Growth and Oxidative Stress in Monoraphidium Capricornutum (Printz) Nygaard under Exposure to Perfluorooctanoic Acid and Cylindrospermopsin

Microalgae are recognized as sensitive bioindicators for assessing aquatic pollution, yet the combined effects of chemically distinct contaminants on them remain poorly explored. This study investigated the chronic toxicity of perfluorooctanoic acid (PFOA), a persistent per- and polyfluoroalkyl substance (PFAS), and the cyanotoxin Cylindrospermopsin (CYN), individually and in binary mixtures, on the freshwater microalga Monoraphidium capricornutum. Algal cultures were exposed for 12 days to PFOA (1000–2000 µg/L) and CYN (50–100 µg/L). Growth effects, antioxidant biomarkers (Glutathione (GSH), Glutathione S-transferase (GST), Superoxide Dismutase (SOD), Catalase (CAT)), and oxidative damage indicators (protein carbonylation and lipid peroxidation) were assessed. The biomarkers showed significant reduction in GST activity (up to 64,37% at the higher concentration of PFOA) and an increase in glutathione concentration (up to 157,31% in exposures to the binary mixtures of PFOA + CYN) indicating a dysfunction in the antioxidant system in parallel with a compensatory attempt by the cell in response to oxidative stress. Although SOD and CAT activities varied, no significant modulation was detected. In addition, the increase in protein carbonylation (up to 36,07% in exposures to the binary mixtures) confirms that the contaminants effectively caused oxidative damage. However, the oxidative defense mechanisms of this species (studied in the first 4 days of exposure) showed that they can be complex but responsive, and therefore likely contributed to recovery to control growth levels after 12 days in the various exposures to contaminants. The findings contribute insights into sublethal stress mechanisms and adaptive responses in aquatic primary producers exposed to emerging contaminants.