Effect of Cr(VI) on Fe(III) reduction in three paddy soils from the Hani terrace field at high altitude

Batch experiments were conducted to investigate the effect of Cr(VI) on Fe(III) reduction in typical paddy soils from the Hani terrace field at different high altitudes. Firstly, soils with and without autoclaving were used to evaluate abiotic and biotic contributions on Fe(III) reduction in different soils. The results showed biotic reaction mainly contributed to Fe(III) reduction in Bada soil. Both abiotic and biotic Fe(III) reductions were limited in Duoyishu soil, while Fe(III) reduction in Laohuzui soil was predominantly driven by abiotic reactions. The difference of Fe(III) reduction was related to organic matter and Fe availability in soils. In the presence of Cr(VI), Fe(III) reduction was evidently inhibited and delayed in all soils. Under anaerobic condition, adsorption and reduction of Cr(VI) occurred simultaneously in soils. The presence of Cr(VI) can influence Fe(III) reduction in several ways, e.g., competition of Fe(III) and Cr(VI) reductions, preferred reduction of Cr(VI), retard of biotic Fe(III) reduction, and consumption of Fe(II) by Cr(VI), all of which may coexist in natural paddy soil. However, the extent of influence exerted by different interaction varies from each other in different soils, which is strongly associated with the soil characteristics.