User Guide to Thresholds and Classification - Environmental ...

336User Guide for Thresholds and Classificationsassessment if no experimentally derived data are available. CLOGP, LOGKOW, and AUTOLOGP are basedupon the addition of group contributions, while SPARC is based upon a more fundamental chemicalstructure algorithm. SPARC can only be employed in a general way for inorganic or organometalliccompounds. Special methods are needed for estimating log KOW for surface-active compounds, chelatingcompounds and mixtures. CLOGP is recommended in the USEPA/EC joint project on validation of QSARestimation methods. Pedersen et al (1995) recommended the CLOGP and the LOGKOW programs forclassification purposes because of their reliability, commercial availability, and convenience of use. Theestimation methods in Table 19D.2 are recommended for classification purposes.Table 19D.2: Recommended Quantitative Structure Activity Relationships (QSARs) for estimating the n-octanolwaterpartition coefficient (K OW)Model Log K OW range Substance utilityCLOGP 0 < log K OW < 9 * The program calculates log K OW for organic compounds containingC, H, N, O, Hal, P, and/or S.LOGKOW(KOWWIN)The program calculates log K OW for organic compounds containing-4 < log K OW < 8 † C, H, N, O, Hal, Si, P, Se, Li, Na, K, and/or Hg. Some surfactants(eg, alcohol ethoxylates, dyestuffs, and dissociated substances)may be predicted by the program as well.AUTOLOGP. log K OW > 5The program calculates log K OW for organic compounds containingC, H, N, O, Hal, P, and S. Improvements are in progress in orderto extend the program‘s applicability.SPARCProvides improvedresults overKOWWIN andCLOGP forcompounds withlog K OW > 5The program is a mechanistic model based on chemicalthermodynamic principles rather than a deterministic model rootedin knowledge obtained from observational data. Therefore,SPARC differs from models that use QSARs (ie, KOWWIN,CLOGP, and AUTOLOGP) in that no measured log K OW data areneeded for a training set of chemicals. Only SPARC can be usedin a general way for inorganic or organometallic compounds.Notes* A validation study performed by Niemelä, who compared experimental determined log KOW values withestimated values, showed that the program precisely predicts the log KOW for a great number of organicchemicals in the log KOW range from below 0 to above 9 (n = 501, r2 = 0.967) (Pedersen et al, 1995, p 581).† Based on a scatter plot of estimated compared with experimental log KOW (Syracuse Research Corporation,1999), where 13,058 compounds have been tested, the LOGKOW is evaluated being valid for compoundswith a log KOW in the interval -4–8.Chemical classes that need special attention with respect to the bioconcentration factorand octanol-water-partition coefficient valuesThere are certain physico-chemical properties, which can make the determination of the BCF or itsmeasurement difficult. These may be substances, which do not bioconcentrate in a manner consistent withtheir other physico-chemical properties, for example, steric hindrance or substances that make the use ofJanuary 2012 EPA0109