The development of a sterile,PAH-spiked,aged marine sediment for biodegradation experiments: chemical results

The fate of polycyclic aromatic hydrocarbon (PAH) mixtures in marine sediments can be difficult to determine due to extraction, analytical and matrix barriers. The purpose of this work was to develop and validate methods to kill indigenous microorganisms in marine sediments, to spike the sediments with a mixture of PAHs in a minimally invasive fashion and to age the treated sediments while following the effects of the treatments on the PAHs and several groups of microorganisms. Following gamma irradiation (0.0, 2.5, 3.5 and 5.0 Mrad), the sediments were mixed with known amounts of PAHs that had been coated onto fine-grained sand. During the subsequent ageing process, levels of extractable PAHs and numbers of microorganisms were monitored. The addition of PAHs to the unirradiated sediment seemed to rapidly induce the degradation of phenanthrene, fluoranthene and pyrene, while these PAHs decreased to a much smaller extent in the irradiated sediments in the 376 days of the experiment. The heavier PAHs, chrysene and benzo(a)pyrene, showed slight decreases in extractable concentrations at all irradiation levels, suggesting PAH sequestration/ageing over time. While some microbial populations recovered rapidly, culturable PAH degraders did not recover at any irradiation level tested and concentrations of light molecular weight PAHs in sediments irradiated at all levels dropped only slightly. This suggests that even the lowest dose (2.5 Mrad) may inhibit PAH degradation sufficiently to permit ageing of the spiked sediments for 6 months to a year. The methods described show promise for the generation of realistic, well-characterized spiked sediments for use in biodegradation and bioavailability experiments.