Vihara Samiduni Jayasinghe, Thilomi Samarakoon, Chamini Hemachandra
Polyethylene terephthalate (PET) microfibers present a common contaminant in freshwater environments, yet their toxicological sensitivity across distinct trophic levels remains poorly studied. This study assessed the comparative toxicity of PET microplastic fibers on the duckweed Lemna minor and the cladoceran Moina macrocopa. Healthy L. minor fronds were exposed to several PET fiber concentrations for seven days, and the frond number, frond area, root length, and chlorophyll a and b contents were determined. For M. macrocopa, an acute immobilization test was performed for 48 h, and the survival, growth, and heartbeat of the neonates were assessed. A chronic reproduction test was also conducted for 7 days using several sublethal PET fiber concentrations. Frond area was significantly reduced in L. minor at PET fiber concentrations ≥50 mg/L (p < 0.05). Average frond number was significantly reduced at ≥150 mg/L, while chlorophyll a and b contents were significantly reduced at 200 mg/L (p < 0.05), while root length was unaffected. Acute exposure of M. macrocopa significantly reduced survival, growth, and heartbeat at ≥5, ≥10, and ≥100 mg/L, respectively (p < 0.05). Chronic exposure significantly reduced total reproduction at ≥5 mg/L (p < 0.05). A dose-dependent effect was observed on other reproduction-related endpoints, although none were statistically significant. These findings demonstrate differential sensitivity of freshwater primary producers and consumers to PET microplastic fiber exposure, with reproductive effects in M. macrocopa occurring at lower concentrations than most growth- and physiological responses in L. minor. An initial scenario-based exploratory ecological risk assessment indicated negligible-to-low current ecological risk under surface water concentrations, though long-term microfiber accumulation and chemical co-exposure pose ongoing ecological concerns.