impact include diesel fuel or mineral oil, surfactants, and biocides. Many 

 hundreds of acute toxicity bioassays have been performed with drilling muds, 

 and nearly 90 percent of the samples were found to be nontoxic or practically 

 nontoxic to marine organisms. 



LABORATORY STUDIES 



To test bioavailability, experiments were conducted with juvenile 

 lobsters and with flounder species. The animals were kept in aquaria with 

 either uncontaminated or highly contaminated bottom sediments and were fed 

 either uncontaminated or highly contaminated food over a period of 99 days-- 

 long enough to consume 4 to 5 times their own body weights. Sufficient 

 drilling mud solids were added to sediment to increase the concentrations of 

 barium in sediment by 10,000 mg/kg. Flounder and lobsters were examined for 

 bioaccumulation of barium and chromium and for growth rate and mortality. In 

 both types of animals, there were no visible effects from eating contaminated 

 food; however, there were some problems from elevated levels of drilling mud 

 solids in the sediment. There was some bioaccumulation of barium, but not 

 chromium, from sediment. It was concluded that minimal bioavailability is 

 associated with sediments and none with food. 



FIELD STUDIES 



Review of many field studies in many regions points to three conclusions: 



■ Effects on the benthic community are found only in the immediate 

 vicinity of oil rigs, usually in tranquil environments, and most 

 recover fully in less than a year after drilling stops. 



■ Bioaccumulation of metals is limited to barium and chromium, with 

 small increases immediately after the discharge. 



■ There has been no demonstrated effect of hydrocarbon contamination. 



50 



