Influence of soot on hydrophobic organic contaminant desorption and assimilation efficiency

Soot, soot-amended sediment, and unamended sediment spiked with hydrophobic organic contaminants (HOC) were subjected to laboratory desorption and assimilation efficiency experiments in an effort to assess and compare the importance of soot in controlling HOC desorption and deposit-feeder assimilation efficiency. Three contaminants, naphthalene (NAP), benzo[a]pyrene (BaP), and hexachlorobenzene (HCB) were sorbed to sediments, sediments amended with soot (2–4% dry wt), and soot for a period of 34 d. Desorption of all three contaminants into seawater from the three prepared sorbates was then monitored, and Nereis succinea assimilation efficiency experiments on the BaP- and HCB-contaminated sorbates were conducted. Both NAP and BaP desorption rates for soot and soot-amended sediments were reduced by at least a factor of two relative to unamended sediment. Hexachlorobenzene desorption rates were similar for both the soot-amended and the unamended sediments. Results of N. succinea assimilation efficiency experiments indicate a trend similar to the desorption experiments: higher assimilation of BaP from unamended relative to soot-amended sediment and little difference in assimilation between treatments for HCB. However, soot was more effective in reducing BaP desorption than assimilation efficiency, which would be consistent with the hypothesis that the gut fluid dissolution by deposit feeders may partially decouple biological availability from chemical availability.