8. Potential Hazardous Elements Fluxes from Soil to Plants and the Food Chain

Chemical elements exist naturally in the environment with different concentrations. However, human activities can increase these concentrations, what represent a serious threat to ecosystems and to the human health. In soil, the chemical elements are distributed in different physicochemical forms; inorganic species, organic complexes, adsorbed on solid phases or as constituents of solid phases with different solubility degrees. Plants can absorb only the elements present in the so-called available fraction, which is associated to the exchange complexes and soluble fractions in the soil solution. Absorption, translocation and accumulation of the elements in the plants depend on the species and ecotype as well as on the plant organ, climatic conditions and season of the year. Usually, essential elements (macro and micro-nutrients) are absorbed and translocated to the aerial part of the plant, while toxic elements are retained in the roots, however some hazardous elements are also transported to shoots. High concentrations of toxic elements in the plants can affect their biological processes and/or trigger different physiological responses to combat the oxidative stress (e.g. antioxidative enzymes, glutathione, phytochelatins). The elements accumulated in edible organs of crops or in spontaneous plants represent the major entry point in the food chain. Even at concentrations below phytotoxic levels, hazardous elements can pose health risks for humans due to the augmentation effect along the food chain. The objective of this chapter was to elucidate/clarify the pathways of the chemical elements in the soil-plant-human system as well as the physiological mechanisms that plants develop to respond to the absorption and accumulation of hazardous chemical elements.