Three-Compartment Model for Contaminant Accumulation by Semipermeable Membrane Devices

Abstract

Passive sampling of dissolved hydrophobic contaminants with lipid (triolein)-containing semipermeable membrane devices (SPMDs) has been gaining acceptance for environmental monitoring. Understanding of the accumulation process has employed a simple polymer film-control model of uptake by the polymer-enclosed lipid, while aqueous film control has been only briefly discussed. A more complete three-compartment model incorporating both aqueous film (turbulent-diffusive) and polymer film (diffusive) mass transfer is developed here and is fit to data from accumulation studies conducted in constantconcentration, flow-through dilutors. This model predicts aqueous film control of the whole device for moderate to high K ow compounds, rather than polymer film control. Uptake rates for phenanthrene and 2,2′,5,5′-tetrachlorobiphenyl were about 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 thicknesses and solute diffusivities in the polymer film are modeled, and overall accumulation by the whole device is predicted to remain under aqueous film control, although accumulation in the triolein may be subject to polymer film control. The predicted half-life and integrative response of SPMDs to pulsed concentration events is proportional to log K SPMD .

Accumulation of organochlorinated pesticides by triolein-containing semipermeable membrane device (triolein-SPMD) and rainbow trout

“…Both processes are related to the lipophilicity of the compound. In the work of Gale [26], three-compartment model was used for evaluating contaminant accumulation by triolein-SPMD. The model predicts aqueous film control for compounds with moderate to high K ow ; rather than polymer film control.…”

Modeling the response of passive samplers to varying ambient fluid concentrations of organic contaminants

“…It is evident from Figure 5 that the sampler begins accumulating contaminant at the same time as the ambient pulse begins. There is no lag time for commencement of accumulation in this treatment, but one is likely to be observed in actual deployments [1,24]. This is a result of consideration of the sampler as a relatively simple single compartment or phase.…”

Review of the background and application of triolein-containing semipermeable membrane devices in aquatic environmental study

“…(1)- (3) is also based on the assumption that the chemicals accumulated by triolein-SPMDs are only in the triolein phase. However, the membrane is a functional constituent in the sampling process rather than simply a container for the triolein (Huckins et al, 1990a;Petty et al, 1994;Gale, 1998;Booij et al, 1998). Studies have indicated that the polyethylene membrane used in triolein-SPMD is a significant reservoir for hydrophobic residues and has a membrane/solute partitioning coefficients only a little less than the inner triolein reservoir (K pw : 0.1-0.5K tw , Gale, 1998).…”

“…However, the membrane is a functional constituent in the sampling process rather than simply a container for the triolein (Huckins et al, 1990a;Petty et al, 1994;Gale, 1998;Booij et al, 1998). Studies have indicated that the polyethylene membrane used in triolein-SPMD is a significant reservoir for hydrophobic residues and has a membrane/solute partitioning coefficients only a little less than the inner triolein reservoir (K pw : 0.1-0.5K tw , Gale, 1998). For example, a typical sampler has a total mass of about 4.5 g, which contains 0.91 g (1 ml) of triolein and represents a polyethylene to triolein ratio of about 4:1 (Huckins et al, 1996).…”

“…polyethylene plus triolein), C SPMD is the concentration in the whole device, and V SPMD is the volume of the whole sampler. A three-compartment (3C) differential equation model has been developed and used to describe the kinetics of the accumulation processes (Gale, 1998). Based on the 3C model, it was suggested that the accumulation of a chemical in a triolein-SPMD may be controlled by either: (1) polymer film diffusion for large molecules with low polymer diffusivity, where steady-state solute concentrations in polyethylene and water are reached before they attained in polyethylene and triolein; (2) aqueous film diffusion for highly polymer-diffusive molecules, where the ratio of the solute concentrations in triolein and polyethylene reaches steady state before the whole device approaches steady state with the water; (3) a combination of aqueous and polymer film diffusion where solute concentrations in polyethylene and triolein reach a relatively constant ratio, but not necessarily the final steady-state value (i.e.…”