Abstract：
Sediment cores are optimal mediums for investigating the historical presence of offshore microplastics (MPs). In this study, two sediment cores were collected at varying water depths, i.e., XS2 (10 m) and XS3 (20 m), from the Xiangshan offshore (XSO) in Ningbo. We focused on the spatiotemporal distribution characteristics of MPs within two sediment cores and explored the response differences of MPs abundance to natural factors and human activities. The results showed that the MPs abundance in sediments has gradually increased since the late 1960s, but with interannual fluctuations. MPs abundance in XS2 and XS3 were 1133-8700 and 633-11433 items/kg dry weight, respectively. The predominant polymers were PA, PU, PET and ACR, with fragmented particles being the most prevalent shape of MPs. The MPs abundance in XS2 and XS3 had a similar response to natural factors, mainly including (i) MPs abundance significantly correlated with the sediment load of the Qiantang River (p < 0.01), indicating that sediment load might be an important factor affecting the MPs abundance and that MPs transported by rivers had characteristics of near-source sedimentation; (ii) typhoons had the effect of weakening the MPs abundance; and (iii) geological activities might be potential contributing factors to variations in MPs\' abundance in deep sediments. Correlation analyses demonstrated that MPs in XSO was the result of multiple sources, stemming from plastic production, sewage discharge, marine fisheries and shipping activities. Notably, XS3 exhibited higher sensitivity to human activities compared to XS2, owing to differences in sampling locations. This study underscores the significance of employing two sediment cores, rather than a single core, as it provides a more comprehensive insight into the overarching trends and disparities in the historical pollution of MPs. Our findings contribute to a deeper understanding of the history of offshore MPs pollution, shedding new light on this critical environmental issue.
摘要：
沉积物核心是调查海上微塑料（MPs）历史存在的最佳介质。在这项研究中,在不同的水深收集了两个沉积物岩心，即，XS2（10米）和XS3（20米），从宁波的象山近海(XSO)。我们重点研究了两个沉积物岩心内MPs的时空分布特征，并探讨了MPs丰度对自然因素和人类活动的响应差异。结果表明，自1960年代后期以来，沉积物中的MPs丰度逐渐增加，但有年际波动。XS2和XS3中的MPs丰度为1133-8700和633-11433项目/kg干重，分别。主要的聚合物是PA，PU,PET和ACR，破碎的颗粒是最普遍的形态。XS2和XS3中的MPs丰度对自然因素有相似的反应，主要包括(I)MPs丰度与钱塘江泥沙负荷显著相关(p<0.01)，表明沉积物负荷可能是影响MPs丰度的重要因素，河流运输的MPs具有近源沉积特征；（ii）台风具有削弱MPs丰度的作用；（iii）地质活动可能是导致深部沉积物中MPs丰度变化的潜在因素。相关分析表明，XSO中的MPs是多种来源的结果，源于塑料生产，污水排放,海洋渔业和航运活动。值得注意的是,由于采样位置的差异，与XS2相比，XS3对人类活动的敏感性更高。这项研究强调了采用两个沉积物岩心的重要性，而不是一个单一的核心，因为它可以更全面地了解国会议员历史污染的总体趋势和差异。我们的发现有助于更深入地了解近海MP污染的历史，对这个关键的环境问题有了新的认识。
