Probabilistic risk assessment
This method preferably compares a frequency distribution of all possible exposure intensities with a threshold using the variation in species sensitivity. If a large data set with sensitivity values (L(E)C50s or NOECs) for different taxonomic groups is available, these values can be used to draw a distribution. This distribution that describes the variability of hazard of a stressor to organisms is called a Species Sensitivity Distribution (SSD). This distribution can be presented as a frequency distribution (cumulative normal distribution curves or other similar distribution curves) of NOEC values for species. In general the method works as follows: sensitivity data are log transformed and fitted to a distribution function. It has been shown that the choice of a distribution is quite arbitrary and is mostly done based on best fit results.
