Toxicity Effects And Enrichment Effects Of PCBs In The Aquatic Food Chain

Polychlorinated biphenyls （PCBs） are a kind of organochlorine compounds compose ofisomers of chlorinated biphenyl, which are transformed from biphenyls by replacing hydrogenatoms with chlorine atoms, with as many as209species of isomers and homologues. Because oftheir stable physicochemical properties, persist, lipophilic, PCBs show a high residual in thewater ecosystem. At present, although PCBs’ manufacture and use have already been banned,PCBs’ residue still potentially threats the environment. The environmental pollution caused byPCBs is always the hot spot of environmental scientific research.In aquatic ecosystems, microalgae as ecosystem the first trophic level, are extremelysensensitive to poison in the water, thereby affecting the balance and stability of ecosustems.Daphnia usually eat algae as food, meanwhile they are also the natural food for fish andinvertebrate predators, that is an important part of material circulation and energy flow in aquaticecosystems. this paper studies the toxicity effects of the two trophic levels in aquatic ecosystems,designed to determine tis potential harm to aquatic organisms. On the basis of toxic effects ofaquatic organisms, used by the indoor and ecological simulation system, this paper studies theeffects of the bioaccumulation of PCBs in the ecosystem food chain, This study can provide areference basis for the ecological risk.Therefore this paper, aiming at PCB₂8, PCB₁₅₃and PCB₁69these three isomers, studies thetoxicity effects of suspended flora and fauna. Through the indoor simulation system, it studiesthe biological enrichment effect of PCB₂8and PCB₁₅₃on phytoplankton （Scenedesmusobliquus）-zooplankton （Daphnia magna）-aquatic animals （Brachydanio rerio） in the short-termindoor ecological system. The study results are:（1） In the toxicity experiments of PCBs on Chalorella pyrenoidosa and Scenedesmusobliquus, firstly this studty measured three kinds of PCBs toxicity by the change of theChalorella pyrenoidosa and Scenedesmus obliquus,growth rate and the EC50of PCBs onCholrella pyrenoidosa and Scenedesmus obliguus at96h, analysed the relationship between thetoxicity of PCBs and its chemical structure. Secondly, measuring the chlorophyll content, solubleprotein content, in vivo antioxidant enzyme activities （SOD and POD）, that discussed the reflectrules of microalgae and the change of antioxidant enzyme. The result of this study is that, the96h-EC50of PCB₂8, PCB₁69and PCB₁₅₃on Cholrella pyrenoidosa respectively is:46.334μg/L,59.200μg/L and93.111μg/L, and that on Scenedesmus obliguus respectively is:57.029μg/L,93.900μg/L and100.926μg/L, belonging to high toxic. Among them the sensitivity of the microalgae for PCB₂8is the highest. The response to the effect of PCBs is different between Cholrellapyrenoidosa and Scenedesmus obliguus, and the latter shows better tolerance. The influence of PCB₂₈, PCB₁₆₉and PCB₁₅₃on the increment and chlorophyll content ofCholrella pyrenoidosa and Scenedesmus obliguus shows clear dose-effect and time-effect change,both representing certain inhibition effect. There is certain doses-effect between PCB₂₈, PCB₁₆₉,PCB₁₅₃and SOD, POD existing in the body of algae. As the concentration of PCB₂₈and PCB₁₅₃increases, SOD and POD activity presents the phenomenon of first induction and then inhibition.SOD activity is more sensitive to PCBs.（2） In the toxicity test of PCBs on Daphina magna, they choosed Daphina magna as theexperimental subjects, and studied the acute and chronic toxic effects of PCBs on Daphinamagna. The result of this study is that, the48h-LC50of PCB₂₈, PCB₁₅₃and PCB₁₆₉on Daphniamagna respectively is:27.08μg/L,183.86μg/L and579.16μg/L, belonging to high toxicsubstances. The sensitivity of Daphnia magna for PCB₂₈is the highest. In chronic test of PCB₂₈,PCB₁₅₃and PCB₁₆₉, all have adverse effect for the growth and reproduction of Daphnia magna.The influence of PCB₂₈is that with the increase of concentration, the depression effect forgrowth and reproduction strengthens. The influence of PCB₁₅₃and PCB₁₆₉for the growth ofDaphnia magna is that with the increase of concentration, the depression effect strengthens,while the influence for the reproduction is that low concentration inhibits it and highconcentration promotes it.（3） In the bioconcentration test of PCBs on the indoor simulated ecosystem, they choosedScenedesmus obliquus as primary producers, Daphina magna as the primary consumer,Brachydanio rerio as secondary consumers. The short-term indoor food chain was seted up:phytoplankton （Scenedesmus obliquus）-zooplankton （Daphnia magna）-aquatic animals（Brachydanio rerio）. The result of this study is that, in the indoor simulating food chain, thebiological enrichment effect of PCBs shows more marked as the chlorinated degree increases,namely PCB₁₅₃> PCB₂₈. The biological enrichment ability of Scenedesmus Obliqnus for PCB₂₈and PCB₁₅₃is different, and its biological enrichment factor （BCF） augments as thehydrophobicity strengthens, namely BCF₁₅₃ BCF（28）. PCBs in the body of Daphnia magna andBrachydanio rerio are primarily obtained through ingesting food with PCBs. PCBs content inalgae cells increases as exposure concentration increases and exposure time extends. PCBscontent in Daphnia magna and zebrafish increases as PCBs content in the food increases. That is,the accumulation amount of PCBs in each trophic level depends on the PCBs concentration inthe lowest trophic level and the water.