Study On The Adsorption And Degradation Of POPs By Phytoplankton And Its Physiological And Ecological Responses

Persistent organic pollutants (POPs) and eutrophication are two of the main environmental problems for large shallow lake ecosystems. The blooming of phytoplankton is one of the most serious consequences on account of eutrophication. When POPs entered into waters, changing the living conditions of phytoplankton, they do a role in the growth and physiological parameters of algae. Also, POPs can easily be absorbed by the phytoplankton due to the high lipophilicity, and thus can be bioconcentrated and biomagnified through both the pelagic and benthic food webs. Therefore, the intensive absorption by phytoplankton will affect the biogeochemical processes of organic toxicants with respect to the distribution, transport as well as the bioaccumulation in aquatic ecosystems. By this taken, phytoplankton could be treated as the end of eutrophication and the beginning of the organic toxicants working on aquatic ecosystems. In our present study, two widely-used POPs including phenanthrene and α-endosulfan as well as three typical algae including Microcystis aeruginosa, Scenedesmus obliquus and Cryptomonas sp. in eutrophic lake were selected as experimental materials. This is the first sight to find out the bidirectional interactions between phytoplankton of different species and polycyclic aromatic hydrocarbons (PAHs) and organochlorine pesticides (OCPs) distribution in environment, which could be defined as a basis for the following study. Additionally, such studies could also provide the basic scientific basis for remedial measures in shallow lakes with respect to both POPs and eutrophication. Several important results were concluded as follows:(1) Growth of three representative algae was investigated in different concentration of phenanthrene and a-endosulfan. The results indicated that the effects of POPs on growth phytoplankton were dependent on the pesticide variety, phytoplankton species, and also related with culture time and pesticide concentration. Low-concentration phenanthrene and a-endosulfan could stimulate the growth and vice versa. Phenanthrene had a better positive influence on the growth of phytoplankton than a-endosulfan and the mixture of phenanthrene and a-endosulfan, while the mixture inhibited more than any single compound. Scenedesmus obliquus reproduced more rapidly than Microcystis aeruginosa and Cryptomonas sp. under the same pesticide concentration.(2) Differences in the photosynthesis of three representative algae were compared in the presence of various phenanthrene and a-endosulfan concentration. The results suggested that higher concentration distinctly reduced the photosynthesis by decreasing the maximal and actual photochemical efficiency (Fv/Fm and Yield). To some extent, low concentration simulated the photosynthesis of algae. Furthermore, the maximal and actual photochemical efficiency of Scenedesmus obliquus were more sensitive to these changes than the other two.(3) Accumulation and biodegradation of phenanthrene and a-endosulfan were associated with three algae. The results showed that Microcystis aeruginosa and Scenedesmus obliquus could accumulate large amount of pollutants at the beginning of the experiments, then decreasing progressively in the later period, while the accumulation concentrations in Cryptomonas sp. were peaked in the middle time. Similarly, Scenedesmus obliquus had a higheset biodegradation of phenanthrene and a-endosulfan among three representative algae, followed by Cryptomonas. sp. and Microcystis aeruginosa. Phenanthrene could be easier to biodegradation than a-endosulfan.