Hiki Kyoshiro, Yaginuma Eiko, Namba Noriaki, Watanabe Haruna, Yamagishi Takahiro, Yamamoto Hiroshi
Health and Environmental Risk Division, National Institute for Environmental Studies, Tsukuba, Ibaraki, Japan.
Department of Urban Engineering, University of Tokyo, Tokyo, Japan.
Environ Toxicol Chem. 2025 Nov 1;44(11):3086-3094. doi: 10.1093/etojnl/vgaf187.
Microplastics (MPs) are ubiquitous in the environment and may pose risks to aquatic ecosystems. Although sediment toxicity tests are crucial for the risk assessment of MPs, exposure concentrations of MPs in sediment toxicity tests have not been quantified well yet. In this study, we developed and demonstrated a practical method to quantify MP number across all compartments of a typical sediment toxicity test system. Fluorescent polyethylene microbeads (30 and 100 µm) were introduced into formulated and field-collected sediments and monitored in the presence or absence of the estuarine amphipod Grandidierella japonica. Under all conditions, the majority of microbeads were retained in the sediment; however, MP distribution varied with sediment type, particle size, and the presence of amphipods. For example, field-collected sediment transferred a higher proportion of MPs to the water surface (8.1% ± 2.8% of added MPs) compared with formulated sediment (0.8% ± 0.7%). Furthermore, 100 µm beads were more abundant on the water surface, lid, and beaker walls than 30 µm beads, whereas 30 µm beads were predominated in the overlying water. The presence of amphipods resulted in many numbers of both 30 and 100 µm beads in nonsediment compartments, likely due to their bioturbation activity. Notably, the accumulation of 100 µm beads on the beaker walls is significant (up to 7.7% of added MPs), indicating a potential decrease in MP exposure to benthic organisms. These findings suggest that assessing MP exposure based solely on nominal and bulk sediment concentrations may underestimate risk. In addition, the presented workflow offers a practical framework to obtain compartment-specific MP counts and can be applied to MPs of other polymers and shapes for more realistic toxicity assessments.
微塑料（MPs）在环境中无处不在，可能对水生生态系统构成风险。尽管沉积物毒性测试对于微塑料的风险评估至关重要，但沉积物毒性测试中微塑料的暴露浓度尚未得到很好的量化。在本研究中，我们开发并展示了一种实用方法，用于量化典型沉积物毒性测试系统所有隔室中的微塑料数量。将荧光聚乙烯微珠（30和100μm）引入配制的和现场采集的沉积物中，并在有或没有河口双壳类动物日本大螯蜚的情况下进行监测。在所有条件下，大多数微珠都保留在沉积物中；然而，微塑料的分布因沉积物类型、粒径和双壳类动物的存在而有所不同。例如，与配制沉积物（0.8%±0.7%）相比，现场采集的沉积物将更高比例的微塑料转移到水面（添加微塑料的8.1%±2.8%）。此外，100μm的珠子在水面、盖子和烧杯壁上比30μm的珠子更丰富，而30μm的珠子在上覆水中占主导地位。双壳类动物的存在导致非沉积物隔室中30和100μm的珠子数量都很多，这可能是由于它们的生物扰动活动。值得注意的是，100μm珠子在烧杯壁上的积累很显著（高达添加微塑料的7.7%），这表明微塑料对底栖生物的暴露可能会降低。这些发现表明，仅基于名义和总体沉积物浓度评估微塑料暴露可能会低估风险。此外，所提出的工作流程提供了一个实用框架，以获得特定隔室的微塑料数量，并且可以应用于其他聚合物和形状的微塑料，以进行更实际的毒性评估。
