The Effect Of Food Quality And Abundance On The Tolerance Of Nano-Zinc Oxide In Daphnia

Most eutrophic waters are at risk of being contaminated by the new environmental pollutant nanoparticles,and as aquaculture waters become eutrophic,which often results in zooplankton,nanoparticles,cyanobacteria,and green algae co-existing in the same aquaculture waters.Phytoplankton as primary producers in the ecosystem,their biomass generally fluctuates with the change of water environment.Therefore,zooplankton as consumers may be exposed to different food conditions,so food and nanoparticles may have interactive effects on zooplankton.Although studies have reported that how the nanoparticles,Chlorella and Microcystis effects the life cycle of D.magna,respectively.However,in aquaculture waters,studies on the tolerance of D.magna to nanoparticles under different food conditions are rarely reported.In order to clarify whether there is an interaction between the two effects on D.magna,this paper explored the comprehensive toxic effects of different foods and nanoparticles on D.magna.We exposed D.magna to different food combined with different concentrations of ZnO NPs to do the chronic life experiments,survival,development,reproduction parameters were recorded.The aim was to explore how abundance,nutritional quality of alga and ZnO NPs affect the ecotoxicological effects of nanoparticles on D.magna life cycle parameters.The main conclusions of this study are as follows:1.The combined effects of ZnO NPs and toxic Microcystis on life history traits of Daphnia magnaThe results showed that both toxic Microcystis and ZnO NPs significantly delayed the development of D.magna to maturation,but there was no significant interaction between the two factors on the times to maturation except the body length at maturation.Both ZnO NPs and toxic Microcystis also significantly decreased the number of neonates in the first brood,total offspring,and number of broods per female,and there was a significant interaction between ZnO NPs and food composition on the reproductive performance of D.magna.Specifically,presence of toxic Microcystis reduced the gap among the effects of different ZnO NPs concentrations on the reproductive performance of D.magna.When the ZnO NPs concentration was at 0.15mg L^-1,the gap of the reproductive performance among different proportions of toxic Microcystis also tended to be narrow.Similar phenomenon also occurred in mortality.Such results suggested that low concentration of ZnO NPs and toxic Microcystis can mutually attenuate their harmful effects on D.magna,which has significantly implications in appropriately assessing the ecotoxicological effects of emerging pollutants in a complex food conditions.2.The combined effects of ZnO NPs and non-toxic Microcystis on on life history traits of Daphnia magnaThe survival time of D.magna was significantly reduced by both non-toxic Microcystis and nanoparticles,but there was no significant interaction between the two factors.D.magna could not reach sexual maturity when the concentration of ZnO NPs was at 0.30 mg L^-1under the food containing non-toxic Microcystis.when ZnO NPs was at 0.25 mg L^-1,D.magna couldn't lay eggs.The two factors significantly delayed the time to maturation and first brood,and decreased the body length of maturation,respectively,and there was no significant interaction between the two factors.The two factors also significantly decreased the offspring of the first brood and the total offspring per female,respectively,but there was no significant interaction between the two factors on the offspring of first brood per female,but had significant interaction on the total offspring per female.Such results suggested that there is urgent need to carefully consider the interaction of non-toxic Microcystis and ZnO NPs on D.magna's toxicity in the eutrophication of aquaculture waters,which is of great significance in revealing the evolution of new environmental pollutants on zooplankton under cyanobacteria conditions.The nutrient quality of nontoxic microcystis increased the damage of nanoparticles to D.magna.3.Combined effects of ZnO NPs and Chlorella abundance on life history traits of Daphnia magnaThe presence of low abundance Chlorella and nanoparticles significantly reduced the survival days of D.magna and delayed its development and reproduction.Moreover,with the increase of ZnO NPs concentration,the decrease of algal abundance significantly enhanced the toxicity of D.magna,and the two factors had obvious interaction.This study also found that under the experimental concentration of any nanoparticle,the time to maturation and first brood showed an exponential decline with the increase of algal abundance,and then reached a constant value.The survival time,body length at maturation and reproduction increased exponentially and then gradually reached a constant value.When the concentration of ZnO NPs was at 0.10 and 0.15 mg L^-1respectively,C.pyrenoidosa's low abundance(0.05 mg C L^-1)couldn't meet the minimum food needs of D.magna's development and reproduction.Only when C.pyrenoidosa's abundance reached 0.15 mg L^-1,D.magna could reach the spawning state under the ZnO NPs exposure.These conclusions highlight the importance of considering the impact of food abundance in the ecotoxicology of nanoparticles on zooplankton,which is important for assessing the ecotoxicological effects of novel environmental pollutants on D.magna in fluctuating food conditions.In summary,the pollutant ZnO NPs significantly harms the survival,development,reproduction and other key life-cycle parameters of D.magna,and this effect is mediated by food conditions?including biomass and the nutritional quality of algal?and with significant interactions.The results of this study have important significance for evaluating the ecotoxicological effects of new environmental pollutants under complex food conditions in nutrient-rich aquaculture waters and to reveal the differential adaptive tolerance of zooplankton to new environmental pollutants in the presence of cyanobacteria.