Effects Of Polystyrene Micro-/nano-plastics On Accumulation And Toxicity Of PAHs In Soil-animal/Plant Systems

Micro-and nano-plastics(MNPs)are recognized as a class of emerging and ubiquitous contaminants in soil,which influence the behavior of pollutants and have potential adverse impacts on organisms.So far,the mechanism of the cumulative effect of different concentrations of MNPs on organic pollutants in terrestrial invertebrates is still unclear.This study explored the potential mechanisms of polystyrene microplastics(MPs,10 μm)and nanoplastics(NPs,100 nm)with different concentrations(10 and100 mg/kg)in soil on the accumulation and toxicity of pyrene in earthworms,Eisenia fetida.The results showed that MPs facilitated the accumulation of pyrene by earthworms in the first week via injuring the integrity of earthworm intestine.The representative antioxidant enzyme activities indicated that MPs induced severer oxidative stress to earthworms than NPs,especially at the concentration of 100 mg/kg,thus leading to increased accumulation of pyrene by earthworms at the initial stage.In addition,high-throughput 16 S rRNA gene sequencing demonstrated that NPs inhibited the pyrene-degrading bacteria in earthworms,resulting in the higher concentration of pyrene in the end.The results elucidated the effects of MNPs with different concentrations on the accumulation of organic pollutants in the terrestrial invertebrates.On the basis of different concentrations of MNPs,the effects of different particle sizes of PS-MNPs on Phenanthrene(Phe)accumulation and toxicity in earthworms were also studied.Results showed that larger-size MPs(10 and 100 μm)facilitated the accumulation of Phe by earthworms in the first week,whereas 100 nm NPs inhibited the elimination of Phe in earthworms afterwards.Higher genotoxicity to earthworms was observed for co-exposure of MPs and Phe,and 10 μm MPs were detected at the highest concentration caused the most serious DNA damage to earthworm coelomocytes.Biomarkers and their m RNA gene expression levels suggested that larger-size MPs caused severer damage to earthworms,thus leading to increased accumulation of Phe by earthworms at the beginning.Moreover,high-throughput 16S rRNA gene sequencing indicated that NPs significantly inhibited Phe-degrading bacteria in earthworms,resulting in the highest residual concentration of Phe.This study highlights the size effects of MNPs and their impacts on the accumulation of organic pollutants by terrestrial organisms.MNPs can not only affect the accumulation and toxicity of organic pollutants in terrestrial invertebrates,but also adversely affect soil plants.However,there are relatively few studies on the effects and toxicity of MNPs on the absorption of organic pollutants by edible higher plants.Here we investigated the impacts and mechanisms of MNPs of different concentrations and sizes on the uptake and toxicity of pyrene in water spinach.The results showed that MNPs had a promotion effect on the uptake of pyrene in various parts of water spinach,leading to the continuous accumulation of pyrene.The promotion effect of high concentration MPs is stronger than that of NPs.The co-exposure of MNPs and pyrene increased the contents of MDA in water spinach and aggravated the damage of lipid peroxidation.The co-exposure to MNPs and pyrene induced the increase of photosynthetic pigment contents and enhanced chloroplast activity.In addition,the co-exposure stimulated the overexpression of psb A and rbc L genes,and caused genotoxicity to water spinach.This study emphasized that the coexposure of MNPs and pyrene caused harmful effects and high concentration of MPs caused greater toxicity to water spinach than NPs.On this basis,the impacts and mechanisms of polystyrene MNPs of different sizes on the uptake of Phe by soybean seedlings were investigated.The results showed that MNPs decreased the uptake of Phe in soybean roots and leaves.MPs showed a higher inhibition of Phe uptake in roots than NPs(4.83 mg/kg)at the beginning with concentrations of 1.89 mg/kg,3.40 mg/kg,and 0.72 mg/kg in groups 1 μm,10μm,and100 μm MPs/Phe,respectively.The combined toxicity of MPs and Phe to soybean plants was higher than that of NPs and Phe,and 100 μm MPs and Phe co-contaminant show the highest toxicity to soybean.The activities of antioxidative enzymes and their gene expression showed that MPs induced higher genotoxic and oxidative damage to soybean roots than NPs,which decreased the activity of roots,thus leading to the lower uptake of Phe by soybean roots and leaves.This study highlights that the combined exposure to MNPs and Phe causes harmful effects on soybean plants and MNPs inhibit the uptake of organic pollutants by higher plants.In this study,the accumulation and toxicity of MNPs in soil medium to PAHs in soil-animal/plant system were studied from different aspects,such as biochemistry,histomorphology and molecules,it provides a theoretical basis for the environmental impact and related mechanism of MNPs and PAHs co-exposure,and has important significance for food safety evaluation and human health risk research.