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The UK environmental regulator, the Environment Agency, is at present in the process of introducing a revision to the effluent discharge consenting system, based on the assessment of whole effluent toxicity - so called Direct Toxicity Assessment (DTA). The concepts of the most ‘sensitive’ species and of risk assessment based on estimation of Predicted Environmental Concentration (PEC) form the basis of the proposed consenting structure. The objective is to control the toxicity of point source discharges to riverine, estuarine and coastal waters and it raises the need for understanding of the nature and expression of toxicity in such discharges. Internationally recognised toxicity test protocols are well established, enabling the quantitative measurement of toxicity with levels of confidence similar to the more traditional physical and chemical determinands, such as individual organic solvents, COD or metals. However, traditional protocols are seen as resource intensive and as involving high cost. This paper presents some experiences from the Zeneca Brixham Environmental Laboratory in the characterisation of the toxicity expressed to freshwater and marine species by several chemical manufacturing effluents and in the conduct of a number of Toxicity Identification Evaluations (TIE) using both standard and enhanced protocols for toxicity testing.

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