Clean Water Act's prohibition of the discharge of toxic pollutants in toxic amounts. WET tests measure wastewater's effects on specific test organisms' ability to survive, grow and reproduce.

The WET methods listed below are specified at 40 CFR 136.3, Table IA. WET test methods consist of exposing living aquatic organisms (plants, vertebrates and invertebrates) to various concentrations of a sample of wastewater, usually from a facility's effluent stream. WET tests are used by the National Pollutant Discharge Elimination System (NPDES) permitting authority to determine whether a facility's permit will need WET requirements.

At the end of 2004, EPA released a draft of the National Whole Effluent Toxicity (WET) Implementation Guidance Under the NPDES Program (PDF) (109 pp, 1.1MB). (The public docket for this guidance can be found at: Regulations.gov (EPA-HQ-OW-2004-0037).


WET Methods and Manuals

Methods for Measuring Acute Toxicity to Freshwater and Marine Organisms

  • Freshwater
    • 2002.0 Ceriodaphnia dubia acute.
    • 2021.0 Daphnia puplex and Daphnia magna acute.
    • 2000.0 Fathead Minnow, Pimephales promelas, and Bannerfin shiner, Cyprinella leedsi, acute.
    • 2019.0 Rainbow Trout, Oncorhynchus mykiss, and brook trout, Salvelinus fontinalis, acute.
  • Marine
    • 2007.0 Mysid, Americamysis bahia, acute.
    • 2004.0 Sheepshead Minnow, Cyprinodon variegatus, acute.
    • 2006.0 Silverside, Menidia beryllina, Menidia menidia, and Menidia peninsulae, acute.

Short-term Methods for Estimating Chronic Toxicity to Freshwater Organisms

  • 1000.0 Fathead minnow, Pimephales promelas, larval survival and growth.
  • 1001.0 Fathead minnow, Pimephales promelas, embryo-larval survival and teratogenicity
  • 1002.0 Daphnia, Ceriodaphnia dubia, survival and reproduction
  • 1003.0 Green alga, Selenastrum capricornutum, growth.

Short-term Methods for Estimating Chronic Toxicity to Marine and Estuarine Organisms

  • 1004.0 Sheepshead minnow, Cyprinodon variegatus, larval survival and growth.
  • 1005.0 Sheepshead minnow, Cyprinodon variegatus, embryo-larval survival and teratogenicity.
  • 1006.0 Inland silverside, Menidia beryllina, larval survival and growth.
  • 1007.0 Mysid, Americamysis bahia, survival, growth,and fecundity.
  • 1008.0 Sea urchin, Arbacia punctulata, fertilization.

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Regulatory Actions

2002 Final Rule

Guidelines Establishing Test Procedures for the Analysis of Pollutants; Whole Effluent Toxicity Test Methods; Final Rule

Proposed Rule

1995 Final Rule

Final Rule published in the Federal Register to add Whole Effluent Toxicity Methods to the list at 40 CFR 136.3 (Tables 1A and II) (October 16, 1995)

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Guidance Documents

Final Report: Interlaboratory Variability Study of EPA Short-term Chronic and Acute Whole Effluent Toxicity Test Methods:

Method Guidance and Recommendations for Whole Effluent Toxicity (WET) Testing (40 CFR Part 136) (PDF) (60 pp, 184K) (July 2000)
Includes specific technical guidance on nominal error rate adjustments, confidence intervals, concentration-response relationships, dilutions series selection, and dilution water. Federal Register Notice of Data Availability (July 28, 2000).

Understanding and Accounting for Method Variability in Whole Effluent Toxicity Applications Under the National Pollutant Discharge Elimination System (scroll to the bottom of the list) (EPA 833-R-00-003)
This document provides guidance to NPDES regulatory authorities and persons interested in whole effluent toxicity testing.

Policy Memo: Clarifications Regarding Flexibility in 40 CFR Part 136 Whole Effluent Toxicity (WET) Test Methods (April 1996)

The NPDES program has guidance on the application of WET testing to permits under the National Pollutant Discharge Elimination System (NPDES).

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