User Guide to Thresholds and Classification - Environmental ...

339User Guide for Thresholds and Classificationsan appropriate bioconcentration test, should be interpreted by a ‗weight-of-evidence approach‘. This impliesthat if experimental determined BCF data, both ≥ and < 500, have been obtained for a substance the data ofthe highest quality and with the best documentation should be used for determining the bioconcentrationpotential of the substance. If differences still remain, if, for example, high-quality BCF values for different fishspecies are available, generally the highest valid value should be used as the basis for classification. Whenlarger data sets (that is, with four or more values) are available for the same species and life stage, thegeometric mean of the BCF values may be used as the representative BCF value for that species.Conflicting log K OW dataThe situations, where multiple log K OW data are available for the same substance, the possibility of conflictingresults might arise. If log K OWhighest quality and the best documentation should be used for determining the bioconcentration potential ofthe substance. If differences still exist, generally the highest valid value should take precedence. In suchsituation, QSAR-estimated log K OW could be used as a guidance.Expert judgementIf no experimental BCF or log K OW data or no predicted log KOW data are available, the potential forbioconcentration in the aquatic environment may be assessed by expert judgement. This may be based on acomparison of the structure of the molecule with the structure of other substances for which experimentalbioconcentration or log K OW data or predicted KOW are available.Decision schemeBased on the above discussions and conclusions, a decision scheme has been elaborated which mayfacilitate decisions as to whether or not a substance has the potential for bioconcentration in aquatic species.Experimentally derived BCF values of high quality are ultimately preferred for classification purposes. BCFvalues of low or uncertain quality should not be used for classification purposes if data on log KOW areavailable because they may give a false and too low BCF value, for example, due to a too short exposureperiod in which steady-state conditions have not been reached. If no BCF is available for fish species, highquality data on the BCF for other species (for example, mussels) may be used.For organic substances, experimentally derived high quality KOW values, or values that are evaluated inreviews and assigned as the ‗recommended values‘, are preferred. If no experimentally data of high qualityare available validated QSARs for log KOW may be used in the classification process. Such validatedQSARs may be used without modification in relation to the classification criteria, if restricted to chemicals forwhich their applicability is well characterised. For substances like strong acids and bases, metal complexes,and surface-active substances a QSAR-estimated value of KOW or an estimate based on individual n-octanol and water solubilities should be provided instead of an analytical determination of KOW.If data are available but not validated, expert judgement should be used.January 2012 EPA0109