Toxicology Of Metal Oxide Nanoparticles On Earthworm And Wheat In Different Types Of Soils

Background:Nanoparticles(NPs)have wide applications in many fields including biomedicine,industrial production,and environmental treatment due to their special effects.Currently,metallic nano oxides hold a pivotal status in the development of nanomaterials.As two of the most commonly used nanomaterials,ZnO nanoparticles(ZnO NPs)and CeO2 nanoparticles(CeO2 NPs)are manufactured at a large scale annually.76.5%of nanomaterials end up as direct release and landfill in soil.Soil serves as the basis for various forms of life and therefore contamination of nanomaterials in soil has aroused great concern.Present researches on nanomaterials’hazard in soil are still far from being sufficient,most of which are conducted under ideal conditions such as hydroponics,artificially simulated soil and so on.However,disparity in soil property(pH,organic matter and ash content)can influence nanomaterials’ toxic effect.Thus,it has practical significance to study the effect of soil type on nanomaterials’ toxicity in China,which is one of the major regions of nanomaterial release and has complicated soil property.This study focused on effects of ZnO NPs and CeO2 NPs to oxidative damage,and biomass of earthworm(Eisenia fetida)and wheat as well as soil enzymatic activities using different types of soil collected from the field and explored the reasons behind such phenomena.It consists of three parts:(1)analysis of bioavailability of ZnO NPs and CeO2 NPs in different types of soil;(2)toxicological effects of ZnO NPs and CeO2 NPs to earthworm and wheat;(3)difference of toxic effects between ZnO NPs and CeO2 NPs in different types of soil.Results:(1)Bioavailability of ZnO NPs increased with rising ZnO NPs concentration whereas the opposite is true for CeO2 NPs,which tended to transform into residual state.Content of Ce in earthworm and wheat increasd with rising CeO2 concentration,suggesting that BCR extraction is not completely applicable to assess the bioavailability of nanomaterials in soil.(2)Wheat root under ZnO NPs treatment accumulate zinc more easily in red soil and may lead to excess zinc accumulation.CeO2 NPs accumulation in wheat root is quite similar in red soil,yellow-brown soil and brown soil and increases as more contaminant is added.Ce content in wheat shoot and earthworm tissue is significantly higher than that in other types of soil,which may give rise to Ce accumulation across the food chain.(3)Toxic effects of ZnO NPs and CeO2 NPs vary in different types of soil.ZnO NPs and CeO2 NPs cause toxic effect to earthworm,induce significant disparity in anti-oxidant system,and increase MDA and PCO content.Toxicity of ZnO NPs and CeO2 NPs to earthworm in red soil is fairly low.In yellow-brown soil and brown soil,ZnO NPs and CeO2 NPs bring about toxic effect to wheat.lead to rise in MDA content,and inhibit SOD and CAT activity at high concentrations.Toxicity of ZnO NPs and CeO2 NPs to wheat in red soil is also very low.Therefore,metallic nano oxides show less toxicity and lower environmental risk when they enter into the red soil.As the concentration of ZnO NPs and CeO2 NPs increases,biomass of wheat in red soil was much lower than that in the other two types of soil,which can be attributed to nanomaterials’ effect on urease activity.(4)CeO2 NPs have similar toxic effect to organisms as ZnO NPs in different types of soil but exhibit lower toxicity.As can be seen from the above,ZnO NPs and CeO2 NPs enter into tissues of earthworm and wheat more easily in red soil but its toxic damage appears to be less than that in other types of soil(paddy soil,yellow-brown soil and brown soil).Toxic risks of ZnO NPs and CeO2 NPs in red soil are the least compared with other types of soil.Nevertheless,these nanomaterials may bioaccumulate across the food chain.ZnO NPs appear to be more toxic than CeO2 NPs to earthworm and wheat in the same type of soil.