Uptake and Degradation of Polycyclic Aromatic Hydrocarbons by Brown Seaweed, Laminaria Joapnica
Abstract: Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous organic contaminants present in environments. In China, with increasing environmental pollution and anthropological disturbances to the coastal environment, developing effective methods for remediating organic pollutants has become an important issue for coastal management and ecosystem restoration. However, little information is available on PAHs uptake and degradation by algae, especially from coastal water.In this study, we investigated the uptake and degradation of two PAHs ( phenanthrene and pyrene), under a range of concentrations from 0.1mg/l to 2.0mg/l, by brown seaweed Laminaria joapnica, and examined the catabolic pathway of PAHs during degradation by seaweed. The uptake and degradation of the two PAHs are concentration and toxicant dependent.In laboratory studies, under a certain range of PAHs concentrations (<0.2mg/l), Laminaria joapnica showed a great capacity to take up and metabolize phenanthrene and pyrene. In laboratory studies, Laminaria joapnica showed a great capacity to take up and metabolize phenanthrene and pyrene. Under the concentration of 0.1mg/l, 99.88-99.89% of phenanthrene and 94-96.5% of pyrene were removed by the seaweed 16 days’treatment, but the percentage of abiotic loss of these two PAHs in control were 46.9% and 44.7% respectively. Our calculation indicates that at the concentration of 0.1/l, about 51.34% of phenanthrene and 45.7% of pyrene taken up by the seaweed were degraded after two weeks demonstrating that this brown seaweed Laminaria joapnica has great ability to uptake and metabolize PAHs. For the degradation products, dihydro-pyrene-diol was identified as the major metabolite, suggesting that the metabolism of pyrene by Laminaria joapnica was carried out through a dioxygenase pathway. We also found some conjugates of dihydro-pyrene-diol as a potential biodegradation product, but the amount was insufficient to qualify.The addition of PAHs into the culture medium inhibited the growth of Laminaria joapnica, especially at high concentrations. PAHs destroyed the seaweed’s chromatophore and the content of chlorophyll-a and carotenoid in seaweed decreased with time and with the increased concentrations of PAHs. The activities of the two enzymes peroxidase(POD) and superoxide dismutase(SOD) of Laminaria joapnica both increased significantly after exposurer to PAHs as a self defence process of the seaweed against oxyradicals result in PAHs addition. The role of POD was important in the first oxidizing PAHs.In summary, the seaweed Laminaria joapnica has great ability to uptake and metabolize PAHs effectively at certain concentration level, and could be used as a potential model in the phytoremediation at the PAH concentration levels found in contaminated coastal water. Our study also indicate that at high concentrations, the toxicity of PAH to seaweed growth is significant. Further studies will be needed to identify the biodegradation pathways and the ecological effects of the degradation product in coastal waters…
Key words: Laminaria joapnica; polycyclic aromatic hydrocarbons(PAHs); pytoremediation; degradation; antioxidant enzymes
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