User Guide to Thresholds and Classification - Environmental ...

331User Guide for Thresholds and ClassificationsThe substance is demonstrated to be ultimately degraded in an aquatic sediment or soil simulationtest with a half-life of < 16 days (corresponding to a degradation of > 70% within 28 days).In those cases where only BOD5 and COD data are available, the ratio of BOD5/COD is greater thanor equal to 0.5. The same criterion applies to ready biodegradability tests of a shorter duration than28 days, if the half-life < 7 days.If none of the above types of data are available then the substance is considered as not rapidlydegradable. This decision may be supported by fulfilment of at least one of the following criteria.The substance is not inherently degradable in an inherent biodegradability test.The substance is predicted to be slowly biodegradable by scientifically valid QSARs, for example, forthe Biodegradation Probability Program, the score for rapid degradation (linear or non-linear model)< 0.5.The substance is considered to be not rapidly degradable based on indirect evidence, for example,knowledge from structurally similar substances.No other data regarding degradability are available.19D.4 BioaccumulationIntroductionBioaccumulation is one of the important intrinsic properties of chemical substances that determine thepotential environmental hazard. Bioaccumulation of a substance into an organism is not a hazard in itself,but bioconcentration and bioaccumulation will result in a body burden, which may or may not lead to toxiceffects. In the harmonised integrated hazard classification system for human health and environmentaleffects of chemical substances (OECD, 1998), the wording ―potential for bioaccumulation‖ is given. Adistinction should, however, be drawn between bioconcentration and bioaccumulation. Here bioconcentrationis defined as the net result of uptake, transformation, and elimination of a substance in an organism due towaterborne exposure, whereas bioaccumulation includes all routes of exposure (that is, via air, water,sediment or soil, and food). Finally, biomagnification is defined as accumulation and transfer of substancesvia the food chain, resulting in an increase of internal concentrations in organisms on higher levels of thetrophic chain. For most organic chemicals uptake from water (bioconcentration) is believed to be thepredominant route of uptake. Only for very hydrophobic substances does uptake from food becomesimportant. Also, the harmonised classification criteria use the bioconcentration factor (BCF) (or theoctanol/water partition coefficient) as the measure of the potential for bioaccumulation. For these reasons,the present guidance document only considers bioconcentration and does not discuss uptake via food orother routes.Classification of a chemical substance is primarily based on its intrinsic properties. However, the degree ofbioconcentration also depends on factors such as the degree of bioavailability, the physiology of testorganism, maintenance of constant exposure concentration, exposure duration, metabolism inside the bodyof the target organism and excretion from the body. The interpretation of the bioconcentration potential in aJanuary 2012 EPA0109