| The environmental bioimpacts and behaviors of nanomaterials have aroused wide attentions due to their rapid developments and applications.Algae,as primary producers in aquatic ecosystem,are often used as test organisms in ecotoxicity risk assessment.However,some pollutants frequently coexist with nanomaterials in actual aquatic ecosystem,and their interactions will affect the joint bioimpact.Among these pollutants,surfactants are commonly used as promoters in the production of nanomaterials or applied in other products.Therefore,it is necessary to consider the effects of nanomaterials and surfactants.However,the joint bioimpacts of nanomaterials and surfactants on algae were still limited.This paper selected a single-cellular green alga Chlorella vulgaris as the model organism,and chose nano-ZnO and sodium dodecyl benzene sulfonate(SDBS)as the representative nanomaterials and surfactants,respectively.Based on studying the inhibition effect of single nano-ZnO or single SDBS on the algal growth,we investigated the joint bioimpacts of nano-ZnO and SDBS(nano-ZnO/SDBS)on the algal growth.Furthermore,we explored the interactions between nano-ZnO and SDBS in physicochemical properties in combined system.The following results are obtained in this paper:(1)The growth of Chlorella vulgaris was obviously inhibited by single nano-ZnO,but not by single SDBS.In the single system of nano-ZnO,the biomass of Chlorella vulgaris increased firstly and then decreased with the elevated concentrations of nano-ZnO(0.005-0.15 mm).The maximum inhibition effect was occurred at 0.04 mM of nano-ZnO.When the concentration of nano-ZnO was 0.005,0.04 and 0.15 mM,the biomass of Chlorella vulgaris after culturing for 7 days was 32.41×105 cells/mL,17.42×105 cells/mL and 18.79×105 cells/mL,respectively,which was only 84.87%,45.60%and 49.20%of the control group(free nano-ZnO).The content of chlorophyll a(Chl-a)was only 84.87%,45.60%and 49.20%of the control group(2.76 mg/L),while the content of chlorophyll b(Chl-b)was 78.26%,30.40%and 33.91%of the control group(1.15 mg/L),respectively.In the single system of SDBS,the biomass of Chlorella vulgaris was 93.40%of control group(Free SDBS)with 20 mg/L SDBS.The content of Chl-a and Chl-b were xx and xx of control group.respectively.In combined system of nano-ZnO and SDBS,the inhibition effect of nano-ZnO on the growth of Chlorella vulgaris was significantly enhanced by SDBS.When the concentration of SDBS was 20 mg/L,and the nano-ZnO was 0.005,0.04 and 0.15 mM,respectively,the biomass of Chlorella vulgaris was 52.42%,43.05%and 45.76%of that in single system of nano-ZnO(0.005,0.04,0.15 mM).The content of Chl-a was 48.32%,30.19%and 35.13%of that in single system of nano-ZnO,while the content of Chl-b was28.89%,14.28%and 17.95%,respectively.(2)In the single system of nano-Zn0(0.005,0.04 and 0.15 mM),Zn elements(nano-ZnO and Zn2+)were mainly distributed in S-EPS on the first day,which were 0.273,1.654 and 8.458 mg/L,respectively.With the cultivation time to the logarithmic phase(4 days),Zn gradually accumulated in the B-EPS and then entered the algal cells.The concentrations of Zn in B-EPS were 0.052,0.703,and 1.037 mg/L,respectively.Also,the concentrations of Zn in cells were 0.132,1.253,and 1.136 mg/L,respectively.The distributions of Zn elements in algal cells were consistent with the Chlorella vulgaris growth tendency,indicating that the inhibition effect of nano-ZnO on the growth of Chlorella vulgaris was related to the entering of the Zn element into algal cells.In the combined system of nano-ZnO and SDBS,Zn element also showed a similar tendency of aggregation from S-EPS to B-EPS and intracellular.However,in the presence of SDBS,the concentrations of Zn elements in the S-EPS in the combined system(CSDBS = 20 mg/L,Cnano-ZnO = 0.005,0.04,0.15 mM)were much less than those in the single system(0.229?1.403?8.442 mg/L).Also,more Zn elements in the B-EPS(0.014?0.574?0.745 mg/L)and intracellular(0.17,1.491,and 1.34 mg/L)were detected in the combined system than in the single system.This indicated that SDBS promoted the accumulation of Zn in B-EPS and cells.On the 4th day,more Zn elements entered the intracellular(0.17,0.571,1.491,and 1.34 mg/L),thus leading to a high toxicity to algal cells in the combined system.This showed that SDBS changed the distributions of nano-ZnO in EPS and algal cells,and thus affected the inhibition effects of Chlorella vulgaris growth by nano-ZnO.(3)Nano-ZnO possessed the characteristic of dissolving out Zn2+,and the existence of SDBS promoted the dissolution of nano-ZnO.When the concentration of nano-ZnO was 0.15 mM,the concentration of Zn2+ in pure water,normal OECD medium and modified OECD medium was 2.90,0.73 and 0.97 mg/L,respectively.In the presence of SDBS,the concentration of Zn2+ was increased by 27.9%,23.3%and 40.2%,respectively.In addition,the presence of SDBS changed the surface charge properties and size of nano-ZnO,enhanced their stability and reduced their hydraulic diameter.In pure water,the zeta potential of nano-ZnO changed from 10.4 mV to-16.7 MV with the increase of SDBS concentration,the relative absorptivity(A/A0)changed from 10.4 mV to-16.7 mV,and the hydraulic diameter decreased from 1494 nm to 325 nm.In the modified OECD medium,the zeta potential increased from-16.1 mV to-21.1 mV,the relative absorptivity(A/A0)changed from 0.52 to 0.82 mV,and the hydraulic diameter decreased from 433.4 nm to 298.5 nm. |
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