What does Semi-Permeable membrane device (SPMD) sampling mean? an insight on the "time-weight integrative" and "SPMD-availability" hypothesis

Abstract

International audienceSPMDs are commonly used integrative passive samplers for hydrophobic organic compounds [1]. Because of steric hindrance in the polyethylene membrane, only a fraction of dissolved organic compounds in water may be accumulated. It is usually assumed that only truly dissolved compounds are available to SPMD. From the accumulated amount of a substance in SPMD, and dissipation of Performance Reference Compounds, the exchange rate constant and the concentration of SPMD-available substance in water can be estimated. It is usually assumed that the SPMD-available concentration estimated from accumulation in SPMD corresponds to the time-weight average (TWA) concentration. Moreover, provided that the half-time is higher than the exposure duration, the sampling is supposed to be fully integrative. In this study, we investigate the significance of the "time-weight" integrative sampling: factors such as deployment duration, exchange rate constants, but also water concentration variations are examined. The chemical form of SPMD-available compounds is also investigated: compiling several field studies, SPMDavailable concentrations are compared to total dissolved concentrations of Polycyclic Aromatic Hydrocarbons (PAHs). Assuming that PAHs that are bond to dissolved organic matter cannot enter the membrane of SPMD, in situ partitioning coefficients KDOC are computed and compared to lab data