DataSheet1_Collecting Microplastics in Gardens: Case Study (i) of Soil.docx

As an emerging contaminant, microplastic is receiving increasing attention. However, the contamination source is not fully known, and new sources are still being identified. Herewith, we report that microplastics can be found in our gardens, either due to the wrongdoing of leaving plastic bubble wraps to be mixed with mulches or due to the use of plastic landscape fabrics in the mulch bed. In the beginning, they were of large sizes, such as > 5 mm. However, after 7 years in the garden, owing to natural degradation, weathering, or abrasion, microplastics are released. We categorize the plastic fragments into different groups, 5 mm–0.75 mm, 0.75 mm–100 μm, and 100–0.8 μm, using filters such as kitchenware, meaning we can collect microplastics in our gardens by ourselves. We then characterized the plastics using Raman image mapping and a logic-based algorithm to increase the signal-to-noise ratio and the image certainty. This is because the signal-to-noise ratio from a single Raman spectrum, or even from an individual peak, is significantly less than that from a spectrum matrix of Raman mapping (such as 1 vs. 50 × 50) that contains 2,500 spectra, from the statistical point of view. From the 10 g soil we sampled, we could detect the microplastics, including large (5 mm–100 μm) fragments and small (<100 μm) ones, suggesting the degradation fate of plastics in the gardens. Overall, these results warn us that we must be careful when we do gardening, including selection of plastic items for gardens.作为一类新兴污染物，微塑料（microplastic）正受到学界日益广泛的关注。然而其污染来源尚未完全明晰，新的潜在污染来源仍在被持续探明。本文报道，微塑料可存在于家庭菜园中，其来源主要有二：一是误将塑料气泡膜与园艺覆盖物（mulches）混合，二是在铺设有覆盖物的床畦中使用了塑料景观织物。初始状态下，这些塑料尺寸较大，例如粒径大于5 mm。但在菜园环境中放置7年后，经自然降解、风化或磨损作用，微塑料被逐步释放出来。我们通过厨房用具类滤器将收集到的塑料碎片划分为三个粒径组别：5 mm–0.75 mm、0.75 mm–100 μm以及100–0.8 μm，证实了我们可自行在菜园中采集微塑料。随后，我们采用拉曼成像（Raman image mapping）与基于逻辑的算法对塑料样品进行表征，以提升检测的信噪比与成像可信度。从统计学视角来看，单条拉曼光谱（乃至单个特征峰）的信噪比，远低于包含2500条光谱的拉曼成像光谱矩阵（例如1 vs. 50×50的矩阵），因此采用该联用方案可有效提升数据质量。在我们采集的10 g土壤样品中，可检测到包括大粒径（5 mm–100 μm）碎片与小粒径（<100 μm）微塑料在内的各类微塑料，这证实了塑料在菜园环境中可发生降解转化。综上，本研究结果警示我们，在开展园艺作业时需格外谨慎，包括审慎选择园艺所用塑料制品。