User Guide to Thresholds and Classification - Environmental ...

253User Guide for Thresholds and Classifications17.1.2. Weight of evidence approachThe best quality data should be used as the fundamental basis for classification. Preferably, classificationshould be based on primary data sources. It is essential that test conditions be clearly and completelyarticulated.Animal data from internationally harmonised test methods are preferred for classification under this subclass.Data should preferably be derived using Organisation for Economic Co-operation and Development TestGuidelines or equivalent according to the principles of Good Laboratory Practice. When such data are notavailable, classification should be based on the best available data using a weight-of-evidence approach.See section 1.3 in chapter 1 for information about assessing data quality.See Appendix 17A for a detailed list of acceptable test methods for specific target organ toxicity (single orrepeated exposure).17.2. Specific target organ toxicity (single or repeated exposure) hazard andclassification criteria17.2.1. Specific target organ toxicity (single or repeated exposure) effects threshold criteriaSchedule 4 to the Hazardous Substances (Minimum Degrees of Hazard) Regulations 2001 states:2 Minimum degrees of hazard(1) A substance with toxic properties is not hazardous for the purposes of the Act unless—…(s) data for the substance indicates, in the opinion of an expert, evidence of a significantadverse biological effect or a significant toxic effect (other than an effect referred to in anyof paras (a) to (r)) on the function or morphology of an organ, or on the biochemistry orhaematology of an organism or human being as a result of exposure to the substanceand, in the case of a significant biological effect, the change is relevant to human health.17.2.2. Specific target organ toxicity (single or repeated exposure) classification criteria forsubstancesSchedule 4 to the Hazardous Substances (Classification) Regulations 2001 identifies two classificationcategories for substances that are target organ toxicants (subclass 6.9).Category 6.9A – substances that are toxic to human target organs or systemsA substance for which data indicate to an expert evidence of a causal relationship between exposure ofhumans to the substance and the development of target organ or systemic toxicity that would not result inthe substance being classified in any of subclasses 6.1 and 6.3–6.8.A substance for which data indicate to an expert evidence of a significant adverse biological effect on thefunction or morphology of an organ or on the biochemistry or haematology of an organism as a result ofJanuary 2012 EPA0109