SPECIFYING THE DIMENSIONS OF AQUATIC LIFE BENCHMARK VALUES IN CLEAR COMPLETE JUSTIFIED PROBLEM FORMULATIONS

摘要

Nations that develop water quality benchmark values have relied primarily on standard data and methods. However, experience with chemicals such as Se, ammonia, and tributyltin has shown that standard methods do not adequately address some taxa, modes of exposure and effects. Development of benchmark values that are protective requires an explicit description of the issues, a problem formulation. In particular, the assessment endpoints and other dimensions should be specified for each chemical so that the necessary data will be obtained and appropriate analyses will be performed. Assessment endpoints specify the entity and attribute to be protected. In addition, the level of protection, including the magnitude of effect and the proportion affected is specified. Magnitude and proportion are included, because they are used to calculate the benchmark concentration. If uncertainty is considered in the benchmark, the proportion of the uncertainty distribution that is protected should be specified. Because effects are related to the duration of exposure and time for recovery, temporal dimensions should be specified. Clearly described exposure metrics are also needed, because the relevant exposure parameter is not always total aqueous concentration. Finally, the benchmark may be applicable to particular geographic or climatological areas, water chemistries, taxa, or habitat types. Considering and justifying all the dimensions is likely to result in protective and more easily communicated benchmarks.