Microplastic pollution disrupts microalgal physiology globally: a meta-analysis

Microplastic (MP) pollution threatens aquatic primary producers, yet global patterns of their impact on microalgal physiology remain unclear. Using a meta-analysis of 3,863 observations from 67 freshwater studies, this research quantifies biological effects (percentages back-transformed from effect sizes). Microplastics significantly inhibited growth (-30%), abundance (-18.1%), and photosynthesis (-13%), while inducing oxidative stress (50%) and promoting metabolite synthesis (21%). Notably, growth and abundance suppression showed limited dependence on mass concentration, likely because mass metrics obscure the higher particle numbers and surface areas of smaller plastics. In contrast, oxidative stress, photosynthetic inhibition, and metabolic accumulation increased dose-dependently. Nanoplastics (≤1 m) suppressed growth and photosynthesis over twice as strongly as larger microplastics (>1 m). Polymer type modulated impacts: PE, PVC, and PS reduced abundance similarly, while PET had the weakest effect. Growth inhibition was phylum-specific (sensitive: Chlorophyta, Cyanophyta; unaffected: Bacillariophyta), whereas photosynthetic and oxidative stress responses were universal. White microplastics consistently inhibited growth and photosynthesis and induced oxidative stress. Time-series analysis revealed divergent trajectories: growth inhibition intensified over time, abundance suppression attenuated, and metabolite accumulation increased, likely reflecting a physiological trade-off. These quantitative associations provide a baseline for refining freshwater environmental risk assessment.