Environmental assessment of the distribution and concentration of heavy metals in water, soil and plant (Sorghum bicolor L. Moench)

Abstract

Heavy metal contamination in arid and semi-arid agroecosystems is an increasing concern for food security and environmental sustainability. The Comarca Lagunera region in northern Mexico is one of the country’s most important agricultural zones, where the use of groundwater enables forage production despite severe water scarcity. This study evaluated the accumulation and distribution of essential and toxic elements in Sorghum bicolor L. Moench grown in Gómez Palacio, Durango, across four phenological stages. Samples of roots, stems, leaves, and spikes were analyzed, along with soil and irrigation water. The elements quantified included copper, zinc, calcium, magnesium, iron, manganese, arsenic, lead, and cadmium, measured using inductively coupled plasma mass spectrometry (ICP-MS). The results showed that copper and zinc tended to accumulate in leaves and stems, whereas calcium and magnesium were concentrated primarily in roots and leaves. Iron and manganese exhibited low internal mobility, remaining mostly in the roots. In contrast, toxic metals displayed limited mobility arsenic, lead, and cadmium accumulated mainly in roots and leaves, with minimal translocation to reproductive organs. In the soil, the concentrations of toxic metals decreased throughout the crop cycle, unlike essential nutrients, which remained stable. In irrigation water, calcium and magnesium remained constant, while iron, manganese, arsenic, and lead showed slight reductions toward plant maturity. These findings highlight the influence of rid conditions on metal dynamics, where soil properties and plant physiology determine the mobility and accumulation of each element. The low translocation of As, Pb, and Cd into the spikes indicates a reduced risk for the direct consumption of sorghum; however, the progressive accumulation of these contaminants in soil and irrigation water represents a potential long-term risk, underscoring the need for monitoring and sustainable management strategies in arid agricultural systems.