In recent years, biodegradable polymers have been hailed as one of the potential solutions to the plastic pollution problem, due to their ability to fully degrade rather than break down in smaller pieces over time. However, complete degradation of biodegradable polymers is often achievable only under strictly controlled conditions (i.e. increased temperature and pressure), which are not found in the natural environment – particularly in aquatic and marine habitats. This study aims to compare the degradation performance of plastic films made of two different biodegradable polymers – polylactic acid (PLA) and polyhydroxyalkanoates (PHA) – to that of low-density polyethylene (LDPE) films, in a simulated marine environment. Plastic films of the three chosen polymers, of equal dimensions, were exposed to natural sunlight within a novel setup - which simulated the sea surface - for six months. Films were chosen as they are among the most frequently reported type of plastic litter in coastal environments worldwide, and because of the increasing adoption on the market of biodegradable films for packaging. Results showed that, after six months, no consistent degradation could be observed on any of the films – not even the biodegradable ones. Between PLA and PHA films, the latter weathered slightly more than the former, but not at a significant level. Interestingly, differences were reported among the different polymer films in terms of type and extent of biofouling, brittleness, surface charge and surface microstructural changes. Overall, this work suggests that biodegradable plastic behaves rather similarly to traditional plastic in the marine environment over a half-year span. Albeit further experiments on even longer timescales are needed, this study provides evidence that, unless properly disposed of in an industrial composter facility, biodegradable plastic may only contribute to the very problem it was intended to solve.

中文翻译：

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不仅钻石是永恒的：模拟海洋环境中塑料薄膜的降解

近年来，可生物降解聚合物被誉为塑料污染问题的潜在解决方案之一，因为它们能够随着时间的推移完全降解而不是分解成更小的碎片。然而，可生物降解聚合物的完全降解通常只能在严格控制的条件下（即升高的温度和压力）才能实现，这在自然环境中是不存在的，尤其是在水生和海洋栖息地。本研究旨在比较由两种不同的可生物降解聚合物——聚乳酸 (PLA) 和聚羟基链烷酸酯 (PHA) 制成的塑料薄膜与低密度聚乙烯 (LDPE) 薄膜在模拟海洋环境中的降解性能。三种所选聚合物的塑料薄膜，尺寸相同，在模拟海面的新颖设置中暴露在自然阳光下六个月。之所以选择薄膜，是因为它们是全球沿海环境中最常报告的塑料垃圾类型之一，而且市场上越来越多地采用可生物降解的包装薄膜。结果表明，六个月后，在任何薄膜上都没有观察到一致的降解——甚至是可生物降解的薄膜。在PLA和PHA薄膜之间，后者的风化程度略高于前者，但不显着。有趣的是，不同聚合物薄膜在生物污垢的类型和程度、脆性、表面电荷和表面微观结构变化方面存在差异。全面的，这项工作表明，在半年的时间里，可生物降解塑料在海洋环境中的表现与传统塑料非常相似。尽管需要更长时间的进一步实验，但这项研究提供的证据表明，除非在工业堆肥设施中妥善处理，否则可生物降解的塑料可能只会助长它旨在解决的问题。