Decoding heavy metals (Cd2⁺ and Cr⁶⁺) / metalloid (As3⁺) toxicity: unmasking physiological, biochemical and genotoxic consequences in green chili

Heavy metal (HM) and metalloid exposure induces oxidative stress in plants resulting in growth inhibition and cellular damage. This study investigated the phytotoxic and genotoxic effects of cadmium (Cd2⁺), chromium (Cr⁶⁺), and arsenic (As3⁺) on Capsicum annuum L. (green chili) cultivated under soil conditions. Increasing concentration of these trio ions significantly reduced growth parameters in a dose-dependent manner. Among them, As3⁺ exhibited the highest toxicity, completely inhibiting seed germination at 100 ppm, reduced the vigor index by 92.5%, and completely suppressed the radicle and plumule elongation. Scanning electron microscopy revealed marked deformation of root tips, while confocal microscopy indicated dose-dependent cytotoxicity in root cells. High concentrations of As3⁺ substantially reduced root and shoot biomass, chlorophyll a, chlorophyll b, carotenoids, and protein content. Conversely, stress markers such as proline, malondialdehyde (MDA), and electrolyte leakage (EL) were increased by 94%, 80%, and 68%, respectively, over control. Antioxidant enzyme activities- CAT, APX, POD, GPX, SOD, and GR in chili leaves were strongly induced at 100 ppm, indicating enhanced oxidative defense pathways. On the other hand, Cd2⁺and Cr⁶⁺ also showed toxic effects in chili plants. Metal uptake was highest at 100 ppm, with roots accumulating more Cd2⁺, Cr⁶⁺, and As3⁺ than shoots. Genotoxic analysis of root meristems revealed a sharp decline in mitotic index (MI) and multiple chromosomal aberrations, including micronuclei, stickiness, laggards, bridges, and fragments. Overall, Cd2⁺, Cr⁶⁺, and As3⁺ severely impaired plant growth, physiological responses, and genome integrity in chili, with As3⁺ exerting strong toxic effects. These findings highlight serious environmental and food-safety concerns, particularly in contaminated agricultural regions where such metals can enter the edible food chain. The results emphasize the need for mitigation strategies and field-based interventions such as microbial remediation or soil amendments to reduce heavy-metal/metalloids risks under real-world conditions.