Statistically stable models for determination of PEC
W J Homan, A L Van Oosten Van
In June 1998 the European Wood Preservative Manufacturer's Group prepared a document to support the Technical Guidance concerning the placing of products on the market with respect to the Directive 98/08/EC (BPD). The essentials of this document were presented at the COST E2 meeting in Cannes last year and at the following IRG conference (Baines and Davis, 1998; IRG/WP/98-50101/20). The document presented a protocol in which a "tiered" approach is followed. The key-factors in this approach are the PNEC (predicted no effect concentration) and the PEC (predicted environmental concentration). The PNEC is calculated from eco-toxicity test results and a safety factor is introduced. In the case of metals which may also be essential trace elements, the background level is suggested as the PNEC, if this level is above the level derived f rom eco-toxicity tests. The calculation of the PEC uses different models. The focus of this paper is the reliability of the models used to determine the PEC, while pointing out that only data and models relevant to the field situation may be used. In the EWPM protocol, initially the environment has to be defined by going through flowcharts and providing an answer of "YES or NO" to each of the questions. In the first tier of the questions there are two options for the treated wood, which is likely to be treated with the candidate wood preservative. It can be assessed as presenting either: a) No risk to the environment, or b) Additional information is required and the next "tier" of questions or tests is involved. In this paper the model for a fresh water environment is presented as an example. However, the models and the systern, can also be applied to other environments. In the above mentioned flowcharts the following assumptions are made: 1.Yes, the substance is toxic and harmful, 2. Yes, if all of the substance in the treated wood entered the water, its concentration would probably be > the PNEC, 3. Yes, the treated wood is in a situation where some of the substance is likely to get into the water. For this reason a simulated exposure test would be carried out and: 4. Yes, the chemical analysis of the wash-off water would be possible and relevant. Therefore PECwater values would need to be calculated to solve the question whether PECwater> PNECwater. By definition, the PEC must be based on the same principle as the PNEC. This implies that the PEC must be relevant for long term exposition, as the PNEC is a long term value, derived from chronic studies.
Keywords: EWPM; DIRECTIVE 98/008/EC; PNEC; PEC; MODEL