ABSTRACT
The objective of this experiment was to assess the effectiveness of a new Type III chemical dispersant on stranded, lightly weathered crude oil and emulsified medium fuel oil (mousse). The oils were applied to field plots on contrasting sediment shorelines (salt marsh and sand flat), where both oils had been shown to be persistent.
On the salt marsh, dispersant-treated oils usually were detected at lower sediment total hydrocarbon (THC) concentrations than were the untreated oils. However, clear trends were not visible until heavy rain removed the oiled, dead vegetation. Subsequently, the THC concentrations measured in the treated crude plots were reduced by half, and stable, lower concentrations were measured in the mousse plots. On the sand flat, the dispersant-treated mousse was detected at consistently lower THC concentrations than was the untreated mousse. The crude-oil-treated plots showed more temporal variability than the mousse-treated plots. Dispersant-treated crude ultimately was detected at half the concentration found in the untreated crude plots.
Although on the salt marsh both dispersant-treated oils were more damaging in the short term to the plant community, the longer-term effects of higher untreated oil concentrations may prove more destabilizing to the salt-marsh habitat as a whole. After erosion, untreated oil may be resuspended to form oil slicks, when public interest in the original spill and the sense of responsibility for its cleanup have all but disappeared.
Under the slightly higher-energy conditions of the sand flat, dispersant use did not dramatically alter the fate of most of the oil. The approximately 10% that remained in the beach was less obvious visually and was removed faster than the untreated oil. The practical implication of this is that if the cleanup authorities can resist amenity and conservationist pressures to disperse the residual oil, such tidal flats will eventually self-clean.
Earlier formulations of chemical dispersant either have been relatively ineffective or have increased contamination on low-energy sediment shores. Several explanations may be advanced for the effectiveness of this dispersant on both oil types. First, it helped prevent the formation of surface oiled pavements and, thus, the burial of oil layers. Second, the contact time of oils and dispersant (>2 hours pre-tidal coverage) may have contributed to the reductions in oil concentrations. Third, at both sites there was sufficient energy input to assist dispersion.
Carbon and Nitrogen Sources Have No Impact on the Organization and Composition of Ustilago maydis Respiratory Supercomplexes
