Abstract
Among the numerous contaminants of soil, glyphosate and paraquat are two of the most widely used herbicides that are commonly detected in the environment. Soil and sediment contaminated with glyphosate, paraquat, and other environmental toxins can be mobilized and redistributed to lawns, vegetable gardens, parks, and water supplies in vulnerable communities at the site of disasters such as hurricanes and flooding. Glyphosate and paraquat bind strongly to soils containing clays, making their bioavailability (bioaccessibility) from these types of soil very low. Because of their affinity for clay-based soils, it is possible that montmorillonite clays could be administered as a therapeutic agent in the diet of animals and humans to decrease short-term exposure and toxicity. In this study, we investigated the sorption mechanisms of glyphosate and paraquat onto active surfaces of calcium montmorillonite (CM) and sodium montmorillonite (SM) clays and derived binding parameters, including capacity, affinity, and enthalpy. Additionally, we used these parameters to predict the reduction in bioavailability under different pH and temperature conditions and to estimate the theoretical dose of clay that could protect against severe paraquat toxicity and lethality. Computational modeling and simulation studies depicted toxin sorption mechanisms at different pH values. Additionally, a toxin-sensitive living organism (Hydra vulgaris) was used to confirm the safety of the clay and its ability to protect against toxicity from glyphosate and paraquat. The high efficacy of CM and SM shown in this study supports the natural binding activity of glyphosate and paraquat to clay-based soils. Following disasters and medical emergencies, montmorillonite clays could be administered by capsules and tablets, or added to food and flavored water, to reduce toxin bioavailability and human and animal exposures.