Toxic Effects Of Oxygenated Polycyclic Aromatic Hydrocarbons On Aquatic Organisms

Oxygenated polycyclic aromatic hydrocarbons（OPAHs）are a class of polycyclic aromatic hydrocarbons（PAHs）derivatives.Studies demonstrated certain OPAHs possessed higher genotoxicity,mutagenicity and carcinogenicity than parent PAHs.Previous studies on OPAHs mainly focused on their distribution in the atmosphere and health impact.However,considering that OPAHs have also been detected in surface waters in recent years,we need to pay attention to the potentially adverse effects of OPAHs on the homeostasis of aquatic ecosystems and aquatic organisms.Therefore,we selected 8 kinds of OPAHs which have been detected in surface waters,including 1-Indanone（1-INDA）,1-Naphthaldehyde（1-NLD）,9-Fluorenone（9-FL）,Acenaphthenequinone（1,2-ACQ）,Anthraquinone（ATQ）,2-Methylanthraquinone（2-MAQ）,benzanthrone（BEZO）and Benz[a]anthracene-7,12-dione（BAQ）.Toxicological experiments were carried out with three aquatic organisms,i.e.,Tetradesmus obliquus（phytoplankton）,Daphnia magna（invertebrate zooplankton）and zebrafish（vertebrate）,to explore the potential hazards of OPAHs to the water environment.The results were as follows:（1）We studied the inhibitory effect of OPAHs on the growth of Tetradesmus obliquus.The results showed that all eight kinds of OPAHs inhibited the growth of algal cells in a dose-response relationship.According to the half maximal effective concentration(EC₅₀)of OPAHs,the order of toxicity was BEZO>2-MAQ>1,2-ACQ>9-FL>1-NLD>1-INDA,while ATQ and BAQ（within their solubility range）didn’t cause half inhibition on algal cell growth.Therefore,we further studied the effect of BEZO(the most toxic OPAHs with a 96 h-EC₅₀ value of 0.0277mg/L)on Tetradesmus obliquus.It was found that BEZO（≥18μg/L）could induce algae cells to produce reactive oxygen species（ROS）,thereby causing serious oxidative damage.It could also destroy the function and integrity of biological membrane and impede photosynthesis by inhibiting chlorophyll synthesis or by causing the loss of chlorophyll.（2）Taking Daphnia magna as the test organism,it was found that exposure to OPAHs could cause acute immobilization of Daphnia magna.The order of toxicity was BEZO>2-MAQ>9-FL>1,2-ACQ>1-NLD>1-INDA,while ATQ and BAQ（within their solubility range）didn’t immobilize Daphnia magna.BEZO is the most toxic OPAHs with a 48 h-EC₅₀ value of0.0231 mg/L.Therefore,the sublethal toxicity of BEZO at low concentrations on Daphnia magna was further studied.It was found that BEZO（≥200 ng/L）could affect the growth and development of Daphnia magna.BEZO also reduced the spawning frequency of Daphnia magna by inhibiting the embryogenesis and egg production thereby resulting in the reduction of offspring,which would inhibit the size of population.The toxic mechanism was BEZO could interfere with the ability of filter-feeding and cause oxidative damage to Daphnia magna.By studying the respective acute toxicity of OPAHs to adults and embryos of zebrafish,it was found that zebrafish was more sensitive to OPAHs in embryonic stage than in adult stage.Therefore,we focused on the toxicity of OPAHs to zebrafish embryos.In addition to ATQ,other OPAHs had acute toxicity to zebrafish embryos and there was an obvious dose-effect relationship.The order of toxicity was BEZO>BAQ>2-MAQ>9-FL>1,2-ACQ>1-NLD>1-INDA.Therefore,we further studied the effect of BEZO(the most toxic OPAHs with a 96 h-LC₅₀ value of 0.0107 mg/L)on zebrafish in embryo-juvenile stage.It was found that BEZO（≥100 ng/L）could induce serious oxidative damage to zebrafish,cause loss of control of physiological and behavioral responses by interfering with neural information transmission,affect heart development and induce zebrafish malformation（hemorrhage,pericardial edema,yolk sac edema,delayed development,tail deformities and spinal curvature）.In conclusion,most of OPAHs caused serious lethal/inhibitory effects on at least one aquatic organism,and Daphnia magna as well as zebrafish were usually more sensitive to OPAHs.The toxicity of different structures of OPAHs varied greatly,and for most of OPAHs,the toxicity had a good correlation with hydrophobicity.Among OPAHs,six kinds of them could cause high/moderate harm to the water environment,which provided a theoretical basis for us to more comprehensively understand the aquatic ecological toxicity of OPAHs and evaluate the risk to aquatic environmental caused by OPAHs at environmentally relevant concentrations.