Toxic contributions of specific drilling mud components to larval shrimp and crabs

We investigated the toxicities of six drilling muds, toxicities of mud fractions (supernatants and suspensions) and the toxicities of common mud components—barite and bentonite (particulates) and ferrochrome lignosulfonate (soluble)—to the stage I larvae of six species of shrimp and crab. The drilling muds we tested were not very toxic to these larvae: LC₅₀'s for supernatants ranged from 0·6 to 82% (vol/vol). Shrimp larvae were slightly more sensitive than crab larvae.Drilling muds were not rapidly toxic, in contrast to toxicants such as the water-soluble fractions of oil. Supernatants, prepared by centrifuging whole muds, were mildly toxic. Suspensions were more toxic than supernatants and toxicity was greatest when particulates remained suspended: for example, used Cook Inlet mud suspensions were about seven times more toxic than supernatants. The toxicity of used Cook Inlet mud was therefore primarily due to suspended solids (88%) rather than chemical toxicity: ferrochrome lignosulfonate was relatively toxic alone, but accounted for only about 6% of the toxicity of used Cook Inlet mud suspensions. Contributions of particulates to mud toxicities varied considerably. Barite and bentonite were not very toxic when tested alone. The toxicity of one mud was caused by its high alkalinity.