Effects Of Microplastics Pan And/or Cu²⁺ On The Physiology And Ecology Of Three Microalgae Strains

In recent years,the pollution of microplastics and heavy metals has become one of the hot topics in the field of environmental ecology.Microplastics and heavy metals are both toxic to phytoplankton because they are easily absorbed by phytoplankton due to their small particle size.Phytoplankton,which including the algae widely present in both fresh water and seawater.The important primary producer plays a key role for carbon concentrating mechanism（CCM）in aquatic or marine ecosystems,and has key response to global warming.Till up now,the eco-toxicological effects of microplastics and/or heavy metals on microalgae is a recent research trend.In the present thesis,I selected the Chlorella pyrenoidosa（freshwater algae）,Chlorella Salina（seawater algae）and Chlorella nannochloropsis（microalgae）as biological materials,and the algae population density,pigment content,chlorophyll fluorescence parameters and chlorophyll fluorescence curves,soluble protein content,the antioxidant enzyme（superoxide dismutase,SOD;catalase,CAT）activity,malondialdehyde（MDA）content,etc.,were measured and compared for revealing the ecotoxicological mechanism of microplastics PAN and/or Cu²⁺on the three algae strains.The main results are as follows:（1）For C.pyrenoidosa,the growth of C.pyrenoidosa was affected by different concentrations of copper ion within 0 to 200μg/L.With the increasing of copper ion concentration,the algae population density of C.pyrenoidosa decreased more obviously.The different concentrations of microplastics PAN were set from 0 to 500 mg/L.With the increasing of PAN concentration,the algae population density was inhibited.These results indicate that copper ions and PAN have inhibitory effects on the growth of C.pyrenoidosa.At treatment groups,which added 50 mg/L PAN,16μg/L Cu²⁺and the mixture with 50 mg/L PAN and 16μg/L Cu²⁺,the algae population density of C.pyrenoidosa was inhibited over time,and the mixture with 50 mg/L PAN and 16μg/L Cu²⁺treatment caused the most significantly algae population density decreasing.The treatment groups all had a downward trend of chlorophyll content.However,the carotenoid content increased during the first three days of pollutants exposure.The Cu²⁺pollution resulted in an obvious K-peak on the OJIP curve.It indicates that the oxygen-evolving complexes（OECs）of C.pyrenoidosa put was damaged by Cu²⁺pollution.The pollutants(PAN and/or Cu²⁺)stimulated the photon absorption of C.pyrenoidosa,while the pollutants stimulated the energy dissipation of C.pyrenoidosa.In the treatment groups,the total protein content showed a downward trend,and the CAT activity,MDA content and H₂O₂content increased respectively along with the increasing concentrations of pollutants.（2）For C.Salina,the growth of C.Salina was affected by different concentrations of copper ion within 0 to 100μg/L.With the increasing of copper ion concentration,the algae population density of C.Salina decreased more obviously.The different concentrations of microplastics PAN were set from 0 to 500 mg/L.With the increasing of PAN concentration,the algae population density was inhibited.It can be seen that copper ions and PAN had inhibitory effects on the growth of C.Salina.At treatment groups,which added 50 mg/L PAN,10μg/L Cu²⁺and the mixture with 50 mg/L and 10μg/L Cu²⁺,the algae population density of C.Salina was inhibited over time,and the mixture with 50 mg/L PAN and 10μg/L Cu²⁺treatment caused the most significantly algae population density decreasing.The treatment groups all had a downtrend of chlorophyll content.However,the carotenoid content increased slightly than that of control group.The pollutants(PAN and Cu²⁺)did not lead to the appearance of K-peak on the OJIP curve.It indicates that the OECs of C.Salina did not damaged by the pollutant exposure.The pollutants(PAN and/or Cu²⁺)stimulated the photon absorption of C.Salina,while pollutants did not stimulate the energy dissipation of C.Salina.In the treatment groups,the soluble protein content showed a downward trend,while the CAT activity,SOD content,MDA content all increased with the increasing concentrations of pollutants.（3）For the C.nannochloropsis,the growth of C nannochloropsis was affected by different concentrations of copper ion within 0 to 1000μg/L.With the increasing of copper ion concentration,the algae population density of C.nannochloropsis decreased more obviously.The different concentrations of microplastics PAN were set at from 0 to1000 mg/L.With the increasing of PAN concentration,the algae population density was inhibited.Above results indicated that copper ions and PAN had inhibitory effects on the growth of C.nannochloropsis.At treatment groups,which added 100 mg/L PAN,37.6μg/L Cu²⁺and the mixture with 100 mg/L of PAN and 37.6μg/L,the algae population density of C.nannochloropsis was inhibitted over time,and with 100 mg/L PAN and 37.6μg/L Cu²⁺treatment caused the most significantly algae population density decreasing.The treatments all resulted in a downtrend of chlorophyll content.However,the carotenoid content increased along with the increasing concentrations of pollutants.The pollutants(37.6μg/L Cu²⁺treatment and the mixture with 100 mg/L PAN and 37.6μg/L Cu²⁺treatment)lead to the K-peak on the OJIP curve.It indicated that the OECs of C.nannochloropsis was damaged by the pollutants(37.6μg/L Cu²⁺treatment and the mixture with 100 mg/L PAN and 37.6μg/L Cu²⁺treatment).The soluble protein content of the treatment groups all showed a downward trend,while the CAT activity and MDA content increased compared with the control group.The above results showed that the physiological and biochemical indexes of freshwater algae and seawater algae tended to be a similar variation trend under the exposure of Cu²⁺and/or microplastic PAN,and both of Cu²⁺and PAN had toxic effects on both of fresh water and seawater.The present results are the basis for the effect of microplastics PAN and/or Cu²⁺on phytoplankton and algae in seawater and fresh water.