The Galeta Oil Spill. IV. Relationship Between Sediment and Organism Hydrocarbon Loads

This is the fourth in a series of articles reporting the results of studies of mangrove communities heavily oiled in the Bahía las Minas (Panamá) oil spill. This paper gives the detailed compositions of oil residues in sediments and encrusting bivalves, and the changes over time. Initial weathering processes removed most of the volatile hydrocarbons and all marker alkanes in oil adsorbed to surface sediments within 6 months after the spill. This initially fast rate of biodegradation was not maintained in the rate of disappearance of the aromatic hydrocarbons over time. Oil leaching out of heavily contaminated sediments was bioaccumulated in bivalves for at least 5 years. The organisms accumulated the whole range of alkylated polynuclear aromatic hydrocarbons (PAHs) in the naphthalene through the benzoperylene elution range, seemingly in proportion to what was leached from sediments. A change in the composition of the aromatics bioaccumulated at most study sites in year 5 indicated depletion of the most soluble and most acutely toxic hydrocarbons in the readily leachable reservoirs. Thus, the next 5 years will probably be the critical time frame when impacts grade from acutely lethal into sublethal. The most residual PAHs in both sediments and bivalves were the dibenzothiophene, phenanthrene and chrysene series. A relative increase in the fluorescence intensity compared to the amount of oil determined by gas chromatography in samples from later years provides indirect evidence for a larger percentage of the signal due to fluorescent derivatives of the PAHs.