The influence of humic and fulvic acids on Cd bioavailability to wheat cultivars grown on sewage irrigated Cd-contaminated soils

Abstract

The soil cadmium (Cd) contamination is a ubiquitous environmental problem that has resulted from intense irrigation with wastewater. This pot trial was conducted with aim to produce safe food with Cd tolerant wheat cultivar in wastewater irrigated soils. For this purpose, two wheat cultivars NARC-2011 (Cd tolerant) and Shafaq-2006 (Cd sensitive) were screened out and selected, after conducting a pilot trial of twelve local wheat cultivars against Cd stress. Both cultivars were grown in naturally contaminated soils with Cd concentrations (4.18, 3.23, 2.29 and 1.25 mg kg−1). After harvesting, NARC-2011 showed significant photosynthetic attributes, grain biochemical parameters and yield. Additionally, Cd concentrations in edible grains of NARC-2011 cultivars were found within standard limits (200 mg kg−1), in all contaminated soils. Furthermore, a marked decrease in Cd bioavailability was noted with cultivar NARC-2011, where contribution of mobile Cd fractions (exchangeable and reducible) percentage was decreased, while immobile Cd fractions percentage increased (oxidizable and residual). Fourier transform infrared (FTIR) spectroscopy reflects the maturity and stability of humic and fulvic like acid fractions and revealed that humification of these compounds after prolonged sludge enriched wastewater irrigation lowered the Cd availability. The wheat cultivar NARC-2011 (Cd tolerant) could be opted to grow on soils irrigated with wastewater for a long time, as Cd bioavailability decreased with ageing due to stabilized humic substances and varietal tolerance.