Predicting the bioavailability of organic xenobiotics to Pontoporeia hoyi in the presence of humic and fulvic materials and natural dissolved organic matter

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Abstract
Dissolved organic carbon (DOC) in water sorbs or binds organic xenobiotics, reducing the amount of compound that is “freely dissolved” and therefore the amount bioavailable to Pontoporeia hoyi. The apparent biological uptake rate constant for each compound is proportional to the inverse of the Aldrich humic acid concentration as a source of DOC. The log of the DOC concentration required to reduce the apparent uptake rate constant by 50% correlates well with the log of the partition coefficient to DOC determined by reverse‐phase methodology for partition coefficients as low as 104. Further, the partitioning to DOC determined by reverse‐phase methodology and from the toxicokinetics in P. hoyi yields partition coefficients similar to those of Aldrich humics measured as DOC and DOC from Lake Michigan interstitial waters. The partition coefficients determined by the two methods correlate well and only vary by a constant bias of a factor of approximately 3. Thus the partition coefficient determined by reverse‐phase methodology can be used to predict the bioavailable concentration of organic compounds in water containing DOC for P. hoyi.