Research needs for environmental health risk assessment.

Risk characterization comprises hazard characterization and exposure assessment. Hazard characterization may not be based on human data alone, as these data (1) are seldom available, (2) are quite insensitive in identifying the hazards, and (3) mostly lack reliable exposure-response information. Thus epidemiological information needs to be complemented with information from experimental animals and in vitro systems. These observations suffer from the necessity for species-to-species extrapolation, which is often based on weakly based generic default values. Default values may be replaced by chemical-specific uncertainty factors, but need to be applied cautiously and preferably in a predetermined framework with transparent guidance on what constitutes reliable evidence. Structure-activity relationships (SARs) are useful in setting priorities for hazard characterization and data generation, but seldom alone constitute a sufficient basis for quantitative hazard characterization. Little progress has been made in the assessment of the hazards from multiple simultaneous or successive exposures. Information on the exposure of the population whose risks are to be assessed relies predominantly on models of varying complexity. In the assessment of exposure to elements, speciation and bioavailability are important parameters for which the information often is limited.