ACUTE BIOASSAYS OF THREE OIL SPILL DISPERSANTS AND DISPERSANT / CRUDE OIL MIXTURES ON CHIRONOMID LARVAE (DIPTERA: CHIRONOMIDAE)J. ROTIMI AND A.B.O. OGEDEGBE
Bioassays were conducted in laboratory microcosms to evaluate the toxicity of three oil spill dispersants-Corexit 9527, Nalco D4106 and Goldcrew and their mixtures with brent crude oil to the early life stages of Chironomus sp, (Diptera:Chironomidae). The results of determination of the 96 hour LC50 values showed variation in toxicity levels amongst the dispersants, Corexit 9527 with LC50 value of 1.2mgL-1 was the least toxic to the insect larvae followed by Goldcrew(0.8mgL-1) and Nalco D4106(0.5mgL-1). Toxicity of the dispersants were however less than that of the crude oil (96h LC50 0.4mgL-1). Mixtures of crude oil and the dispersants were less toxic to the test organisms than the crude oil alone; Crude oil-Corexit 9527 mixtures was 5.75 times less potent as crude oil, while crude oil - Nalco D4106 was 4.5 times less potent and Goldcrew was 2.5times less potent. Knowledge of the relative toxicities of dispersants and crude oil/dispersant mixtures is important for time-sensitive decisions in response to oil spills in the environment.
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