Assessment of heavy metal contamination of sediments in popular tourist beaches of the Kerala State, southern India: Implications on textural and mineralogical affinities and mitigation

Beaches form one of the most contaminated sedimentary environments by a myriad variety of anthropogenic activities, including tourism and recreational activities. The concentrations of metals and their pollution levels were studied for four tropical tourist beaches in Kerala state, Southern India. Bulk geochemical and mineralogical analyses of 16 sediment samples were performed to determine the environmental status and the environmental risk level using various geochemical indices. Based on the enrichment of TiO₂ and SiO₂ concentrations, the samples were grouped into ilmenite-rich samples (IRS) and quartz-rich samples (QRS) respectively and the geochemical signatures are significantly different. Mineralogically, the IRS group is dominated by ilmenite, quartz, sillimanite, zircon and rutile while the QRS group consists of quartz, spinel and calcite and garnets are common in both groups of sediments. Despite the variation in the trends of pollution indices, it has been found that Kovalam beach sediments are enriched with W, Th and U where, IRS with enrichment of W, U and Th while QRS only enriched with W and Th and not U. The mineralogical affinity of W with secondary tungsten-bearing minerals has been documented by the XRD analysis and these metals are mainly controlled by the geogenic sourced minerals. However, in terms of ecological risk, Pb, As and Cu have a considerable to moderate risk in both groups of sediments. Overall, both group of sediments shows a moderate risk. Based on the biological effect assessment the elements of concern are Pb and Zn in IRS and possible effect by the Cr, Cu and As in IRS and only by Cu in QRS. Though the prevalence of geogenic and anthropogenic processes and influences of metal enrichments are documented by the study, their relative influences, mobility and bioavailability need to be systematically studied.