Volatile methylsiloxanes in surface water and sediment of an Indian river: Levels, spatiotemporal variations, and...

Volatile methylsiloxanes (VMS), widely used in beauty and personal care products, are emerging contaminants due to their persistence, bioaccumulation, and toxicity properties. The occurrence of VMS in aquatic systems has been reported worldwide, but data from India remain limited. The present study aimed to investigate the occurrence, spatiotemporal variations, and ecological risk of VMS in an Indian river. River water and sediment samples were collected during the winter and summer seasons. The mean concentrations of total VMS in river water were 1430 and 1810 ng L ^-1 in winter and summer, respectively. However, in sediments, mean VMS concentrations were higher during winter (12,100 ng g ^-1) than summer (4950 ng g ^-1). Among the VMS, octamethylcyclotetrasiloxane and decamethylcyclopentasiloxane were the most abundant in river water and sediments. The water-sediment (log Kow) and organic carbon-based (log Koc) distribution coefficients indicated no equilibrium between water and sediment under field conditions. No significant correlation was observed between VMS concentrations and water and sediment organic carbon content. Based on the concentration of VMS in river water, the cumulative riverine input flux was estimated to be 1.29 tons year ^-1 (average: 0.65 tons year ^-1). The hazard quotients for VMS exceeded the threshold level, indicating a significant ecological risk to the aquatic environment.