Context: A significant amount of conventional plastics waste, especially in the form of microplastics (MPs), has accumulated in soils due to its limited degradation. Oxo-degradable and biodegradable plastics have also contributed to MP contamination in soils.

Aims: In this study, we examined the degradation of a conventional plastic [fruit and vegetable (F&V) bag], two biodegradable plastics (bin liner and mulch film) and an oxo-degradable plastic (drinking straw).

Methods: These plastics (5 mm) were mixed into a soil and incubated in the laboratory at 37 ± 1°C for 185 days. The CO₂-carbon (C) mineralisation of the four plastics was determined using a δ¹³C technique, because the difference in the δ¹³C values of studied plastics and the experimental soil was ≥10‰.

Key results: Bin liner showed the greatest C mineralisation (5.7%), followed by mulch film (4.1%), straw (0.4%) and F&V bag (0.3%) at the end of the incubation period. All plastics, except the mulch film for 23–77 days of incubation, caused a positive priming effect on soil organic carbon (SOC). Fourier transform infra-red spectroscopy and scanning electron microscopy analyses were consistent with the C mineralisation data.

Conclusions: This study determines the degradation of various MPs in soil using a reliable and practical δ¹³C method, which has been lacking in this field of study. The priming effect of various MPs on SOC is a significant finding.

Implications: The lack of consideration of priming effect on SOC may overestimate the mineralisation of plastics in soil.

背景：大量传统塑料废物，尤其是微塑料 (MP) 形式的废物，由于其降解有限而在土壤中积累。可氧化降解和可生物降解的塑料也导致了土壤中的 MP 污染。

目的：在这项研究中，我们研究了传统塑料[水果和蔬菜 (F&V) 袋]、两种可生物降解塑料（垃圾箱衬垫和地膜）和一种氧化降解塑料（吸管）的降解情况。

方法：将这些塑料（5 毫米）混合到土壤中，并在实验室中在 37 ± 1°C 下培养 185 天。四种塑料的CO _{2 -碳(C)矿化度采用δ} ¹³ C技术测定，因为所研究的塑料和实验土壤的δ ¹³ C值差异≥10‰。

主要结果：孵化期结束时，箱内衬显示出最大的碳矿化度（5.7%），其次是地膜（4.1%）、稻草（0.4%）和食品和包装袋（0.3%）。除培养 23-77 天的地膜外，所有塑料都会对土壤有机碳 (SOC) 产生积极的启动效应。傅里叶变换红外光谱和扫描电子显微镜分析与C矿化数据一致。

结论：本研究采用可靠实用的 δ ¹³ C 方法测定了土壤中各种 MP 的降解情况，这是该研究领域所缺乏的。各种 MP 对 SOC 的启动效应是一个重要的发现。

影响：缺乏对 SOC 的启动效应的考虑可能会高估土壤中塑料的矿化程度。