Microplastics (MPs) as complex synthetic pollutants represent a growing concern for the aquatic environment. Previous studies examined the toxicity of MPs, but infrequently used a natural particle control such as kaolin. The cause of toxicity, either the physical structure of the particles or chemical components originating from the MPs, has rarely been resolved. Moreover, the ecotoxicological assessment of biodegradable plastics has received little attention.

To narrow down the main driver for toxicity of irregular biodegradable MPs, we conducted a series of 28-days sediment toxicity tests with the freshwater oligochaete Lumbriculus variegatus and recorded the number of worms and dry weight as endpoints. Therefore, MPs containing several biodegradable polymers were either mixed with the sediment or layered on the sediment surface with concentrations from 1 to 8.4% sediment dw^-1. Kaolin particles were evaluated in parallel as particle control. Furthermore, aqueous leachates and methanolic extracts as MP equivalents as well as solvent-treated, presumably pure MPs were investigated after mixing them into the sediment.

Our results reveal that MP mixed with the sediment induced stronger adverse effects than layered MP. Kaolin particles caused no adverse effects. In contrast, they enhanced dry weight in both applications. The impact of aqueous leachates was comparable to the control without MPs, whereas methanolic extracts affected the worm number at the highest concentration with 100% mortality. Solvent-treated, presumably pure MP resulted in mostly higher worm numbers when compared to untreated MPs mixed into the sediment.

This study demonstrates that MPs mixed into the sediment affect L. variegatus more than MPs that are layered on the sediment surface. Kaolin as a natural, fine-sized particle control created somewhat favorable conditions for the worm. The main driver for toxicity, however, proved to be chemicals associated with the plastic product and its previous content.

作为复杂的合成污染物的微塑料（MPs）对水生环境越来越关注。先前的研究检查了MP的毒性，但很少使用天然颗粒控制剂，例如高岭土。毒性的原因，无论是颗粒的物理结构还是源自MP的化学成分，都很少得到解决。而且，对可生物降解塑料的生态毒理学评估很少受到关注。

为了缩小不规则可生物降解MP毒性的主要驱动力，我们使用淡水低聚斑潜蝇Lumbriculus variegatus进行了一系列28天的沉积物毒性测试，并记录了蠕虫的数量和干重作为终点。因此，含有几种可生物降解聚合物的MP会与沉积物混合，或者以1至8.4％的沉积物dw ^-1浓度沉积在沉积物表面。并行评估高岭土颗粒作为颗粒对照。此外，在将水浸出液和甲醇提取物作为MP当量以及溶剂处理过的大概是纯MP混合后，研究了它们的沉淀物。

我们的研究结果表明，与分层MP相比，与沉积物混合的MP具有更强的不利影响。高岭土颗粒没有引起不利影响。相反，它们在两种应用中均增加了干重。含水浸出液的影响与没有MP的对照相当，而甲醇提取物以最高浓度影响蠕虫数量，死亡率为100％。与未经处理的MP混入沉淀物中相比，溶剂处理的大概是纯MP导致的蠕虫数量更多。

这项研究表明，与沉积在泥沙表面的MP相比，混入泥沙的MP对variegatus的影响更大。高岭土作为一种天然的细颗粒控制剂，为蠕虫创造了一些有利条件。然而，证明毒性的主要驱动力是与塑料产品及其先前含量有关的化学物质。