User Guide to Thresholds and Classification - Environmental ...

271User Guide for Thresholds and Classifications18. Ecotoxicity – General Information18.1. IntroductionThe four subclasses under the ecotoxicity property in the Hazardous Substances and New Organisms Act1996 (HSNO Act) are:subclass 9.1 – aquatic ecotoxicity (see chapter 19 below).subclass 9.2 – ecotoxicity to the soil environment (see chapter 20 below).subclass 9.3 – ecotoxicity to terrestrial vertebrates (chapter 21 below).subclass 9.4 – ecotoxicity to terrestrial invertebrates (see chapter 22 below).A threshold is also set for a substance that is used as a biocide. If a substance is used as a biocide and doesnot trigger one of the above thresholds, then it is classified as 9.1D (biocide). See chapter 23 for moreinformation on the biocidal classification.This introductory chapter covers matters that are common across the four subclasses.The key terms used in this chapter are defined in section 18.618.2. Classification of substances18.2.1. Content of following sectionsEach of the following sections explains how to classify a substance for each of the four subclasses. Eachsection outlines the key considerations required to assign a classification to a substance and acceptable testmethods for deriving data for classification purposes. Additional guidance is provided where it may bedifficult to interpret the regulations or for more complex types of data.18.2.2. Consideration of metabolitesWhen you are evaluating the ecotoxicity hazards of a substance, the metabolites of the substance may alsobe relevant for classifying the parent substance.Data on metabolites in aquatic and terrestrial systems come from the relevant degradation studies, includinginformation on the time course of appearance and concentration. These metabolites are relevant fororganisms that may be exposed through the environmental medium (soil or water) or food.Supporting evidence is needed to evaluate the hazards of major metabolites, but a qualitative approach canbe used for minor metabolites. Valuable sources of information include:the molecular structure of the metabolite (that is, is the active part intact?);the occurrence of metabolites in the medium in existing tests with the substance or major metabolites;for mammals and birds, the appearance of the metabolite in rats and poultry;general knowledge about the relationship between the toxicity of the metabolite and its parent substance(for example, from the aquatic data set (fish, Daphnia, algae));information about pesticidal activity from biological screening data; andJanuary 2012 EPA0109