Performance Reference Compounds Research Articles

Application of low-density polyethylene (LDPE) passive samplers for monitoring PAHs in groundwater

Equilibrium passive sampling continues to find increasing use for performing in situ assessments and monitoring of hydrophobic organic compounds (HOCs). Although this method has been successfully used in several field studies including open surface waters and sediments, comparatively, their use in groundwater has been very limited. In this study, low-density polyethylene (LDPE) passive samplers were deployed for 80 days in three groundwater wells contaminated with polycyclic aromatic hydrocarbons (PAHs). Prior to deployment, LDPE was loaded with performance reference compounds (PRCs) consisting of deuterated PAHs and their release used to ascertain system equilibrium. Within the 80-day deployment period, LDPE-groundwater equilibrium was confirmed for PAHs with molecular weights (MWs) in the range of 178 to 228 (i.e. anthracene, chrysene). Measured freely dissolved concentrations (Cw) were between one to three orders of magnitude lower than the total filtered concentrations (Ctotal) in the studied wells. The sum of PAHs (ΣPAHs) measured based on Cw and Ctotal were 2.05, 0.07 and 29.2 μg L−1 and 197, 59.7 and 1010 μg L−1, at wells 1, 2 and 3, respectively. A separate dataset, comprising long-term (2010 to 2022) concentrations of PAHs in total (i.e., unfiltered) groundwater, is also presented to provide insight into PAH contamination levels at the assessed groundwater wells based on conventional measurement. Estimated in situ LDPE daily clearance volumes (2.34 to 27.56 Ld−1) for the target analytes were far less than the daily turnover of ground water (144 to 348 Ld−1) encountered in the wells eliminating the possibility of depletive sampling of the groundwater by the passive samplers. These results represent the first published study on the practical application of equilibrium passive sampling using LDPE for monitoring and quantitatively assessing PAHs in groundwater. Also, this work demonstrates that LDPEs are a useful tool for measuring the Cw of PAHs in groundwater, a critical contaminant in many ecological and human health risk assessments.

Direct visualization of pyrene diffusion in polyethylene and polyoxymethylene passive samplers

While passive sampling of ultra-low aqueous concentrations of hydrophobic organic compounds in environmental aqueous media has emerged as a promising analytical technique, there is a lack of good understanding of the fundamental diffusive processes. In this research, we used a fluorophore, pyrene, as a model compound to track diffusion in polymers through absorption and environmental media exchange processes. We directly tracked the penetration of pyrene into polyethylene (PE) and polyoxymethylene (POM) rods during absorption from water by sectioning the rod after different stages of absorption and observing the fluorescence signal through a microscope. Diffusion profiles of pyrene in polymers were simulated by numerical integration of Fickian diffusion. The results indicated that the uptake process in PE is governed by Fick's law and the absorption and desorption kinetics are similar in this polymer. However, the observed uptake profiles of pyrene in POM were non-Fickian and the release kinetics out of POM was slower compared to uptake into the polymer. We show that slower desorption from POM makes corrections for nonequilibrium using performance reference compounds (PRCs) problematic for deployments in water or sediment where there is significant advection. However, for static sediment deployments, the overall kinetics of exchange is controlled by slow transport through sediment and the hysteretic behavior of POM may not preclude the use of PRCs to interpret equilibrium status.

Prediction of the accumulation behavior of pesticides in PDMS-coated stir bars used as passive samplers in freshwaters

Passive samplers accumulate organic contaminants at rates that depend on in-field exposure conditions such as freshwater flow velocity, water temperature and water quality. Time-weighted average concentrations can be determined by using a correction process such as the performance reference compound (PRC) method. This study presented a new approach to predict the accumulation behavior of pesticides in polydimethylsiloxane-coated stir bars under different exposure conditions and assign a specific PRC to each pesticide for quantitative purposes. We used an experimental design with eight simultaneous accumulation kinetics of 13 pesticides and elimination kinetics of three PRC candidates run in a flow-through system to determine the effects of flow velocity, water temperature and dissolved organic matter on the kinetic constants. We identified the parameters that had a significant effect on the accumulation of each pesticide and assigned a PRC candidate to each pesticide. We then used a discriminant function analysis to find the parameters that had a significant effect on accumulation of the 13 pesticides via their physical-chemical properties and to predict through a stochastic approach the parameters for seven other pesticides. This approach provides a better framework for identifying a PRC than conventional methods to determine unbiased concentrations in future monitoring efforts.

Determination of pesticide residue in marginal lagoons of natural parks in Brazil using an improved calibrate passive sampler

Passive sampling is a sensitive and efficient method for analyzing pesticides in water. This article describes a hollow fiber liquid-phase microextraction (HF-LPME) device that was improved using polypropylene membranes grafted with nanocellulose for the passive sampling of pesticides in water. A comprehensive gas chromatography time-of-flight mass spectrometry (GCxGC/Q-TOFMS) system was used to separate, identify, and quantify pesticides. The sampling rates of 38 moderately hydrophobic to hydrophobic agricultural pesticides (2.18 < log Kow < 6.89) from different chemical classes, including the main triazine, organochlorine and organophosphate compounds, were calculated. A calibration process was applied to evaluate the role of flow velocity and select potential candidates for a possible performance reference compound (PRC). Sampling rates varied between 0.17 mL d−1 and 23.15 mL d−1. The accumulation curves identified linear periods ranging from 3 to 18 days. The new passive sampler device was applied for 8 days in rivers and marginal lagoons of natural parks of the São Francisco basin in Minas Gerais, Brazil and identified 10 target pesticides. Furthermore, 10 non-targeted pesticides were detected by the GCxGC/Q-TOFMS method.

Determination and comparison of freely dissolved PAHs using different types of passive samplers in freshwater

Polycyclic aromatic hydrocarbons (PAHs) are well-known for their recalcitrant properties and biotoxicity in organisms, leading to serious environmental and health problems. Despite various analytical methods available, accurate determination of the bioavailable fraction is warranted in order to evaluate the precise toxic potentials of these compounds. Currently, the passive sampler is used worldwide to measure the bioavailable PAHs in the environment using the equilibrium partitioning principle. In this study, we co-deployed different types of passive samplers, which are linear low-density polyethylene (LLDPE) and low-density polyethylene (LDPE), to determine freely dissolved concentrations (Cfree) of PAHs using the performance reference compounds (PRCs) in Kentucky Lake (KL), Ohio River (OH), and Mississippi River (MS). The fractional equilibrium (feq) of BeP-d12 was observed to be high in LLDPE compared with LDPE in OH and MS. In contrast, the feq of all PRCs was similar in both passive samplers in KL due to slow flow velocity. The sum of average freely dissolved PAH concentrations in LLDPE and LDPE during the exposure period were 2.89 and 1.27 ng/L in KL, 8.13 and 3.31 ng/L in OH, and 5.19 and 3.82 ng/L in MS, respectively. The results revealed that LLDPE is a suitable alternative tool to LDPE for both short-term and long-term monitoring of PAHs.

Incorporating performance reference compounds in retractable/reusable solid phase microextraction fiber for passive sampling of hydrophobic organic contaminants in water

Solid phase microextraction (SPME) has been used to measure aqueous-phase hydrophobic organic chemicals (HOCs) in equilibrium passive sampling mode for over two decades. However, determination of the extent of equilibrium has not been well-established for the retractable/reusable SPME sampler (RR-SPME), especially in the field applications. The goal of this study was to establish a method regarding to sampler preparation and data processing to characterize the extent of equilibrium of HOCs on the RR-SPME (100-μm thickness of polydimethylsiloxane (PDMS) coating) by incorporating performance reference compounds (PRCs). A fast (4 h) PRC loading protocol was identified with using a ternary solvent mixture (i.e., acetone-methanol-water mixture (4:4:2, v/v)) to accommodate diverse carrier solvents of the PRCs. The isotropy of the RR-SPME was validated by a paired, co-exposure approach with 12 different PRCs. The aging factors measured with the co-exposure method approximately equal to one, indicating the isotropic behavior was not changed after storage at 15 °C and −20 °C for 28 days. As a method demonstration, the PRC-loaded RR-SPME samplers were deployed in the ocean off Santa Barbara, CA (USA) for 35 days. The PRCs approaching the extents of equilibrium ranged from 20 ± 15.5 % to 96.5 ± 1.5 % and showed a declining trend along with log KOW increase. A generic equation relationship was deduced based on a correlation relationship of desorption rate constant (k2) and log KOW to extrapolate non-equilibrium correction factor from the PRCs to the HOCs. The merit of the present study is manifested by its theory and implement to enable the RR-SPME passive sampler to be utilized in environmental monitoring.

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.

An improved Chemcatcher-based method for the integrative passive sampling of 44 hydrophilic micropollutants in surface water – Part B: Field implementation and comparison with automated active sampling

Integrative passive sampling is particularly useful in the monitoring of hydrophilic contaminants in surface water, but the impact of hydrodynamics on contaminant uptake still needs to be better considered. In part A (Glanzmann et al., 2023), Chemcatcher-like hydrophilic samplers (i.e., SDB-RPS extraction disks covered by PES microporous membranes) were calibrated to determine the sampling rates RS of 44 hydrophilic contaminants (pesticides, pharmaceuticals, industrial products) taking into account the hydrodynamic conditions. In this study, Chemcatcher-like passive sampling devices that allowed co-deploying hydrophilic samplers and performance reference compounds (PRC)-spiked silicone disks were tested in a Swiss river with intermediate water velocities (5–50 cm s−1, 23 cm s−1 on average) during 11 consecutive 14-day periods. The PRC dissipation from silicone disks – combined with the calibration data from part A – allowed to determine in-situ RS that took into account hydrodynamic conditions. The obtained aqueous time-weighted average (TWA) concentrations were found to be robust with good concordance between duplicates (mean quotient of 1.16 between the duplicates). For most measurements (76 %), TWA concentrations showed no major difference (<factor 2) from concentrations obtained with automated sampling (14-day composite samples). This observation was also valid for TWA concentrations calculated with extrapolated RS at infinite water velocity (RS,MAX), revealing that the added value of using in-situ RS compared to RS,MAX is limited above intermediate water velocities (>20 cm s−1). RS from the literature (RS,LIT) – obtained at water velocities between 8 and 37 cm s−1 – were also shown to provide comparable TWA concentrations in the studied hydrodynamic conditions (average water velocity of 24 cm s−1). The estimated errors due to the use of RS,MAX or RS,LIT rather than in-situ RS are given as a function of the water velocity to determine in which conditions the developed method is required (or not) in monitoring programs.

A field-validated equilibrium passive sampler for the monitoring of per- and polyfluoroalkyl substances (PFAS) in sediment pore water and surface water.

A simple equilibrium passive sampler, consisting of water in an inert container capped with a rate-limiting barrier, for the monitoring of per- and polyfluoroalkyl substances (PFAS) in sediment pore water and surface water was developed and tested through a series of laboratory and field experiments. The objectives of the laboratory experiments were to determine (1) the membrane type that could serve as the sampler's rate-limiting barrier, (2) the mass transfer coefficient of environmentally relevant PFAS through the selected membrane, and (3) the performance reference compounds (PRCs) that could be used to infer the kinetics of PFAS diffusing into the sampler. Of the membranes tested, the polycarbonate (PC) membrane was deemed the most suitable rate-limiting barrier, given that it did not appreciably adsorb the studied PFAS (which have ≤8 carbons), and that the migration of these compounds through this membrane could be described by Fick's law of diffusion. When employed as the PRC, the isotopically labelled PFAS M2PFOA and M4PFOS were able to predict the mass transfer coefficients of the studied PFAS analytes. In contrast, the mass transfer coefficients were underpredicted by Br- and M3PFPeA. For validation, the PC-based passive samplers consisting of these four PRCs, as well as two other PRCs (i.e., M8PFOA and C8H17SO3-), were deployed in the sediment and water at a PFAS-impacted field site. The concentration-time profiles of the PRCs indicated that the samplers deployed in the sediment required at least 6 to 7 weeks to reach 90% equilibrium. If the deployment times are shorter (e.g., 2 to 4 weeks), PFAS concentrations at equilibrium could be estimated based on the concentrations of the PRCs remaining in the sampler at retrieval. All PFAS concentrations determined via this approach were within a factor of two compared to those measured in the mechanically extracted sediment pore water and surface water samples obtained adjacent to the sampler deployment locations. Neither biofouling of the rate-limiting barrier nor any physical change to it was observed on the sampler after retrieval. The passive sampler developed in this study could be a promising tool for the monitoring of PFAS in pore water and surface water.

Calibration and field validation of POCIS passive samplers for tracking artificial sweeteners as indicators of municipal wastewater contamination in surface waters.

Polar organic chemical integrative samplers (POCIS) are widely used to track contaminants in surface waters. However, POCIS have not been used previously to monitor for artificial sweeteners as an indicator of wastewater pollution. In this study, we report for the first time the POCIS sampling rates (Rscal) for four artificial sweetener compounds, acesulfame (0.001 L/day), sucralose (0.114 L/day), cyclamate (0.001 L/day), and saccharin (0.002 L/day). We also prepared a modified POCIS with Strata X-AW anion exchange resin as a sorbent (i.e., ax-POCIS) and determined the sampling rates for sucralose (0.060 L/day) and acesulfame (0.128 L/day). Rscal values were adjusted according to the rate of loss of the performance reference compound, metoprolol-d6 from deployed POCIS to yield field sampling rates (i.e., Rsfield). Field validation of the monitoring method was conducted in Presqu'ile Bay on the north-central coast of Lake Ontario that is impacted by discharges from a sewage lagoon. POCIS were deployed at four sites within the bay and in the lagoon discharge. The four artificial sweeteners, as well as caffeine, ibuprofen, and other microcontaminants of sewage origin, were present throughout the bay at estimated concentrations in the ng/L range, and in the lagoon discharge at estimated concentrations higher by approximately one order of magnitude. Because acesulfame is present in ionic form over the pH range of natural waters, there are uncertainties related to the sampling rates using the standard POCIS. Sucralose is recommended as the best choice for source tracking using POCIS. There was good agreement between the concentrations of sucralose estimated from POCIS and the measured concentrations in grab samples of surface water in the bay. The present study provides key data for monitoring artificial sweeteners using POCIS.

Interlaboratory Study of Polyethylene and Polydimethylsiloxane Polymeric Samplers for Ex Situ Measurement of Freely Dissolved Hydrophobic Organic Compounds in Sediment Porewater.

We evaluated the precision and accuracy of multilaboratory measurements for determining freely dissolved concentrations (C free) of polycyclic aromatic hydrocarbons (PAHs) and polychlorinated biphenyls (PCBs) in sediment porewater using polydimethylsiloxane (PDMS) and low‐density polyethylene (LDPE) polymeric samplers. Four laboratories exposed performance reference compound (PRC) preloaded polymers to actively mixed and static ex situ sediment for approximately 1 month; two laboratories had longer exposures (2 and 3 months). For C free results, intralaboratory precision was high for single compounds (coefficient of variation 50% or less), and for most PAHs and PCBs interlaboratory variability was low (magnitude of difference was a factor of 2 or less) across polymers and exposure methods. Variability was higher for the most hydrophobic PAHs and PCBs, which were present at low concentrations and required larger PRC‐based corrections, and also for naphthalene, likely due to differential volatilization losses between laboratories. Overall, intra‐ and interlaboratory variability between methods (PDMS vs. LDPE, actively mixed vs. static exposures) was low. The results that showed C free polymer equilibrium was achieved in approximately 1 month during active exposures, suggesting that the use of PRCs may be avoided for ex situ analysis using comparable active exposure; however, such ex situ testing may not reflect field conditions. Polymer‐derived C free concentrations for most PCBs and PAHs were on average within a factor of 2 compared with concentrations in isolated porewater, which were directly measured by one laboratory; difference factors of up to 6 were observed for naphthalene and the most hydrophobic PAHs and PCBs. The C free results were similar for academic and private sector laboratories. The accuracy and precision that we demonstrate for determination of C free using polymer sampling are anticipated to increase regulatory acceptance and confidence in use of the method. Environ Toxicol Chem 2022;41:1885–1902. © 2022 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC. This article has been contributed to by U.S. Government employees and their work is in the public domain in the USA.

Partial loading of performance reference compounds in passive samplers and its effect on the fractional approach to steady state

Passive sampling for hydrophobic organics in soils and sediments is typically accomplished by measuring the equilibrium accumulation of the target compounds onto a sorbing polymer. Because the samplers do not often achieve equilibrium in the environment, the release of performance reference compounds (PRCs) pre-loaded on the sampler is used to estimate the extent of equilibrium uptake of a similar target compound. In this work, we evaluate the effect of non-equilibrium loading of PRCs on the estimated equilibration of target compounds. A numerical transport model considering both internal and external mass transfer resistances to the polymer during loading from a finite reservoir was constructed to predict PRC distribution polymer sheets. An analytical internal diffusion, external mass transfer limited model is then employed to simulate the release of the PRCs and predict both the apparent and actual approach to equilibration for the uptake of target compounds. Partial equilibration during loading of PRCs does not lead to inaccuracies in target compound equilibration except when internal resistances control both PRC release and target compound uptake, under which conditions the PRCs overestimate the extent of equilibration of target compounds. This is likely to occur during short PRC loading times (e.g., <1 month) and thick polymer sheets (e.g., >100 µm in thickness). If external mass transfer resistances control PRC release and target compound uptake, even partially loaded PRCs can accurately indicate the extent of equilibration of target compounds as long as the initial PRC loading is adequately characterized.

Passive sampling hydrophilic and hydrophobic bisphenol analogues using hydrophilic-lipophilic balance sorbent-embedded cellulose acetate membrane in surface waters

Bisphenol analogues (BPs) are ubiquitous emerging contaminants in water environments and have wide polarity ranges (1.65 < log Kow < 7.2). Integrated passive sampling strategy rarely contains hydrophilic and hydrophobic organics simultaneously, while the method has good application perspective in monitoring organic contaminants. This work evaluated passive sampling performance for fifteen BPs in a newly developed passive sampler, i.e., hydrophilic-lipophilic balance sorbent-embedded cellulose acetate membrane (HECAM). In the dynamic accumulation experiments, both hydrophilic and hydrophobic BPs (including moderately hydrophilic BPs) well followed first-order kinetic uptake in the HECAMs. The estimated uptake rate constants, elimination rate constants, and equilibrium partition coefficients for BPs ranged from 4.4 L g−1 d−1 to 14.7 L g−1 d−1, 0.22 d−1 to 0.72 d−1, and 3.99 to 4.64, respectively. The kinetic parameters for BPs in HECAM show limited correlations to log Kow values, which the rule differs from traditional passive sampler. In the study of elimination kinetics, three deuterium labeled compounds showed incomplete elimination in HECAM and did not follow first-order isotropic exchange kinetics. Dual sorption mechanisms including both adsorption and partition were found for chemicals in HECAM, which the partitioned part could release to water and the adsorbed part could not easily release to water from HECAM. As a result, performance reference compounds (PRCs) calibration may be inapplicable to HLB sorbent-based passive sampler. The field deployment of HECAM in coastal waters of Guangdong, China resulted in the detection of eleven BPs, which indicated that the waters have been polluted by various BPs. Finally, monitoring strategy of simultaneous passive sampling hydrophobic and hydrophilic organic contaminants in surface waters was recommended.

Determining the Mass Transfer Coefficient of the Water Boundary Layer at the Surface of Aquatic Integrative Passive Samplers.

Passive sampling devices (PSDs) offer key benefits for monitoring chemical water quality, but the uptake process of PSDs for hydrophilic compounds still needs to be better understood. Determining mass transfer coefficients of the water boundary layer (kw) during calibration experiments and in situ monitoring would contribute toward achieving this; it allows for combining calibration data obtained at different temperature and hydrodynamic conditions and facilitate the translation of laboratory-derived calibration data to field exposure. This study compared two kw measurement methods applied to extraction disk housings (Chemcatcher), namely, alabaster dissolution and dissipation of performance reference compounds (PRCs) from silicone. Alabaster- and PRC-based kw were measured at four flow velocities (5-40 cm s-1) and two temperatures (11 and 20 °C) in a channel system. Data were compared using a relationship based on Sherwood, Reynolds, and Schmidt numbers. Good agreement was observed between data obtained at both temperatures, and for the two methods. Data were well explained by a model for mass transfer to a flat plate under laminar flow. It was slightly adapted to provide a semi-empirical model accounting for the effects of housing design on hydrodynamics. The use of PRC-spiked silicone to obtain in situ integrative kw for Chemcatcher-type PSDs is also discussed.

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.

In Situ Passive Sampling to Monitor Long Term Cap Effectiveness at a Tidally Influenced Shoreline.

Polydimethylsiloxane solid-phase microextraction passive samplers were used to evaluate long-term performance of a sand/gravel cap placed in 2005 in a tidally influenced shoreline in Puget Sound to reduce polycyclic aromatic hydrocarbon (PAH) transport into overlying surface water. Sampling in both 2010 and 2018 measured porewater concentrations of <1 ng/L total PAHs in the cap layer. d-PAH performance reference compounds were used to evaluate the extent of equilibration of the contaminants onto the samplers and to estimate net upwelling velocities through a mass-transfer model. The upwelling velocities were used to predict long-term migration of selected PAHs through the cap, showing that the cap is expected to continue being effective at limiting exposure of contaminants at the cap–water interface.

Partial Loading of Performance Reference Compounds in Passive Samplers and its Effect on the Fractional Approach to Steady State

Partial Loading of Performance Reference Compounds in Passive Samplers and its Effect on the Fractional Approach to Steady State

Field comparison of passive polyurethane foam and active air sampling techniques for analysis of gas-phase semi-volatile organic compounds at a remote high-mountain site

Polyurethane foam passive air samplers (PUF-PAS) are good candidates for the determination of gas-phase semi-volatile organic compound (SVOC) air concentrations in high-mountain areas over long periods because they do not require an energy supply. However, the harsh meteorological conditions present in such locations can increase the uncertainties inherently associated to PAS sampling rates due to the many variables involved in their calculation and to the assumptions made regarding PUF diffusive uptake mechanics, which can considerably bias the resulting concentrations. Therefore, we studied the performance of PUF-PASs in a remote location in the Pyrenees mountain range for the analysis of several SVOCs in air, including polychlorobiphenyls (PCBs), hexachlorobenzene, pentachlorobenzene, polycyclic aromatic hydrocarbons (PAHs), and the less studied emerging organophosphate flame retardants (OPFRs). An in-situ PUF-PAS calibration using Performance Reference Compounds (PRCs) provided compound- and sampler-specific sampling rates, showing mean experimental errors (12%) that adequately conformed to an estimate of their expanded theoretical uncertainties (15%). This showcases the suitability of this calibration strategy in an area with conditions beyond those typically considered in calibration efforts available to date. Moreover, gas-phase concentrations of the studied pollutants from PUF-PAS samples showed very good agreement (R2 up to 0.91, p < 0.01) when compared to those obtained using a conventional high-volume active air sampler (PUF-AAS), with some minor deviations observed for PAHs caused by the seasonality in their atmospheric concentrations. No relevant levels of pollutants preferentially bound to the particle phase were detected in the PUF-PASs, the particle infiltration efficiency of the sampler configuration used was found to be low, and compounds typically distributed between the gas and particle phases of AAS samples revealed profiles consistent with their vapor pressures, except for some OPFRs.

Accumulation and passive sampling of bisphenol analogues using triolein-embedded cellulose acetate membrane in waters

Bisphenol analogues (BPs) are emerging contaminants that have been widely detected in water environments. The presence of substituted hydrophilic and hydrophobic groups in the molecule may lead to unclear performance in passive sampling. This study tested the accumulation capacity and passive sampling of fifteen BPs in a triolein-embedded cellulose acetate membrane (TECAM) passive sampler. In a dynamic accumulation experiment, twelve hydrophobic BPs accumulated in the TECAM with concentrations ranging from 251 ng g−1 to 6283 ng g−1, and three hydrophilic BPs did not accumulate during the 72 h exposure duration. BPs accumulations were determined by the hydrophilic and hydrophobic substituent groups in molecule structures. The estimated passive sampling parameters showed correlations to both the log Kow values and chemical structures, and compared to other contaminants, such as organophosphorus flame retardants. Environmental factors, including flow rate, temperature, salinity, and pH, that affect the accumulation of BPs in the TECAM were tested, and the flow rate was found to be an important factor affecting the uptake rate. The isotropic exchange kinetics for BPs in the TECAM were verified, and the results indicated that BPs can be calibrated with performance reference compounds (PRCs) in field applications. Finally, a field deployment of TECAM in river waters successfully estimated the time-weighted concentrations of two hydrophobic BPs. To address the inherent weaknesses of TECAM in sampling hydrophilic and moderately hydrophobic BPs, future studies should explore alternative passive samplers, such as hydrophilic-lipophilic balance sorbent-embedded cellulose acetate membranes, to sample BPs in surface waters.

Field application of a novel active-passive sampling technique for the simultaneous measurement of a wide range of contaminants in water

A first test of the field capabilities of a novel in situ sampling technique combining active and passive sampling (APS) was conducted in the sea. The proof-of-concept device uses a pump to draw water into a diffusion cell where dissolved target substances are accumulated onto sorbents which are selective for different classes of contaminants (i.e., metal cations, polar and non-polar organic compounds), simultaneously. A controlled laminar flow established in the diffusion cell enables measurements of contaminant concentrations that are fully independent from the hydrodynamic conditions in the bulk solution. APS measurements were consistent with those obtained using conventional passive sampling techniques such as organic diffusive gradients in thin films (o-DGT) and silicone rubber (SR) samplers (generally < 40% difference), taking into account the prevailing hydrodynamic conditions. The use of performance reference compounds (PRC) for hydrophobic contaminants provided additional information. Field measurements of metal ions in seawater showed large variability due to issues related to the device configuration. An improved field set-up deployed in supplementary freshwater mesocosm experiments provided metal speciation data that was consistent with passive sampling measurements (DGT), taking into account the hydrodynamic conditions. Overall, the results indicate that the APS technique provides a promising approach for the determination of a wide range of contaminants simultaneously, and independently from the hydrodynamic conditions in the bulk solution.