User Guide to Thresholds and Classification - Environmental ...

321User Guide for Thresholds and ClassificationsInterpreting data qualityStandardisationMany factors can influence the results of toxicity tests with aquatic organisms. These factors includecharacteristics of the test water, experimental design, chemical characteristics of the test material, andbiological characteristics of the test organisms. Therefore, it is important in conducting aquatic toxicity teststo use standardised test procedures to reduce the influence of these sources of extraneous variability. Thegoal of test standardisation and international harmonisation of these standards is to reduce test variabilityand improve precision, reproducibility, and consistency of test results.Data hierarchiesSee section 1.3 in chapter 1 for information about assessing data quality.19D.3 DegradationIntroductionDegradability is one of the important intrinsic properties of chemical substances that determine their potentialenvironmental hazard. Non-degradable substances will persist in the environment and may consequentlyhave a potential for causing long-term adverse effects on biota. In contrast, degradable substances may beremoved in the sewers, in sewage treatment plants or in the environment. Classification of chemicalsubstances is primarily based on their intrinsic properties. However, the degree of degradation depends notonly on the intrinsic recalcitrance of the molecule, but also on the actual conditions in the receivingenvironmental compartment, for example, redox potential, pH, presence of suitable micro-organisms,concentration of the substances and occurrence and concentration of other substrates. The interpretation ofthe degradation properties in an aquatic hazard classification context therefore requires detailed criteria thatbalance the intrinsic properties of the substance and the prevailing environmental conditions into aconcluding statement on the potential for long-term adverse effects. The purpose of the present section is topresent guidance for interpretation of data on degradability of organic substances. The guidance is based onan analysis of the above-mentioned aspects regarding degradation in the aquatic environment. Based on theguidance a detailed decision scheme for use of existing degradation data for classification purposes isproposed. The types of degradation data included in this guidance document are ready biodegradabilitydata, simulation data for transformation in water, aquatic sediment and soil, BOD 5 /COD-data and techniquesfor estimation of rapid degradability in the aquatic environment. Also considered are anaerobic degradability,inherent biodegradability, sewage treatment plant simulation test data, abiotic transformation data such ashydrolysis and photolysis, removal process such as volatilisation and finally, data obtained from fieldinvestigations and monitoring studies.The term degradation is defined as the decomposition of organic molecules to smaller molecules andeventually to carbon dioxide, water, and salts. For inorganic compounds and metals, the concept ofdegradability as applied to organic compounds has limited or no meaning. Rather the substance may beJanuary 2012 EPA0109