Effects Of Soil Application Of ZnO NPs On The Physiological Toxicity Of Earthworms And The Growth Of Cucumber Seedlings

Zinc oxide nanoparticles(ZnO NPs)are widely used in various industries owing to their unique physical and chemical properties.While they have tremendous benefits,they also carry potential risks,such as cytotoxicity and genotoxicity and so on.In the soil environment,ZnO NPs may pose a severe threat to organisms in terrestrial ecosystems.Therefore,in the present study,pot experiments were used to evaluated the effects of different concentrations of ZnO NPs and different types of zinc sources(ZnO NPs,ZnO and Zn SO₄·7H₂O at the experimental concentration of 50 mg kg^-1)on earthworm physiology and cucumber seedling growth under the diverse culture systems.In the subchronic toxicity test of the earthworm,five different concentration gradients of ZnO NPs were set:0,50,250,500,1000 mg kg^-1.And in the earthworm-cucumber seedling system,four different concentration gradients of ZnO NPs were set:0,50,500 and 1000 mg kg^-1.The effects of ZnO NPs on soil system were determined by studying the survival rate and DNA damage of earthworms,the biomass and root activity of cucumber seedlings,as well as their antioxidant capacity and tissue zinc content.We hope to provide a scientific basis for evaluating the effects of ZnO NPs as a new fertilizer on crop growth and animal safety in soil environment.The main research results are as follows:1.In the subchronic toxicity test of the earthworm,the survival rate was greater than87.5%,and there was no significant difference between the groups treated with different concentrations of ZnO NPs.In each treatment,the protein content of earthworms was significantly higher than that of the control group.In terms of antioxidant capacity,ROS level,MDA content and antioxidant enzyme activity all showed a trend of increasing first and then decreasing,but the critical concentration varied greatly,indicating that each index had different responsiveness to oxidative damage.Regarding the genotoxicity of ZnO NPs,when the concentration was more than 250 mg kg^-1,the content of 8-OHd G was significantly increased by 65.0%compared with the control and DNA damage was serious,indicating that ZnO NPs had genotoxicity.For cucumber seedlings,ZnO NPs treatment exacerbated plant oxidative stress.Except that SOD was inhibited at 1 000 mg kg^-1,the activities of SOD,CAT,POD and the content of MDA all increased with the increase of the ZnO NPs concentration.From the perspective of seedling growth parameters,with 500 mg kg^-1 as the critical concentration,ZnO NPs showed a trend of promoting the seedling growth at low concentration and inhibiting at high concentration.2.In the earthworm-cucumber seedlings culture system,earthworm physiology and cucumber seedlings growth were affected by the interaction between plants and animals.For earthworms,MDA content increased significantly under 1000 mg kg^-1 ZnO NPs treatment,which increased by 19.2%compared with the control,while there was no significant change in antioxidant enzymes.From the growth and development of seedlings,the addition of earthworms could significantly promote seedling growth,including increasing biomass and improving root activity.Simultaneously,earthworms could inhibit or alleviate the damage caused by ZnO NPs to plants to a certain extent,especially in 500 and 1000 mg kg^-1 treatments.In terms of zinc content,the earthworm could regulate the zinc effectively and keep it at a relatively stable level.However,with the implantation of seedlings,the zinc content in earthworms increased significantly,from 125?130 mg kg^-1 in single culture to 200?215 mg kg^-1.As for cucumber seedlings,zinc content increased with the increase of the treatment concentration.In contrast,the treatment combined with earthworms reduced the plants?zinc content,reflecting the regulation and alleviation of cucumber seedlings growth under stress conditions by earthworms.3.Compared with three different types of zinc sources,we found that ZnO NPs had the least effect on the contents of antioxidant enzymes and MDA of earthworms,and could promote the synthesis of protein in earthworms.Regarding the content of zinc in the tissues,the absorption of zinc by earthworms was independent of the type of zinc source and maintained at the level of 200?215 mg kg^-1.However,for cucumber plants,ZnO NPs was better than that of ZnO and Zn SO₄.After the introduction of earthworms,the growth and development trend of cucumber seedlings changed.In terms of biomass and root activity,the effect of earthworms and Zn SO₄ treatment was better.However,from the perspective of antioxidant capacity,the interaction between earthworms and common ZnO was more able to resist the oxidative damage of the plants.The results of IBR analysis showed that in a multi-species system dominated by earthworm and cucumber seedlings,ZnO NPs had less effect on the two than ZnO and Zn SO₄.It shows that in actual production activities,ZnO NPs is a safe and efficient zinc fertilizer.The above results indicated that the effects of ZnO NPs on plants and animals were different in different culture systems.In the multi-species culture system,the environmental impact was closer to the ecological effects in the natural environment.In general,we believe that in alkaline soil,as a new type of fertilizer,ZnO NPs can significantly promote the growth of cucumber seedlings with appropriate and reasonable application,and will not cause significant effects on earthworms.It indicates that ZnO NPs has biological safety in agricultural production and application.