Evaluation of Biocompatibility and Biodegradation of Three Different Oil Dispersants in Persian Gulf: Siri Island Water



Zolfaghari BA¹ ; Mehrabian S² ; Emtiazjoo M³ ; Farkhani D⁴ ; Hosseini SM⁵ Show Affiliations
Source: Journal of Environmental Studies Published:2009

Abstract

The main causes of oil pollution in the oceans are extraction of oil, transportation with ballast water release, tanker accidents and also war-related incidents. The spills are particularly destructive for local wildlife and plant life when they get close to shorelines. They also damage boats, fishing gear and harbor installations and greatly diminish the value of the shore as recreational resources. Many methods have been used to remove oil spills from water including physical removal of crude oil, chemical remediation of the spills using dispersants and so-called sinking agents, and, in some cases, intentionally burning floating petroleum slicks. Using chemical dispersants as an oil spill countermeasure is the most frequently employed clean-up method because such liquids can be readily applied to large oil spills and also this method is generally more cost-effective than physical remediation methods. On the other hand the exclusive property of these dispersants to make oil spills dispersed into water will enhance the biodegradability of crude oil due to the increased exposed surface of the spills to such agents. Nevertheless, not all surfactant compositions are efficient in dispersing spilled oil products and many of the effective ones have the drawbacks of being toxic and/or not biodegradable. Persian Gulf is recognized as the world's largest source of fossil fuels and thus enshrining its importance as the world's most strategic waterway. The result of this extensive marine traffic is a high risk of oil pollution, both intentional and accidental. To diminish risk of more environmental pollution, use of highly biocompatible dispersants has been recommended. In this paper, we study biodegradability and the impacts of three dispersants; Parsl, Pars2 (produced by Iranian Offshore Oil Company) and Gamlen on degradation of crude oil in Siri Island water. Biodegradability of Gamlen and its effects on dispersing of oil had been already studied and it is being used in Persian Gulf water. Here, we present the most dispersing, effective and biodegradable component for dispersion of crude oil in Siri Island water. Due to the location of one of the biggest offshore oil drilling rig and high traffic density of oil vessels in the sea lanes of Siri Island, this is one of the numerous shorelines contaminated by oil spills. The culture used in the investigation was originally isolated from 8 sampling stations located at different longitude and latitude in the Siri Island offshore Total microorganisms were isolated through common microbiological experiments under the sterile condition. The total microorganisms were cultured with presence of Pars 1, Pars2, Gamlen separately and also the combination of each with oil at a dispersant-to-oil ratio of 1/20. Dispersants were the only source of carbon in the culture. The ability of bacteria and fungi to grow at the sides of wells was assayed using well method and their growth rate was measured through optical density reading. In this regard, isolated Gamlen, flask 4: Pars 1 and oil, flask 5: Pars 2 and oil, flask 6: Gamlen and oil. Six control flasks contained sterile media, dispersants and/or crude oil. All flasks were incubated at 30 °C shaking at 120 rpm for 28 days. In different time intervals (24, 48 and 72 hours and 1, 2, 3, and 4 weeks) the optical density of each sample was measured using spectrophotometer at wave length of 600 nm. Then the OD reading results were studied and the obtained data was analyzed using SPSS 15 soft ware, ANOVA and Tukey statistical tests. In order to identify the biodegradation of above-mentioned dispersants and their mixture with oil in 8 sampling stations, the BOD and COD of each sample was measured in the presence of total microorganisms. The procedure was as follows: 1 ml of water obtained from each station was inoculated into Marine Broth in 8 screwed cap tubes and one tube was kept as control. After incubating the tubes at 37 °C for the period of 48-72 hours, all culture media of 8 tubes containing the grown microorganisms were put together in Nutrient Broth media and cultured over the night. Therefore, a culture media containing all microorganisms obtained from 8 sampling stations was prepared. Consequently, 1 ml of bacterial suspension obtained from total microorganisms' culture was inoculated to each 8 flasks containing 100 ml of manual media. Furthermore, the component was individually added to the series of flasks so that each flask contained only one type of dispersant or its mixture with oil as follows: 1ml crude oil, 1ml Pars 1, 1 ml Gamlen, 1ml Pars2, 1 ml mixture of crude oil and Pars 1, 1 ml mixture of crude oil and Pars 2, 1 ml mixture of crude oil and Gamlen and their BOD and COD was measured after 5 days using the standard method. The results obtained from Well method showed the highest number of bacteria and fungi belongs to those which have been cultured in the presence of Pars 1, Pars 2 or separate mixture of each with crude oil. The OD reading showed that the highest growth occurred in the presence of either Pars lor Pars 2 or their separate mixture with crude oil. The results of ANOVA and Post Hoc Tukey statistical tests showed F indicates meaningful differences (P ≤ 0.006) in the effects of isolated microorganisms on different dispersants after 24 hours. The comparison of the mean growth rate using Hoc Tukey test exhibited that there is meaningful differences between Parsl and Gamlen dispersants (P ≤ 0.046) and also between Gamlen and combination of crud oil with Parsl (P ≤ 0.005) In other words, the effect of microorganisms on Parsl dispersant is more than that on Gamlen dispersant. The results of ANOVA test on day 28 (P - 0.755) showed that there is no meaningful differences in effects of microorganisms among each dispersant separately or their combination with crude oil. The results obtained from BOD and COD analysis showed BOD and COD levels in culture having only Siri Island crude oil are very low but when it is treated by dispersants the levels are dramatically increased. However, as the results show, among different combinations of crude oil and dispersants, the highest BOD and COD firstly belongs to the mixture of crude oil and Pars 2 and secondly to the mixture of crude oil and Pars 1. Moreover, the highest BOD and COD among three different dispersants belong to, Parsl. The overall results show that Parsl and Pars2 dispersants produced by Iranian Offshore Oil Company, is more effective than Gamlen dispersant. The growth index represents the mass of microorganisms at the side of wells containing dispersants which indicate the ability of microorganisms to use crude oil and dispersant components. Therefore, microorganisms grown around the wells are considered as petroleum-degrading microorganisms. Since the highest numbers of microorganisms grown around wells containing Parsl, Pars2 and also their separate mixtures with crude oil, it is concluded that both Pars 1 and Pars 2 dispersants are more effective in biodegradation of crude oil and on the other hand they have more biodegradability and bio-adaptability properties comparing Gamlen dispersant. In this agreement, the highest optical density belonged to bacterial culture containing above-mentioned dispersants as the exclusive carbon source. The result of statistical calculations on isolated bacteria and fungi showed that in the first 24 hours noticeable growth has occurred in the presence of Pars 1 dispersant as well as its combination with crud oil showing meaningful difference compared to the growth of the same organisms in the presence of the other dispersants or their combination with Siri island crud oil. This finding confirms that Pars 1 dispersant has more adaptability to Siri island ecosystem and also it has more ability in biodegradation of crude oil comparing the Evaluation of Biocompatibility and Biodegradation of Three Different..... other two dispersants. There was no meaningful differences in the effect of microorganisms on each dispersant and also on their combination with crude oil after 28 days, however since the entered material to the ecosystem needs to be degraded fast, Pars 1 dispersant which shows more degradability in the first 24 hours comparing other dispersant, is more adaptable to the environment.