Research Product

Toxicity tests were conducted with two laboratory-prepared generic drilling fluids (muds) and six commonly used drilling fluid additives to determine their toxicity, alone and combined, to mysids (Mysidopsis bahia). In 25 tests, the acute toxicity of combinations of one, two, or three of the drilling fluid additives mixed with either drilling fluid was less than the toxicity predicted from the empirical 96-h LC50s for drilling fluid additive(s) and/or drilling fluid alone; the observed 96-h LC50s of the mixtures were from 1.3 to 23.6 times the values predicted from the presumption of additive toxicity. Based on the drilling fluid additives and drilling fluids tested, a conservative estimate of the acute toxicity of mixtures of drilling fluid additives and drilling fluids would be derived if the toxicity of drilling fluid additive(s) and drilling fluid were separately determined and additive toxicity presumed.