Strong sorption of native PAHs to pyrogenic and unburned carbonaceous geosorbents in sediments

It has recently been shown that the presence of carbonaceous geosorbents (CG, including black carbon (BC), unburned coal, and kerogen) can cause strong sorption of polycyclic aromatic hydrocarbons (PAHs) in sediments. We studied sorption of native PAHs in four Norwegian harbor sediments of which high fractions (21-56%) of the total organic carbon (TOC) consisted of CG carbon (CGC), as shown by organic petrography. PAH sorption coefficients were 1-2 orders of magnitude above predictions based on amorphous organic carbon partitioning alone. In recent studies, such strong sorption was attributed solely to BC sorption under the implicit assumption that sorption is linear for coal and kerogen. The most important result of the present study is that total sorption is better explained by considering all three nonlinearly sorbing CGC materials than by only considering BC. In addition, it was evaluated whether activated carbon (AC) amendments could be effective in reducing the freely dissolved pore-water concentrations (C-W) and thus the environmental risks of the PAHs in such strongly sorbing sediments. The results indicated that an addition of 2 weight % AC reduced the C-W by factors of 21-153 for the four sediments (average values for all PAHs). It was shown that phenanthrene sorption to AC was, on average, reduced by a factor of 6 in sediment-AC mixtures compared to pure AC.