User Guide to Thresholds and Classification - Environmental ...

282User Guide for Thresholds and Classifications19. Aquatic Ecotoxicity – Subclass 9.119.1. Basic elements and general considerationsThe basic elements to consider in determining aquatic hazard classification under the HazardousSubstances and New Organisms Act 1996 (HSNO Act) are:acute aquatic ecotoxicity;potential for or actual bioaccumulation;degradation (biotic or abiotic) for organic chemicals; andchronic aquatic ecotoxicity.While data from internationally harmonised test methods are preferred, data from national methods may alsobe used where they are considered as equivalent. In general, freshwater and marine species toxicity datacan be considered as equivalent data, preferably derived using test guidelines from the Organisation forEconomic Co-operation and Development (OECD) or according to the principles of Good LaboratoryPractice (GLP). Where such data are not available, classification should be based on the best available datausing a weight of evidence approach.See section 18.6 in chapter 18 for definitions of the key terms used in this chapter.See section 1.3 in chapter 1 for information about assessing data quality.See Appendix 19A for a detailed list of acceptable test methods for aquatic toxicity, aquatic degradation, andbioaccumulation.See Appendix 19B and Appendix 19C for comparisons of the HSNO aquatic hazard classifications withthose of the GHS and EU.19.1.1. Acute aquatic toxicityAquatic toxicity testing involves dissolving the substance under test in the water used and maintaining astable bioavailable exposure concentration over the course of the test. Some substances are difficult to testunder standard procedures, so special guidance has been developed on interpreting and using the datawhen applying the classification criteria.Acute aquatic toxicity is normally determined using:a fish 96-hour LC50 (OECD Test Guideline 203 or equivalent);a crustacean 48-hour EC50 (OECD Test Guideline 202 or equivalent); and/oran algal 72- or 96-hour EC50 (OECD Test Guideline 201 or equivalent).These species are considered surrogates for all aquatic organisms. Data on other species such as thefloating aquatic macrophyte Lemna spp. may also be considered if the test methodology is suitable. ForLemna, a standard 7- or 14-day EC50 test is considered appropriate (OECD Test Guideline 221).Although the algal growth inhibition test is a chronic test, the EC50 is treated as an acute value forclassification purposes. The algal EC50 should normally be based on growth rate inhibition. If only the EC50January 2012 EPA0109