Basic Study On Separation And Environmental Degradation Characteristics Of Plastic Film Microplastics In Soil

According to the national conditions,the main direction of degradation plastics in China is still the film.Under the comprehensive environment of light,temperature,water,gas and biology,the degradation of polyethylene film can be greatly accelerated,such as degradation of polyethylene film quality,mechanical properties decline or partial biological phagocytosis.Based on the controlled planting-large root cellar experimental equipment（hereinafter referred to as root cellar）,natural organic composting experimental device（hereinafter referred to as composting experimental device）,the screening,characterization and degradation law of polyethylene micro plastics of plastic film residues in different types of soil（sand soil,clay and loam soil）were carried out through planting two crops for 10 years and every year The degradation of polyethylene micro plastics under long-term natural conditions and its influence on soil ecosystem were analyzed,and the accumulation,degradation and ecological environment effects of micro plastics in soil were revealed.The main results are as follows:（1）Degradation characteristics of polyethylene microplastics in soil.The extraction of plastic film from different soil with different molecular weights and cumulants was studied.It was found that after 10 years of cultivation,the average extraction rate of plastic film was 5.55%,which was 58.8%lower than that planted in five years,and decreased by 83.59%compared with that in three years.Combined with high temperature gel chromatography,it was found that the Mwof M3,M4 and M7 had a greater degree.The weight average molecular weight of the plastic in m3 was 46.8%lower than that of 10 years ago,55.46%lower than that of 10years ago,and 76.76%in M4.FT-IR results showed that a new C-O absorption peak appeared at 1300～1100 cm^-1 for the extracted 5000 molecular weight plastic.Compared with the original sample,the infrared spectra of LLDPE extracted from soil showed a new absorption peak at 1000-800 cm^-1,and the extracted LLDPE was 2919.55 cm^-1,2849.61 cm^-1,1462.96cm^-1 The area of absorption peak increased at cm^-1.（2）Degradation characteristics of plastic film residue under natural organic matter composting.After 10 years of natural organic matter stacking,the extraction rate of light/thermal degradation mulch film was 19.32%～28.60%,and the extraction rate of common plastic mulch residue was between 21.62%～44.65%.The results of high temperature gel chromatography showed that after ten years of natural composting,the average molecular weight Mw of residual weight of light/thermal degradation film in 1,50 and 100 years decreased by 94679.33,93510.00 and 69443.67 respectively.The dispersion coefficient increased from 3.71 to 71.77,61.53,75.73,while the weight average molecular weight（Mw）of the common plastic film residues accumulated in 1 year,50 years and 100 years decreased by 71569.00,61033.33,65358.67,and the dispersion coefficient increased from 3.68 to 83.06,103.68,96.78,respectively The analysis of Tcand Tm in the residue treatment group showed that the plastic film residue with less accumulation showed higher Tc and lower Tm,and the ordinary plastic film residue treatment group also showed the same rule.Moreover,the analysis of the same accumulation of light/thermal degradation plastic film residue and ordinary plastic film residue showed that the light/thermal degradation plastic film residue was the best The melting peak area of film residue is smaller than that of common film residue.FT-IR results showed that after ten years of natural composting,new carbonyl peaks appeared in both light/thermal degradable film powder and common film powder,and the carbonyl peak index increased with the addition of light/thermal degradable masterbatch.（3）Effect of residual plastic film on soil enzyme activity.The highest urease activity of treatment 9 was 0.22 mg/g·h,and the lowest activity of treatment 4 was 0.15 mg/g·h The p value of soil type,soil depth,molecular weight of plastic film and accumulation of plastic film on soil urease activity was less than 0.05.The influence of various factors on soil urease activity was as follows:soil type>accumulation of plastic film>molecular weight of plastic film>soil depth;treatment 7 had the lowest sugarcane enzyme activity,and its activity was17.42.The highest activity of sucrase was 25.68 mg/g·h The p value of soil type,soil depth,molecular weight of plastic film and accumulation of plastic film on soil sucrase activity was less than 0.01.The influence of various factors on soil sucrase activity was as follows:soil type>accumulation of plastic film>soil depth>molecular weight of plastic film;treatment5 had the highest phosphatase activity,which was 0.0475 The activity of treatment 7 was the lowest（0.0314 mg/g·h）Under the influence of soil type,the p value of soil phosphatase activity was less than 0.01,and the p value of soil phosphatase activity under the influence of soil depth,molecular weight of plastic film and accumulation of plastic film was more than0.05.The influence of various factors on soil phosphatase activity was as follows:soil type>soil depth>accumulation of plastic film>molecular weight of plastic film.（4）Effect of residual plastic film on Maize Growth.The results showed that the range of plant height caused by molecular weight and accumulation of plastic film was 11.23,18.39,6.66and 10.07 at panicle stage and anthesis and grain stage,respectively;the range of leaf length caused by molecular weight and accumulation of plastic film was 12.92,15.79,12.42 and14.98 at two stages,respectively;the range of transpiration rate（Tr）caused by molecular weight and accumulation of plastic film was 0.15 The differences of photosynthetic rate（A）caused by molecular weight and accumulation of plastic film in two periods were 3.57,4.37,2.14 and 1.82 respectively;the differences of stomatal conductance（Gs）caused by molecular weight and accumulation of plastic film in two periods were 0.08,0.08,0.07 and 0.06respectively;the differences of intercellular carbon dioxide concentration（Ci）caused by plastic film in two periods were 0.05,0.33,1.28 and 0.58 respectively The range of chlorophyll content（a+b）was 0.02,0.12,0.11,0.18 in two periods,and the range of initial fluorescence Fo in photosystem PSⅡwas 30.84,233.63317.66,196.81 in two periods;The maximum fluorescence Fm was 2181.72,797.31,965.11 and 372.34 respectively,the maximum photochemical efficiency Fv/Fm was 0.02,0.01,0.005 and 0.007 respectively,and the potential activity Fv/Fo was 0.02,0.01,0.005 and 0.007 respectively The results showed that the range of DIo/R_C was 0.29,0.23,0.14 and 0.03 respectively;the range of DIo/R_C caused by the molecular weight and accumulation of plastic film in the two periods was 0.08,0.06,0.19 and 0.23 respectively;the range of TRo/R_C caused by the molecular weight and accumulation of plastic film in the two periods was 0.06,0.07,0.08 and 0.04 respectively The energy ET_O/R_C captured by the reaction center for electron transfer in the two periods was0.06,0.06,0.04 and 0.12,respectively;the photosynthetic index piabs in the two periods was0.53,0.81,0.79 and 0.63,respectively;the 100 grain weight of maize was 0.53,0.81,0.79 and0.63,respectively The range is 0.52 and 0.43 respectively.