聚乳酸塑料在淡水沉积物中的降解过程

Degradation process of polylactic acid plastics in freshwater sediments

为探究商用聚乳酸(PLA)可生物降解塑料在淡水沉积物中的降解过程,以主要成分为PLA的可生物降解塑料袋(PLAB)、塑料吸管(PLAS)以及塑料杯(PLAC)为研究对象,构建了室内沉积物实验体系,研究了3种塑料片表面性质的变化,分析了塑料片表面生物膜及微生物的响应.结果表明,180d后塑料片表面变得更加粗糙,其中PLAB表面出现大量不规则凸起、裂缝和孔洞并存在质量损失(7.30%),表现出最高的降解程度.同时,仅PLAB的红外光谱明显变化,其C=O与C-O等特征峰峰强增大,羰基指数升高13.65%;XPS光谱中PLAB和PLAS的O/C值升高了13.89%和5.17%,且3种塑料片的RO-C=O相对含量均降低,说明3种塑料都发生了降解.实验结束时,塑料片表面生物膜富集了PLA降解菌(假单胞菌属)以及可能驱动PLA降解的脱硫杆菌微生物.PLAB具有荧光强度最强的成熟生物膜且其表层沉积物生物膜生物量显著高于对照组(P<0.05).PLAB可能因其表面最为粗糙而促进了附着生物膜的形成及周围微生物的生长,同时PLAB含有水解速率更高的聚己二酯对苯二甲酸丁二醇酯(PBAT)组分,进而表现出最高的降解程度.此外,PLA塑料片的加入提高了表层沉积物的微生物多样性,改变了优势门类的相对丰度并可能影响元素循环.

In order to investigate the degradation process of commercial polylactic acid(PLA)plastics in freshwater sediments,a laboratory sediment system was established and the alternation in surface property,the attached biofilm and the microorganism communities on biodegradable plastic bag(PLAB),plastic straw(PLAS)and plastic cup(PLAC),with PLA as the main component,were identified.The results showed that the surface of plastics became rougher after 180days incubation in sediment,and PLAB with numerous protrusions,cracks and holes on the surface exhibited a mass loss(7.30%),showing the highest degree of degradation.Meanwhile,the infrared spectrum of PLAB changed significantly,with increased peak intensities of characteristic peaks such as C=O and C-O as well as a 13.65%increase in carbonyl index.The XPS spectra indicated that the O/C value of PLAB and PLAS were increased by 13.89%and 5.17%,respectively.The relative content of RO-C=O in the three plastics were reduced,indicating that all the studied plastics underwent degradation.At the end of the experiment,the surface of plastics was colonized by PLA degrading bacteria(Pseudomonas)and Desulfobacterota which may drive the degradation of PLA.PLAB had the strongest fluorescence intensity of mature biofilm,and its biofilm biomass in surface sediment was significantly higher than that of control(P<0.05).PLAB favored the formation of biofilm and the growth of the surrounding microbes,which may be attributed from its roughest surface.In addition,as components of PLAB,poly(butyleneadipate-co-terephthalate)(PBAT)displayed higher hydrolysis rate,which may be responsible for its most obvious degradation among the three plastics.Moreover,PLA plastics increased the microbial diversity in surface sediment and changed the relative abundance of dominant phyla,and may affect element cycles.