SSD Tool

SSD Tool: Scenario-based Species Sensitivity Distributions (SSD)

This software was developed by a consortium of partners to facilitate the uptake of novel approaches to estimate aquatic threshold concentrations (e.g. the concentration at which 5% of the species are exposed above their EC50, HC5). The software improves on existing approaches (Aldenberg & Jaworska, 2000) by allowing for:

  • Non-exchangeability of species: The standard SSD approach is based on the assumption that the sensitivity of a species for a chemical cannot be predicted a priori. Craig et al. (2012) have demonstrated non-exchangeability by using a large database of tolerances to pesticides for fish species. The model approaches underpinning the SSD Tool account for the fact that some species seem to be more (and less) sensitive to chemicals than others.
  • Censored data: The SSD Tool will allow < and > data when these are available.
  • A non-lognormal distribution shape: The SSD Tool model does not assume that species sensitivities can best be described by a lognormal distribution.

The Hierarchical SSD (hSSD) software tool is hosted by Durham University and can be downloaded here.


 

Supporting documentation:

  • Craig, P. 2013. Exploring novel ways of using species sensitivity distributions to establish PNECs for industrial chemicals: Final report to Project Steering Group 3 April 2013. Durham University.
    Link to publisher’s webpage
  • ECETOC Workshop Report No.28: Estimating toxicity thresholds for aquatic ecological communities from sensitivity distributions. 11-13 February 2014.

Predicting the toxicity of chemicals to aquatic communities is an integral element in environmental risk assessment. It is therefore a major component in environmental protection strategies and in the process of managing the safe use and disposal of chemicals. Hazard (toxicity) is most frequently predicted using concentration effect data from single species toxicity tests which measure effects on individuals. However, the protection goals are generally wider i.e. populations, communities and ecosystems. Species sensitivity distributions, SSDs, describe the statistical distribution of species sensitivity to a toxicant and so can predict hazardous concentrations (HCps) affecting a certain percentage (p) of all the species in a community. Estimated HCps for environmental protection are usually the 5th percentile of the distribution and are used to derive a protective threshold concentration for an ecosystem.

ECETOC and the Environment Agency for England organised a three day workshop in February 2014 to discuss and review current statistical SSD models, when and how they should be used in regulatory applications and their ecological significance. A number of recommendations were made on how SSD methods could be further developed to improve the quality of decisions needed from both the prospective risk and retrospective impact assessment of chemicals.

The findings were published as ECETOC Workshop Report No.28: Estimating toxicity thresholds for aquatic ecological communities from sensitivity distributions. 11-13 February 2014.
Link to Workshop Report no.28