SLOW-STIRRING METHOD FOR DETERMINING THE n-OCTANOL/WATER PARTITION COEFFICIENT (P_(ow)) FOR HIGHLY HYDROPHOBIC CHEMICALS: PERFORMANCE EVALUATION IN A RING TEST

摘要

The n-octanol/water partition coefficient (P_(ow)) is one of the most important parameters employed for estimating a chemical's environmental fate and toxicity. The currently adopted test guidelines for its determination do not allow for reliable determination of log P_(ow) greater than 5. The slow-stirring experiment, in contrast, has been demonstrated to provide reliable log P_(ow) data up to log P_(ow) of 8.3. To validate this method and to obtain its approval as an official Organization for Economic Cooperation and Development (Paris, France) test guideline, a ring test was performed to evaluate the accuracy and precision of the slow-stirring experiment for determination of log P_(ow), particularly for highly hydrophobic compounds. Up to 15 volunteer laboratories tested 1,2,3,4-tetrachlorobenzene, hexachlorobenzene, 2,2′,3,3′,5,5′,6,6′-octachlorobiphenyl, and decachlorobiphenyl (4.5 < log P_(ow) < 8.2). The ring-test results for the respective chemicals were 4.62, 5.50, 7.39, and 8.18. The results deviated by less than 0.1 log P_(ow) units from the reference log P_(ow). In addition, the relative standard deviations of log P_(ow) were less than 2%. Using the protocol of the ring test, log P_(ow) of p,p′-DDT was determined to be 6.24 +- 0.05 (mean +- standard deviation). In combination, these results indicate that the slow-stirring method is precise and accurate and, thus, allows for reliable determination of log Pov, of highly hydrophobic chemicals.