3-COMPARTMENT MODEL FOR CONTAMINANT ACCUMULATION BY SEMIPERMEABLE-MEMBRANE DEVICES

Passive sampling of dissolved hydrophobic contaminants with lipid (tri olein)-containing semipermeable membrane devices (SPMDs) has been gain ing acceptance for environmental monitoring. Understanding of the accu mulation process has employed a simple polymer film-control model of u ptake by the polymer-enclosed lipid, while aqueous film control has be en only briefly discussed. A more complete three-compartment model inc orporating both aqueous film (turbulent-diffusive) and polymer film (d iffusive) mass transfer is developed here and is fit to data from accu mulation studies conducted in constant-concentration, flow-through dil utors. This model predicts aqueous film control of the whole device fo r moderate to high K-OW compounds, rather than polymer film control. U ptake rates for phenanthrene and 2,2',5,5'-tetrachlorobiphenyl were ab out 4.8 and 4.2 L/day/standard SPMD, respectively. Maximum 28 day SPMD concentration factors of 30 000 are predicted for solutes with log K- OW values of > 5.5. Effects of varying aqueous and polymer film thickn esses and solute diffusivities in the polymer film are modeled, and ov erall accumulation by the whole device is predicted to remain under aq ueous film control, although accumulation in the triolein may be subje ct to polymer film control. The predicted half-life and integrative re sponse of SPMDs to pulsed concentration events is proportional to log K-SPMD.