Which of the following describes Whole Effluent Toxicity (WET) testing requirements?

• A. Toxicity-based limits require toxicity tests of the effluent.
• B. WET is based on ambient water quality standards.
• C. WET does not involve biological testing.
• D. WET only applies to air emissions.

Answer: (A)

Whole Effluent Toxicity testing focuses on the biological effects of the entire discharge on aquatic life. The idea is to determine whether the effluent, as discharged, has toxicity that would harm organisms in the receiving water. Permits set toxicity-based limits, and compliance is shown by conducting standardized toxicity tests on samples of the effluent itself (often using dilution series and test species) to see if the observed effects stay within those allowed limits. This approach captures the combined influence of all pollutants and their interactions, not just individual chemical concentrations. It’s distinct from ambient water quality standards, which assess the state of the water body rather than the discharged effluent. And since WET relies on actual biological testing with aquatic organisms, it inherently involves living test species. In short, the requirement is that the effluent’s toxicity be measured and kept within permitted thresholds.