| With the development of nanotechnology,nanomaterials have been widely used in medical imaging,biomedicine,printing,dyeing textiles,engineering,nanocomposites production,bioremediation,aerospace and military industries.In the past two decades,the amount of nanomaterials and nanoproducts used has increased from several kilograms to tens of thousands of tons.In the process of production,transportation,consuming and abandonment of nanomaterials,some nanoparticles will inevitably enter the ecosystem and the environment.Eco-environmental effects of nanoparticles have become a research hotspot in the field of environment,and attracted extensive attention of scholars throughout the world.Plants are the producers of ecosystems and the starting point of biological accumulation,and during the growth process,plants will directly contact with water,atmosphere,soil and other environmental media and thus contact with nanoparticles and other related substances in the environmental media.Further,plants will absorb these nanoparticles through bio-accumulation and then transport to a higher trophic level even the human body through the food chain and thus cause health risks to human.Nano-PbO2 has many typical characteristics,such as strong corrosion resistance,high oxygen evolution potential in aqueous solution,high current density,high catalytic activity,high hardness and low cost.Since the 1930s,lead dioxide acting as an alternative anode material has been widely used in industrial production.In addition,PbO2 is also a common by-product in drinking water distribution system because of the chlorination disinfection,but the potential ecological risk of nano-PbO2 is rarely reported.Based on the discovery that PbO2 nanoparticles exist in the sediments of water supply pipelines,the formation mechanism of nano-PbO2 in water distribution system was simulated by chemical synthesis.At the same time,PbO2 nanoparticles with high purity were synthesized by hydrolysis synthesis method and taking the plant effect of nanoparticles as the starting point,the present study aims at using the hydroponic experiments to(1)study the effects of nano-PbO2 on seed germination and seedling growth of Zea mays L.;(2)reveal the toxic effects of nano-PbO2 on Zea mays L.and the corresponding toxic mechanism;(3)explore the absorption and transportation of nano-PbO2 within the Zea mays L.body;(4)elucidate the possible pathways of nano-PbO2 entering the plant and the rules related to nano-PbO2 distributing and accumulating in the plant and(5)illustrate the law of toxicological effects of nano-PbO2 on higher plants as well as the principle and mechanism of corresponding toxicological effects.In this study,?-PbO2 nanoparticles were synthesized by hydrolysis.By means of XRD,XPS,SEM,EDS and other technical means,the average physical size of nano-PbO2 was 10 nm,the purity was more than 99.99%,and the specific surface area was 28.65 m2/g.The study of sediment in drinking water pipeline showed that nano-scale PbO,PbO2 and elemental lead existed in drinking water pipelines and drinking water distribution system.Lead dioxide is a high valence oxide of lead.Although it is more stable than PbO,it will release a large number of lead ions once the water quality or environment changes,which will reduce the quality of water and cause the healthy risk of humans exposed to lead.The results of hydroponic experiments on maize exposed to synthetic nano-PbO2 showed that concentration of nano-PbO2 below 30 mg/L promoted the germination of maize seeds,while concentration higher than this value inhibited the germination.At the same time,concentration of nano-PbO2 above 30 mg/L also inhibited the root elongation of maize seeds and caused root morphological abnormalities,reduction of aerial parts biomass,leaf yellowing and dry-up.The 17-day exposure experiment of maize seedlings showed that the lead content in maize seedlings treated with nano-PbO2 was significantly higher than that in the control group and the group treated with 1mg/L lead ion.The estimation of the maximum lead ion released from the suspension of nano-PbO2 and accumulated in plant body showed that the lead transport in maize was mainly driven by nano-PbO2,but its cumulative amount did not increase with the increase of the exposure concentration of nano-PbO2.The lead content in maize seedlings treated with more than 30 mg/L of nano-PbO2 was lower than that of maize seedlings treated with other concentrations.However,the migration coefficient of lead decreased with the increase of the concentration of nano-PbO2.This is mainly related to the fact that the plant cell membrane can only penetrate the particles below 10 nanometers,while the high concentration of nanoparticle suspension is easy to aggregate,which makes the particle size increase rapidly and it is difficult to penetrate the cell membrane.Meanwhile,5-50 mg/L of nano-PbO2 inhibited the absorption of potassium,calcium,magnesium,iron,zinc and manganese by maize seedlings,and the content of these nutrient elements in maize seedlings decreased with the increase of the concentration of nano-PbO2.This partially explained why the growth of maize seedlings showed changes in root morphology,leaf withering and yellowing,and leaf edge curling.In addition,for the blank control group and the group treated with lmg/L lead ion,the absorption and transportation of lead and nutrient elements in maize seedlings showed consistency,but there was signifi cant difference between these two treatment groups and the experimental groups treated with 5-50mg/L nano-PbO2.Therefore,under this experimental condition,the absorption and transport of lead in maize seedlings were mainly affected by nanoparticles rather than ions released by nanoparticles. |
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