Assessing the risk of cyanobacterial toxins in freshwater ecosystems: microcystin-LR exposure in Chironomus riparius larvae.

Cyanobacteria produce a variety of secondary metabolites, including the potent and widespread toxin microcystin-LR (MC-LR). While the toxic effects of MC-LR on aquatic species are well documented, its impact on Chironomid larvae, key organisms in freshwater food chains, remains insufficiently understood. This study investigated the acute toxicity of MC-LR at environmentally relevant concentrations (5, 10, 15, and 30 µg/L) on Chironomus riparius (Diptera, Chironomidae). The effects of the tested concentrations were evaluated using a multi-biomarker approach, including hemoglobin levels, oxidative stress markers (advanced oxidation protein products [AOPP], malondialdehyde [MDA], catalase [CAT], and superoxide dismutase [SOD] activity), and DNA damage in 4th instar larvae of C. riparius. Using this approach, MC-LR exposure significantly increased DNA damage in larvae across all concentrations, with a clear dose-response relationship. Hemoglobin levels declined with increasing MC-LR concentration, with significant reductions at 5 and 10 µg/L MC-LR. Antioxidant responses showed a concentration-dependent decrease in CAT activity. SOD activity and MDA levels showed increasing trends, although these changes were not statistically significant. AOPP levels were significantly elevated at 10 µg/L MC-LR. This study demonstrates that MC-LR affects physiological and biochemical processes in 4th instar C. riparius larvae, representing the first assessment of sublethal effects under environmentally relevant conditions. Such alterations indicate early physiological stress with potential consequences for larval fitness and trophic interactions in freshwater ecosystems. These findings may have ecological implications through their influence on physiological functioning, particularly processes related to oxygen transport, oxidative balance, and DNA integrity, although confirmation under chronic exposure conditions is required.