Abstract:

In recent years, the widespread distribution of microplastics in marine environment and their biotoxic effects and health risks on aquatic fauna have received much attention. In the natural marine environment, the surface of microplastics is susceptible to colonization by a variety of microorganisms, leading to the formation of biofilms, which may affect the biotoxicity of microplastics. However, these effects are still poorly understood. Therefore, using the typical bivalve Meretrix lyrata as the test animal in Hainan, with its important respiratory and feeding organ, the gills, as the target organ, we investigated the influence of biofilms on the biological toxicity of microplastics. By exposing the clams to different types of pristine and biofilm-coated microplastics (polystyrene PS, polyethylene PE, polyethylene terephthalate PET) at a concentration of 100 μg∙L⁻¹ for 14 days, we studied the enrichment characteristics of microplastics in the gills of the clams and their effects on the gill tissue’s pathological damage, antioxidant, and immune defense system-related indicators. The results showed that both pristine and biofilm-coated microplastics were accumulated in the gills of the clam, with the accumulation increasing with prolonged exposure time, and the biofilm-coated microplastics exhibiting a more significant biological enrichment effect. The observed accumulation of microplastics led to various degrees of mechanical damage in the gills, including pathological phenomena, such as gill filaments adherence, atrophy and breakage, gill filament cell necrosis, cilia loss, etc., with biofilm-coated microplastics causing more pronounced damage to the gill’s microscopic structure compared to pristine microplastics. Microplastic stress resulted in increased activities of superoxide dismutase (SOD), catalase (CAT), and alkaline phosphatase (ALP), decreased glutathione (GSH) content, and no significant change in malondialdehyde (MDA) content. Both different types of pristine and biofilm-coated microplastics induced oxidative stress and immune responses in the gills of bivalve clam, without causing lipid peroxidation damage. In addition, the results revealed that the biofilm-coated microplastics showed stronger toxic effects on gills of clam compared to microplastics acting alone. The present research provides a scientific basis for evaluating toxicity mechanisms and health risks of biofilm-coated microplastics to aquatic organisms in the marine environments.

Key words: microplastics, biofilm, accumulation, pathological damage, oxidative stress, toxic effects

摘要：

近年来，微塑料在海洋环境中的广泛分布及其生物毒性效应与健康风险备受关注。天然海洋环境中，微塑料表面易被多种微生物定殖并形成生物膜，这可能影响微塑料的生物毒性，然而目前对其影响仍知之甚少。以海南典型双壳贝类文蛤（Meretrix lyrata）为受试动物，并以其重要的呼吸和滤食器官鳃为靶器官，研究生物膜对微塑料生物毒性的影响。通过将文蛤暴露在质量浓度为100 μg∙L⁻¹的不同类型原始和生物膜附着的微塑料（聚苯乙烯PS、聚乙烯PE、聚对苯二甲酸乙二醇酯PET）环境中14 d，研究微塑料在文蛤鳃中的富集特征及其对鳃组织的病理损伤、抗氧化及免疫防御系统相关指标的影响。结果表明，原始和生物膜附着微塑料均能在文蛤鳃组织中富集，富集量随暴露时间延长而增加，且生物膜附着微塑料的生物富集效应更显著；微塑料富集导致鳃组织发生不同程度的机械损伤，出现鳃丝粘连、萎缩及断裂、鳃丝细胞坏死、纤毛脱落等病理现象，其中附着生物膜的微塑料比原始微塑料对鳃显微结构的损伤更为明显；微塑料胁迫造成超氧化物歧化酶（SOD）、过氧化氢酶（CAT）和碱性磷酸酶（ALP）活性升高，谷胱甘肽（GSH）含量下降，丙二醛（MDA）含量无显著变化；不同类型原始和附着生物膜微塑料均诱导了文蛤鳃组织的氧化应激和免疫反应，但未产生脂质过氧化损伤。此外，实验结果表明生物膜附着的微塑料比微塑料单独作用对文蛤鳃的毒性效应更强。该研究为评价海洋环境中附着生物膜的微塑料对水生生物的毒性机制及健康风险提供科学依据。

关键词: 微塑料, 生物膜, 富集, 病理损伤, 氧化应激, 毒性效应