We investigated the carbonyl index (CI) of small microplastics (SMPs; 50–350 μm) and large microplastics (LMPs; >350 μm) in the surface waters of the Tokai region and Tokyo Bay in Japan. The degradation was evaluated by determining the CI from the infrared spectrum of microplastics (MPs) adopting the specified area under the band technique. Average CIs of SMPs and LMPs in polyethylene were 2.47 and 0.67 off Tokai and 2.71 and 0.76 in Tokyo Bay, respectively. No significant differences in the CI were found between polyethylene and polypropylene. However, significant differences in CIs were found between SMPs and LMPs. The relationship between the major length of MPs and CI was significantly negative for both polyethylene and polypropylene (p < 0.05). The results indicate that as MPs degrade, they become finer and exhibit a higher CI at the sea surface.

中文翻译：

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海面小型化微塑料的羰基指数


我们研究了日本东海地区和东京湾表层水中小微塑料 （SMPs;50-350 μm） 和大微塑料 （LMP;>350 μm） 的羰基指数 （CI）。通过采用波段技术下指定区域的微塑料 （MP） 的红外光谱确定 CI 来评估降解。聚乙烯中 SMP 和 LMP 的平均 CI 分别为 Tokai 的 2.47 和 0.67，东京湾的 2.71 和 0.76。聚乙烯和聚丙烯之间的 CI 没有显着差异。然而，在 SMPs 和 LMPs 之间发现 CI 存在显著差异。聚乙烯和聚丙烯的 MPs 主要长度与 CI 之间的关系均呈显著负 （p < 0.05）。结果表明，随着 MP 降解，它们会变得更细，并在海面表现出更高的 CI。