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Whole Effluent Assessment

The COHIBA project aims to evaluate the ecotoxicity of effluents throughout the Baltic Sea region, based on the Whole Effluent Assessment (WEA) approach.

At the moment most of the restrictions that limit discharges and emissions are based on concentrations of chemicals. Unlike this conventional chemical-specific approach, the innovative WEA approach aims to determine whether effluents discharged into the Baltic Sea are toxic to aquatic organisms.

Traditional effluent analyses aim to determine concentrations of specific substances or groups of substances, such as PCBs. But most effluents contain varying cocktails of different chemicals, which could either individually or in combination be harmful to marine life.

Some of the chemicals in wastewater effluents have been modified by the human body or by microbes during the treatment process. Chemicals may also have been degraded partially or completely during treatment into other more or less harmful substances. This can make it hard to accurately identify the substances in the mixtures present in effluents.  

Testing toxicity on aquatic organisms

Lemna growth inhibiton test
Lemna growth inhibiton test. Photo: Timo Vänni/SYKE
Whole effluent assessment aims to detect harmful impacts by directly exposing test organisms to effluent samples in controlled laboratory conditions. The COHIBA project uses various short-term tests to analyse effluents from municipal and industrial wastewater treatment plants. These tests focus on factors including survival rates of the water flea Daphnia magna, luminescence of Vibrio fisheri bacteria, and green algal growth. 

Well-treated effluents should not be acutely toxic. One problem is that many organic chemicals are bioaccumulative, and their impacts might only become evident after longer periods of exposure than are possible in the short-term tests. Longer-term tests involving more chronic exposure enable assessments of impacts on organisms' vital functions or life-cycle stages, including reproduction, growth, and hormonal impacts or effects on their genetic material. The COHIBA project also investigates such effects.

Toxicity-based discharge limits

The ultimate goal of the project is to define toxicity-based discharge limits for effluents discharged into waters in the Baltic Sea region. These "toxicity threshold values" could then be applied by HELCOM in a set of standardized tests to limit effluent toxicity.

This WEA approach is preferable to chemical analysis in that it measures the combined effects of all of the potentially harmful properties of effluents. Besides, it is expected that WEA is less costly than advanced chemical measurements of effluents and will allow saving resources for more detailed studies of identified toxic streams.

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