Field study on desorption rates of polynuclear aromatic hydrocarbons from contaminated marine sediment

The present study examines desorption kinetics of hydrophobic organic contaminants from sediment under conditions mimicking marine disposal. Trays of contaminated marine sediment were deployed in the subtidal zone of a pristine field site, and samples were taken at time intervals to study the desorption of acenaphthene, benzo[a]anthracene, benzo[b]fluoranthene, benzo[k]fluoranthene, benzo[a]pyrene, chrysene, fluoranthene, naphthalene, and phenanthrene over a period of 51 d. Results of the study indicated that 49.4 to 98.0% of the polycyclic aromatic hydrocarbons (PAHs) in the contaminated sediment were desorbed upon disposal in the coastal environment. The field desorption kinetics of these PAHs can be described by a two-compartment model. The measured slow desorption rate constants, k₂, for acenaphthene, benzo[a]anthracene, benzo[b]fluoranthene, benzo[k]fluoranthene, benzo[a]pyrene, chrysene, fluoranthene, naphthalene, and phenanthrene were found to be 0.018, 0.061, 0.016, 0.028, 0.035, 0.021, 0.083, 0.031, and 0.080/d, respectively. Some of these data were in accordance with literature-reported values from laboratory desorption studies in which desorbed PAHs were directly extracted from the aqueous phase. However, they were at least an order of magnitude smaller than those obtained by conventional gas-stripping desorption techniques.