Characterization and Degradation of Petroleum Hydrocarbons Following an Oil Spill into a Coastal Environment of South Texas, U.S.A.

Petroleum hydrocarbons were characterized at eleven sites withinthe sediments of a coastal stream in south Texas, U.S.A. following a medium sized crude oil spill. Bank and open-water(deep) sediments were collected at each site. Hydrocarbonstargeted for analysis included 22 aliphatic hydrocarbons (C-11to C-34) and 16 polynuclear aromatic hydrocarbons. Sedimentconcentrations were measured at intervals of 1, 2, 3, 4, 6, and12 months post-spill. Higher hydrocarbon concentrations were observed for a longerduration within the deep sediments than bank sediments. Initialhydrocarbon constituents in impacted sediments matched the crudeoil fingerprint accurately with the exception of the lighter-endhydrocarbons. The lighter-end aliphatic hydrocarbons areaffected immediately by evaporation and dissolution processesduring the spill event and were found below the detection levelsat most of the sites. Total hydrocarbon concentrations insediments within each hydrocarbon group returned to backgroundlevels by the end of the study period. Observed decreases inhigh molecular weight polycyclic aromatic hydrocarbons (PAH)concentrations exceeded known environmental degradation rateswhich suggests the influence of a sediment transport process. Overall, the fate of petroleum hydrocarbons within this type ofenvironment were likely related to both degradation and sedimenttransport processes. By the end of the study period, most individual PAH constituent concentrations were below thresholdconcentrations thought to produce toxic effects in marine andestuarine organisms. PAH constituents concentrations remainingabove threshold concentrations included benz(a)anthracene,chrysene, and benzo(a)pyrene.