Lexikon
Species Sensitivity Distribution (SSD) method is based on statistical extrapolation and aims to determine the predicted no effect concentration of a chemical substance, which does not effect the ecosystem.
If a large data set with No Observed Effects Concentrations, NOECs from long-term experiments for different taxonomic groups is available, these values can be used to draw the distribution curve. This distribution that describes the variability of hazard of a substance 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. From this curve we can read Xm, the mean toxicity expressed as the mean NOEC value of a substance. The Sm represents the toxicity range or variation in sensitivity of a substance.
The main assumption on the use of SSDs in risk assessment is that the distribution based on a selection of species (tested in laboratory experiments) are representative for all species (in the field).