Spatial variations of linear and cyclic volatile methyl siloxanes in a river basin and their air-water exchange

Linear and cyclic volatile methylsiloxanes (VMS) are Si and O containing organic compounds that are increasingly subject to scientific studies in recent years. They are used as solvents and coating materials in personal care products, cleaning materials and industrial applications. In this study, it was aimed to investigate the spatial variations of VMS levels in river water and ambient air in Kucuk Menderes Basin and their air-water exchange patterns. Grab river water samples and passive ambient air samples collected from 10 sites throughout Kucuk Menderes Basin located in Izmir region in Turkey, and they were analyzed for VMS. The concentrations of Sigma VMS in river water and ambient air ranged from 48.4 to 148 ng L-1 and from 41.7 to 433 ng m(-3), respectively. Among the VMS compounds, the predominant compounds were found to be D5 and D3 in ambient air and river water, respectively. In general, concentrations of all VMS congeners increased towards downstream of the river for both water and ambient air samples and there were substantial fluctuations between the sampling points. These fluctuations may be due to wastewater discharges at some sites (increase), followed by loss by volatilization along the river (decrease). VMS concentrations measured in air and river water samples were used to estimate the net air-water exchange fluxes. In all cases, fluxes were negative, ranging between -159 (L4) and -11100 (D3) ng m(-2) day, indicating volatilization from water is a source for atmospheric VMS.