Soot sorption of non-ortho and ortho substituted PCBs

Field-observations of distribution coefficients well above expectations from bulk organic-matter partitioning for several chlorinated aromatic compound classes have lead to the hypothesis that enhanced affinity to soot may not be limited to polycyclic aromatic hydrocarbons but may extend as a significant process for a wider range of hydrophobic organic compounds. This suggestion was here tested in soot–column sorption experiments with a series of ortho- and non-ortho substituted polychlorinated biphenyls (PCBs), using diesel particulate matter (NIST standard reference material SRM-1650) as model soot sorbent. For congeners of similar hydrophobicity, considerably higher affinities toward the soot sorbent were observed for the non-ortho substituted PCBs. Mono- to tetra-ortho substituted PCBs exhibited log-based soot–water distribution coefficients (Ksc) from 5.25 to 5.51 l/kgsc at solute concentrations corresponding to 1–13 μg/l. In contrast, biphenyl, mono- and dichloro- non-ortho substituted PCBs yielded logKsc values between 5.09 and 6.35 l/kgsc. These results are 20–50, and 75–110 times higher, respectively, than the corresponding Kow-predicted Koc numbers. This strong interaction with soot, particularly of non-ortho substituted PCBs, may fundamentally affect their environmental distribution and bioavailable exposure.