PMMA Microplastics Induce Sublethal Cardiovascular and Developmental Effects During Early Development of Zebrafish (Danio rerio)

Microplastics are increasingly recognized as emerging contaminants with potential toxicological effects on aquatic organisms. Among widely used industrial polymers, poly(methyl methacrylate) (PMMA) has been detected in environmental matrices, raising concerns regarding its biological impacts. This study evaluated the developmental toxicity of 40 µm spherical PMMA microplastics in zebrafish (Danio rerio) using a standardized early-life stage exposure (3 hpf–6 dpf). Before exposure, particles were physicochemically characterized by Fourier Transform Infrared Spectroscopy (FTIR), Field Emission Scanning Electron Microscopy (FESEM), and micro-Raman spectroscopy (µRaman). Embryos were exposed to nominal concentrations ranging from 0.5 to 20 mg/L, and endpoints including survival, hatching rate, spontaneous movements, heart rate, morphology, and locomotor activity were assessed. PMMA exposure did not induce significant mortality or morphological abnormalities at any tested concentration. However, significant sublethal effects were observed, including accelerated hatching at 20 mg/L and increased heart rate across exposure groups, further supported by a positive concentration–response trend across vessel-level values, indicating altered developmental timing and cardiovascular function. These findings demonstrate that PMMA microplastics, despite low acute toxicity, can induce early physiological disturbances in a vertebrate model. The results highlight the importance of incorporating sensitive functional endpoints into hazard assessment frameworks and contribute to a more comprehensive evaluation of the environmental risks associated with microplastics traditionally considered to have low intrinsic reactivity.