Arsenic distribution in sediments of multi-tier sedimentary formation of coastal Pondicherry, India – Implications on groundwater quality.

In this work, sediments collected from a 150-m deep litho-section of a coastal region and encompassing Quaternary, Tertiary and Cretaceous sedimentary formations were studied for arsenic distribution and other trace and redox sensitive elements. Arsenic concentration in the sediments is found to vary from <0.5 to 30 mg·kg⁻¹ and showed an increasing trend with the depth. The highest As content is observed at a depth of 129–131 m bgl belonging to Cretaceous formation. Though XRD studies do not indicate any arsenic mineral in sediments, positive correlations between As–Fe and S, as well as ESEM-EDS and TXRF studies confirm the presence of As sorbed to FeS mineral. The organic matter and As correlations suggest microbial mediated reduction process, which may pose future risk to water quality of this prolific coastal fresh water aquifer system. The elemental profiles infer that Cretaceous and Tertiary formations demonstrate inner shelf and marginal marine condition respectively. [Display omitted] • As content ranges from 0.5 to 30 ppm with high content observed in deeper sediments. • Elemental correlations and mineralogical evidences suggest presence of As bound iron minerals. • Reducing conditions govern the As sorption mechanism on sediments. • Quaternary and Tertiary aquifers seem to be resilient to As contamination. • Cretaceous aquifers seem to be more vulnerable to arsenic contamination. [ABSTRACT FROM AUTHOR]