Oxidative stress in the algae Chlamydomonas reinhardtii exposed to biocides

The toxicity of biocides can be associated with the formation of reactive oxygen species (ROS) and subsequent oxidative damage, interfering with the normal function of photosynthetic organisms. This study investigated the formation and effects of ROS in the unicellular green algae Chlamydomonas reinhardtii exposed to three environmentally relevant biocides, aclonifen, dichlofluanid and triclosan. After a first screening to identify which biocides induced ROS, a 24h multi-endpoint analysis was used to verify the possible consequences. A battery of high-throughput methods was applied in algae for measuring ROS formation, reduced glutathione (GSH), lipid peroxidation (LPO), photosystem (PS) II performance and pigments (chlorophylls a, b and carotenoids). Results show that only aclonifen induced ROS after the first 6h exposure, with the other two biocides not showing any ROS formation. Aclonifen, a Protox and carotenoid inhibitor, induced a concentration-dependent ROS formation, LPO and interfered with algae pigments content, while no alterations were detected in GSH content. A significant effect was also seen in the photosynthetic process, especially a reduction in the maximum and effective quantum yields, accompanied by alterations in energy dissipation in PSII reaction centers and the impairment of the electron transport rate. This study demonstrated the successful use of a battery of high-throughput methods for quickly screening biocides capacity to induce the formation of ROS and the subsequent effects in C. reinhardtii, thus revealing their mode of action (MoA) at concentrations before an impact on growth can become effective.