Estimation of “environmentally sensitive” dispersal ratios for chemical dispersants used in crude oil spill control
- 120 Downloads
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.
KeywordsCrude oil Dispersants Dispersal ratios Spill control Joint action
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.
- Anderson PD, Weber LJ (1975) The toxicity to aquatic population of mixtures containing certain heavy metals. In: Proceedings of the international conference on heavy metal in the environment, Institute of Environmental Studies, University of Toronto, pp 933–953Google Scholar
- Enserik EL, Maas-Diepeven JL, Van Leeuwen CJ (1991) Combined effects of metals; an ecotoxicological evaluation. Water Res 25(5):579–687Google Scholar
- Fabregas J, Herrero C, Veiga M (1984) Effect of oil and dispersant on growth and Chlorophyll a content of marine microalgae Tetraselmis suecica. Appl Environ Microbiol 47(2):445–447Google Scholar
- Fingas MF, Kyle DA, Lambert P, Wang Z (1995) Analytical procedures for measuring oil spill dispersant effectiveness in the laboratory. In: Proceedings of the 18th arctic marine oil spill program technical seminar, Environment Canada, Edmonton, Alberta, pp 339–354Google Scholar
- Finney DJ (1971) Probit analysis, 3rd edn. Cambridge University Press, LondonGoogle Scholar
- Kingham JD (1981) Oil spill chemicals: environmental implication and use policy. In: Proceedings of the international seminar on the petroleum industry and the Nigerian Environment. FMW&H/NNPC, PTI, Effurun, Delta State, Nigeria, pp 179–185Google Scholar
- National Research Council (1989) Using oil spill dispersants on the sea. National Research Council Marine Board, National Academy Press, Washington, DC 335 ppGoogle Scholar
- Nelson-Smith A (1967) Oil emulsifiers and marine life. In: The journal of the Devon Trust for nature conservation, Ltd. Supplement. Conservation and the Torrey canyon, Kingsbridge, England, pp 29–33Google Scholar
- Otitoloju AA (2001) Joint action toxicity of heavy metals and their bioaccumulation by benthic animals of the Lagos lagoon. Ph.D. thesis, University of Lagos, 234 ppGoogle Scholar
- Otitoloju AA (2006) Joint action toxicity of spent lubrication oil and laundry detergent against Poecilia reticulata (Telostei: Poeciliidae). Afr J Aquat Sci 31(1):125–129Google Scholar
- Ross SI (1997) A review of dispersant use on spills of North Slope crude oil in Prince William Sound and the Gulf of Alaska. Prince William Sound Regional Citizens’ Advisory Council, AnchorageGoogle Scholar