Effect of environmental factors on the mechanism of arsenic release from clay layers during natural compaction

Abstract

Listen

Translate article

Clay layers are presumed sources of original arsenic (As) in the groundwater of underlying aquifers. However, studies have focused less on the release mechanism of As from clay layers compared to well-studied As release from aquifers, especially during the natural compaction process of clay layers and its role in As mobilization. Herein, simulation experiments of the natural compaction of clay layers were performed at different compaction rates and temperatures. Hydrochemistry, parallel chemical extraction, and high-throughput sequencing of the full-length 16S rRNA gene were employed to investigate the release mechanism of As from clay layers during compaction. While the compaction rate and temperature were found to promote the release of As from clay sediments, increasing the compaction rate caused As to enter pore water through reductive dissolution from crystalline iron (hydr)oxides to ferrihydrite and very poorly crystalline goethite; Meanwhile, temperature increment only increased the microbial activity and did not alter the release mechanism of As. When the natural burial rate of clay layers was altered, the compaction rate has greater effect than temperature on As release from clay sediments.. Under natural compaction, the concentration of As transported to the groundwater by clay layers was found to be 43.58–116.70 μg/L. These results suggested that the contribution of the natural compaction of As-rich clay layers to the formation of high As groundwater in aquifers is underestimated.