Microplastic particles (1-5mm) in soil samples collected in 2019, Northern Germany

The study took place in Schleswig-Holstein, Northern Germany, in spring 2019. We have chosen 15 arable fields that are part of the federal soil monitoring scheme by LLUR and as such are representative of the different soil conditions in the region. At each of the 15 study fields, boreholes were placed along the corner points of a square of approximately 40 m edge length. At each of the corner points, three boreholes were drilled down to depths of 10, 20 and 30 cm, respectively. As a consequence, we had 4 x 3 x 3 = 36 sampling units with a wet weight of ~ 200 g soil per unit that integrated over soil depths of 0-10 cm, 10-20 cm and 20-30 cm, respectively, per study site. Each sampling unit was dimensioned with a ruler and stored in an individual glass container. Thus, in this study a total of 540 sampling units with a total of 123.3 kg soil material was inspected for plastic particles between 1 and 5 mm. In the laboratory, the wet soil mass of each sampling unit was quantified and then the soil volume was reduced by wet sieving. To facilitate the sieving, the soil was first soaked in lukewarm tap water in a beaker (1 l) to dissolve loamy aggregates. Aggregates that did not dissolve easily were gently broken down with the fingers and carefully homogenized with a metal whisk. Then the soil was placed on a steel analysis sieve with a mesh size of 1 mm and rinsed under running tap water until only particles of > 1 mm remained. This material was then transferred into glass petri dishes by using a squeeze bottle made of Polyethylene (PE) filled with tap water and a metal spoon. Excess water was removed from the petri dishes with a disposable syringe (PE and Polypropylene (PP)) and an attached injection cannula (outer diameter 0.8 mm; PP and metal). Next, the content of each petri dish was visually examined twice (once by IK Harms and once by S Troegel) for MP under a stereomicroscope with transmitted light and a 133 Trino Zoom (BMS) with two WF 10x/22 mm oculars. All particles that matched the criteria for the proper identification of MP recommended by Hidalgo-Ruz et al. (2012) were picked and individually placed in 96-well micro test plates that were made from Polystyrene (PS).本研究于2019年春季在德国北部石勒苏益格-荷尔斯泰因州开展。我们选取了15个隶属于LLUR主管的联邦土壤监测计划的耕地田块，这些田块可代表该区域不同的土壤条件。在15个研究田块中，各沿边长约40米的正方形的四个角点布设钻孔；在每个角点处，分别钻取深度为10 cm、20 cm和30 cm的三个钻孔。由此，每个研究样点共获得4×3×3=36个采样单元，每个单元湿重约200 g，分别对应0-10 cm、10-20 cm及20-30 cm三个土层深度的混合土壤样品。每个采样单元均用直尺标定尺寸，并分装至独立的玻璃容器中保存。综上，本研究共获取540个采样单元，总土壤样品量达123.3 kg，用于检测粒径1~5 mm的微塑料（Microplastic, MP）。在实验室中，我们首先测定每个采样单元的湿土质量，随后通过湿筛法缩减土壤体积。为便于筛分操作，先将土壤置于1 L烧杯中，用温自来水浸泡以消解壤质团聚体；对于难以消解的团聚体，用手指轻轻碾碎，并使用金属搅拌器充分均质化。随后将土壤转移至孔径为1 mm的钢制分析筛上，用流动自来水冲洗，直至仅留存粒径>1 mm的颗粒。接着使用装有自来水的聚乙烯（PE）挤瓶与金属小勺，将筛上残留物转移至玻璃培养皿中；再使用一次性注射器（材质为聚乙烯PE与聚丙烯PP）及配套的注射针头（外径0.8 mm，材质为PP与金属）抽除培养皿中的多余水分。随后，借助配备透射光源、搭载133 Trino Zoom（BMS）光学系统及两支WF 10×/22 mm目镜的体式显微镜，由IK Harms与S Troegel分别对每个培养皿中的样品进行两次目视检查，以识别微塑料。所有符合Hidalgo-Ruz等人（2012）推荐的微塑料正确鉴定标准的颗粒，均被挑出并单独分装至聚苯乙烯（PS）材质的96孔微量检测板中。