Genotoxic Effects of Water in Aquatic Ecosystems with Varying Cyanobacterial Abundance Assessed Using the Allium Test

Cyanobacterial blooms in aquatic ecosystems are a major global environmental concern. While the mutagenic and mitosis-disrupting properties of isolated cyanobacterial toxins are well documented, evidence of cytogenotoxic effects resulting from cyanobacterial blooms in natural aquatic ecosystems remains limited. In this study, water genotoxicity was evaluated in microcosms simulating cyanobacterial blooms of varying abundance. In microcosms with initially high cyanobacterial abundances (4.6 × 107 and 2.2 × 107 cells L−1) and biomass (58 mg L−1 and 20 mg L−1), significant toxic, cytotoxic, mitosis-disrupting, and mutagenic effects were observed: root elongation was inhibited by up to 49.6% (Day 1), the mitotic index decreased by ~33% (Treatment I, Day 42) vs. Control, and total chromosomal aberrations and lagging chromosomes increased by ~2.5-fold on Day 1 (Treatment I) and ~4.7-fold on Day 42 (Treatment I) vs. Control; micronuclei increased ~10-fold on Day 42 in Treatment I and II. In microcosms with lower cyanobacterial abundance (1.2 × 107 cells L−1) and biomass (9 mg L−1), significant reductions were observed only in root growth and in the mitotic index compared with Control. Future research should aim to identify a broader spectrum of cyanobacterial toxins and to investigate their environmental fate and persistence in aquatic ecosystems, particularly since genotoxic effects were detected even during the post-bloom period: on Day 42 extracellular microcystins in water were <LOQ in Treatments I and III (and 0.025 µg L−1 in Treatment II), yet chromosome lagging and micronuclei remained elevated. The observed genotoxicity associated with cyanobacterial metabolites underscores the need for thorough risk assessments of cyanobacterial blooms in aquatic environments.