Inadequacy of Partition Coefficient Calculations in Evaluating Bioaccumulation

Use of partition coefficients (log Kow) is key to today’s environmental profiling of chemical substances. Kow is the ratio of the solubility of the substance in n-octa — nol to its solubility in water. While such measurements of this ratio work well in the majority of “straightforward” substances, and are part of a normal base set of testing parameters, there is an obvious difficulty with HPPs. In the case of inor­ganic HPPs, for example, both solubilities are essentially zero. And so we arrive at the impossible task of assessing the log of 0/0! The case of organic HPPs is very similar. With a solubility in water of essentially zero and a low parts per million or billion solubility in n-octanol, we have another untenable calculation for most high-performance pigments. In view of this anomaly, some years ago Drs. Anliker and Moser of ETAD compared predicted bioaccumulation data for pigments, using log Kow figures from solubility measurements, with results obtained from

actual bioaccumulation experiments [9]. This exercise clearly shows the folly of relying on predicted calculations for HPPs and underlines the need to disregard such calculations in favor of actual experimentation.


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