current speed, such as the Gulf of Mexico, cutting piles are observed 

 after drilling, but the size of a pile diminishes considerably with 

 time, resulting in its eventual disappearance (Shinn 1975; Zingula 1975; 

 Miller 1976; Zingula and Larsen 1977). 



Like cuttings, drilling muds do not form significant accumulations 

 on the bottom in areas of high current velocity (Environmental Devices 

 Corporation 1976; Dames and Moore 1978; ECOMAR, Inc. 1978). However, 

 in the Gulf of Mexico, accumulations do occur near drilling operations 

 (Gettleson 1980, in press). The drilling mud probably accumulates in a 

 layer of variable thickness on the sediment surface, depending on the 

 hydrographic factors present at the time of the discharge. 



Results of field studies have shown detrimental effects of drilling 

 muds on bottom communities of the Texas-Louisiana shelf, but the effects 

 have been generally restricted to areas within meters of the point of 

 discharge (e.g. Fish et al. 1974; Perry 1974) . Similar findings have 

 been made in other marine systems. A study in Lower Cook Inlet, Alaska, 

 showed no detectable effect of drilling fluid discharges on local 

 benthic communities (Lees and Houghton 1980), although Crippen et al. 

 (1980) found a decrease in the infaunal population in the immediate 

 vicinity of a drilling island in the Beaufort Sea, and observed 

 increased concentrations of heavy metals (primarily mercury) in the 

 sediment and biota of the area. The latter study also found that 

 increased sediment loads occasionally smothered benthic infaunal 

 communities. Benech et al. (1980) found that pontoons on a submersible 

 drilling rig supported different assemblages of fouling species, 

 depending on their location relative to the drilling mud discharge 

 point. The fouling community was particularly decreased in areas where 

 mud particulates accumulated. Although very high concentrations of 

 drilling muds have been used to retard coral growth, and coral growth in 

 the Flower Garden Bank was determined by Hudson and Robbin (1980) to 

 have decreased greatly beginning in 1957. it is unlikely that the 

 decrease is in anyway associated with petroleum development. The area 

 was not developed until 1974 and barium and chromium concentrations have 

 showed no corresponding increase which would appear to be causative. 



Laboratory analyses of drilling fluids have shown a wide range of 

 biological effects which depend upon the type, concentration and method 

 of preparation of the test material and upon the organism studied. 

 Short term toxicity has been detected, but only at test solution 

 concentrations far greater than those which occur in the environment 

 outside the immediate vicinity of a discharge (see Ayers et al. 1980a 

 for a review) . 



Usually, drilling muds appear relatively non- toxic at the 

 concentrations encountered in the environment. Dilution of the plumes 

 is rapid; and indirect or sublethal effects of discharged drilling 

 fluids are virtually unknown, as are the long-term effects. In the 

 gulf, the primary threat of significant detrimental effects from 



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