The Predicted Environmental Concentration [PEC] is an important element of the eco-toxicological risk assessment1. There is no straightforward way to derive the PEC from laboratory studies, because the PEC depends not only on the substance intrinsic properties (biodegradability, log Kow), but also on several external parameters (total annual production volume, dilution factor, use pattern), which are difficult to determine. Nevertheless, the standard approach for PEC derivation is its calculation using the EUSES program and the above mentioned parameters.
As an alternative to the EUSES calculation method, the environmental concentration of a chemical could be directly measured in relevant aquatic compartments2. On a technical level this requires a lot of experience and a strict quality control regime needs to be applied. Especially, if the concentrations in the aquatic environment are low and the substance to be measured shows critical properties (e.g. a high adsorptivity) utmost care must be taken while the samples are collected and analysed.
Concentration values in the freshwater environment may vary considerably with respect to space and time. Spatial variation can be minimised if the monitoring is thoroughly planned and the exposure pattern of the chemical substance considered is carefully studied. Hence, a monitoring program requires a detailed planning to assure that the reliability and representativeness of data obtained. Nevertheless, if the quality is safeguarded, analytical data derived from monitoring programs in the aquatic environment are preferred since they are perceived as being ’real’.
1 Technical Guidance Document on Risk Assessment, Part II, European Chemical Bureau, 2003
2 Monitoring and Modelling of Industrial Organic Chemicals, with Particular Reference to Aquatic Risk Assessment, ECETOC Technical Report No. 76, ECETOC, 1999