In recent decades, intensified industrial and agricultural activities have caused widespread and ongoing metal(loid) contamination in soils, creating serious environmental and health risks worldwide. This study assesses the combined interactions and effects of natural organic matter humic acid (HA) at 0.4% by weight/weight and iron oxides goethite nanorods (GN) at 1% by weight/weight on the leachability of arsenate As(V) and chromate Cr(VI) in soil under two scenarios. In the predosing scenario, soil containing GN and/or HA was packed into a column and treated with solutions of Cr(VI), As(V), or both (each at 20 mg L−1) at a flow rate of 0.5 mL min−1. In the postdosing scenario, the soil was spiked with As(V), Cr(VI), or both, then mixed with GN and/or HA and incubated for 24 h, and packed into columns. Then, both the soil columns were leached with a 0.01-M CaCl2 solution. The effluent analyses showed that in the predosing scenario, HA was effective in adsorbing/reducing Cr(VI), achieving decrements of 36% and 90% in the absence and presence of As, respectively. GN decreased As leachability by approximately 70%, though its efficiency decreased in the presence of Cr(VI). Conversely, HA increased As leachability, particularly in the presence of Cr(VI). Similar outcomes were observed in the post-dosing scenario. Compared to the predosing scenario, the post-dosing scenario showed improved performance regarding Cr(VI) and As(V) adsorption and retention. The findings underscore the significant impact of coexisting oxyanions on the leachability of contaminants in soil, particularly when iron oxides and organic matter are present. These factors should be carefully considered before applying any treatment that relies on redox or adsorption processes, highlighting the complex interactions in soil remediation strategies.
Shirzadeh et al. (Sun,) studied this question.