User Guide to Thresholds and Classification - Environmental ...

390User Guide for Thresholds and Classificationsunderestimation of the hazard in acute tests; the availability of soluble metal compounds can decreaserapidly after addition to soil. Strongly sorbed metals are less available than weakly sorbed metals. For metalsalts, the counter-ion may influence the toxicity of the metal, for example, sulphate or chloride ions. Organicanions may reduce metal toxicity. A transformation test is needed to ensure that such effects are adequatelyevaluated (Fairbrother et al, 2002).See Fairbrother et al (2002) for guidance on testing the toxicity of poorly soluble metals in soil, including asuggested transformation protocol.20.1.3. Default classification in absence of data on degradation in soilWhere there are no data on the degradation of a substance, the default position is that the substance willattract the same classification as if those data were available and indicate that the substance has a DT50 >30 days.20.1.4. MetabolitesData on metabolites in soil come from soil degradation studies, including information on the time course ofappearance and concentration. These metabolites are relevant for soil organisms and ground-dwellingarthropods.Where the parent substance degrades to a more hazardous metabolite, the rate at which it is formed shouldbe taken into consideration when assigning a classification to the parent substance.See chapter 18 for further information on the evaluation of metabolites.20.1.5. Weight of evidenceThe 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 are clearly and completelyarticulated.See section 18.4.3 in chapter 18 above for a discussion on the assessment of multiple tests on the samespecies.See section 1.3 in chapter 1 above for information about assessing data quality.20.2. Hazard threshold and classification criteria for the soil environment20.2.1. Hazard threshold criteria for the soil environmentSchedule 6 to the Hazardous Substances (Minimum Degrees of Hazard) Regulations 2001 states:2 Minimum degrees of hazard(1) A substance with ecotoxic properties is not hazardous for the purposes of the Act unless—…(b) the substance is ecotoxic to soil organisms because—January 2012 EPA0109