ORGANIC AND ORGANOMETALLIC COMPOUNDS IN ESTUARINE SEDIMENTS FROM THE GULF-OF-MEXICO (1993-1994)

Sediment samples from 281 estuarine sites in the Gulf of Mexico were c ollected in 1993-1994 and analyzed for several classes of organic and organometallic compounds as part of the Environmental Monitoring and A ssessment Program of the United States Environmental Protection Agency . Polynuclear aromatic hydrocarbons (PAHs) were the contaminant class found most frequently and in the highest concentrations; the sum of 24 congeners (Sigma PAHs) ranged from <5 ng g(-1) to 15,500 ng g(-1) (dr y wt basis). A low percentage of samples (3.9%) exceeded 2000 ng g(-1) Sigma PAHs, and only six samples (2.1%) exceeded 4000 ng g(-1), a lev el above which adverse biological effects may be expected to occur Les s than 4% of sediments exceeded 20 ng g(-1) for the sum of 20 polychlo rinated biphenyls (Sigma PCBs) and only four samples (1.4%) exceeded 2 0 ng g(-1) for the sum of several organochlorine pesticides (Sigma OCP s). A sample from Freeport Harbor, Texas, contained 4230 ng g(-1) Sigm a PAHs, 322 ng g(-1) Sigma PCBs, and 49.6 ng g(-1) Sigma OCPs. Tributy ltin exceeded 100 ng g(-1) in only four samples, all of which were fro m stations in Corpus Christi Bay or Galyeston Bay in Texas. The detect ion of a suite of organophosphate pesticides was very rare and did not exceed 15 ng g(-1). Sediments from the tidally influenced section of the Mississippi River in Louisiana contained low to moderate levels of all classes of organic compounds. The most contaminated sites were in urban estuaries (e.g., Corpus Christi, Galveston, and Pensacola (Flor ida bays), underscoring the need to concentrate future monitoring and assessment efforts at the regional and local level.