合肥工业大学郭志：“可生物降解塑料”会是更好的选择吗？
2023-12-14 12:26阅读：
导读 | Introduction
无论您现在身处何处，请你环顾一下四周，您一定会找到至少一种塑料制品，这就是塑料的使用现状，毫不夸张的说，我们正处在一个塑料时代。人类对塑料制品的需求不断增加，导致全球塑料产量从1950年的150万吨增加到2021年的3.9亿吨。然而，大多数塑料产品回收率低，降解速度慢，导致它们在环境中不断积累，对生态环境构成了严重的威胁。
为了减少传统塑料对生态系统的影响，人们开发了各种可生物降解的塑料如聚乳酸（PLA）,
可降解塑料要完全降解最后变成二氧化碳和水，需要在50高温下。然而，自然环境难以达到降解必要的温度，如果PLA塑料袋被随意丢弃，在自然界中可能并不能真正被降解掉。如果达不到降解条件，“可降解塑料”和普通塑料基本无差别，也会变成塑料垃圾，对生态系统产生影响。
It is no exaggeration to say that we are in an age of
plastics. The increasing human demand for plastic products has led
to an increase in global plastic production from 1.5 million tons
in 1950 to 390 million tons in 2021. However, most plastic products
have low recycling rates and slow degradation rates, causing them
to accumulate in the environment, and pose a serious ecological
th
reat to the ecosystem. To reduce the impact of conventional
plastics on the ecosystem, various biodegradable plastics such as
polylactic acid (PLA) have been developed, and degradable plastics
need to be subjected to high temperatures of 50°C to be completely
degraded and finally turned into carbon dioxide and water. However,
it is difficult for the natural environment to reach the necessary
temperature for degradation, and if PLA plastic bags are casually
discarded, they will not be degraded in nature. If the degradation
conditions are not met, 'degradable plastics' and ordinary plastics
are no different, will also become plastic waste, and have an
impact on the ecosystem.
一、 实验设计 | Experimental design
本研究采用了三因素实验设计，其中包括两种不同类型的商用塑料（聚乙烯和聚乳酸）、三种剂量（以塑料/土壤干重计）以及三种类型的土壤，从而产生了
18 个不同的处理组，每个处理组有三个重复。薄膜碎片的大小和浓度是根据全面的文献综述确定的，以确保符合现实环境下的塑料污染情况。将约
1kg 的土壤和土壤/塑料混合体装于 18*20cm 的花盆中，保持盆中各种土壤含水率为各种土壤田间最大持水量的
60%。土壤微宇宙系统持续培养120天。
在实验期间，通过称量每个样本的重量来监测每天的失水量，并根据需要补充水分。为了更好地模拟自然环境，所有实验组在研究期间都放在室外，让它们接受自然光，但避免降雨。在添加塑料薄膜后的第二天对土壤进行取样，并在第
15、30、45、60、90 和 120
天进一步采集样本，每个容器中采集三个重复样本，以尽量减少土壤异质性造成的影响。对这些土壤样本进行直接分析，以确定其性质、微生物种群和代谢物水平，并用一个子样本确定土壤水分含量。
A three-factor experimental design was used, which included
two different types of commercial plastics (polyethylene and
polylactic acid), three doses (w/w), and three types of soil,
resulting in 18 different treatment groups with three replicates
per treatment group. The size and concentration of film fragments
were determined based on a comprehensive literature review to
ensure that they corresponded to plastic contamination in a
realistic environment. Approximately 1kg of soil and soil/plastic
mixtures were packed in 18*20cm pots, maintaining the water content
of the various soils in the pots at 60% of the maximum
water-holding capacity of the various soils in the field. The soil
microcosm system was incubated continuously for 120 days. During
the experiment, daily water loss was monitored by weighing each
sample and replenishing water as needed. To better mimic the
natural environment, all experimental groups were placed outdoors
during the study period to allow them to receive natural light but
avoid rainfall. Soil samples were taken the day after the addition
of plastic sheeting and further samples were taken on days 15, 30,
45, 60, 90, and 120, with three replicates in each container to
minimize the effects caused by soil heterogeneity. These soil
samples were directly analyzed for properties, microbial
populations, and metabolite levels, and a subsample was used to
determine soil moisture content.
二、土壤养分基质 | Soil nutrient substrate
对培养期间的土壤养分基质（氨态氮、速效磷、速效钾、土壤有机质）的变化进行了分析（图1）。在培养期间土壤的养分基质含量均发生了不同程度的变化，这种变化与土壤的类型，塑料类型及塑料的添加比例相关。从结果上看PLA显著降低了土壤中氨态氮、速效磷、速效钾的含量，但是增加了土壤中有机质的含量。而PE的添加在大多数情况下却没有显著改变土壤中养分基质的含量，这归因于PLA的可生物降解性，导致其能为土壤中的微生物提供潜在的碳源。
The changes in soil nutrient matrix (ammonia nitrogen,
available phosphorus, available potassium, soil organic matter)
during culture were analyzed (Figure 1). The nutrient matrix
content of soil changed in different degrees during culture, which
was related to the type of soil, the type of plastic, and the
proportion of plastic added. The results showed that PLA
significantly reduced the contents of ammonia nitrogen, available
phosphorus, and available potassium in the soil, but increased the
content of organic matter in soil. In most cases, the addition of
PE did not significantly change the content of the nutrient matrix
in the soil, which is attributed to the biodegradability of PLA,
which can provide a potential carbon source for soil
microorganisms.
三、微生物群落对塑料添加的响应
| Microbial community response to plastic
addition
Figure 2 shows the response of the microbiome to the addition
of plastics. Plastic exposure had a significant effect on the
dominant bacteria in the soil compared to the control (Figure 2A),
and the Sobs index also changed significantly, which was attributed
to the soil type, plastic type, and plastic addition dose. Notably,
the effect of PLA appears to be greater in wetland soils (Figure
2D).
四、土壤代谢对塑料添加的响应
| Soil metabolism in response to plastic
addition
土壤中存在的塑料可能直接或间接地与土壤微生物相互作用，进而影响土壤微生物群的代谢谱。PLS-DA 负载图（图
3A）表明，对照土壤和塑料暴露土壤是不同的，这表明土壤代谢物谱发生了重大变化。其中与C、N、P等营养基质相关的代谢物如脂肪酸、氨基酸、糖类等具有显著性变化（图3B-D）。
The presence of plastics in the soil may directly or
indirectly interact with soil microorganisms, which in turn affects
the metabolic profiles of the soil microbiota.PLS-DA loading maps
(Fig. 3A) showed that the control soil and the plastic-exposed soil
were different, which suggests significant changes in the soil
metabolite profiles. Among the metabolites related to nutrient
substrates such as C, N, and P such as fatty acids, amino acids,
and sugars had significant changes (Fig. 3B-D).
五、相关性分析 | Relevance analysis
为了验证土壤养分基质、酶活性，代谢产物与土壤中微生物群落的变化有关，对这些变量进行了RDA冗余分析和相互作用网络分析。结果表明塑料可作为土壤微生物的碳基质，从而会改变微生物群落的结构和活性进而影响土壤中微生物代谢产物。
In order to verify that soil nutrient substrates, enzyme
activities, and metabolites were related to changes in microbial
communities in the soil, RDA redundancy analysis and interaction
network analysis were performed on these variables. The results
showed that plastics can act as a carbon substrate for soil
microorganisms, and thus will change the structure and activity of
microbial communities and thus affect the microbial metabolites in
the soil.
总结 | Conclusions
通过室外环境土培实验，研究了现实情况下可生物降解塑料和不可生物降解塑料对土壤微环境的影响。结果表明，可生物降解塑料与不可生物降解塑料都会对土壤生态系统造成影响，值得注意的是，在某些情况下可生物降解塑料PLA的影响似乎更大。本研究结果为了解塑料对环境的影响以及随后的营养物质变化与微生物代谢行为之间的关系提供了宝贵的信息。
The effects of biodegradable and non-biodegradable plastics
on the soil microenvironment were investigated through an outdoor
environmental soil cultivation experiment. The results showed that
both biodegradable and non-biodegradable plastics affect soil
ecosystems, notably in some cases the impact of the biodegradable
plastic PLA seems to be greater. The results of this study provide
valuable information for understanding the impact of plastics on
the environment and the subsequent relationship between nutrient
changes and microbial metabolic behavior.
