可降解塑料对淡水沉积物的长期影响研究

Long Term Effect of Degradable Plastic on Freshwater Sediment

微塑料对环境的影响是目前环境研究的热点之一,可降解塑料必将取代大部分传统塑料,但是其自然降解过程对淡水沉积物的影响,目前鲜有报道。该研究在室内构建水柱反应器模拟淡水湖泊环境,考察不同时间段(90 d和365 d)内,聚乳酸(PLA)和聚己二酸/对苯二甲酸丁二醇酯(PBAT)2种常用的可降解塑料对沉积物的影响。理化指标分析表明,2种可降解塑料在短期内(90 d)明显提高了间隙水总有机碳(TOC)和总氮(TN)含量(P<0.05)。PLA和PBAT在长时间段内(365 d)对细菌群落的α多样性有显著促进作用,并且促进了变形菌门相对丰度的提高。PLA和PBAT在90 d时间段内,反硝化功能基因nirS数量分别为(2.33±0.33)×10^(8) copies/g沉积物和(2.16±0.09)×10^(8) copies/g沉积物,反硝化功能基因nirK基因数量分别为(1.24±0.18)×10^(7) copies/g沉积物和(1.37±0.23)×10^(7) copies/g沉积物,显著高于对照组(P<0.05)。然而在365 d时间内,可降解塑料的nirS和nirK基因以及厌氧氨氧化微生物的数量均显著低于对照组(P<0.05),且PBAT组数量明显低于PLA组。冗余分析发现反硝化nirS和nirK基因的数量与氨氮、TN和TOC呈正相关,与总磷呈负相关,厌氧氨氧化微生物与环境因子的相关性则与反硝化基因完全相反。该研究的结果初步揭示了不同可降解塑料在不同时间段内对沉积物的影响,对于进一步探究可生物降解塑料的环境效应及其影响机制具有重要作用。

The effect of microplastics on the environment is currently one of the hotspots in environmental research.Biodegradable plastics will inevitably replace most of the traditional plastics.However,there are few reports on the effect of their natural degradation process on freshwater sediment.This study constructed a water column reactor indoors to simulate the environment of shallow freshwater lake,and investigated the effects of two commonly used biodegradable plastics,PLA and PBAT,on sediment at different time periods(90 and 365 days).The analysis of physicochemical parameters showed that the two degradable plastics significantly increased the total organic carbon(TOC)and total nitrogen(TN)concentrations of interstitial water in the short term(90 days)(P<0.05).PLA and PBAT significantly promoted theαdiversity of bacterial communities over a long period of time(365 days)and increased the relative abundance of Proteobacteria.The number of denitrifying nirS genes in PLA and PBAT during the 90-day period was(2.33±0.33)×10^(8)copies/g sediment and(2.16±0.09)×10^(8)copies/g sediment respectively and the number of denitrifying nirK gene was(1.24±0.18)×10^(7)copies/g sediment and(1.37±0.23)×10^(7)copies/g sediment respectively,both of them were significantly higher than the control group(P<0.05).However,within 365 days,the number of nirS and nirK genes and anammox bacteria in degradable plastic groups were all significantly lower than the control group(P<0.05).Besides,the number these two kinds of bacteria in PBAT group was significantly lower than those of PLA group.Redundancy analysis revealed that the number of nirS and nirK genes was positively correlated with NH_(4)^(+)-N,TN,and TOC,and negatively correlated with total phosphorus.The correlation between anammox bacteria and environmental factors was completely opposite to that of denitrifying genes.This study preliminarily investigates the effects of different biodegradable plastics on sediment at different time periods,which may play an important role in further understanding the environmental effects and effect mechanisms of biodegradable plastics.