微塑料是一种新型污染物，近些年来受到越来越多关注。2021年我国提出《国民经济和社会发展第十四个五年规划和2035年远景目标纲要》，对包括微塑料在内的新污染治理做出明确要求。受各种自然因素和人为因素影响，微塑料最终都趋向埋藏在海洋沉积物中，因此对海洋沉积物中微塑料开展研究有重要科学和实际意义。渤海位于37°07′ N-41°00′ N，117°35′ E-121°10′ E之间，是中国最大的内海，平均深度18 m，环渤海经济带是我国重点开发地区之一，也是我国第三个经济“增长极”。随着环渤海经济带的快速发展，渤海受人类活动影响日益严重，微塑料污染是主要环境问题之一，亟待开展全面深入的研究。本研究2020年采集了4根渤海沉积柱，测定柱状沉积物中微塑料的丰度和种类，阐明渤海沉积物中微塑料的垂向分布特征，反演了渤海沉积物微塑料污染历史，进行了渤海沉积物中微塑料污染的生态风险评价，主要研究结果和结论如下：

渤海沉积物中微塑料丰度范围为1608.4-24596.4 items/kg，中位值丰度和平均丰度分别为7546.7 items/kg和7812.7±4535.8 items/kg。水平空间上，渤海湾沉积柱中微塑料丰度显著低于辽东湾、渤海中心区域（渤海中央）和渤海海峡沉积柱中微塑料丰度。这种水平空间差异与微塑料来源和渤海环流传输有关。垂直方向上，随深度加深，微塑料丰度整体呈现下降趋势，但下降的速率逐渐变缓，0-30 cm 深度范围内微塑料丰度下降的速率高于30-140 cm深度。浅层（0-50 cm）沉积物微塑料丰度显著高于中层（50-100 cm）沉积物微塑料丰度，中层沉积物微塑料丰度显著高于深层（100-140 cm）沉积物微塑料丰度。

渤海沉积物中微塑料形状主要为纤维、碎片、薄膜和颗粒四种，其中碎片占比最高，且随深度增加表现为下降趋势，表明微塑料老化可能导致微塑料碎片转化为其他形状。微塑料颜色主要为黑色、蓝色、白色、粉色、透明、红色、黄色、绿色，其中透明微塑料占比最高，且随深度增加表现为下降趋势，而黄色微塑料的占比则表现为升高趋势，表明随微塑料老化透明微塑料可转化为有色微塑料，尤其是黄色微塑料。渤海沉积物中粒径＜100 mm的微塑料占比大，随深度加深表现为下降的趋势，表明小粒径微塑料更易于老化分解。微塑料成分包括聚乙烯（PE）、人造丝（Rayon）、聚氯乙烯（PVC）、聚丙烯（PP）、聚对苯二甲酸乙二醇酯（PET）、聚丙烯酸丁酯（PBA）和聚甲基丙烯酸甲酯（PMMA），其中PE占比为43%。浅中层中微塑料组成相对丰富，深层的微塑料组成相对单一，表明早期人类使用的塑料成分较单一。

文献综述表明渤海区域沉积速率为0.42 cm/a，据此推算采集的0-141 cm沉积柱形成年代范围约为2020年-1700年。二十世纪初塑料制品开始较大规模使用对应的沉积深度约为50 cm, 二十世纪初以来渤海沉积物剖面微塑料丰度快速升高。1949年以来，渤海沉积物剖面中微塑料丰度的变化与社会经济指标密切相关，如环渤海地区农用塑料薄膜使用量、海水养殖产量、废水排放量、初级塑料产量、化学纤维产量、海洋捕捞产量、港口货物吞吐量、国民生产总值等。微塑料丰度随上述8项社会经济指标升高而升高。沉积物剖面中微塑料丰度随农用塑料薄膜使用量的增加线性增加，随其余7种社会经济指标的增加表现为快速增加和缓慢增加两个阶段。结果表明渤海沉积物中微塑料主要来自农膜使用、日用品和工业品破碎、渔业用具磨损、纺织品洗涤产生含纤维废水。定量化分析渤海各区域污染源相对数量，发现海湾处微塑料污染源较多，渤海海峡处污染源较少。

沉积物微塑料风险评价显示渤海沉积物中微塑料潜在风险较高，但是目前微塑料污染生态风险较低，因此需要对微塑料后续的生态风险保持关注。

Microplastics, as a new type of pollutant, have received increasing attention in recent years. The “14th Five-Year Plan for National Economic and Social Development and the Outline of Long-term Goals for 2035” proposed in 2021，sets clear requirements for controlling new pollutants, including microplastics. Affected by various natural and man-made factors, microplastics tend to eventually be buried in marine sediments. Therefore, considering scientific and practical significance, it is crucial to conduct research on microplastics in marine sediments. The Bohai Sea, located between 37°07′ N-41°00′ N and 117°35′ E-121°10′ E, is the largest inland sea in China, with an average depth of 18m. The Bohai Rim Economic Belt is one of the key development areas in China, which is called “the third economic growth pole”. With the rapid development of the Bohai Rim Economic Belt, the Bohai Sea has been increasingly affected by human activities, and the pollution has gradually intensified. Among the pollution problems, microplastic pollution has been the major one and requires urgent comprehensive and in-depth research. This study took four sediment cores in 2020 in the Bohai Sea to measure the abundance and types of microplastics in the sediment, clarify the vertical distribution characteristics in the Bohai Sea sediment cores, reconstruct the history of microplastic pollution in the Bohai Sea sediments, and evaluate microplastic pollution level in the Bohai Sea sediments. The study obtains the following results and conclusions:

In the Bohai Sea sediments, the abundance of microplastics ranges from 1608.4 items/kg to 24596.4 items/kg, with the median abundance and average abundance being 7546.7 items/kg and 7812.7±4535.8 items/kg. Horizontally, the abundance of microplastics in the sediment core in Bohai Bay sediments is significantly lower than that in LiaoDong Bay, the central region of the Bohai Sea and Bohai Strait sediments., which is related to the source of microplastics and the circulation transport in the Bohai Sea. Vertically, as the depth increases, the overall abundance of microplastics shows a downward trend while the rate of decline gradually slows down. The rate of decline of the microplastics abundance in the 0-30 cm depth range was higher than that in the 30-140cm depth range. The abundance of microplastics in shallow (0-50 cm) sediments is significantly higher than that in middle (50-100 cm) sediments, while the abundance in middle (50-100 cm) sediments is significantly higher than that in deep (100-140 cm) sediments.

The main shapes of microplastics in the Bohai Sea sediments include fibers, fragments, films, and granules. The fragments account for the highest proportion, and the proportion shows a downward trend with the increasing depth, indicating that the aging of microplastics might cause fragments to transform into other shapes. The main colors of microplastics include black, blue, white, pink, transparent, red, yellow, and green. The transparent microplastics account for the highest proportion and the proportion shows a downward trend with the increasing depth, while the proportion of yellow microplastics increases, indicating that the aging process could cause the color of microplastics to transform from transparent into colored, especially yellow. Among the microplastics in the Bohai Sea sediment, the particles with the size less than 100μm account for a large proportion, indicating that microplastics in smaller sizes are more susceptible to aging and decomposition. The ingredients of microplastics include polyethylene (PE), rayon, polyvinyl chloride (PVC), polypropylene (PP), polyethylene terephthalate (PET), poly(butyl acrylate) (PBA) and polymethylmethacrylate (PMMA), and PE accounts for the highest proportion of 43%. The composition of microplastics in the shallow and middle layers is relatively rich, while the composition of microplastics in the deep layers is relatively uniform, indicating that the plastic components used in early years were relatively uniform.

According to the existing literature, it is inferred that the sedimentation rate in the Bohai Sea is 0.42 cm/a. Based on this, the formation age of the collected sedimentary columns, ranging from 0 to 141 cm, is estimated to be approximately 2020-1700. At the beginning of the 20th century, plastic products began to be used on a large scale, corresponding to a sedimentation depth of about 50 cm. Since the beginning of the 20th century, the abundance of microplastics in the Bohai Sea sediment profile has increased rapidly. Since 1949, the change of the microplastics abundance in sediment profiles of the Bohai Sea has been related to socioeconomic indicators, such as agricultural plastic film usage in the Bohai Rim region, mariculture production, wastewater discharge, primary plastic production, chemical fiber production, and marine fishing Output, port cargo throughput, gross national product, etc. The abundance of microplastics increases with the increase of the above 8 socioeconomic indicators. The abundance of microplastics in the sediment profile increased linearly with the increase in the use of agricultural plastic films, and showed two stages of rapid increase and slow increase with the increase of the remaining seven socioeconomic indicators. The analysis results show that microplastics in Bohai Sea sediments mainly come from the use of agricultural films, fragmentation of daily necessities and industrial products, wear and tear of fishing equipment, and fiber-containing wastewater from textile washing. Quantitative analysis of the relative number of pollution sources in various regions of the Bohai Sea revealed that there are more microplastic pollution sources in the bay and fewer pollution sources in the Bohai Strait.

Microplastic risk assessment shows that the potential risk of microplastics in Bohai Sea sediments is high, but the current ecological risk of microplastic pollution is low, so we need to remain concerned about the subsequent ecological risks of microplastics.