Role of Soot Carbon and Other Carbon Matrices in the Distribution of PAHs among Particles, DOC, and the Dissolved Phase in the Effluent and Recipient Waters of an Aluminum Reduction Plant

The speciation of polycyclic aromatic hydrocarbons (PAHs) in natural waters affects both the chemical fate and the bioavailability of these compounds. PAHs may be dis solved or sorbed to particles or dissolved organic carbon (DOC). Furthermore, soot carbon has recently been shown to control the sorption of PAHs onto particles in natural waters. The present study investigated the distribution of individual PAHs among these three phases by examining the effluent and recipient waters of a Søderberg aluminum plant and evaluating the importance of soot carbon partitioning. The results showed that soot carbon may control partitioning between the dissolved and particulate phases and that the partition coefficients were orders of magnitude higher than would be expected on the basis of organic carbon−water partitioning alone. The carbon-normalized partition coefficient for the distribution of individual PAHs between DOC and the dissolved phase (K DOC) exhibited no more than a weak correlation with hydrophobicity (K ow) as compared with what was found for the partition coefficients for particles. This indicates that there are different sorption mechanisms at work with DOC than with particulate organic carbon and soot. In the recipient water, up to 90% of the total concentration of individual PAHs was accounted for by a nonfilterable DOC-associated phase, which was not retained by the polyurethane foam (PUF) adsorbent.