Several metals are present in most drilling muds (Table 1). Concentrations of individual metals may vary depending on the composition of the base ingredients and additives. The metals of greatest concern because of their abundance in drilling muds and cuttings and their potential toxicity to marine organisms include arsenic, barium, chromium, cadmium, copper, iron, lead, mercury, nickel, and zinc. Some of these metals are added intentionally to drilling muds as metal salts and organo-metallic compounds, if approved by local regulations. These metals are included in the added metals category. Most metals in drilling discharges are trace impurities in drill cuttings and major mud ingredients, particularly barite, ilmenite, and clay.
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