The Toxic Effects Of 1,4-dichlorobenzene On Chlorella Pyrenoidosa

1,4-Dichlorobenzene(1,4-DCB)is a common organic contaminant and it is widely used as industrial and agricultural products.However,the leakage and unreasonable emission of 1,4-DCB had brought some problems to aquatic environment and human health due to its high stability,mobility and toxicity.But little is known about the toxicity of 1,4-DCB to algae.Therefore,study on the toxic effects of 1,4-DCB on algae is important.Regarding Chlorella pyrenoidosa as testing organisms,and it was exposed to different concentrations of 1,4-DCB(0,1,5,10,15,20 mg/L)for 9 days.The toxic effects of 1,4-DCB on C.pyrenoidosa were studied from four aspects:cell morphology,antioxidant system,membrane permeability,and photosynthesis.The results indicated four points:(1)algal growth was inhibited in a time-and concentration-dependent manner.When 1,4-DCB concentrations were?10 mg/L,the cell density decreased significantly.After treatment with 20 mg/L 1,4-DCB for 9 days,the submicroscopic structure of cells was damaged badly.C.pyrenoidosa underwent cell wall disintegration,cell membrane disruption,and chloroplast and pyrenoid deformation.The plasmolysis appeared.The leakage of intracellular content was also observed.(2)Low concentrations of 1,4-DCB(?5 mg/L)enhanced the activities of peroxidase(POD)and superoxide dismutase(SOD),but higher concentrations(?10 mg/L)caused a sharp decline as a result of reactive oxygen species(ROS)accumulation.(3)When 1,4-DCB concentrations were?10 mg/L,malonaldehyde(MDA)content and relative conductivity increased significantly over time.At the same time,the content of soluble protein(SP)and soluble sugar(SS)all decreased.(4)After treatment with 1,4-DCB(>10 mg/L),the contents of photosynthetic pigments decreased significantly,thephotosystem II reaction center was irreversibly damaged,and the quantum Yield of photosystem II decreased significantly.Also,there were sharp decreases in the efficiency of photosynthetic electron transport and energy conversion.Photosystem II became overloaded as the amount of excitation energy distributed to it increased.All of these events weakened the photochemical reaction,and ultimately led to serious inhibition of photosynthesis.These results illustrated that C.pyrenoidosa is a good model system for evaluating the effects of contaminants on aquatic ecosystems.It is concluded that 1,4-DCB exerts toxic effects on cell morphology,the antioxidant system,membrane permeability,and photosynthesis of C.pyrenoidosa,especially at concentrations exceeding 10 mg/L.