Amorphous Silica-Based Fertilizer Reduces Cd Uptake and Translocation and Human Health Risk in Polluted Soil Grown with Cowpea (Vigna unguiculata (L.) Walp)

The entry of cadmium (Cd) in the soil-crop system poses a risk to human health due to food chain contamination. Applying silicon (Si) to soils can immobilize Cd, mitigate phytotoxicity, and reduce human exposure to the metal. Here, we aimed to assess the effects of an amorphous silica fertilizer (ASF) on the availability of Cd and Si in the soil and their accumulation by cowpea (Vigna unguiculata) grown on a Cd-polluted soil. In addition, Cd distribution into roots, shoots, and grains, the mineral composition of plants, and the human health risks from exposure to polluted soil and grain consumption were also evaluated. There was a 13% reduction in soil Cd availability with the application of 1350 kg ha(-1) ASF compared to the control. In the plant, the Cd concentrations reduced from 37% in roots, 40% in shoots, and 38% in grains. ASF fertilization improved plant nutritional status and increased cowpea growth and grain yield. Besides reducing Cd concentrations in the grains, Si also significantly decreased the Cd bioaccessibility in the soil and grains (from 70 to 34% and from 83 to 52%, respectively), resulting in negligible risk. Thus, the application of 1350 kg ha(-1) ASF is recommended for risk management in soils polluted by Cd and cultivated with cowpea, given that Si could mitigate the Cd stress caused, induce Cd phytostabilization, and reduce metal translocation to cowpea grains.