Comparative assessment of MP effects on pigment composition and lipid profiles in three marine microalgae

Microplastics (MPs) are emerging marine contaminants, yet polymer-specific effects on microalgal physiology and lipid metabolism remain insufficiently understood. This study evaluated the responses of three commercially and ecologically relevant marine microalgae-Nannochloropsis sp., Chaetoceros sp., and Isochrysis sp.-grown in f/2 medium under controlled laboratory conditions and exposed to polyethylene (PE) and polypropylene (PP) MPs at 50 and 100 mg/L in 50:50 and 70:30 (PE: PP) ratios. MP morphology and algal-MP interactions were examined using scanning electron microscopy (SEM). Growth, pigment content, and total lipids were quantified, and fatty acid methyl ester (FAME) profiles were analysed by gas chromatography-flame ionization detection (GC-FID). Elevated MP exposure significantly inhibited growth, with stronger effects under PE-dominant treatments. Nannochloropsis sp. showed the greatest growth reduction (29.36%), followed by Isochrysis sp. (23.58%) and Chaetoceros sp. (15.70%). At 100 mg/L, chlorophyll and carotenoid contents declined across all species. Total lipid content decreased under PE-rich MP exposure, accompanied by marked alterations in fatty acid methyl ester (FAME) profiles. Nannochloropsis sp. exhibited increased proportions of unsaturated fatty acids, particularly α-linolenic acid (C18:3n3), indicating metabolic adjustment to MP-induced stress. In contrast, Chaetoceros sp. showed reduced nervonic (C24:1) and oleic (C18:1) acids, suggesting disruption of long-chain fatty acid biosynthesis, while Isochrysis sp. displayed significant reductions in tricosanoic acid (C23:1) relative to the control. Overall, long-chain fatty acids dominated (55-75%), with MP stress promoting species-dependent elongation and desaturation processes. These findings demonstrate that MP polymer composition critically influences microalgal growth, pigment production, and lipid metabolic pathways, with implications for algal biochemical composition and biofuel-relevant traits. Future studies should examine long-term, environmentally relevant microplastic exposures and underlying mechanisms affecting microalgal physiology and lipid metabolism.