The identification of thresholds of acceptability and danger: the biological route.

The application of scientific concepts to management decisions is a clear need nowadays. The regulation of environmental pollutants requires the application of cost/benefit analysis. Human health and ecosystem status can be seriously affected and, therefore, are essential parts of the cost assessment. Ecotoxicology must provide the scientific basis for the prediction, control, monitoring and diagnosis of the expected/observed effects of chemical substances on the structure and function of ecosystems. The basic problem is to select which levels of risk/alteration can be accepted, taken into account the degree of uncertainty in the assessment. This paper summarizes some biologically based approaches that try to reduce the level of uncertainty and/or to improve the decisions on the basic thresholds: acceptable/unacceptable and safe/dangerous. The presentation will focus on two specific aspects. Starting with prediction related topics, the first aspect will regard on the evolution of Hazard and Risk Assessments and the biological developments that try to improve these evaluations. The discussion will cover ecotoxicological concepts included in the adopted criteria for different regulatory aspects, i.e. setting Water Quality Objectives, classifying potential hazards using the "inherent" toxicity of a substance, or predicting Non Effect Concentration in risk characterization procedures. The second aspect will cover the use of biologically based systems as complementary and even alternative tools in management decisions related to the control, monitoring and diagnosis of the environmental alterations produced by highly toxic chemicals on biological systems.