Ecotoxicity Study Of Microplastics And Nanoparticles On The Soil Animal Eisenia Andrei

Polyvinyl chloride microplastics（PVC）and nanoparticles（La₂O₃NPs and Cd S NPs）continue to enter the soil environment as agricultural films and nanopesticides,causing ecological hazards.Studies on the effects of microplastics and nanoparticles on soil ecological functions are dominated by single contamination and less by combined contamination.In this paper,we have conducted a comprehensive study on the single and combined contamination of soil-earthworm system with polyvinyl chloride microplastics（PVC）and nanoparticles（La₂O₃NPs and Cd S NPs）as the research objects and Eisenia andrei as soil test animals,and the main findings are as follows.（1）Effect of microplastics on aging of nanoparticles in soil:The effect of PVC addition on speciation,bioavailability and bioaccessibility of La and Cd in single and combined contamination of La₂O₃NPs and Cd S NPs during aging was investigated by aging experiments.The results showed that aging increased the BCR₁-La and Cd（La 0.08%-3.36%,Cd 0.79%-3.65）,bioavailable La and Cd（La 11.84%-19.39%,Cd2.41%-16.04%）and bioaccessible La and Cd（La 66.66%-277.79%,Cd3.11%-165.06%）.The addition of PVC aging for 28 d increased the BCR₁-La（1.11%-2.42%）,BCR₂-La（0.77%-1.97%）,bioavailable La（1.87%-9.87%）and bioaccessible La（1.00%-86.19%）in the La₂O₃NPs single contaminated soil,and decreased the content of La₂O₃NPs and Cd S NPs combined contaminated soil;the addition of PVC aging for 28 d increased the content of bioavailable Cd（3.11%-165.06%）and decreased the content of BCR₁-Cd（0.53%-2.25%）,BCR₂-Cd（1.34%-1.46%）and bioavailable Cd（0.98%-8.74%）.（2）Effect of earthworm activity on microplastic and nanoparticle contaminated soil:The effects of earthworm activity on soil enzyme activity,speciation,bioavailability and bioaccessibility of La and Cd in microplastic and nanoparticle contaminated soil were investigated by earthworm exposure experiments.The results showed that earthworm activity significantly increased sucrase（9.66%-168.50%）,neutral phosphatase（6.06%-49.12%）,urease（6.92%-23.19%）and protease（6.90%-184.00%）activities in contaminated soils,while inhibited catalase activity（9.10%-42.34%）.The earthworm activity increased the mean values of GMean and T-SQI indexes of comprehensive evaluation of soil enzyme activity to 2.10 and 69.29,which increased by 11.14%and 13.59%,respectively,compared to the increase in the no-earthworm treatment group.Earthworm activity decreased the percentage of BCR₁（La 0.55%-9.00%,Cd 0.38%-14.45%）,BCR₂Cd（5.56%-9.64%）and increased the percentage of BCR₄Cd（1.44%-17.95%）in the soil nanoparticles.Earthworm activity reduced the bioavailable and bioaccessible content of La and Cd in contaminated soils to some extent,but the overall effect was not significant（p>0.05）.The results indicate that earthworm activity can reduce the content of BCR₁-La and Cd in soil nanoparticles,increase the content of BCR₄-Cd,reduce the activity of nanoparticles and mitigate the harm to soil ecological functions.（3）Effects of nanoparticles on the acute toxicity of earthworms:The effects of single contaminated soil with nanoparticles（La₂O₃NPs and Cd S NPs）on the avoidance behavior,escape behavior,morphological abnormalities and acute toxicity of earthworms were investigated by earthworm avoidance experiments and acute toxicity experiments.The results showed that the avoidance effect values of earthworms in La₂O₃NPs-contaminated soil were less than 80%,while the net avoidance effect values were greater than 80%when the concentration of Cd S NPs was higher than 6400 mg Cd/kg,and earthworms had obvious avoidance responses to them.The escape rate of earthworms in La₂O₃NPs contaminated soil at the same concentration level was lower than that of Cd S NPs.The morphological effects of La₂O₃NPs contaminated soil on earthworms were mainly manifested by atrophy,while Cd S NPs were mainly manifested by atrophy,the black body color and link fracture.In addition,the LC₅₀results obtained by fitting logistic functions showed that the LC₅₀of earthworms on La₂O₃NPs contaminated soil decreased abruptly from10670.33 mg La/kg（48h）to 1543.47 mg La/kg（14d）as the exposure time of earthworms in the two types of nanoparticles contaminated soil increased;the LC₅₀of earthworms on Cd S NPs contaminated soil decreased from 13667.48mg Cd/kg（24 h）to 753.08mg Cd/kg（14d）,and the toxicity of nanoparticles was enhanced.（4）Effects of microplastics and nanoparticles on earthworm growth and biomarkers response:The effects of microplastics（PVC）and nanoparticles（La₂O₃NPs and Cd S NPs）contaminated soil on earthworm growth and biomarkers response were investigated using earthworm exposure experiments.The results showed that microplastics and nanoparticles contaminated soil significantly inhibited earthworm growth,and the longer the exposure time and higher the concentration of pollutants,the greater the growth inhibition effect.Compared with the CK group,microplastic and nanoparticles stress decreased protein content,cellulase activity and Na⁺-K⁺-ATP activity in earthworms by up to 48.19%,74.71%and 92.03%;and increased MDA content（21.66%-411.80%）,SOD activity（49.52%-670.31%）and CAT activity in earthworms（0.05%-119.83%）,POD activity（25.48%-239.44%）,and ACh E activity（19.74%-180.32%）.The order of the magnitude of the integrated biomarker index values（IBRv2）index values was A<B<AC<C<AB<ABC<BC（A,B and C represent PVC,La₂O₃NPs and Cd S NPs single contaminated soil,respectively）,indicating that PVC and La₂O₃NPs were synergistic,PVC and Cd S NPs were antagonistic,La₂O₃NPs and Cd S NPs were synergistic;the higher the concentration of pollutants in the same pollution situation,the higher the IBRv2 index values,and the stronger the combined toxicity to earthworms.The order of IBRv2 magnitude at different exposure times was:IBRv2-7 d（29.39）<IBRv2-14 d（34.62）<IBRv2-21 d（35.14）<IBRv2-28 d（36.33）,indicating that the combined toxicity of microplastics（PVC）and nanoparticles（La₂O₃NPs and Cd S NPs）contaminated soil to earthworms gradually increased with increasing exposure time.In this paper,we studied the ecotoxicity study of polyvinyl chloride microplastics（PVC）and nanoparticles（La₂O₃NPs and Cd S NPs）contaminated soil to earthworms,elucidated the toxic effects of microplastics and nanoparticles on soil-earthworm system,and provided more basic and comprehensive data on the ecotoxicity of microplastics and nanoparticles.