Polymer-water Partition Coefficients Research Articles

Ethylene vinyl acetate copolymer is an efficient and alternative passive sampler of hydrophobic organic contaminants. A comparison with silicone rubber

There is a growing demand for assessing the concentrations of Hydrophobic Organic Contaminants (HOCs) in aquatic environments, including Persistent Organic Pollutants (POPs). The hydrophobicity of POPs challenges their quantification in waters due to the sub-trace concentrations, especially when using conventional spot sampling. The results from the conventional samples are only a “snapshot” of the concentrations (if detected) at the specific sampling moment. Contrary, passive sampling provides average concentration levels over weeks or months from the quantification of accumulated pollutants during the deployment period. The present work compared ethylene vinyl acetate (EVA) and silicon rubber (SR) as monophasic passive samplers to measure dissolved concentrations of HOCs. Four classes of POPs were studied: (i) polychlorinated dibenzo-p-dioxins (PCDDs), (ii) polychlorinated dibenzofurans (PCDFs), (iii) polychlorinated biphenyls (PCBs), including the dioxin-like congeners, and (iv) the polybrominated diphenyl ethers (PBDEs). The polymer-water partition coefficients (Kpw), determined by the cosolvent and crossed calibrations, were, on average, one logarithmic unit larger in EVA than in the SR. The diffusion coefficients (Dp) estimated by the “film-stacking” method were, on average, two orders of magnitude smaller in the EVA than in the SR. For both polymers, the theoretical model of mass transfer resistance confirmed that the water boundary layer controlled the absorption, thus allowing the use of Performance Reference Compounds (PRCs) to estimate the in-situ sampling rates.Larger Kpw's in EVA may be an advantage because they imply longer time scales to reach equilibrium, higher absorption capacities and hence a higher absorbed contaminant mass, especially for compounds that reach equilibrium relatively faster (log Kow < 5). In addition, the longer times to attain equilibrium for EVA maintain this sampler longer in the linear phase of absorption, and the time-weighted average concentration may only be assessed in this phase when the compounds have not yet reached equilibrium.

Performance comparison of silicone and low-density polyethylene as passive samplers in a global monitoring network for aquatic organic contaminants

Contamination with hydrophobic organic compounds (HOCs) such as persistent organic pollutants negatively affects global water quality. Accurate and globally comparable monitoring data are required to understand better the HOCs distribution and environmental fate. We present the first results of a proof-of-concept global monitoring campaign, the Aquatic Global Passive Sampling initiative (AQUA-GAPS), performed between 2016 and 2020, for assessing trends of freely dissolved HOC concentrations in global surface waters. One of the pilot campaign aims was to compare performance characteristics of silicone (SSP) and low-density polyethylene (PE) sheets co-deployed in parallel under identical conditions, i.e. at the same site, using the same deployment design, and for an equal period. Individual exposures lasted between 36 and 400 days, and samples were collected from 22 freshwater and 40 marine locations. The sampler inter-comparability is based on a rationale of common underlying principles, i.e. HOC diffusion through a water boundary layer (WBL) and absorption by the polymer. In the integrative uptake phase, equal surface-specific uptake in both samplers was observed for HOCs with a molecular volume less than 300 Å3. For those HOCs, transport in the WBL controls the uptake as mass transfer in the polymer is over 20-times faster. In such a case, sampled HOC mass can be converted into aqueous concentrations using available models derived for WBL-controlled sampling using performance reference compounds. In contrast, for larger molecules, surface-specific uptake to PE was lower than to SSP. Diffusion in PE is slower than in SSP, and it is likely that for large molecules, diffusion in PE limits the transport from water to the sampler, complicating the interpretation. Although both samplers provided mostly well comparable results, we recommend, based on simpler practical handling, simpler data interpretation, and better availability of reliable polymer-water partition coefficients, silicone-based samplers for future operation in the worldwide monitoring programme.

Calibration parameters for the passive sampling of organic UV filters by silicone; diffusion coefficients and silicone–water partition coefficients

In recent years, organic ultraviolet filters (UVFs) received considerable attention as a group of emerging contaminants, including in Australia where the use of UVFs is particularly relevant. Passive sampling using polymers has become widely used for routine monitoring of chemicals in the aquatic environment. Application of passive samplers for monitoring chemicals in the water relies on calibration data such as chemical's polymer-water partition coefficient (Kpw) and diffusion coefficients in the sampling material (Dp), for understanding uptake and kinetic limitations. In the present study, Kpw and Dp for nine UVFs were estimated. Kpw values were determined in different water – polymer partition experiments where (1) a given mass of chemicals was dosed into the water and (2) into the polymer. Diffusion coefficients were determined using the stacking method. The estimated log Kpw and log Dp ranged from 2.9 to 6.4 L kg−1 and -11.1 to −10.5 m2s-1, respectively. The sufficient high Dp allows application of kinetic models that only consider water boundary-controlled uptake for converting silicone sampler uptake into an aqueous phase concentration using the presented Kpw.

Detection of tris(2,3-dibromopropyl) phosphate and other organophosphorous compounds in Arctic rivers.

The flame-retardant tris(2,3-dibromopropyl) phosphate (TDBrPP) was in the 1970s banned for uses in textiles that may be in contact with the skin, owing to strong suspicions that the substance was a human carcinogen. The substance is looked for but rarely detected in samples from the built and natural environments, but there are indications that TDBrPP is still in use. Here, we report the measurement of a polymer-water partition coefficient (Kpw) for two types of silicone rubber (SR), allowing quantitative estimation of freely dissolved concentrations of TDBrPP by passive sampling in water. We found levels of 100 to 200pg/L in two Arctic rivers that were sampled during a 2014-2015 survey of contamination using passive samplers in Norwegian and Russian rivers draining into the Barents Sea. We also report the widespread presence of other organophosphorus flame retardants in this survey of eight rivers that drain into the Barents Sea.

Development and evaluation of MTLSER and QSAR models for predicting polyethylene-water partition coefficients

Current study was aimed to make further improvements in measuring low density polyethylene (LDPE) -water partition coefficient (KPE-w) for organic chemicals. Modified theoretical linear solvation energy relationship (MTLSER) model and quantitative structure activity relationship (QSAR) model were developed for predicting KPE-w values from chemical descriptors. With the MTLSER model, α (average molecular polarizability), μ (dipole moment) and q- (net charge of the most negative atoms) as significant variables were screened. With the QSAR model, main control factors of KPE-w values, such as CrippenLogP (Crippen octanol-water partition coefficient), CIC0 (neighborhood symmetry of 0-order) and GATS2p (Geary autocorrelation-lag2/weighted by polarizabilities) were studied. As per our best knowledge, this is the first attempt to predict polymer-water partition coefficient using the MTLSER model. Statistical parameters, correlation coefficient (R2) and cross-validation coefficients (Q2) were ranging from 0.811 to 0.951 and 0.761 to 0.949, respectively, which indicated that the models appropriately fit the results, and also showed robustness and predictive capacity. Mechanism interpretation suggested that the main factors governing the partition process between LDPE and water were the molecular polarizability and hydrophobicity. The results of this study provide an excellent tool for predicting log KPE-w values of most common hydrophobic organic compounds, within the applicability domains to reduce experimental cost and time for innovation.

Comparing polyethylene and polyoxymethylene passive samplers for measuring sediment porewater concentrations of polychlorinated biphenyls: Mutual validation and possible correction by polymer-polymer partition experiment

Two sediment passive samplers, polyethylene (PE) and polyoxymethylene (POM), were compared and mutually validated for measuring freely dissolved concentrations (Cfree) of polychlorinated biphenyls (PCBs) in sediment porewater. PE and POM strips in commonly used dimensions (30 and 76 μm in thickness, respectively) were exposed to sediment slurries for 28 d. The Cfree values calculated using literature polymer-water partition coefficients were consistently higher for PE than for POM by a factor of 2 on average. Time series experiments over 96 d show that 28 d are sufficient for attaining partition equilibrium of PCBs for PE, whereas even 96 d may not be enough for POM. To gain additional insight, POM and PE strips were co-exposed to bovine serum albumin suspension spiked with PCBs. The POM/PE concentration ratios increased over 56 d, and the ratios at 28 d were in agreement with the POM-to-PE ratios of PCB concentrations from the 28-d sediment slurry experiments. This agreement suggests that the use of apparent POM-water partition coefficients (i.e., non-equilibrium concentration ratios) suitable for a 28-d exposure to sediment slurries may correct the non-attainment of equilibrium and could provide more accurate Cfree values.

Polymer-water partition coefficients in polymeric passive samplers.

Passive samplers are of the most applied methods and tools for measuring concentration of hydrophobic organic compounds in water (c 1W ) in which the polymer-water partition coefficients (D) are of fundamental importance for reliability of measurements. Due to the cost and time associated with the experimental researches, development of a predictive method for estimation and evaluation of performance of polymeric passive samplers for various hydrophobic organic compounds is highly needed and valuable. For this purpose, in this work, following the fundamental chemical thermodynamic equations governing the concerned local equilibrium, successful attempts were made to establish a theoretical model of polymer-water partition coefficients. Flory-Huggins model based on the Hansen solubility parameters was used for calculation of activity coefficients. The method was examined for reliability of calculations using collected data of three polymeric passive samplers and ten compounds. A regression model of form ln(D)=0.707ln(c 1p )-2.7391 with an R 2 =0.9744 was obtained to relate the polymer-water partition coefficients (D) and concentration of hydrophobic organic compounds in passive sampler (c 1p ). It was also found that polymer-water partition coefficients are related to the concentration of hydrophobic organic compounds in water (c 1W ) as ln(D)=2.412ln(c 1p )-9.348. Based on the results, the tie lines of concentration for hydrophobic organic compounds in passive sampler (c 1p ) and concentration of hydrophobic organic compounds in water (c 1W ) are in the form of ln(c 1W )=0.293ln(c 1p )+2.734. The composition of water sample and the interaction parameters of dissolved compound-water and dissolved compound-polymer, temperature, etc. actively influence the values of partition coefficient. The discrepancy observed over experimental data can be simply justified based on the local condition of sampling sites which alter these effective factors.

Determination of polydimethylsiloxane–water partition coefficients for ten 1-chloro-4-[2,2,2-trichloro-1-(4-chlorophenyl)ethyl]benzene-related compounds and twelve polychlorinated biphenyls using gas chromatography/mass spectrometry

Polymer-water partition coefficients (Kpw) of ten DDT-related compounds were determined in pure water at 25°C using commercial polydimethylsiloxane-coated optical fiber. Analyte concentrations were measured by thermal desorption-gas chromatography/full scan mass spectrometry (TD–GC/MSFS; fibers) and liquid injection-gas chromatography/selected ion monitoring mass spectrometry (LI–GC/MSSIM; water). Equilibrium was approached from two directions (fiber uptake and depletion) as a means of assessing data concordance. Measured compound-specific log Kpw values ranged from 4.8 to 6.1 with an average difference in log Kpw between the two approaches of 0.05 log units (∼12% of Kpw). Comparison of the experimentally-determined log Kpw values with previously published data confirmed the consistency of the results and the reliability of the method. A second experiment was conducted with the same ten DDT-related compounds and twelve selected PCB (polychlorinated biphenyl) congeners under conditions characteristic of a coastal marine field site (viz., seawater, 11°C) that is currently under investigation for DDT and PCB contamination. Equilibration at lower temperature and higher ionic strength resulted in an increase in log Kpw for the DDT-related compounds of 0.28–0.49 log units (61–101% of Kpw), depending on the analyte. The increase in Kpw would have the effect of reducing by approximately half the calculated freely dissolved pore-water concentrations (Cfree). This demonstrates the importance of determining partition coefficients under conditions as they exist in the field.

Passive sampling methods for contaminated sediments: Practical guidance for selection, calibration, and implementation

This article provides practical guidance on the use of passive sampling methods (PSMs) that target the freely dissolved concentration (Cfree) for improved exposure assessment of hydrophobic organic chemicals in sediments. Primary considerations for selecting a PSM for a specific application include clear delineation of measurement goals for Cfree, whether laboratory-based “ex situ” and/or field-based “in situ” application is desired, and ultimately which PSM is best-suited to fulfill the measurement objectives. Guidelines for proper calibration and validation of PSMs, including use of provisional values for polymer–water partition coefficients, determination of equilibrium status, and confirmation of nondepletive measurement conditions are defined. A hypothetical example is described to illustrate how the measurement of Cfree afforded by PSMs reduces uncertainty in assessing narcotic toxicity for sediments contaminated with polycyclic aromatic hydrocarbons. The article concludes with a discussion of future research that will improve the quality and robustness of Cfree measurements using PSMs, providing a sound scientific basis to support risk assessment and contaminated sediment management decisions. Integr Environ Assess Manag 2014;10:210–223. © 2014 The Authors. Integrated Environmental Assessment and Management published by Wiley Periodicals, Inc. on behalf of SETAC.

Optimized parameters of SMPE analysis for atrazine and its application to measure speciation

The uptake kinetics and partitioning behavior of atrazine between water and two polymeric coating (polydimethylsiloxane (PDMS) or polyacrylate (PA)) fibers commercially available for solid phase microextraction fiber (SPME) are presented. The SPME technique is associated with gas chromatography coupled to flame ioniser detector (GC-FID) in order to quantify the atrazine concentrations in the two phases. First, the equilibrium-time profiles for the two coatings were previously studied in order to establish the time needed for equilibrium. The parameters such as effects of extraction time, stirring rate and pH, that might affect the sensibility and accuracy of the SPME method, were investigated and optimized. It was observed that polymer-water partition coefficient of atrazine to PDMS (KPDMS–water) was 55±2, while the KPA–water was 210±5. Furthermore, the extraction efficiency increases with the stirring rate and decreases with varying pH. The SPME technique was applied to determine speciation of atrazine in colloid suspensions; results and comparison with free atrazine solution were presented.

Comparison of polymeric samplers for accurately assessing PCBs in pore waters

Assessing the hazard posed by sediments contaminated with hydrophobic organic compounds is difficult, because measuring the freely dissolved porewater concentrations of such low-solubility chemicals can be challenging, and estimating their sediment-water partition coefficients remains quite uncertain. We suggest that more accurate site assessments can be achieved by employing sampling devices in which polymers, with known polymer-water partition coefficients, are used to absorb the contaminants from the sediment. To demonstrate the current accuracy and limitations of this approach, we compared use of three polymers, polydimethylsiloxane, polyoxymethylene, and polyethylene, exposed to a single sediment in two modes, one in which they were exhaustively mixed (tumbled) with the sediment and the other in which they were simply inserted into a static bed (passive). Comparing porewater concentrations of specific polychlorinated biphenyl (PCB) congeners with results obtained using air bridges, we found the results for tumbled polymers agreed within 20%, and the passive sampling agreed within a factor of 2. In contrast, porewater estimates based on sediment concentrations normalized to f(OC)K(OC), the weight fraction of organic carbon times the organic-carbon normalized partition coefficient, averaged a factor of 7 too high. We also found good correlations of each polymer's uptake of the PCBs with bioaccumulation by the polychaete, Neanthes arenaceodentata. Future improvements of the passive sampling mode will require devices that equilibrate faster and/or have some means such as performance reference compounds to estimate mass transfer limitations for individual deployments.

Polymer selection for passive sampling: A comparison of critical properties

Next to the bi-phasic semipermeable membrane devices (SPMDs), single-phase passive samplers are becoming more popular for the sampling of hydrophobic contaminants. We therefore evaluated some critical properties of 13 polymers: low-density polyethylene (LDPE), polyoxymethylene (POM), silicone rubbers (SRs), including polydimethylsiloxane, and ethylene/octene co-polymer (EXACT). Polymer comparison included four critical properties: release of oligomers, swelling in solvents (dichloromethane, hexane, ethyl acetate, acetone and methanol), contaminant diffusion coefficients and partition coefficients for naphthalene, fluoranthene, benzo[a]pyrene and dibenz[a,h]anthracene. Amounts of extracted oligomers ranged from 2% to 4% for SRs and LDPE, to about 1% for EXACT. No oligomer release was observed for POM. Diffusion coefficients were higher in all SRs compared with LDPE and EXACT. No measurable diffusion was observed in POM after 24h of exposure. Differences in polymer-water partition coefficients spanned two orders of magnitude, with the lowest values observed for POM and the highest values observed for LDPE and EXACT. For the ten tested SRs, this range was less than 0.4 log units. Transport resistances estimated on the basis of diffusion coefficients and partition coefficients were generally lower for SRs than for LDPE and EXACT.

Determination of Diffusion Coefficient of a Small Hydrophobic Probe in Poly(lactide-co-glycolide) Microparticles by Laser Scanning Confocal Microscopy

The diffusion coefficient of a small hydrophobic probe in poly(lactide-co-glycolide) (PLGA) microparticles was determined by laser scanning confocal microscopy (LSCM). PLGA microparticles preincubated in a physiological buffer for various times were immersed in an aqueous solution of the pH-insensitive fluorescent probe bodipy at 37 °C. Probe concentration gradients inside individual microparticle matrices were then recorded by LSCM, which were accurately fit by the solution to Fick's second law of diffusion to determine an effective probe diffusion coefficient (D) in the polymer matrix. Values of D varied less than expected from the blank eroding polymer and were in the range (3−10) × 10-12 cm2/s. The apparent polymer-water partition coefficient of the probe was also determined to be roughly 20, indicative of strong partitioning into the polymer phase. The diffusion of bodipy in microparticles varied over 3 orders of magnitude between 22 and 43 °C, indicative of transport control in the polymer phase as ...

Enhanced solubilization of aromatic solutes in aqueous solutions of N-vinylpyrrolidone/styrene

The partitioning behavior of several aromatic hydrocarbons between N-vinylpyrrolidone/styrene (NVPS) and water is reported. Values of log K pw , concentration-based polymerwater partition coefficient, in this study are 3.39±0.04, 3.38±0.01, and 4.69±0.02 for toluene, naphthalene, and phenanthrene, respectively, in aqueous NVPS solution. A relationship between log K pw and log K ow , octanol-water partition coefficient, is proposed to extend predictive analysis to other solutes. The high molecular weight (∼3.4 million g/mol) and high organic solubilization of NVPS make it attractive for use in organic-contaminated water remediation. Potential applications are briefly discussed

The correlation of polymer-water and octanol-water partition coefficients: estimation of drug solubilities in polymers

Extrathermodynamic relationships between the octanol-water and polymer-water partition coefficients of a number of solutes in 6 polymer-water systems were established: log P (polymer-water) = a log P (octanol-water) + b The solutes were steroids, narcotic amines, and one barbiturate, with log P oct values incrementally spanning the range from 1 to 4. The polymers were 5 rubbery polymers ( T g < 37°C), polyethylene, polydimethylsiloxane, polyethylene-co-vinyl acetate, poly-ε-caprolactone, and poly-ε-caprolactam-co-ε-caprolactone, and one hydrogel, poly-2-hydroxyethyl methacrylate, with solubility parameters increasing from 15.1 to 25.5 J 1/2. cm 3/2. The slopes and intercepts of the correlation equations were shown to be proportional to the polymer polarity and to the logarithm of the solubility of water in the polymers, respectively. The log P correlations provided a means of estimating the relative solubilities of a new polymer ab initio. When combined with calculated or known aqueous drug solubilities, the correlations could be used to estimate absolute drug solubilities in a polymer.