Probabilistic risk assessment of agrochemicals in the environment

Concern for the environment has resulted in greater scrutiny of both old an d new plant protection products and increased efforts have been directed to developing more rigorous but more realistic procedures for the ecotoxicolo gical risk characterization of these agrochemicals. These techniques includ e probabilistic analysis of toxicity and exposure data and better understan ding of the relationship between structure and function in populations of w ildlife and the role of keystone species in maintaining ecosystem functioni ng. The ecological risk assessment method described here is centered on the use of probabilistic distribution functions that independently describe ex posure concentrations and toxicological responses of organisms to the chemi cal of concern. The distributions are transformed to permit calculation of linear regression parameters. The regression parameters for the two distrib utions are then used to determine joint probabilities which interrelate the exposure and toxicology data. For ease of presentation the results are pre sented as an exceedence plot which depicts, based on the exposure data the percent of species likely to be affected and the percent of observations li kely to cause this level of effect. In this paper, the use of the method is illustrated using data for chlorpyrifos in North American aquatic environm ents. These probabilistic risk assessment methods are being assessed for in corporation into assessment procedures in a number of regulatory jurisdicti ons. (C) 2000 Elsevier Science Ltd. All rights reserved.