Assessment factors in species sensitivity distributions for the derivation of guideline values for aquatic contaminants

Abstract

The development of the Species Sensitivity Distribution (SSD) more than 30 years ago was in direct response to the many criticisms concerning the use of subjective Assessment (or Application) Factors (AFs) in widespread use at the time. While not perfect, SSD modelling is statistically defensible whereas AFs are not. While intuitively appealing, we believe recent guidance recommending the use of AFs in conjunction with SSD modelling is concerning and has the potential to impose unnecessary, time-consuming and expensive follow-up investigations on both regulators and the regulated. This paper outlines our concerns and presents results of more contemporary analyses to quantify the impact of ar..