Life Stages and Sensitivity 



Larvae are more sensitive than adults to contaminants and early juvenile 

 stages are particularly sensitive to physical disruption. Inhibition of 

 larval settlement on sediments whose attractiveness is affected by 

 contaminants could result in reduced recruitment of commercial species. Any 

 disturbance that drives juveniles from their nursery habitat will expose them 

 to more predation. 



Drilling Muds 



Assuming a wellsite 1 km from a canyon rim, the available information 

 suggests that very little biological impact due to drilling can be expected 

 within the canyon. The main concern during the exploration phase is drill 

 muds and cuttings, most of which would initially accumulate within 200 m of 

 the platform.* Some quantities can be expected to drift into the canyon, 

 especially if it is downcurrent from the platform. However, there is little 

 or no chance of burial of organisms or of chemical contamination of the 

 sediments, much less bioaccumulation of harmful materials at distances greater 

 than a few hundred meters from the wellsite. The metals found in drilling 

 muds are virtually all insoluble, and thus not available to animals. 

 Furthermore, barium, the most plentiful metal in drilling muds, is not toxic 

 to marine organisms when present as barium sulfate. In general, drilling-mud 

 metals are present in chemical forms that limit their bioavailability to 

 marine organisms. 



Produced Water 



Produced water is usually a saline brine with constituents similar to 

 those in seawater, as well as some hydrocarbons (including aromatics) and 

 metals. The metals may be concentrated up to three orders of magnitude above 



'See also reviewer comment in Appendix A. 



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