Oil spill clean-up: The effect of three dispersants on three subtropical/tropical seagrasses

Abstract

Three seagrasses found throughout the Greater Caribbean tropical/subtropical region as major critical habitat organisms were tested in the laboratory for toxicity limits to three dispersants commonly stockpiled in the region. At concentrations in the recommended dosage level, that is, below 1 ml dispersant with 10 ml oil in 100 000 ml seawater, even for 100 h no large mortality occurred (15–18 barrels per acre as calculated by Exxon, 1985). At an order of magnitude higher, especially for longer time periods, the more sensitive seagrasses Syringodium filiforme and then Halodule wrightii succumbed. The dispersants had widely differing effects, with Corexit 9527 and Arcochem D609 having far less toxic effect than Conco K(K) at the same exposure time and concentration. There was comparatively little difference between effects of oils (Louisiana crude versus Murban). Types and brands of dispersants should be referred to specifically in oil spill contingency plans since such widely varying ecological toxicity occurs among various dispersants. Use of the word ‘dispersant’ as a policy tool should be used with caution, realizing that dispersants vary widely in toxicity effects. Further testing of seagrasses in other ocean basins and those dispersants to be used there is highly recommended.