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Unraveling the HistoricalTrajectory and Dynamic Mechanismsof Microplastic Degradation in Sediment Cores over the Last Century
Summary
Scientists studied nearly 100 years of buried mud layers in mangrove forests and found that microplastics have been steadily breaking down since they first appeared around 1953, with tiny gut bacteria and other microbes playing the biggest role in that breakdown. This matters because it shows plastics don't just sit unchanged in the environment forever—they slowly degrade into smaller fragments, which raises questions about how these breakdown particles might spread and eventually make their way into water, food, and ultimately our bodies over time.
Microplastics (MPs) in sediments serve as chronographic markers of the Anthropocene, enabling the reconstruction of plastic pollution history and the revelation of natural degradation patterns during sedimentation. However, the associations between temporal span, MP abundance, and their degradation patterns remain poorly understood. This study investigated MP abundance and degradation in mangrove sediment cores (1931–2023) and assessed the contribution rates and dynamic mechanisms of four influencing factor categories: anthropogenic activities, climate/meteorological conditions, sediment physicochemical properties, and biological information. The results showed that the earliest detectable MPs appeared in 1953, with abundance ranging from 16 ± 14.97 to 3056 ± 207.62 items kg–1. The carbonyl, hydroxyl, assimilation, and yellowness indices exhibited a fluctuating upward trend with increasing depth, with annual variation rates of 0.0163, 0.0187, 0.0175, and 0.5357, respectively; the carbonyl index could effectively estimate sediment age (R2 = 0.55). Importantly, microbial communities were identified as the most critical factor affecting MP degradation: community richness (Acidobacteriota and Pseudomonadota) and diversity (Chao1, Shannon, and Simpson indices) contributed the most, and MP degradation indicators were positively correlated with species composition (path coefficient = 0.530). This study provides new insights into the reliability of sedimentary MPs as Anthropocene chronostratigraphic markers and their long-term natural degradation patterns under historical changes.