Whole Effluent Toxicity (WET) Testing

Aquatic Laboratories is a leading provider for Whole Effluent Toxicity (WET) testing required under the Clean Water Act (CWA) Section 402 NPDES permitting program.

As a nationally recognized TNI / NELAC certified lab, Aquatic Laboratories has taken great care and effort to refine and control testing procedures so that our clients get the most timely, accurate, reliable, and reproduceable results technically feasible.

WET testing methods include two basic types of WET tests, acute and chronic (including sublethal endpoints). WET test methods performed by Aquatic Laboratories include procedures for freshwater test species, including using an invertebrate and vertebrate species to identify the most sensitive species for use with the NPDES permits program. Ceriodaphnia dubia (freshwater flea) and Pimephales promelas (fathead minnow) are examples of EPA approved indicators or surrogates used in the protection of freshwater aquatic community organisms.


Background on Whole Effluent Toxicity (WET)

  • As the US EPA notes, Whole Effluent Toxicity (WET) describes the aggregate toxic effect of an aqueous sample (e.g., whole effluent wastewater discharge) as measured by an organism's response upon exposure to the sample (e.g., lethality, impaired growth, or reproduction). WET tests replicate the total effect of environmental exposure of aquatic life to pollutants in an effluent without requiring the identification of the specific pollutants.
  • WET testing is a vital component to implementing water quality standards under the NPDES permits program in accordance with the CWA Section 402. It supports meeting the goals of the CWA Section 101(a) and (2), especially with respect to restoring and maintaining "the chemical, physical, and biological integrity of the Nation’s waters and “…the protection and propagation of fish, shellfish, and…”
  • WET tests are used for water quality assessment, permit limit development, and compliance assessment. To protect water quality,  WET tests are required in NPDES permits together with requirements based on chemical-specific water quality criteria.
  • WET limits may be included in permits to ensure that the state quality criteria for aquatic life protection are met. WET monitoring requirements are included in permits to generate valid WET data used to determine whether reasonable potential for WET has been demonstrated (e.g., toxicity that would result in an excursion of state WQS). If reasonable potential has been demonstrated, then a WET limit is included in the NPDES permit. WET test results are therefore typically used in determining compliance with NPDES WET permit limits.