Integrated assessment of environmentally realistic heavy metal and trace element contamination in Yeşilırmak river triggers genotoxic and oxidative damage in Allium cepa L

In this study, the toxicity of heavy metals and trace elements detected by inductively coupled plasma-mass spectrometry (ICP-MS) analysis in the Yeşilırmak River was investigated using the Allium cepa test. Toxicity indicators included physiological parameters such as germination percentage, biomass increase, and root length; genotoxicity parameters such as micronuclei, mitotic index, chromosomal aberrations, and chlorophyll a and b content; and biochemical parameters such as malondialdehyde and antioxidant enzyme activities (superoxide dismutase and catalase). Finally, anatomical changes were examined under a microscope. According to ICP-MS results, heavy metals and trace elements (or elements containing naturally occurring radioisotopes), including titanium, rubidium, strontium, barium, gadolinium, and uranium, were detected in the stream water above acceptable parameter values. A decrease in germination rate, root length, and biomass increase was observed in onions treated with Yeşilırmak water. While mitotic index decreased, abnormalities such as micronuclei, vagrant chromosomes, fragments, chromatin distribution imbalance, bridges, sticky chromosomes, nucleolar buds, and disoriented aberrations significantly increased (p < 0.05). Furthermore, the Comet assay and gel electrophoresis also indicated significant DNA damage. Biochemical analyses revealed a threefold increase in malondialdehyde levels, a two- to threefold increase in superoxide dismutase and catalase enzyme activities, and a more than 50% decrease in chlorophyll a and b levels. The co-occurrence of trace element and heavy metal contamination threatens not only A. cepa but also many aquatic organisms and other non-target organisms. Therefore, prioritizing the protection of water resources before addressing toxicity is highly valuable.