Dual roles of AQDS as electron shuttles for microbes and dissolved organic matter involved in arsenic and iron mobilization in the arsenic-rich sediment

Microbially-mediated arsenic (As) metabolism and iron (Fe) bioreduction from sediments play crucial roles in global As/Fe cycle, and their mobilization is associated with the various effects within the alliance of "mediator-bacteria-DOM (Dissolved Organic Matter)". The gradient levels (0.05, 0.10 and 1.00 mM) of sodium anthraquinone-2,6-disulphonate (AQDS) as a mediator were investigated for their impact on reductive dissolution of As(V) and Fe(III) from arsenic-rich sediment. For the overall performance of AQDS-mediated reductive dissolution on As(V) and Fe(III), a more positive effect resulting from 0.05 mM AQDS was observed compared to 0.10 mM, whereas an inhibitory effect was observed with 1.00 mM. Compared to the biotic supplementation with acetate as electron donors, approximately 13- and 6-fold increased levels of As(III) were released with 0.05 and 0.10 mM, respectively, compared to 1.00 mM AQDS (107.51 μg/L), and approximately 4- and 3-fold increased Fe(II) levels (40.72 mg/L) were observed during the same conditions. Multiple-dynamic effects of "bacteria-AQDS-DOM", which result from AQDS, shifted the microbial community and synchronously derived terrestrial DOM, which potentially changes the DOM substrate and complex formation of As(III)-Fe(II)-humic DOM. High-throughput sequencing results indicated an increase in the abundance of metal-reducing bacteria (e.g., Bacillus (> 16%), Lactococcus (> 13%), Pseudomonas (> 4%) and Geobacter (> 3%)) when supplemented with 0.05 and 0.10 mM of AQDS. However, a boost increasing the abundance of metal oxidizing bacteria was observed with Alicyclobacillus (> 16%), Burkholderia (> 7%), and Bradyrhizobium (> 5%) upon supplementation with 1.00 mM AQDS. These novel insights have profound environmental implications and significance in terms of engineering, not only for understanding the cycle of As/Fe in sediment biochemical processes but for considering future alternative bioremediation treatments. - Highlights: • AQDS increases/decreases Fe(III)/As(V) bioreduction from sediment. • Complex formation between As and Fe was induced by humic DOM. • Specific metal-reducing bacteria increases/decreases Fe(III)/As(V) reduction with AQDS amendment. • Potential risk of AQDS mediated hazardous metal mobilization should be considered.