An improved Chemcatcher-based method for the integrative passive sampling of 44 hydrophilic micropollutants in surface water - Part A: Calibration under four controlled hydrodynamic conditions

Breaking barriers in passive sampling: The potential of PTFE membranes in the monitoring of hydrophilic micropollutants

Passive samplers are key tools to sample hydrophilic micropollutants in water. Two main approaches address the influence of hydrodynamics: (1) determining site-specific sampling rate (RS) by characterizing kw, the mass transfer coefficient of the water-boundary layer (WBL), and (2) reducing WBL impact using a diffusive material to control the uptake. The first requires calibration data and the second has only been achieved using fragile diffusive material. This study assesses the transfer of hydrophilic contaminants through polytetrafluoroethylene (PTFE; 30 µm thick), a new membrane material with lower sorption than commonly used polyethersulfone (PES). Combined for the first time in a Chemcatcher-like configuration, we calibrated the modified samplers for 44 micropollutants to provide RS - kw relationships for in-situ RS determination (approach 1). Micropollutants accumulated over 2000 times more on the sorbent than on PTFE. PTFE-based RS (0.027 to 0.300 L day-1) were 2.5 higher than previously reported with PES. Membrane property measurements (porosity, tortuosity) indicated that accumulation is primarily controlled by the membrane. Extrapolation indicated that using thicker PTFE membranes (≥ 100 µm) would shift uptake control entirely to the membrane in river conditions (approach 2). This finding could enable RS prediction based on contaminants properties, thus representing a significant advancement in passive sampling.

Ongoing Laboratory Performance Study on Chemical Analysis of Hydrophobic and Hydrophilic Compounds in Three Aquatic Passive Samplers

The quality of chemical analysis is an important aspect of passive sampling-based environmental assessments. The present study reports on a proficiency testing program for the chemical analysis of hydrophobic organic compounds in silicone and low-density polyethylene (LDPE) passive samplers and hydrophilic compounds in polar organic chemical integrative samplers. The median between-laboratory coefficients of variation (CVs) of hydrophobic compound concentrations in the polymer phase were 33% (silicone) and 38% (LDPE), similar to the CVs obtained in four earlier rounds of this program. The median CV over all rounds was 32%. Much higher variabilities were observed for hydrophilic compound concentrations in the sorbent: 50% for the untransformed data and a factor of 1.6 after log transformation. Limiting the data to the best performing laboratories did not result in less variability. Data quality for hydrophilic compounds was only weakly related to the use of structurally identical internal standards and was unrelated to the choice of extraction solvent and extraction time. Standard deviations of the aqueous concentration estimates for hydrophobic compound sampling by the best performing laboratories were 0.21 log units for silicone and 0.27 log units for LDPE (factors of 1.6 to 1.9). The implications are that proficiency testing programs may give more realistic estimates of uncertainties in chemical analysis than within-laboratory quality control programs and that these high uncertainties should be taken into account in environmental assessments.

Performance comparison of three passive samplers for monitoring of polar organic contaminants in treated municipal wastewater

Over the past decades, several types of passive samplers have been developed and used to monitor polar organic compounds in aquatic environments. These samplers use different sorbents and barriers to control the uptake into the sampler, but their performance comparison is usually not well investigated. This study aimed to directly compare the performance of three samplers, i.e., the Polar Organic Chemical Integrative Sampler (POCIS), the Hydrogel-based Passive Sampler (HPS, an upscaled version of o-DGT), and the Speedisk, on a diverse suite of pharmaceuticals, per- and polyfluoroalkylated substances (PFAS), and pesticides and their metabolites. The samplers were deployed side-by-side in the treated effluent of a municipal wastewater treatment plant for different exposure times. All samplers accumulated a comparable number of compounds, and integrative uptake was observed for most compounds detected up to 28 days for POCIS, up to 14 days for HPS, and up to 42 days for Speedisk. In the integrative uptake phase, consistent surface-specific uptake was observed with a significant correlation between samplers (r ≥ 0.76) despite differences in sampler construction, diffusion barrier, and sorbent material used. The low sampling rates compared to the literature and the low estimated overall mass transfer coefficient suggests that the water boundary layer was the main barrier controlling the uptake for all samplers. Although all devices provided comparable performance, Speedisk overcomes POCIS and HPS in several criteria, including time-integrative sampling over a long period and physical durability.

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 R_S 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 R_S 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 R_S at infinite water velocity (R_S,MAX), revealing that the added value of using in-situ R_S compared to R_S,MAX is limited above intermediate water velocities (>20 cm s^-1). R_S from the literature (R_S,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 R_S,MAX or R_S,LIT rather than in-situ R_S are given as a function of the water velocity to determine in which conditions the developed method is required (or not) in monitoring programs.