This web page contains a compilation of documentation on the science and applications of non-testing methods, including (Quantitative) Structure-Activity Relationships and chemical grouping methods. More information is available from the links below.
Among the different methods that can be used in the hazard assessment of chemicals are the so-called non-testing methods, which comprise (Q)SAR models and other, less formalised, approaches based on the grouping of chemicals (read-across and chemical category formation). To address financial and animal welfare concerns, the REACH legislation explicitly expresses the need to use non-testing methods to reduce the extent of experimental testing.
Qualitative and Quantitative Structure-Activity Relationships - (Q)SARs
Structure-activity relationships and quantitative structure-activity relationships, collectively referred to as (Q)SARs, are theoretical models that can be used to predict the physicochemical, biological and environmental fate properties of molecules. They are sometimes called in silico models because they can be applied by using a computer.
A structure-activity relationship (SAR) is a qualitative relationship that relates a (sub)structure to the presence or absence of a property or activity of interest. The substructure may consist of adjacently bonded atoms, or an arrangement of non-bonded atoms that are collectively associated with the property or activity.
A quantitative structure-activity relationship (QSAR) is a mathematical model (often a statistical correlation) relating one or more quantitative parameters derived from chemical structure to a property or activity of interest. QSARs are quantitative models yielding a continuous or categorical result.
Chemical categories and read-across
A chemical category is a group of chemicals whose properties are likely to be similar or show predictable trends across members of the group, usually as a result of structural similarity. Application of the chemical category approach provides various means of filling data gaps, thereby avoiding the need to test all members of the category for all properties/endpoints.
Threshold of Toxicological Concern
A Threshold of Toxicological Concern (TTC) for a chemical refers to a concentration level that is considered to be of negligible risk to human health or an environmental compartment. If the toxicological threshold is based on the statistical analysis of the toxicological data of a group of structurally-related (or even structurally-different) chemicals, the TTC concept can be regarded as an extension of the chemical category approach.
OECD Principles for the Validation of (Q)SARs
Background documents on (Q)SARs
More information on the development, assessment, and (potential) applications of (Q)SARs, especially in a regulatory context, can be found in the document area.