Report No: SR 3846/1


SR 3846/1

March 1996


This manual provides guidance on conducting practical ecotoxicological risk assessments for the aquatic environment. The main objective of this manual is to define a possible strategy for the acquisition, interpretation and application of ecotoxicological information and associated environmental standards. It is designed for a variety of uses, including as a training document and an operational tool, in order to assist staff in the River Purification Authorities and Department of the Environment for Northern Ireland in their performance of operational activities associated with the control of surface water contamination.

The field of ecotoxicological risk assessment is continually evolving and there are many different approaches in current use. Common elements of risk assessment approaches are:

      1. hazard identification,
      2. effects assessment,
      3. exposure assessment, and
      4. risk characterisation.

i Hazard identification is the qualitative identification of the nature of adverse effects which a chemical has an inherent capacity to cause. The aim of hazard identification is to ensure risk assessments are correctly targeted, saving valuable time and resources.

(ii) and (iii) The risk associated with any substance released to the aquatic environment depends on a combination of the effects that different concentrations have on aquatic organisms and the extent (concentration and duration) of exposure. An effects assessment of a substance will be based on available toxicity data, while exposure assessment is based on a knowledge of the sources of exposure, the quantity of substance released to the environment and the likely persistence of the substance. These investigations lead to the estimation of a Predicted No Effect Concentration and Predicted Environmental Concentration, respectively.

(iv) Risk characterisation uses the results from the preceding stages to identify and estimate (usually quantitatively) the likely incidence and consequence of adverse effects in the aquatic environment resulting from actual or predicted exposure to a chemical.

Time constraints and limited resources often influence the level of detail which can be considered in a risk assessment. The strategy proposed in this manual for operational risk assessment consists of three tiers: preliminary, intermediate and detailed. Preliminary risk assessments have the least stringent data-requirements. Because of this, confidence in the overall assessment will be low and therefore in most instances an intermediate risk assessment is preferable. Detailed assessments, requiring large, quality assessed data-sets, are envisaged only for special cases where there is particular cause for concern.

Copies of this report are available from FWR, price 50.00, less 20% for Members.