Assessing the oil degradation potential of endogenous micro-organisms in tropical marine wetland

As part of a larger study on the bioremediation of oil spills in tropical mangrove habitats, we conducted a series of flask experiments to test for the presence of hydrocarbon degrading microbes in the habitats and to test the biodegradability of selected oils (Gippsland, Arabian Light and Bunker C), which are transported along the Australian coast. We also tested for potential inhibition by natural organics in the mangrove pore wasters and evaluated an oxygen release compound. Evaporation was a significant factor in removing the light alkane and light aromatic hydrocarbons from air and nitrogen sparged flasks. Evaporation removed 50 % of the Gippsland, 30 % of the Arabian Light and 7 % of the Bunker C oils. Oxygen was necessary to support biodegradation. All three oils tested were "biodegradable" to the limited extent of the saturated hydrocarbon fractions. Degradation removed another 4 to 23 % of the Gippsland, , 32 % of the Arabian Light,, and 36 % of the Bunker C oils. Based on these results, we would expect the Gippsland Ccrude oil to be less persistent than the others oils in mangrove sediment. because It it has a higher content of light hydrocarbons, which are readily removed by both physical and microbial processes. Comparison of the efficiency of inoculates from the three tropical intertidal habitats (Avicennia & Rhyzophora mangroves, plus salt marsh sediments) indicated that hydrocarbon degrading microbes were isolated from all three habitats. There was no inhibition of degradation due to addition ofincubation in mangrove pore waters. The oxygen release compound did not facilitate degradation in the closed flask experiments. These results were then used to formulate an oil bioremediation strategy of forced aeration to be trialed in a field experiment in mangrove habitats in Queensland, Australia