Trade-off between arsenic and straw-derived DOM immobilization in their co-sorption on γ-Al2O3: Implications for arsenic mobility and carbon sequestration in farmlands

Straw-derived dissolved organic matter (DOM) is widespread in farmland soils, but the relationship between straw-derived DOM and As in their co-sorption on minerals and the underlying mechanisms remain unclear. Here, batch experiments and spectroscopic analyses were employed to investigate the co-sorption of straw-derived DOM and As(III/V) on γ-Al 2 O 3 . Results showed a trade-off between the As(III/V) and DOM immobilization on γ-Al 2 O 3 under different pH levels, which was caused by competitive sorption. The rape straw-derived DOM (DOM_Ra) exhibited a stronger inhibition on As(III/V) sorption than rice straw-derived DOM (DOM_Ri). This could be due to more aromatic fractions in the DOM_Ra and DOM_Ri, which were preferentially sorbed by γ-Al 2 O 3 . In turn, the preferential sorption of aromatic DOM components was weakened by As(V) sorption, which, however, was not found in As(III) and DOM co-sorption. Furthermore, spectral results indicated that carboxylic groups on the sorbed DOM could provide additional binding sites for As(III/V) to form ternary complexes, but its role was overwhelmed by the DOM competitive sorption, which ultimately exhibited the inhibitory effect of DOM on As(III/V) sorption. These findings enhance the fundamental understanding of the co-sorption of As(III/V) and DOM on soil minerals and contribute to predicting As mobility and OM stability in As-contaminated farmlands with straw return.