Whole Effluent Toxicity (WET) testing was created to measure toxin levels in wastewater. We regulate wastewater discharge through permits. The permits limit different contaminants and result in cleaner water. However, not all individual tests can tell you the combined effect of all the regulated contaminants. To find out the toxicity levels of the overall effluent — or wastewater discharge — the WET test was developed.
WET is implemented through the National Pollution Discharge Elimination System (NPDES) permits. Typically, WET tests are only needed for discharges that may be toxic to the aquatic environment.
Whole effluent toxicity (WET) testing
WET testing is essential to maintain the integrity of aquatic ecosystems. WET testing looks holistically at toxins in the entire effluent — or wastewater discharge. WET tests are done throughout the U.S. to address acute and chronic levels of exposure to wastewater discharges. Acute levels look at the survival rate of an organism within 96 hours of exposure to the effluent. Chronic levels measure how much an organism is impacted by the effluent over time. Chronic testing looks at whether or not the effluent impairs an organisms survival, development, growth, or reproduction.
What is the problem?
Aquatic animals thrive under healthy conditions and can become sick and die under toxic conditions. Wastewater that enters streams, rivers, and lakes can have a major impact on aquatic life and human health.
Some pollutants (such as pesticides or metals) can build up in the food chain. They get into fish and shellfish and become dangerous for people to eat. Toxic conditions also can close down water recreation areas.
Water turns toxic with excessive contaminants such as:
- Heavy metals
Permit requirements ensure the measurement and limitation of harmful contaminants in wastewater effluents. However, those individual components do not measure how toxic the water may be.
What is the solution?
The solution is to test wastewater effluent to measure the toxicity before it affects Washington's water. The WET test gives reliable results about the toxic effects of wastewater on aquatic life. This gives us the foundation to identify and reduce toxins that may negatively impact water quality.
What is our role?
We protect aquatic life and human health from toxic discharges into Washington waters. We issue water quality permits — known as National Pollution Discharge Elimination System (NPDES) permits — that include WET testing to limit and control toxic substances. We verify data quality, monitor for permit compliance, and enforce for noncompliance. Our WET coordinator also offers technical support and guidance for permittees to meet WET testing requirements.