Abstract
The toxicities of two dispersants (Biosolve and OSD 9460), Forcados light crude oil and their mixtures based on ratios 6:1, 9:1, and 12:1 (v/v) were evaluated against the juvenile stage of African catfish, Clarias gariepinus, in laboratory bioassays. On the basis of the derived toxicity indices, Biosolve (96-h LC50 = 0.211 μl/l) was found to be about 27,284 times more toxic than crude oil (96-h LC50 = 5.757 ml/l) and 6,450 times more toxic than OSD 9460 (96-h LC50 = 1.361 ml/l). OSD 9460 was also found to be four times more toxic than crude oil when acting alone against C. gariepinus. Toxicity evaluations of the mixtures of crude oil/dispersants mixtures varied, depending largely upon the proportion of addition of the mixture components. The interactions between mixture of crude oil and Biosolve at the test ratios of 6:1, 9:1, and 12:1 were found to conform with the model of synergism (SR = 7,655, 14,876, and 8,792, respectively), and the mixtures were therefore more toxic than the crude oil acting singly. Similarly, the interactions between mixture of crude oil and OSD 9460 at the test ratios of 6:1 and 9:1 also conformed to the model of synergism (SR = 2.2 and 1.84, respectively). Interactions between the dispersant OSD 9460 and the crude oil at test ratio 12:1, however, conformed to the model of antagonism (SR = 0.84), indicating that the mixture was less toxic than crude oil acting alone. The results of the emulsification potential of OSD 9460 and Biosolve [measured in terms of optical transmittance (%)] prepared at the dispersal ratios 6:1, 9:1, and 12:1 revealed that the dispersal ratio of 6:1 achieved the highest emulsification of the crude oil with optical transmittance value of 4% and 6%, respectively. Estimation of an “environmentally sensitive” dispersal ratio for OSD 9460 and Biosolve revealed the optimum dispersal ratio for OSD 9460 range between ratios 7.5:1 and 9:1, while for Biosolve such an optimum dispersal ratio was indeterminate within the range of test dispersal ratios. The implications of these results in setting manufacturer’s and regulatory dispersal ratios for chemical dispersants used for oil spill control were discussed.
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Acknowledgments
The authors are grateful to the Department of Petroleum Resources in Nigeria for assistance rendered in obtaining crude oil used for the study. We are equally grateful to the Late Prof. K.N. Don-Pedro and Dr. L.O. Chukwu for providing us with the dispersants.
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Otitoloju, A.A., Popoola, T.O. Estimation of “environmentally sensitive” dispersal ratios for chemical dispersants used in crude oil spill control. Environmentalist 29, 371–380 (2009). https://doi.org/10.1007/s10669-008-9212-2
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DOI: https://doi.org/10.1007/s10669-008-9212-2