Whole Effluent Toxicity Audit Checklist

Whole effluent toxicity testing (WET) is a key way that we enforce compliance with the Clean Water Act and NPDES permit limits. WET tests measure wastewater’s impact on organisms’ survival, growth and reproduction capabilities – as determined by measurement of WET results against test organisms’ survival rates in an incubation environment.

As part of most toxicity testing programs, AWETS must include organisms from various trophic levels and taxonomic groups for effective testing results.

Checklist I: Monitoring
An effective monitoring strategy is key to meeting animal protection goals and decreasing our dependence on single-species WET tests. A Toxicity Identification Evaluation (TIE) plan forms part of this monitoring approach; it involves investigating sources of toxicity such as how treatment plant processes impact WET test results or through experimental manipulations to uncover possible sources of toxicant contamination in effluent.

Not only should a TIE be employed, but also an array of tests should be utilized; including tests that measure biologically relevant effects like chronic testing or bioaccumulation capacity of effluent. Testing should include organisms from various taxonomic groups to ensure ecological relevance is assessed accurately; moreover, reduction of vertebrate testing through strategic combinations of tests, analytical tools, and biological monitoring should also be considered.

Checklist II: Analysis
Effluent Toxicity Testing, commonly known in the US and Europe as WET testing and WFD testing respectively, is an integral component of wastewater discharge monitoring; however, its performance alone cannot ensure environmental protection, particularly with complex effluents.

Consideration must be given to the sensitivities and ecological functions of different taxa and ecological functions when selecting appropriate tests, taking into account factors like specific eutrophication levels in receiving water bodies, biodiversity value and conservation needs as well as bioaccumulation/concentration potentials.

Testing should also take multiple trophic levels into account, including non-lethal modes of action such as endocrine disruption. Alternatives to traditional fish tests exist or are being developed, including BE-SPME and receptor-based methods which offer greater ecological sensitivity and wider coverage than fish embryo toxicity tests while providing enough assurance levels to apply WET or WEA testing as part of a weight-of-evidence approach to effluent quality assessment.

Checklist III: Toxicity Reduction Evaluation
A toxicology risk evaluation (TRE) is an investigation designed to pinpoint the source and appropriate solutions of whole effluent toxicity, and identify its control methods. A TRE is typically required under most NPDES permits and should be conducted whenever WET test failures are witnessed.

Based on the type of facility and circumstances surrounding a failed test, an environmental regulatory evaluation (TRE) may involve extensive characterization (using TIE procedures), source investigations or both approaches; source investigations could involve treatment or process modifications, wastewater sample collection for further testing and analysis, or any other activities to locate sources of toxicity.

The TRE phase involves developing a plan of actions in case of WET test failure and then evaluating their efficacy at reducing observed toxicity (see Fig 1). These could include identifying toxicants and their sources through TIE procedures; trying to eliminate those toxicants through treatability tests; or exploring ionic imbalances as potential sources of toxicity (see Fig 1).

Checklist IV: Toxicity Monitoring
Monitoring phase of WET programs is critical to ensure accuracy. Testing Reproducibility Environments (TREs) provide an invaluable way to avoid costly and time-consuming compliance issues due to inaccuracy of WET test results.

Test results should be monitored using a control chart to ascertain whether they are stable or trending upward, so as to detect potential issues and take preventative steps early to limit an increase in field toxicity.

Grab samples can reveal spikes and ebbs in response curves, particularly for highly toxic effluents or very short-term tests that produce immediate responses (e.g. larval fish growth or gross morphological changes). Furthermore, handling and shipping the sample differently may increase variation in test responses.

WET tests do not give an exact representation of what would occur in the field for five reasons: relative sensitivity of test organisms compared with species/taxonomic group used in receiving environment; covariates that affect toxicity (e.g. mixtures that may have additive or synergistic effects); adaptations that arise in field settings; and hormesis.