Department of Earth Sciences, The University of Hong Kong, Pokfulam, Hong Kong; The Swire Institute of Marine Science, The University of Hong Kong, Pokfulam, Hong Kong.
Sci Total Environ. 2024 Aug 15;938:173397. doi: 10.1016/j.scitotenv.2024.173397. Epub 2024 May 24.
Bioplastics are increasingly used as a solution to tackle plastic pollution problems. However, their degradability in natural environments is currently under debate. To evaluate their degradation efficiencies, we conducted in-situ degradation experiments in an open-air and two marine environments in Hong Kong. Three groups of biodegradable plastic were tested, namely (1) additive-modified low-density polyethylene (LDPE), labelled as oxo-biodegradable or photodegradable plastics, (2) polylactic acid (PLA), and (3) polyvinyl alcohol (PVA)/starch blends. Most biodegradable plastics fail to completely degrade but remain visually present after six months of exposure. Only PLA is able to demonstrate 100 % disintegration in one to three months in marine settings, suggesting that subtropical marine environments may favor PLA degradation. Biodegradable plastics that are bio-based (PLA and PVA/Starch blends) show notably larger mass losses by 23-100 % than the fossil-based ones (modified-LDPE). Our results reveal higher degradation efficiencies of PLA and PVA/Cassava starch blend in marine than open-air settings (with mass losses larger by 50 %, and by 39-41 %, respectively), potentially via biodegradation and hydrolysis. Meanwhile, modified-LDPE and PVA/Corn starch blends in general show higher degradation efficiencies in open-air than marine settings (with mass losses larger by 2 %, and by 17-33 %, respectively), potentially via abiotic oxidation. Since all tested biodegradable plastics exhibit potential fragmentation signs, further investigation is needed to characterize the behaviours of the microplastics generated. The current labelling on biodegradable bags fails to provide comprehensive information regarding their actual environmental degradation behaviours, especially considering their fragmentation risk and limited degradation exhibited in this study. This highlights the imperative for improved messaging to ensure consumers are better informed about these products.
生物塑料作为解决塑料污染问题的一种解决方案，其应用日益广泛。然而，它们在自然环境中的降解性目前仍存在争议。为了评估它们的降解效率，我们在香港的一个露天和两个海洋环境中进行了原位降解实验。我们测试了三组可生物降解塑料，分别是：（1）添加改性低密度聚乙烯（LDPE），标记为可氧化或光降解塑料；（2）聚乳酸（PLA）；（3）聚乙烯醇（PVA）/淀粉共混物。大多数可生物降解塑料在暴露六个月后仍未能完全降解，仍可见到残留物。只有 PLA 能够在一到三个月内在海洋环境中完全分解，这表明亚热带海洋环境可能有利于 PLA 的降解。生物基的可生物降解塑料（PLA 和 PVA/淀粉共混物）的质量损失明显大于化石基的（改性 LDPE），达到 23-100%。我们的结果表明，PLA 和 PVA/木薯淀粉共混物在海洋环境中的降解效率高于露天环境（质量损失分别大 50%和 39-41%），这可能是通过生物降解和水解作用实现的。同时，改性 LDPE 和 PVA/玉米淀粉共混物在露天环境中的降解效率一般高于海洋环境（质量损失分别大 2%和 17-33%），这可能是通过非生物氧化作用实现的。由于所有测试的可生物降解塑料都表现出潜在的碎片化迹象，因此需要进一步研究来表征产生的微塑料的行为。目前可生物降解袋上的标签未能提供有关其实际环境降解行为的全面信息，尤其是考虑到它们在本研究中表现出的碎片化风险和有限的降解性。这凸显了改进信息传递的必要性，以确保消费者更好地了解这些产品。
