ABSTRACT
Models of species sensitivity distributions (SSDs) with respect to a toxic substance can be used in two conceptually distinct ways (Chapters 1 and 4). The first use is to estimate the concentration that affects a particular proportion of species, the HC
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This is the older so-called inverse use, and is employed in the derivation of environmental criteria. The second use is the forward use of SSDs, which estimates the potentially affected fraction (PAF) of species, or the probability of effects on a species (PES) at a given concentration.
