TR 084 – Scientific Principles for Soil Hazard Assessment of Substances

TR 084 : Scientific Principles for Soil Hazard Assessment of Substances | July 2002

This report reviews the scientific principles that should underpin any future terrestrial (soil) hazard classification scheme for organic and inorganic substances. The terrestrial effects of a substance are determined by a combination of its intrinsic toxicity and bioavailability, and these two factors are considered to be the main drivers for soil hazard classification. Experimental effects data are always a combination of both factors, and need to be standardised and normalised before they are useful for classification purposes. Surrogate data, including read-across from aquatic effects data and equilibrium partitioning for organic substances, and 'transformation  data for substances of low solubility, may lead to both over- and under-estimates of terrestrial hazard, and should be applied with caution.

Modifying factors to be included in a soil classification scheme are related to elimination (the length of time a substance is likely to stay in the soil compartment) or possible long-term effects (long-term toxicity). Factors not recommended for inclusion in such a scheme are bioaccumulation and slope of the dose-response curve.

Certain main elements of a terrestrial classification scheme, including selection of the most appropriate terrestrial test guidelines, assessment of data quality and relevance, read-across methods from aquatic data and how to incorporate the modifying factors, merit further development.

The Task Force considered that the current EC risk phrases related to individual terrestrial organisms living in soil were not appropriate and would be better replaced by a classification based on two or three toxicity classes amended by a term for potential long-term effects. This is analogous to the existing classification scheme for the aquatic environment and would therefore encourage harmonisation, and improve transparency and ease of use.