Phyto-cytogenotoxic effects of glyphosate-based herbicide contaminated soil: assays using Allium cepa

Glyphosate is the most widely used herbicide worldwide; however, most toxicity studies utilizing plants have been conducted in aqueous solutions, thus overlooking the role of soil properties in modulating herbicidal effects. The aim of this study was to examine the phyto-, cyto-, and genotoxic responses following Allium cepa exposure to glyphosate-contaminated soil. This would thus address a critical knowledge gap regarding herbicide-initiated toxicity under realistic environmental conditions. Glyphosate concentrations were tested in a geometric series with a 2× ratio, ranging from 1 to 1024 mg a.i./kg of soil, based upon levels found in agricultural environments. The parameters examined included germination rate, root length, cell viability, mitotic index, and frequency of chromosomal alterations. Glyphosate concentrations ranging from 16 to 1024 mg a.i./kg inhibited root growth and damaged cell membrane integrity, whereas levels from 1, 4, and 128 mg a.i./kg increased cell division associated with reduced mitotic index at 512 mg a.i./kg. Genotoxic effects were observed from 4 to 1024 mg a.i./kg. While low and intermediate concentrations primarily triggered genotoxic effects, the highest concentrations (256 to 1024 mg a.i./kg) promoted marked cytotoxicity. These findings provide novel evidence that glyphosate in soil might induce biphasic and multiparametric responses in A. cepa, reinforcing the importance of using soil-based bioassays for environmental risk assessment.