Integrated assessment of clothianidin toxicity in Allium cepa L.

Abstract

Clothianidin (CLO), a widely used neonicotinoid insecticide, poses potential risks to non-target plant species. However, its multidimensional toxicity profile has not been sufficiently investigated. In this study, the toxic effects of environmentally relevant CLO concentrations (0.10, 0.67, and 20.0 µg/L) on Allium cepa L. were comprehensively evaluated by integrating physiological, cytogenetic, molecular, biochemical, and anatomical parameters. CLO exposure resulted in a dose-dependent decrease in germination (from 100% to 60%), root elongation (from 9.66 to 2.45 cm), and weight gain (from + 9.10 to + 3.40 g). Mitotic activity was significantly suppressed, with the mitotic index decreasing from 8.82% in the control group to 6.35% at the highest dose. Micronucleus and chromosomal abnormality frequencies also increased, particularly those of sticky chromosomes, vagrant chromosomes, fragments, and unequal distribution of chromatin. The increase in tail DNA percentages from 3.30% in the control group to 60.2% at the highest CLO concentration indicates significant DNA damage, showing a shift from minimal to high DNA damage. Biochemically, CLO exposure was associated with oxidative stress, as indicated by significant increases in malondialdehyde levels (from 2.13 to 10.6 µM/g FW) and antioxidant enzyme activities (superoxide dismutase : from 53.1 to 125 U/mg FW; catalase: from 0.47 to 1.17 OD 240nm /min/g FW)]. Furthermore, photosynthetic pigments were significantly reduced, with chlorophyll a and b decreasing by 60% and 68%, respectively. Anatomical observations supported these findings, revealing dose-dependent tissue damage, including epidermal and cortical cell damage, flattened nucleus, and vascular tissue thickening. Overall, the results demonstrate that CLO causes growth inhibition, oxidative stress, genotoxic damage, and structural changes in A. cepa , suggesting that its phytotoxic effects occur via interconnected cytogenetic and oxidative stress pathways. These findings highlight the potential ecological risks of CLO for non-target plant species and underscore the need for further mechanistic studies.