Assessment of heavy metal and pesticide contamination in organic crops using Allium cepa

Increasing requirements for the environmental safety of agricultural systems necessitate reliable bioindicative methods for assessing the toxicity of soil contaminants to plants. This study aimed to compare the phyto-, cyto-, and genotoxic effects of binary combinations of heavy metals (Cd+Pb, Cu+Zn) and glyphosate using the Allium cepa test system. A controlled laboratory experiment with 20 onion bulbs per group, five repetitions, and one control and three experimental treatments was conducted. Morphometric analysis of root growth (root length and fresh weight), visual evaluation of morphological damage, cytogenetic analysis of apical meristem cells (mitotic index and chromosomal aberration frequency and spectrum), and Student’s t test were used to assess. EC50 was calculated using nonlinear regression, and compared to maximum permissible concentration standards. The highest phytotoxicity was observed for the Cd+Pb combination, which reduced root growth by 55.1%, followed by Cu+Zn (47.2%), while glyphosate showed the lowest effect (39.0%). Cytogenetic analysis revealed significant inhibition of mitotic activity (54.2%, 38.5%, and 26.3%, respectively) and increased chromosomal aberrations, with heavy metals showing predominantly clastogenic effects and glyphosate characterised by a higher proportion of chromosomal bridges. Experimentally determined EC50 values for Cu, Zn, Pb, and Cd were 3-25 times lower than current maximum permissible concentrations, indicating biologically significant effects at concentrations considered permissible. The results demonstrated the high sensitivity of the Allium cepa test system and indicated that existing environmental standards for heavy metals may underestimate risks to plant organisms, particularly in agricultural systems where copper-containing products are permitted