Measured partition coefficients for parent and alkyl polycyclic aromatic hydrocarbons in 114 historically contaminated sediments: part 2. Testing the K(OC)K(BC) two carbon-type model.

Polycyclic aromatic hydrocarbon (PAH) desorption partition coefficients between black carbon and water (K(BC)) were determined using 114 historically contaminated and background sediments from eight different rural and urban waterways. Black carbon was measured after oxidation at 375 degrees C for 24 h. Organic carbon-water partition coefficients (K(OC)) required for the calculation of K(BC) values were determined for two- to six-ring parent and C1- to C4-alkyl PAHs based on the lower range of measured K(OC) values from the same sediments and comparisons to literature K(OC) values. Approximately 2,050 log K(BC) values were determined on sediments having a range of total organic carbon from 0.3 to 42% by weight, black carbon from 0.1 to 40% by weight, and total PAH concentrations (U.S. Environmental Protection Agency 16 parent PAHs) from 0.2 to 8,600 microg/g. Contrary to expectations, PAH partitioning was not better explained using the combined K(OC) and K(BC) models rather than the simple K(OC) model (i.e., K(BC) values for each individual PAH ranged nearly three orders of magnitude). No effect of PAH concentration on measured K(BC) values was apparent. Values of K(BC) also showed no trends with total organic carbon, black carbon, or the presence or absence of a non- aqueous phase liquid. Multiple linear regression analysis with K(OC) and K(BC) as fitted values also failed to explain the variance of the experimental data (r(2) values typically less than 0.20, and standard errors greater than two orders of magnitude). These results demonstrate that models of PAH partitioning that account for different carbon types, although useful for understanding partitioning mechanisms, cannot yet be used to accurately predict PAH partitioning from historically contaminated sediments.