Assessing the influence of contaminated rice straw decomposition on the speciation of cadmium and arsenic in a naturally contaminated soil

PurposeStraw return is a common agronomic practice for improving soil fertility and sustaining crop productivity. This paper considers the potential impacts of contaminated straw return on the availability of metal(loid)s and on microbial activity in paddy soils. MethodsCadmium (Cd) and arsenic (As) co-contaminated soils were collected and incorporated with contaminated rice straw (RS) or coupled with straw-decomposing microbial inoculants (SD), and were incubated for 75 days under laboratory-controlled conditions. ResultsThe results showed that addition of straws (both RS and SD) increased soil total Cd and As concentrations by 0.07-0.11 and 1.83-1.89 mg & BULL;kg(-1), respectively. In contrast to the control treatment (no straws, CK), RS and SD treatments significantly increased soil-available As concentrations throughout the incubation period, whereas available Cd concentrations decreased from day 10 to day 45. A remarkable rise in all Cd fractions was observed in the straw-applied treatments compared with CK. The easily soluble, Ca-associated and residual fractions of As were decreased and changed into Al-associated and Fe-oxyhydroxides As fractions. Compared with RS treatment, applying SDMIs accelerated the decomposition process of the straw and the transformation of Cd and As, and increased the richness and diversity of the bacterial community. Based on redundancy analysis, pH and dissolved organic carbon (DOC) were identified as the most important controlling factors for redistribution of Cd and As fractions during straw decomposition. ConclusionsThese results highlight that we should be cautious when returning co-contaminated rice straw to paddy fields, as this practice may increase the risk of more As production. SDMI utilization is an effective strategy to immobilize Cd, but it may enhance the availability of As.