Experimental Solubility Approach to Determine PDMS–Water Partition Constants and PDMS Activity Coefficients

Abstract

Freely dissolved aqueous concentration and chemical activity are important determinants of contaminant transport, fate, and toxic potential. Both parameters are commonly quantified using Solid Phase Micro-Extraction (SPME) based on a sorptive polymer such as polydimethylsiloxane (PDMS). This method requires the PDMS-water partition constants, KPDMSw, or activity coefficient to be known. For superhydrophobic contaminants (log KOW >6), application of existing methods to measure these parameters is challenging, and independent measures to validate KPDMSw values would be beneficial. We developed a simple, rapid method to directly measure PDMS solubilities of solid contaminants, SPDMS(S), which together with literature thermodynamic properties was then used to estimate KPDMSw and activity coefficients in PDMS. PDMS solubility for the test compounds (log KOW 7.2-8.3) ranged over 3 orders of magnitude (4.1-5700 μM), and was dependent on compound class. For polychlorinated biphenyls (PCBs) and polychlorinated dibenzo-p-dioxins (PCDDs), solubility-derived KPDMSw increased linearly with hydrophobicity, consistent with trends previously reported for less chlorinated congeners. In contrast, subcooled liquid PDMS solubilities, SPDMS(L), were approximately constant within a compound class. SPDMS(S) and KPDMSw can therefore be predicted for a compound class with reasonable robustness based solely on the class-specific SPDMS(L) and a particular congener's entropy of fusion, melting point, and aqueous solubility.

Iron Plaque Prevents Partitioning of Polycyclic Aromatic Hydrocarbons on Rice (Oryza sativa) Root Surface

“…Hung et al (2010) studied the discrepancy of partition coefficients in different studies and found that residual lipid in cell walls would sharply increase the partition coefficients of cell wall materials because of the high partition coefficients of PAHs in lipids. The root materials were ground into powders in previous studies (Hung et al 2010; Hale et al 2011; Szymanska‐Chargot et al 2015). Some of the ground root sorbents can dissolve out organic matter and as colloidal particles in water, which could increase the apparent solubility of PAHs (Grant et al 2016). Polycyclic aromatic hydrocarbons were dissolved into methanol in most past sorption experiments, and the influence of methanol concentration cannot be neglected.…”

“…Partition coefficients are determined by equilibration of the materials with a water phase that contains the solutes of interest, followed by their concentration in the water phase and sorbents (Hung et al 2010). The sparing water solubility of HOCs can reduce the accuracy of analysis when determining the partition coefficients (Ma et al 2011; Grant et al 2016). Dissolved organic matter (DOM) and particles released from sorbents would influence the results of partition coefficients between water and sorbents (Wood et al 2015).…”

“…Dissolved organic matter (DOM) and particles released from sorbents would influence the results of partition coefficients between water and sorbents (Wood et al 2015). The partition coefficients extrapolated from cosolvent models could give more precise partition coefficients because cosolvent addition such as methanol or acetone can stabilize the solutions, increase the solubility of solute, and decrease DOM and particles released from sorbents (Grant et al 2016). Various cosolvent models have been employed to measure the partition coefficients of PAHs between sediments and water due to the high DOM contents and naturally colloidal particles in sediments (Holmćn and Gschwend 1997; Wood et al 2015).…”

“…Various cosolvent models have been employed to measure the partition coefficients of PAHs between sediments and water due to the high DOM contents and naturally colloidal particles in sediments (Holmćn and Gschwend 1997; Wood et al 2015). Cosolvent models also have been facilitated to evaluate the partition coefficients of PAHs and polychlorinated biphenyls (PCBs) on Si rubber and single‐phase polymers in passive samplers for monitoring HOCs in aqueous environments (Monteyne et al 2013; Grant et al 2016).…”

A chemical activity approach to exposure and risk assessment of chemicals

“…To monitor for exceedance of thermodynamically based environmental quality criteria in the environment, various standard techniques can be used. Passive sampling techniques may provide a particularly simple and economically attractive method for monitoring if environmental quality objectives are met (Mayer et al ) because the concentrations of chemicals in samplers can be related to chemical activities in a highly reproducible manner (Grant et al ). The equilibrium partitioning approach (Di Toro et al ) has been used to develop sediment benchmarks for a range of organic chemicals (US Environmental Protection Agency ; Booij et al ).…”