Permeability/performance reference compounds (PRCs) are analytically noninterfering organic compounds with moderate to high fugacity from semipermeable membrane devices (SPMDs) that are added to the lipid prior to membrane enclosure. Assuming that isotropic exchange kinetics (IEK) apply and that SPMD-water partition coefficients are known, measurement of PRC dissipation rate constants during SPMD field exposures and laboratory calibration studies permits the calculation of an exposure adjustment factor (EAF). In theory, PRC-derived EAF ratios reflect changes in SPMD sampling rates (relative to laboratory data) due to differences in exposure temperature, membrane biofouling, and flow velocity-turbulence at the membrane surface. Thus, the PRC approach should allow for more accurate estimates of target solute/vapor concentrations in an exposure medium. Undersome exposure conditions, the impact of environmental variables on SPMD sampling rates may approach an order of magnitude. The results of this study suggest that most of the effects of temperature, facial velocity-turbulence, and biofouling on the uptake rates of analytes with a wide range of hydrophobicities can be deduced from PRCs with a much narrower range of hydrophobicities. Finally, our findings indicate that the use of PRCs permits prediction of in situ SPMD sampling rates within 2-fold of directly measured values.

Polymer-water partition coefficients (Kpw) of hexachlorobenzene, 41 polychlorinated biphenyls (PCBs), and 26 polyaromatic hydrocarbons (PAHs) were determined for low-density polyethylene (LDPE) and five different silicone rubbers. Partition coefficients were determined in ultra pure water and in a range of methanol-water mixtures. Different cosolvent models for the effect of methanol concentration on the polymer-mixture partition coefficient (Kpm) were used to validate the Kpw in pure water. Linear regression of logKpm against the mole fraction (x) methanol over range 0 < x < 0.3 yielded the best results. The obtained logKpws were best described by a correlation with molecular weight, for PCBs in combination with the fraction of chlorine atoms in the meta and para positions (standard deviations of approximately 0.08 log units). Correlations with logKow were less good (standard deviations of approximately 0.21 log units), partly as a result of uncertainties in the logKow estimates that were used. Similar Kpws were found for different batches of silicone rubber from the same supplier. Differences in logKpws for silicone rubbers obtained from different suppliers ranged from 0.16-0.58.

The effect of temperature on sampling rates and sampler-water partition coefficients of semipermeable membrane devices (SPMDs) and low-density polyethylene (LDPE) strips was studied in an experimental setup under controlled flow conditions. Aqueous concentrations of chlorobenzenes, polychlorinated biphenyls (PCBs), and polyaromatic hydrocarbons (PAHs) were maintained by continuous circulation of the water over a generator column. Sampling rates for standard design SPMDs (460 cm2) were in the range of 20-200 L d(-1). No significant differences were observed between sampling rates of SPMDs and LDPE strips, but the latter samplers reached equilibrium faster because of their smaller sorption capacity. Sampling rates at 30 degrees C were higher than at 2 degrees C by a factor of about 3. Sampling rate modeling indicated boundary layer-controlled uptake for compounds with log octanol-water partition coefficients smaller than 4.4 and aqueous boundary-layer controlled uptake for more hydrophobic compounds. SPMD-water partition coefficients did not significantly change with temperature, but LDPE-water partition coefficients were larger at 2 degrees C than at 30 degrees C by a factor of 2. For field application of SPMDs, the results imply that temperature is not a key factor that controls uptake rates unless large geographical and temporal scales are involved. The results confirm that water flow velocity has a profound effect on sampling rates.