THE RATES OF TRANSPORT AND FATES OF PETROLEUM HYDROCARBONS IN A CONTROLLED MARINE ECOSYSTEM, AND A NOTE ON ANALYTICAL VARIABILITY

Abstract

ABSTRACT In order to predict the chemical behavior of oil spilled in a marine environment, it is necessary to quantify the rates of the different transport mechanisms operating on the oil. At the Marine Ecosystems Research Laboratory (MERL), University of Rhode Island, the fluxes of water and sediment are controlled, making possible accurate budgeting of petroleum hydrocarbons in an environment approximating a temperate estuary. Four separate laboratories have cooperated in a study on the MERL tanks to which known amounts of water-accommodated No. 2 fuel oil have been added. A preliminary budget has been completed, indicating that the primary loss was to the atmosphere via evaporation. Biodegradation was important for some classes of hydrocarbons and increased with temperature and duration of oil exposure. Particulate material adsorbed hydrocarbons amounting to approximately 15 percent of the oil added to the tanks, and carried them to the sediment where 7–16 percent of the added oil was eventually found. The sedimentary hydrocarbons were depleted in low molecular weight aromatic compounds (up to three rings) relative to the original oil. An unexpected but valuable result of these studies has been a better understanding of the levels of variability to be expected when naturally inhomogeneous systems are studied by different methods in different laboratories. Variability has been determined for measuring lipids in uncontaminated water (x = 8.2 µg/1; σn–1 = 6.5; one laboratory; 43 samples taken over a period of 8 weeks) and in tank sediments (x = 146 µg/g dry weight; σn–1 = 33.6; two laboratories; 37 samples taken over a period of six months). Comparisons have also been conducted on rates of biodegradation obtained by two different methods (gas chromatographic analyses of water column hydrocarbons with emphasis on the changing ratios of n-alkanes to isopre-noids, and laboratory studies of individual radio-labelled hydrocarbons converted to 14CO2).