Reichelt Sophia, Gorokhova Elena
Department of Environmental Science (ACES), Stockholm University, SE-106 91, Stockholm, Sweden.
Environ Pollut. 2023 Nov 1;336:122369. doi: 10.1016/j.envpol.2023.122369. Epub 2023 Aug 17.
The ubiquitous occurrence of microplastics is raising broad concerns and motivating effect studies. In these studies, however, particle behaviour in the water and aggregation are rarely considered leading to contradictory results reported by different studies. Using an environmentally relevant experimental setup with Daphnia magna as a test organism, we investigated how experimental conditions affect particle aggregation and the aggregate heterogeneity in terms of the particle size distribution. The experimental factors considered were (1) exposure duration (48 h vs 120 h), (2) the total mass of suspended solids (0-10 mg/l) composed of natural mineral particles (kaolin) and microplastics, (3) the proportion of the microplastics in the particle suspension (0-10% by mass), (4) dissolved organic matter (DOM; 0 vs 20 mg agarose/l), and (5) presence of the test organism (0 and 5 daphnids/vial). We found that particle aggregation occurs within the first 48 h of incubation in all treatments, no substantial change in the aggregate heterogeneity is observed afterwards. The median aggregate size was ∼2-fold higher than the nominal average particle size of clay and microplastics in the stock suspensions used to prepare the experimental mixtures. The strongest positive driver of the aggregate size and heterogeneity was DOM, followed by the presence of daphnids and the concentration of the suspended solids in the system. Also, microplastics were found to facilitate aggregation, albeit they were the weakest contributor. Moreover, besides directly increasing the aggregation, DOM relaxed the effects of the total solids and daphnids on the aggregate size. Thus, the particle size distribution was established early during the exposure and shaped by all experimental factors and their interactions. These findings improve our understanding of the processes occurring in the exposure systems when conducting effect studies with microplastics and other particulates and demonstrate the necessity to access the particle size distribution to characterise the exposure. Aslo, relevant experimental designs with microplastics must include relevant natural particulates and DOM to ensure environmentally realistic particle behaviour and adequate particle-biota interactions.
微塑料的普遍存在引发了广泛关注并推动了效应研究。然而，在这些研究中，很少考虑水中的颗粒行为和聚集情况，导致不同研究报告的结果相互矛盾。我们使用与环境相关的实验装置，以大型溞作为受试生物，研究了实验条件如何影响颗粒聚集以及颗粒大小分布方面的聚集体异质性。所考虑的实验因素包括：（1）暴露持续时间（48小时与120小时）；（2）由天然矿物颗粒（高岭土）和微塑料组成的悬浮固体总质量（0 - 10毫克/升）；（3）颗粒悬浮液中微塑料的比例（质量分数0 - 10%）；（4）溶解有机物（DOM；0与20毫克琼脂糖/升）；（5）受试生物的存在（0和5只溞/小瓶）。我们发现，在所有处理中，颗粒聚集在孵育的前48小时内发生，之后聚集体异质性未观察到实质性变化。聚集体的中位尺寸比用于制备实验混合物的储备悬浮液中粘土和微塑料的标称平均颗粒尺寸高约2倍。聚集体尺寸和异质性的最强正向驱动因素是DOM，其次是溞的存在和系统中悬浮固体的浓度。此外，发现微塑料有助于聚集，尽管其作用最弱。而且，除了直接增加聚集外，DOM还缓解了总固体和溞对聚集体尺寸的影响。因此，颗粒大小分布在暴露早期就已确定，并由所有实验因素及其相互作用塑造。这些发现增进了我们对在用微塑料和其他颗粒进行效应研究时暴露系统中发生的过程的理解，并证明了获取颗粒大小分布以表征暴露的必要性。此外，涉及微塑料的相关实验设计必须包括相关的天然颗粒和DOM，以确保环境现实的颗粒行为和充分的颗粒 - 生物相互作用。
