typically no significant trace metal contamination was observed (Tillery 

 1980). 



Based upon studies in the BGOF, Gallaway et al. (1980) concluded 

 that (1) produced waters are slightly toxic, but direct effects are 

 generally restricted to within only a few meters of the outfall, and (2) 

 that measurable uptake of contaminants is minimal and restricted to 

 those species in the biofouling food chain. 



Brent et al. (1979) found that producing platforms increased total 

 organic carbon loading of the system from 2 to 4 mg/£ above background 

 levels. The area affected by increased loading extended some 800 to 

 1 ,600 m from the platforms. They further pointed out that, given the 

 naturally high organic load in waters of the Texas-Louisiana shelf and 

 its effect on oxygen resources, this could be an area of some concern. 



OIL SPILLS 



The National Academy of Sciences (1975) estimated that the major 

 sources of hydrocarbons into the world's oceans were from transportation 

 (34.9$) and river runoff (26.2$). In contrast, offshore production 

 activities were estimated to account for only 1.3$ of the total 

 hydrocarbon loading of oceans. Total volume of oil spilled in the Gulf 

 of Mexico from offshore production activities (including pipeline 

 failures) was 51,421 barrels (bbl) during 1971-75 (Danenberger 1976) and 

 only 1,978 bbl were recorded to have been spilled from production 

 activities during 1976-79 (D0I/BLM 1981). In comparison, Bedinger et 

 al. (1980) estimated that the annual hydrocarbon input to the gulf from 

 the Mississippi River may average about 151,000 bbl. 



From 1 974-79 , 3.115 oil spills were recorded that were directly 

 attributable to marine-transportation (other than pipelines, DOI/BLM 

 1981). Although most (97$) of these spills were less than 50 bbl 

 (DOI/BLM 1981), one, the 1979 Burma Agate collision with a freighter, 

 was estimated to have spilled 198,000 bbl of oil, of which 150,000 bbl 

 burned in the ensuing fire (Kana and Thebeau 1980). Thus, as in the 

 general case of the world's oceans, oil and gas production activities on 

 the Texas-Louisiana continental shelf, particularly since 1971 » appear 

 to account for only a small portion of the total hydrocarbon input to 

 the system. 



Prior to 1971, only spills of major significance (^50 bbl) were 

 recorded. Some of these spills were massive. Among the most 

 spectacular were the Exxon pipeline break in 1967 (160,000 bbl), the 

 1970-71 Shell Timbalier blowout and fire (53,000-130,000 bbl), and the 

 1970 Chevron Main Pass incident (30,500 bbl). These last two incidents, 

 in conjunction with the Santa Barbara blowout which occurred during the 



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