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In this article, strontium distribution in sedimentary coastal aquifers of Eastern India was studied and its association with groundwater particles has been ascertained using hydrochemical and morphological tools. Groundwater contains Sr 2+ in the range of 0.08-4.0 mg/L with higher concentrations in Cretaceous formation. The particle number in groundwater varies from 4.5 × 10 5 to 3.3 × 10 6 per liter and follows the power law distribution with respect to the particle diameter. The calculated β values (2.54 and 4.03) signify the abundance of smaller particles over larger ones. The particle concentration of size range 0.45-8 μm is found to be 0.64-2.6 mg/L. Elemental data of groundwater particles clearly suggest their origin from the host rock minerals. Zeta potential data indicates diverse nature of colloids suggesting prevalence of both positive and negative charged species in the groundwater. The hydrochemical interpretation along with speciation studies infers that high Sr 2+ in groundwater is a result of incongruent dissolution of carbonate minerals and the dissolved Sr 2+ partitions into both dissociated and un-dissociated forms. Based on the Sr 2+ /Ca 2+ ratio and mineral saturation indices, it can be inferred that the Sr 2+ is preferentially associated with colloids over large particles and the migration takes place through sorption of Sr 2+ onto clay-bound (extrinsic) colloids in groundwater. This study describes the mechanism of strontium release into groundwater and provides insights into the role of groundwater particles in controlling the strontium migration to deep aquifers., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 Elsevier Ltd. All rights reserved.)

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., (Copyright © 2021 Elsevier Ltd. All rights reserved.)

Groundwater chemistry is mainly governed by lithological variations, space and resident time. In addition, hydrogeochemical characteristics of groundwater in the lithological contact zones are too complex. Hence, Cretaceous–Tertiary (KT) boundary from Ariyalur district, Tamilnadu, India, was selected for this study to identify the hydrogeochemistry of groundwater. This study includes 284 groundwater samples from four different seasons (pre-monsoon, post-monsoon, southwest monsoon and northeast monsoon). Groundwater samples were collected and analysed for major cations and anions, including physical parameters using standard procedures. High electrical conductivity (EC) showed the longer residence time of groundwater in hard rock region at the central and southern part of the study area. Ca2+, Na+, Cl− and HCO3− are the dominant ions in all the four seasons. The seasonal composition migration was observed from Na–Ca–Cl–HCO3 type to Na–Mg–Cl–HCO3 type, and Ca-HCO3 is the predominant water type in piper plot. Interpretation of data reveals that the groundwater quality was unsuitable for domestic and irrigation purposes during pre- and southwest monsoon seasons. Rock–water interaction and dissolution of minerals are the main sources of groundwater chemistry. Agriculture activities during monsoonal seasons also play a role in controlling the hydrogeochemistry of groundwater in this region. [ABSTRACT FROM AUTHOR]