Quantal response of Paleomonetes africanus in locally formulated drilling mud lubricants

The toxic potency of three locally formulated drilling mud lubricants against Paleomonetes africanus, a brackish water crustacean commonly found in the oil producing Niger Delta (Nigeria), was evaluated. A 96?h exposure to quantal (lethal) doses of the mud lubricants gave LC₅₀ (median lethal concentration) of 350, 620 and 210?mg?L^?1, respectively. The mud lubricant with the highest molecular weight of 40,000?g?mol^?1 (lubricant 2) had the least toxicity on the organisms, attributable to the reduced rate of diffusion into the vital cells of the test organism. The higher toxicity of lubricant 3 over lubricant 1, despite its higher molecular weight, might be as a result of its higher acid value of 21.60?mg?KOH?g^?1. The results show that the test lubricants would be environmentally friendly within the baseline concentrations and lethal times (LT₅₀) measured.