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Unraveling the Historical Trajectory and Dynamic Mechanisms of Microplastic Degradation in Sediment Cores over the Last Century
Summary
Scientists studied nearly 100 years of sediment layers in mangrove forests and found that microplastics have been piling up since at least 1953, breaking down slowly over time as they age. The biggest driver of this breakdown turned out to be bacteria living in the sediment, not just sunlight or weather — meaning the microbes in soil and water play a bigger role in shaping how plastic waste degrades (and what byproducts it leaves behind) than previously realized. This matters because as microplastics break down, they can release chemicals and smaller particles that may eventually make their way into water, food sources, and ultimately human bodies.
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 ( R 2 = 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.