Kinetic Passive Sampling: In Situ Calibration Using the Contaminant Mass Measured in Parallel Samplers with Different Thicknesses

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 K_OW increase. A generic equation relationship was deduced based on a correlation relationship of desorption rate constant (k₂) and log K_OW 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.

Chemometers: an integrative tool for chemical assessment in multimedia environments

We propose novel chemometers - passive equilibrium samplers of, e.g., silicone - as an integrative tool for the assessment of hydrophobic organic compounds in multimedia environments. The traditional way of assessing levels of organic pollutants across different environmental compartments is to compare the chemical concentration normalized to the major sorptive phase in two or more media. These sorptive phases for hydrophobic organic compounds differ between compartments, e.g., lipids in biota and organic carbon in sediments. Hence, comparability across media can suffer due to differences in sorptive capacities, but also extraction protocols and bioavailability. Chemometers overcome these drawbacks; they are a common, universal and well-defined polymer reference phase for sampling of a large range of nonpolar organic pollutants in different matrices like biota, sediment and water. When bringing the chemometer into direct contact with the sample, the chemicals partition between the sample and the polymer until thermodynamic equilibrium partitioning is established. At equilibrium, the chemical concentrations in the chemometers can be determined and directly compared between media, e.g., between organisms of different trophic levels or inhabiting different areas, between organs within an organism or between biotic and abiotic compartments, amongst others. Chemometers hence allow expressing the data on a common basis, as the equilibrium partitioning concentrations in the polymer, circumventing normalizations. The approach is based on chemical activity rather than total concentrations, and as such, gives a measure of the "effective concentration" of a compound or a mixture. Furthermore, chemical activity is the main driver for partitioning, biouptake and toxicity. As an additional benefit, the extracts of the chemometers only require limited cleanup efforts, avoiding introduction of a bias between chemicals of different persistence, and can be submitted to both chemical analysis and/or bioanalytical profiling.

A look down the drain: Identification of dissolved and particle bound organic pollutants in urban runoff waters and sediments

Urban runoff contains a range of organic micropollutants which, if not removed during wastewater treatment, pose a risk to aquatic environments. These mixtures are complex and often site-specific. Street drains provide an ideal sampling point given they collect the runoff from local and defined catchments. In this study, runoff was collected and sampled in five street drains located in a medium sized town in Germany. A specially constructed trap was used to collect the particulate and total water fractions of the runoff. In addition, passive samplers were deployed to determine the freely dissolved concentrations of selected compounds in the runoff. In sum, 187 polar organic micropollutants could be quantified using LC-HRMS. Thirty of these could only be detected by the use of passive samplers. Traffic derived pollutants such as corrosion inhibitors, rubber- and plastic additives, but also pollutants of industrial origin were strongly represented with sum median concentrations of 100 μg/kg dry weight (DW) in the sediment and 400 ng/L in the water fraction. Several of these substances are of concern due to their environmental persistence and mobility. Perfluorinated compounds and pesticides occurred at lower levels of several μg/kg DW sediment or ng/L water. A number of substances including pharmaceuticals, sweeteners and stimulants indicated domestic wastewater influences. Furthermore, a total of 62 parent and alkylated PAHs were quantified by GC-MS and contributed 30-70% to the sum concentrations of the micropollutants. Non-EPA PAHs dominated the carcinogenic PAH toxicity. The increased PAH alkylation indices (0.7-0.9) showed these primarily came from combustion sources. The runoff particles were additionally microscopically characterized, and correlations were found between the rubber particle counts and the PAH alkylation-index as well as the levels of 2-(methylthio)benzothiazole, a marker compound for tire leaching.