Study On The Toxic Effects Of Microplastics And Their Combined Pollution With Cadmium On Sweet Potato

Plastic products have been developed and produced in large quantities,but the recovery rate of waste plastics is not high,which leads to the gradual fragmentation of a large number of plastics in the environment into microplastics.Environmental microplastic pollution has become one of the hot issues in current research.The research on soil microplastic pollution and its harm to plants is still in its infancy.In this paper,the pollution of soil microplastics in some sweet potato(Ipomoeabatatas(Linn.)Lam)producing areas in China was investigated,and the effects of polyethylene microplastics and their artificial aging on soil physical and chemical properties,adsorption of heavy metal cadmium in soil,and toxic effects of combined pollution of microplastics and cadmium on sweet potato seedlings were studied.the results are as follows:Microplastics were extracted and analyzed from 30 main producing areas of sweet potato in China.It was found that microplastics existed in the soil of all sweet potato plantations,but the abundance of microplastics was significantly different in different places.The abundance of microplastics in the area with the highest amount of microplastics is nearly200000 items/kg,which is nearly 5 times that of the lowest region.The distribution law of microplastics shows two points: first,compared with the areas with low latitudes,the pollution of soil microplastics in high latitudes tends to be serious;second,the abundance of microplastics in the eastern region is generally higher than that in the central region.The microplastics in sweet potato planting land exist in the form of film,fragment,network and fiber,among which film and fragment microplastics are the main types of farmland microplastics,and the sum of them accounts for about 90%.According to the statistics based on the longest size of microplastics,it is found that 97.9% of the microplastics are less than1 mm,and the microplastics less than 100 μm account for 77.3%.It can be seen that the size of the microplastics in the sweet potato planting area is smaller and the degree of plastic fragmentation is high.After artificial aging,some 5 μm polyethylene microplastics were mixed into the soil to prepare 1%(10 g/kg)and 5%(50 g/kg)concentrations of microplastics and aged microplastic contaminated soil.The pot experiment showed that the contents of soil available phosphorus and available potassium decreased significantly after the addition of microplastics and aging microplastics.The biomass of sweet potato seedlings increased significantly,which was36.62% higher than that of the control group without microplastics.It is speculated that microplastics and aging microplastics bring adsorbed nutrient elements into sweet potato and promote the growth of sweet potato biomass.Although the determination of SOD,POD,GSH and MDA in sweet potato leaves showed that the addition of microplastics and aging microplastics caused damage to sweet potato,the absorption of nutrient elements by microplastics and aging microplastics was more beneficial to the growth of sweet potato.On this basis,the adsorption experiment found that although the contact area between microplastics or aging microplastics in solution and ions in aqueous solution was limited,microplastics and aging microplastics still showed obvious adsorption effect on phosphate and potassium ions in aqueous solution.the highest content of phosphorus and potassium in the solution can be reduced by 6.39% and 18.71%,respectively.After "Fucai 18" was cultured with 5 μ m fluorescent microplastic ball for 3 days,it was found that the microplastic ball entered the root and stem of sweet potato by fluorescence microscope and frozen scanning electron microscope.Generally speaking,in this study,the short-term treatment of microplastics and aging microplastics did not cause obvious toxicity to sweet potato seedlings.Compared with the effects of microplastics and aging microplastics on soil physical and chemical properties in non-cadmium contaminated soils,microplastics and aging microplastics did not change the p H and electrical conductivity of cadmium contaminated soils,and the adsorption rate of available potassium and available phosphorus decreased by about 30% in microplastics-cadmium composite treatment.The pot experiment showed that the content of cadmium in the tissues of vegetable sweet potato "Fucai 18" seedlings increased significantly with the addition of microplastics in cadmium contaminated soil,and the increase was positively correlated with the treatment concentration of microplastics and aging microplastics.in particular,the content of cadmium in sweet potato leaves exceeded the food limit after the addition of different concentrations of microplastics.At the same time,compared with the sweet potato cultured in single cadmium contaminated soil,the sweet potato biomass under combined pollution decreased significantly,and the sweet potato biomass decreased by 18.53% under 5% microplastic concentration.The contents of SOD,POD,GSH and MDA increased with the increase of the concentration of microplastics or aging microplastics in soil.The adsorption experiments in cadmium solution also show that microplastics and aging microplastics have obvious adsorption capacity for cadmium ions in solution,and the adsorption effect of microplastics for cadmium ions in solution is about 3times higher than that of aging microplastics.This study showed that in cadmium contaminated soil,microplastics had obvious effect on the adsorption and transfer of cadmium in soil.Microplastic pollution could aggravate the toxicity of cadmium in soil to sweet potato seedlings,increase the accumulation of Cadmium in sweet potato tissues,and increase the food safety risk of vegetable sweet potato.With the aging of microplastics,the adsorption,transfer and enrichment of Cadmium in plants will decrease.