New study uncovers potential risk of arsenic release from sediment under organic matter influence

Newswise — A study carried out by researchers at the Chinese Research Academy of Environmental Sciences aimed to evaluate the influence of environmental factors and microbial communities on the mobilization of arsenic (As). The research, published in Volume 15 of the journal Environmental Science and Ecotechnology, provides valuable insights into the biogeochemical processes responsible for the release of As in the environment.

The investigation focused on various processes, such as desorption, reduction, complexation, and co-precipitation, which impact the behavior of As in the environment. Of particular importance was the interaction between Fe (hydro) oxides and organic matters (OMs), especially dissolved organic matter (DOM), which played a critical role in controlling the release of As. The OMs were characterized using fluorescence indices, indicating continuous biological activities throughout the experimental period.

The analysis of microbial communities revealed the presence of bacteria capable of reducing Fe, Mn, and As, as well as bacteria involved in metabolic transformations using EOM. Introduction of bio-reactive and chemically reactive OMs created a reduction environment that facilitated the release of As, Fe, and Mn, particularly at high concentrations of OM. Glucose and sodium lactate, easily metabolized by microorganisms, resulted in higher releases of these elements compared to the control group without OMs. The addition of humic acid (HA), a chemically reactive OM, significantly influenced the release of Fe and Mn, although its impact on As release was relatively less pronounced.

The study also observed the formation of secondary Fe minerals, such as siderite and mackinawite, which incorporated As and contributed to the reduction of As, Fe, and Mn concentrations in the aqueous phase. Microbial decomposition altered the characteristics of DOM, leading to the production of amino acids and the presence of polysaccharides, as indicated by specific functional groups.

In addition, the researchers employed canonical correspondence analysis (CCA) and redundancy analysis (RDA) to explore the relationship between environmental factors, microbial communities, and As mobilization. Positive correlations were found between As(III), Fe, and Mn, while a negative correlation was observed with oxidation-reduction potential (ORP). Several bacterial genera associated with As metabolism were identified, highlighting their role in the release process.

Highlights

•Groundwater arsenic mobilization regulated by exogenous organic matter (EOM) was revealed.

•Reactivity of Fe (hydro)oxides and SO₄²⁻ reduction control groundwater As level.

•Secondary risk of anthropogenic EOM for groundwater As and Mn release merit noting.

The research significantly enhances our understanding of the intricate factors influencing the release of arsenic (As) and sheds light on the microbial processes involved in As mobilization in aquatic environments. The findings have important implications for managing and mitigating groundwater pollution caused by the infiltration of EOM. Specific sites, such as landfills, petrochemical sites, and managed aquifer recharge projects, are identified as particularly vulnerable to contamination. Further investigations are necessary to explore the effects of hydrodynamics and hydrogeochemical environments in practical applications. These findings underscore the need for comprehensive strategies to effectively control and mitigate the environmental risks associated with EOM infiltration, aiming to safeguard groundwater quality.