Polymers as Reference Partitioning Phase: Polymer Calibration for an Analytically Operational Approach To Quantify Multimedia Phase Partitioning

Development of new PDMS in tube extraction microdevice for enhanced monitoring of polycyclic aromatic hydrocarbons and their derivatives in water

Contamination by polycyclic aromatic hydrocarbons (PAHs) is an urgent environmental concern, given its atmospheric dispersion and deposition in water bodies and soils. These compounds and their nitrated and oxygenated derivatives, which can exhibit high toxicities, are prioritized in environmental analysis contexts. Amid the demand for precise analytical techniques, comprehensive two-dimensional chromatography coupled with mass spectrometry (GCxGC/Q-TOFMS) has emerged as a promising tool, especially in the face of challenges like co-elution. This study introduces an innovation in the pre-concentration and detection of PAHs using an extraction fiber based on polydimethylsiloxane (PDMS), offering greater robustness and versatility. The proposed technique, termed in-tube extraction, was developed and optimized to effectively retain PAHs and their derivatives in aqueous media, followed by GCxGC/Q-TOFMS determination. Fiber characterization, using techniques such as TG, DTG, FTIR, and SEM, confirmed the hydrophobic compounds retention properties of the PDMS. The determination method was validated, pointing to a significant advancement in the detection and analysis of PAHs in the environment, and proved effective even for traces of these compounds. The results showed that the detection limits (LOD) and quantification limits (LOQ) ranged from 0.07 ng L-1 to 1.50 ng L-1 and 0.33 ng L-1 to 6.65 ng L-1, respectively; recovery ranged between 72 % and 117 %; and the precision intraday and interday ranged from 1 % to 20 %. The fibers were calibrated in the laboratory, with exposure times for analysis in the equilibrium region ranging from 3 to 10 days. The partition coefficients between PDMS and water were also evaluated, showing logarithm values ranging from 2.78 to 5.98. The fibers were applied to the analysis of real water samples, demonstrating high capacity. Additionally, given the growing demand for sustainable methods, the approach presented here incorporates green chemistry principles, providing an efficient and eco-friendly solution to the current chemical analysis scenario.

Polyparameter Linear Free Energy Relationships for Partitioning of Neutral Organic Compounds to Storage Lipids

Storage lipids are an important compartment in the bioaccumulation of neutral organic compounds. Reliable models for predicting storage lipid-water and storage lipid-air partition coefficients (Kislip/w and Kislip/a), as well as their temperature dependence, are considered useful. Polyparameter linear free energy relationships (PP-LFERs) are accurate, general, and mechanistically clear models for predicting partitioning-related physicochemical quantities. About a decade ago, PP-LFERs were calibrated for Kislip/w at the physiological temperature of 37 °C. However, to date, a comprehensive collection and sufficiently reliable PP-LFERs for Kislip/w and Kislip/a at the most common standard temperature of 25 °C are still lacking. In this study, experimentally based Kislip/w and/or Kislip/a values at 25 °C for 278 compounds were extensively collected or converted from the literature. Subsequently, PP-LFERs were calibrated for Kislip/w and Kislip/a at 25 °C, performing well over 10 orders of magnitude with root-mean-square errors of 0.17-0.21 log units for compounds with reliable descriptors. Furthermore, standard internal energy changes of transfer from water or air to storage lipids for 158 compounds were derived and used to calibrate PP-LFERs for estimating the temperature dependence of Kislip/w or Kislip/a. Additionally, using PP-LFERs, low-density polyethylene was confirmed to be a better storage lipid analogue than silicone and polyoxymethylene in the equilibrium passive sampling of nonpolar and H-bond acceptor polar compounds.

Quantitative thermodynamic exposure assessment of PCBs available to sandworms (Alitta virens) in activated carbon remediated sediment during ongoing sediment deposition

Marine mesoscale studies with sandworms (Alitta virens) were conducted to isolate important processes governing the exposure and bioaccumulation of polychlorinated biphenyls (PCBs) at contaminated sediment sites. Ex situ equilibrium sampling with silicone-coated jars, and in situ passive sampling with low-density polyethylene (LDPE) were used to determine the performance of an activated carbon (AC) amendment remedy applied to the bed sediment. A quantitative thermodynamic exposure assessment ('QTEA') was performed, showing that PCB concentrations in polymers at equilibrium with the surficial sediment were suited to measure and assess the remedy effectiveness with regard to PCB bioaccumulation in worms. In practice, monitoring the performance of sediment remedies should utilize a consistent and predictive form of polymeric sampling of the sediment. The present study found that ex situ equilibrium sampling of the surficial sediment was the most useful for understanding changes in bioaccumulation potential as a result of the applied remedy, during bioturbation and ongoing sediment and contaminant influx processes. The ultrathin silicone coatings of the ex situ sampling provided fast equilibration of PCBs between the sediment interstitial water and the polymer, and the multiple coating thicknesses were applied to confirm equilibrium and the absence of surface sorption artifacts. Overall, ex situ equilibrium sampling of surficial sediment could fit into existing frameworks as a robust and cost-effective tool for contaminated sediment site assessment.

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 (K_pw), determined by the cosolvent and crossed calibrations, were, on average, one logarithmic unit larger in EVA than in the SR. The diffusion coefficients (D_p) 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 K_pw'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 K_ow < 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.

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.

Comparing Equilibrium Concentrations of Polychlorinated Biphenyls Based on Passive Sampling and Bioaccumulation in Water Column Deployments

Biomonitoring at contaminated sites undergoing cleanup, including Superfund sites, often uses bioaccumulation of anthropogenic contaminants by field-deployed organisms as a metric of remedial effectiveness. Bioaccumulation studies are unable to assess the equilibrium status of the organisms relative to the contaminants to which they are exposed. Establishing equilibrium provides a reproducible benchmark on which scientific and management decisions can be based (e.g., comparison with human dietary consumption criteria). Unlike bioaccumulating organisms, passive samplers can be assessed for their equilibrium status. In our study, over a 3-year period, we compared the bioaccumulation of selected polychlorinated biphenyls (PCBs) by mussels in water column deployments at the New Bedford Harbor Superfund site (New Bedford, MA, USA) to codeployed passive samplers. Based on comparisons to the calculated passive sampler equilibrium concentrations, the mussels were not at equilibrium, and the subsequent analysis focused on evaluating approaches for estimating equilibrium bioaccumulation. In addition, a limited evaluation of metal bioaccumulation by the exposed mussels and a metal passive sampler was performed. In general, mussel and passive sampler accumulation of PCBs was significantly correlated; however, surprisingly, agreement on the magnitude of accumulation was optimal when bioaccumulation and passive sampler uptake were not corrected for nonequilibrium conditions. A subsequent comparison of four approaches for estimating equilibrium mussel bioaccumulation using octanol-water partition coefficients (KOW ), triolein-water partition coefficients (KTW ), and two types of polymer-lipid partition coefficients demonstrated that field-deployed mussels were not at equilibrium with many PCBs. A range of estimated equilibrium mussel bioaccumulation concentrations were calculated, with the magnitude of the KOW -based values being the smallest and the polymer-lipid partition coefficient-based values being the largest. These analyses are intended to assist environmental scientists and managers to interpret field deployment data when transitioning from biomonitoring to passive sampling. Environ Toxicol Chem 2023;42:317-332. Published 2022. This article is a U.S. Government work and is in the public domain in the USA.

Silicone wristbands as personal passive samplers of exposure to polychlorinated biphenyls in contaminated buildings

Polychlorinated biphenyls (PCBs) were used in a number of industrial products from 1950 to 80s, including building materials. As a result, some buildings exhibit high levels of PCBs in the indoor environment. The aim of this study was to test silicone wristbands as a method for estimating personal exposure to PCBs in buildings both in controlled experiments and field settings. In the controlled study, the sampling kinetics of silicone wristbands were investigated in a 31-day uptake study. The field study focused on the application of wristbands as a personal exposure measure. It included 71 persons in a contaminated housing estate and 23 persons in a reference group. The linear uptake of PCBs ranged from 2 to 24 days for PCB-8, 18, 28, 31, 40, 44, 49, 52, 66, 99, and 101 under controlled conditions. A generic sampling rate (R_k) of 2.3 m³ d^-1 corresponding to a mass transfer coefficient of 17 m h^-1 was found in the controlled kinetic study. Partitioning coefficients were also determined for the nine congeners. In the field study, an apparent generic field sampling rate (R_f) of 2.6 m³ d^-1 was found; when adjusted to reported hours exposed, it increased to 3.5 m³ d^-1. The wristbands were shown to be a good tool for predicting airborne exposure, as there was a highly significant difference between the exposed and reference group as well as a clear trend when used for ranking of exposure. In correlation analyses, highly significant correlations were observed between air and wristband levels, though adjusting by self-reported exposure time only increased the correlation marginally in the field study. The obtained kinetic data can be used for estimating the magnitude of external exposure. The advantages provided by the wristbands in the form of easy use and handling are significant, though the limitations should also be acknowledged.

Exploring the partitioning of hydrophobic organic compounds between water, suspended particulate matter and diverse fish species in a German river ecosystem

BACKGROUND

Bioaccumulation of hydrophobic organic compounds (HOCs) along freshwater food chains is a major environmental concern as top predators in food webs are relevant for human consumption. To characterize and manage the associated risks, considerable numbers of organisms are sampled regularly for monitoring purposes. However, ethical and financial issues call for an alternative, more generic and more robust approach for assessing the internal exposure of fish that circumvents large variability in biota sampling due to interindividual differences. Passive sampling devices (PSDs) offer a fugacity-based approach for pollutant enrichment from different abiotic environmental compartments with a subsequent estimation of bioaccumulation in fish which we explored and compared to HOC concentrations in fish as determined using traditional approaches.

RESULTS

In this study, concentrations in silicone-based PSDs applied to the water phase and suspended particulate matter (SPM) of a river polluted with HOCs were used to estimate the concentration in model lipids at thermodynamic equilibrium with either environmental compartment. For comparison, muscle tissue of seven fish species (trophic level 1.8 to 2.8) was extracted using traditional exhaustive solvent extraction, and the lipid-normalized concentrations of HOCs were determined. The PSD-based data from SPM proved to be a more conservative estimator for HOCs accumulated in fish than those from water. Body length of the fish was found to be more suitable to describe increasing accumulation of HOCs than their trophic level as derived from stable isotope analysis and might offer a suitable alternative for future studies.

CONCLUSIONS

By combining fugacity-based sampling in the abiotic environment, translation into corresponding concentrations in model lipids and body length as an indicator for increasing bioaccumulation in fish, we present a suggestion for a robust approach that may be a meaningful addition to conventional monitoring methods. This approach potentially increases the efficiency of existing monitoring programs without the need to regularly sacrifice vertebrate species.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1186/s12302-022-00644-w.

Probing the Thermodynamics of Biomagnification in Zoo-Housed Polar Bears by Equilibrium Sampling of Dietary and Fecal Samples

In a proof-of-concept study, we recently used equilibrium sampling with silicone films to noninvasively derive the thermodynamic limit to a canine's gastrointestinal biomagnification capability (BMFlim) by determining the ratio of the products of the volume (V) and fugacity capacity (Z) of food and feces. In that earlier study, low contaminant levels prevented the determination of contaminant fugacities (f) in food and feces. For zoo-housed polar bears, fed on a lipid-rich diet of fish and seal oil, we were now able to measure the increase in f of nine native polychlorinated biphenyls (PCBs) upon digestion, providing incontestable proof of the process of gastrointestinal biomagnification. A high average BMFlim value of ∼171 for the bears was caused mostly by a remarkable reduction in fugacity capacity driven by a high lipid assimilation capacity. Lipid-rich diets increase the uptake of biomagnifying contaminants in two ways: because they tend to have higher contaminant concentrations and because they lead to a high Z value drop during digestion. We also confirmed that equilibrium sampling yielded similar Z values for PCBs originally present in food and feces and for isotopically labeled PCBs spiked onto those samples, which makes the method suitable for investigating the biomagnification capability of organisms, even if native contaminant concentrations in their diet and feces are low.

Passive Sampling Helps the Appraisal of Contaminant Bioaccumulation in Norwegian Fish Used for Regulatory Chemical Monitoring

Hexachlorobenzene (HCB), listed on the Stockholm Convention on persistent organic pollutants and regulated as a hazardous priority pollutant by the Water Framework Directive (WFD), is ubiquitously distributed in the environment and assumed to mildly biomagnify in aquatic foodwebs. The proposal to include trophic magnification factors (TMFs) in the procedure for comparing contaminant levels in biota at different trophic levels (TLs) with WFD environmental quality standards requires adequate selection of TMFs. In the first step of our study, we compared two independently obtained datasets of pentachlorobenzene (PeCB) and HCB concentration ratios from passive sampling (PS) in water and in fish through routine monitoring programs in Norway to evaluate possible biomagnification. In this procedure, PeCB is used for benchmarking the bioconcentration in fish, and the observed HCB/PeCB ratios in fish are compared with ratios expected in the case of (i) HCB bioconcentration or (ii) biomagnification using published TMF values. Results demonstrate that it is not possible to confirm that HCB biomagnifies in fish species that would be used for WFD monitoring in Norway and challenges the proposed monitoring procedures for such compounds in Norwegian or European waters. In the second step, fish-water chemical activity ratios for HCB and PeCB as well as for polychlorinated biphenyls where biota and PS were conducted alongside were calculated and found to rarely exceed unity for cod (Gadus morhua), a fish species with a TL of approximately 4.

Polyethylene-Water and Polydimethylsiloxane-Water Partition Coefficients for Polycyclic Aromatic Hydrocarbons and Polychlorinated Biphenyls: Influence of Polymer Source and Proposed Best Available Values

For most passive sampling applications, the availability of accurate passive sampler-water partition coefficients (K_p-w ) is of key importance. Unfortunately, a huge variability exists in literature K_p-w values, in particular for hydrophobic chemicals such as polycyclic aromatic hydrocarbons (PAHs) and polychlorinated biphenyls (PCBs). This variability is a major source of concern in the passive sampling community, which would benefit from high-quality K_p-w data. Hence, in the present study "best available" PAH and PCB K_p-w values are proposed for the two most often applied passive sampling materials, that is, low-density polyethylene and polydimethylsiloxane (PDMS), based on (1) a critical assessment of existing literature data, and (2) new K_p-w determinations for polyethylene and PDMS, with both polymers coming in six different versions (suppliers, thicknesses). The experimental results indicated that K_p-w values for PDMS are independent of the source, thus allowing straightforward standardization. In contrast, K_p-w values for polyethylene from different sources differed by up to 30%. Defining best available K_p-w values for this polymer therefore may require standardization of the polymer source. Application of the proposed best available K_p-w values will substantially improve the accuracy of freely dissolved concentration results by users and the potential for comparisons across laboratories. Environ Toxicol Chem 2022;41:1370-1380. © 2022 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Estimating the Bioaccumulation Potential of Hydrophobic Ultraviolet Stabilizers Using Experimental Partitioning Properties

Although hydrophobic ultraviolet (UV) stabilizers are an emerging environmental concern because of their widespread occurrence, persistence, and bioaccumulation potential, experimental values of their partitioning properties required for risk assessment are scarce. In this study, n-octanol-water partition (Kow) and lipid-water partition constants (Klipw), which are key parameters for environmental risk assessment, were experimentally determined for five selected hydrophobic UV stabilizers (UV326, UV327, UV328, UV329, and UV531) based on third-phase partitioning among polydimethylsiloxane (PDMS), water, and n-octanol/lipid. The partition constants between PDMS and water (KPDMSw), obtained using the dynamic permeation method were used to derive Kow and Klipw. The obtained log Kow and log Klipw values were in the ranges of 7.08-7.94 and 7.50-8.34, respectively, indicating that the UV stabilizers exhibited a high bioaccumulation potential in aquatic environments. The experimental Kow and Klipw values obtained in this study provide valuable information for the evaluation of the fate, distribution, bioavailability, and toxicity of the UV stabilizers in aquatic environments.

Equilibrium sampling of suspended particulate matter as a universal proxy for fish and mussel monitoring

Bioaccumulation of persistent and hydrophobic organic compounds in the aquatic environment puts secondary consumers, such as fish, at risk. To assess their exposure, monitoring programs with high numbers of individuals have been conducted worldwide over decades that require major efforts and raise ethical issues. This study aimed at testing suspended particulate matter (SPM) as an alternative and accessible abiotic matrix to estimate the internal exposure concentrations of such chemicals in fish and mussels. Muscle tissues of bream (Abramis brama), tissues of zebra mussels (Dreissena polymorpha) and SPM were collected from four major German rivers, Elbe, Danube, Saar and Saale, in 2018 within the national monitoring program of the German Environmental Specimen Bank. We used (i) total solvent extraction for biota samples to quantify the lipid-normalized concentrations of polychlorinated biphenyls, polycyclic aromatic hydrocarbons and hexachlorobenzene and (ii) passive equilibrium sampling of SPM to derive equilibrium partitioning concentrations in lipids and (iii) set these independent data sets into context. Since the ratio of lipid-normalized concentration / equilibrium partitioning concentration in lipids was in most cases < 1.0, SPM may serve as a conservative proxy for the internal concentration of bream and mussels, although bream of high age (i.e., older than 10 years) showed a tendency for this ratio to exceed 1.0. This observation indicates that age-dependent biomagnification can exceed the predictions based on thermodynamic equilibrium relative to SPM.

Evaluating the fate of hexabromocyclododecanes in the coastal environment: Fugacity analysis using field data

Abundant use of plastic materials has increased the amount of microplastics (MPs) and related hazardous chemicals in the marine environment. Hexabromocyclododecanes (HBCDs), brominated flame retardants added to expanded polystyrene (EPS), have been detected in biotic and abiotic samples. In this study, the partition constants of HBCDs between plastics and seawater (K_Psw) were determined. Fugacities of HBCDs in EPS, seawater, sediment, and mussels were obtained to determine the directions of the diffusive flux. The fugacities in EPS (f_EPS) were greater than those in seawater (f_sw), sediment (f_sed), and mussels (f_swmussel-EPS and f_mussel-rock) by three orders of magnitude, indicating that EPS plastics are a significant source of HBCDs. The f_mussel-rock of α-HBCD in rock mussels was greater than f_sw by factors of 1.7, whereas the f_mussel-rock of γ-HBCD was smaller than f_sw by factors of 16, indicating the bioisomerization from γ-to α-HBCD. The relatively constant concentration ratio of β-HBCD to the total HBCDs indicated that β-HBCD is a sufficient tracer for determining the diffusive flux. The f_sed values of HBCDs were greater than f_sw by factors of 17-28, implying a probable advective vertical flow of HBCDs from the EPS plastics, which requires further investigation.

Dynamic passive sampling of hydrophobic organic compounds in surface seawater along the South Atlantic Ocean east-to-west transect and across the Black Sea

Mapping of hydrophobic organic compounds (HOCs) in surface seawater on an east-to-west transect of the South Atlantic Ocean (SAO) and across the Black Sea (BS) in 2016 was performed by a dynamic passive sampling device containing silicone-based passive samplers. In SAO as well as in BS the measurements confirmed freely dissolved concentrations of polychlorinated biphenyls, DDT and its metabolites, chlorobenzenes, cyclodiene pesticides, and brominated flame retardants in the range of units to low hundreds of pg per litre. The findings indicate that the spatial distribution of HOCs and emerging pollutants in the SAO and the BS is influenced by riverine inputs, ocean currents and atmospheric deposition from continental plumes. Observed concentration gradients indicate that eastern SAO receives DDT from sources in South Africa, whereas the emissions of endosulfan originate in South America. Elevated HOC concentrations in the northwestern BS are related to their discharge by rivers from the European continent.

Passive Dosing of Petroleum and Essential Oil UVCBs-Whole Mixture Toxicity Testing at Controlled Exposure

Petroleum products and essential oils are produced and used in large amounts and are categorized as "Substances of Unknown or Variable composition, Complex reaction products or Biological materials (UVCBs)." These UVCBs are notorious difficult-to-test substances, since they are complex mixtures of hydrophobic and volatile compounds. This study introduces two passive dosing (PD) approaches for whole UVCB toxicity testing: (1) headspace PD applies the UVCB and purified lipid oil as a donor to control exposure via the headspace and (2) silicone rod PD applies UVCB-loaded silicone rods to control exposure via an aqueous test medium and headspace. Headspace gas chromatography-mass spectrometry measurements were used to cross-validate the approaches at the saturation level and to confirm exposure and maintain mixture composition at varying donor concentration levels. Both approaches were applied to whole-mixture toxicity tests of petroleum and essential oil UVCBs with daphnia and algae. Finally, the observed toxicity was linked to concentrations in the donor and in lipid membranes at equilibrium with the donors. Dose-response curves were similar across the dosing approaches and tested species for petroleum products but differed by an order of magnitude between essential oils and PD systems. All observed toxic effects were consistent with baseline toxicity, and no excess mixture toxicity was observed.

Bioavailable Environmental Pollutant Patterns in Sediments from Passive Equilibrium Sampling

Sediment-associated risks depend on the bioavailable fraction of organic chemicals and cannot be comprehended by their total concentrations. The present study investigated contamination patterns of bioavailable chemicals in sediments from various sites around the globe by using passive equilibrium sampling. The extracts had been characterized previously for mixture effects by in vitro reporter gene assays and were in this study analyzed using gas chromatography-high resolution mass spectrometry for 121 chemicals including both legacy and emerging contaminants. The spatial distribution of the detected chemicals revealed distinct contamination patterns among sampling sites. We identified compounds in common at the different sites but most contaminant mixtures were site-specific. The mixture effects of the detected chemicals were predicted with a mixture toxicity model from effect concentrations of bioactive single chemicals and detected concentrations, applying a joint model for concentration addition and independent action. The predicted mixture effects were dominated by polycyclic aromatic hydrocarbons, and among the chemicals with available effect data, 17% elicited oxidative stress response and 18% activated the arylhydrocarbon receptor. Except for two sites in Sweden, where 11 and 38% of the observed oxidative stress response were explained by the detected chemicals, less than 10% of effects in both biological end points were explained. These results provide a comprehensive investigation of bioavailable contamination patterns of sediments and may serve as an example of employing passive equilibrium sampling as a monitoring technique to integrate the risk of bioavailable sediment-associated chemicals in aquatic environments.

Comparison of In Situ and Ex Situ Equilibrium Passive Sampling for Measuring Freely Dissolved Concentrations of Parent and Alkylated Polycyclic Aromatic Hydrocarbons in Sediments

Equilibrium passive sampling methods (EPSMs) allow quantification of freely dissolved contaminant concentrations (C_free ) in sediment porewater. Polydimethylsiloxane (PDMS) is a convenient sampling polymer that can be equilibrated in field (in situ) or laboratory (ex situ) sediments to determine C_free , providing reliable compound-specific PDMS-water partition coefficients (K_PDMS-water ) are available. Polycyclic aromatic hydrocarbons (PAHs) are an important class of sediment contaminants comprised of parent and alkylated homologs. However, application of EPSM to alkylated PAHs is challenged by lack of K_PDMS-water measurements. Our first objective was to obtain K_PDMS-water for 9 alkylated PAHs and biphenyls using 3 different PDMS-coated fibers. Quantitative relationships were then established to define K_PDMS-water for 18 parent and 16 alkyl PAHs included in the US Environmental Protection Agency's sediment quality benchmark method for benthic life protection based on additive toxic units. The second objective was to compare C_free in porewater obtained using both in situ and ex situ EPSMs at 6 Baltic Sea locations. The results indicated that in situ and ex situ C_free for alkyl PAHs generally agreed within a factor of 3. Further, all sites exhibited additive toxic units <1, indicating that PAHs pose a low risk to benthos. The results extend practical application of EPSMs for improved risk assessment and derivation of porewater-based remediation goals for PAH-contaminated sediments. Environ Toxicol Chem 2020;39:2169-2179. © 2020 SETAC.

Passive air sampling for semi-volatile organic chemicals

During passive air sampling, the amount of a chemical taken up in a sorbent from the air without the help of a pump is quantified and converted into an air concentration. In an equilibrium sampler, this conversion requires a thermodynamic parameter, the equilibrium sorption coefficient between gas-phase and sorbent. In a kinetic sampler, a time-averaged air concentration is obtained using a sampling rate, which is a kinetic parameter. Design requirements for kinetic and equilibrium sampling conflict with each other. The volatility of semi-volatile organic compounds (SVOCs) varies over five orders of magnitude, which implies that passive air samplers are inevitably kinetic samplers for less volatile SVOCs and equilibrium samplers for more volatile SVOCs. Therefore, most currently used passive sampler designs for SVOCs are a compromise that requires the consideration of both a thermodynamic and a kinetic parameter. Their quantitative interpretation depends on assumptions that are rarely fulfilled, and on input parameters, that are often only known with high uncertainty. Kinetic passive air sampling for SVOCs is also challenging because their typically very low atmospheric concentrations necessitate relatively high sampling rates that can only be achieved without the use of diffusive barriers. This in turn renders sampling rates dependent on wind conditions and therefore highly variable. Despite the overall high uncertainty arising from these challenges, passive air samplers for SVOCs have valuable roles to play in recording (i) spatial concentration variability at scales ranging from a few centimeters to tens of thousands of kilometers, (ii) long-term trends, (iii) air contamination in remote and inaccessible locations and (iv) indoor inhalation exposure. Going forward, thermal desorption of sorbents may lower the detection limits for some SVOCs to an extent that the use of diffusive barriers in the kinetic sampling of SVOCs becomes feasible, which is a prerequisite to decreasing the uncertainty of sampling rates. If the thermally stable sorbent additionally has a high sorptive capacity, it may be possible to design true kinetic samplers for most SVOCs. In the meantime, the passive air sampling community would benefit from being more transparent by rigorously quantifying and explicitly reporting uncertainty.

Evaluating Polymeric Sampling as a Tool for Predicting the Bioaccumulation of Polychlorinated Biphenyls by Fish and Shellfish

Recent research has shown that polymeric sampling data generally can predict the bioaccumulation of hydrophobic organic contaminants by benthic and sessile invertebrates. Based on literature data, this review evaluated polymeric sampling as a tool for predicting the bioaccumulation of polychlorinated biphenyls (PCBs) by pelagic and mobile fish and shellfish. Lipid-normalized concentrations (C_L) were linked to corresponding equilibrium polymer concentrations (C_P) to evaluate the (1) correlation between C_L and C_P, (2) accuracy when using C_P as surrogates for C_L, (3) effects of experimental variables on these results, and (4) implications associated with this approach. Generally, strong positive log-log linear correlations existed between C_L and C_P, meaning that increasing bioaccumulation was well-reflected by increasing polymer accumulation. Further, the majority of the regression lines, as well as individual C_L to C_P ratios, were within a factor of 10 from the hypothetical 1:1 relationship, suggesting that polymers accumulated concentrations comparable to body residues in fish and shellfish. Interestingly, overall stronger correlations and lower C_L to C_P ratios resulted when C_P were based on sediment compared to water column-deployed samplers. These findings provide a tool for environmental managers when assessing and managing risk associated with PCB-contaminated sediments and waters in protecting vulnerable fish and shellfish species.

Quantifying the Biomagnification Capability of Arctic Wolf and Domestic Dog by Equilibrium Sampling

The mechanism underlying contaminant biomagnification is a decrease in the volume (V) and the fugacity capacity (Z) of food during digestion in the gastrointestinal tract. Traditionally, biomagnification is quantified by measuring contaminant concentrations in animal tissues. Here, we present a proof-of-concept study to noninvasively derive the thermodynamic limit to an organism's biomagnification capability (biomagnification limit -BMF_lim) by determining the ratio of the V·Z-products of undigested and digested food. We quantify Z-values by equilibrating food and feces samples, which have been homogenized and spiked with polychlorinated biphenyls (PCBs), with silicone films of variable thickness coated on the inside of glass vials. We demonstrate the feasibility of this method for wolf (Canis lupus hudsonicus) and domestic dog (Canis lupus familiaris). For an adult wolf eating a relatively lean meat diet, a BMF_lim (averaged over several PCB congeners) of approximately 41 was observed, whereas the BMF_lim reached 81 for an adult domestic dog eating a lipid-rich diet. Besides the dietary lipid content that strongly affects the Z-value of the diet, the capability of an animal to digest its diet also influences the BMF_lim by controlling the Z-values of their feces and the volume reduction of the food in the gastrointestinal tract. Less efficient digestion leads to a lower BMF_lim in a juvenile dog (approximately 35) compared to its older self, even though their diets had similar lipid contents. The effect of the volume reduction (V_D/V_F ranging from 4 to 15) was comparable to the effect of the Z-value reduction (Z_D/Z_F from 3 to 20).

Accelerated equilibrium sampling of hydrophobic organic chemicals in solid matrices: A proof of concept on how to reach equilibrium for PCBs within 1 day

Equilibrium sampling of hydrophobic organic chemicals (HOCs) is increasingly used to measure freely dissolved concentrations and chemical activities in sediments and soils. However, for the most hydrophobic chemicals (Log K_ow > 6) such equilibrium sampling requires often very long sampling times in the order of weeks to months. The aim of the present study was to explore two strategies for markedly increasing the HOC mass transfer from matrix to sampler with the overall goal to shorten equilibration times down to a few hours. Two Solid Phase Microextraction (SPME) approaches were thus developed and tested in sediment and soil contaminated by polychlorinated biphenyls (PCBs). In the first method, the SPME fiber was immersed directly in the aqueous suspension of the sample under vigorous agitation. In the second method equilibration took place via the headspace and was accelerated by elevating the temperature. Headspace-SPME at 80 °C provided fast equilibration within approximately 2 h without contacting the sample and thus avoiding fiber fouling. Both SPME methods were calibrated by passive dosing from preloaded silicone rods and yielded similar results, supporting the validity of HS-SPME at elevated temperatures on a proof of principle level. Finally, by using ¹³C labelled PCB standards, total concentrations were simultaneously measured, which in turn allowed calculation of matrix-water distribution coefficients.

SSP silicone-, lipid- and SPMD-water partition coefficients of seventy hydrophobic organic contaminants and evaluation of the water concentration calculator for SPMD

Passive sampling is increasingly applied for monitoring neutral hydrophobic compounds (HOC) in various environmental media like water, sediment, air and also soft biota tissue. Passive samplers for HOC are often constructed from permeable polymers like silicone and polyethylene (PE), while also SPMD are often applied. Their HOC uptake can be converted to freely dissolved or equivalent lipid-based concentrations using appropriate partition coefficients with or without the use of kinetic uptake models to adjust for non-equilibrium. To facilitate such conversions for seventy HOC partition coefficients are derived by combining polymer-water for Altesil™ silicone and PE, with new and earlier published polymer-polymer, polymer-lipid partition coefficients. Derived SSP silicone-water, lipid-water (K_lip/w), and SPMD-water (K_spmd/w) partition coefficients demonstrate good agreement with literature data, except for K_spmd/w. For SPMD, this work demonstrates a linear K_spmd/w - K_ow relationship (R² = 0.99) in contrast to the parabolic K_spmd/w - K_ow relationship utilized in the USGS "SPMD Water Concentrations Calculator". Following a thorough evaluation of this Calculator it is recommended that in combination with revised K_spmd/w, a radical different model approach should be used for obtaining accurate water concentrations from passive sampling with SPMD.

Passive equilibrium sampling of hydrophobic organic compounds in homogenised fish tissues of low lipid content

Passive equilibrium sampling using polymer samplers in lean tissue is one of the current challenges in assessing bioaccumulation and biomagnification due to the long time needed to reach equilibrium. Despite recent progress achieved by rolling pieces of intact fish fillet with sheets of silicone, there is still a need for a passive sampling method for homogenates that achieves equilibrium before tissue decay starts. In this work, a new approach for relocation of silicone passive samplers in homogenates of lean fish was established for three homogenates with lipid contents varying from 1.2% to 6.1%. Results showed that for 20 model hydrophobic organic compounds with log K_OW between 3.9 and 7.8, equilibrium between the silicone and the tissue was achieved in less than 3 days at 4 °C. The concentrations in lipids obtained using passive equilibrium sampling and those from traditional total solvent extraction agreed well, within a factor of 1.3. This new procedure extends the use of passive samplers to homogenised fish tissues of low lipid content, which is highly relevant for environmental studies focused on bioaccumulation of contaminants.

Monitoring wastewater discharge from the oil and gas industry using passive sampling and Danio rerio bioassay as complimentary tools

Produced water (PW) represents the largest volume waste stream in oil and gas production operations from most offshore platforms. PW is difficult to monitor as releases are rapidly diluted and concentrations can reach trace levels. The use of passive samplers can over come this. Here polyethylene (PE) was calibrated for a diverse range of PW pollutants. Zebrafish were exposed to dilutions of PW and passive sampler extracts in order to investigate the relationship between freely dissolved chemical concentrations and acute toxic effects. The raw PW had an LC50 of 13% (percentage of PW in the standardized zebrafish medium). Observed non-viable deformations to embryos (at 5 hpf) included heart and yolk edema, head, spine and tail deformations. The dose-response relationship of lethal effects showed that if 0.0041 g of PE is exposed to this PW, then extracted, 50% of exposed D. rerio will suffer lethal effects. The sum of tested freely dissolved concentrations that led to 50% lethal effects (mortality and non-viable deformations) was 2.32 × 10^-4 mg/L for PW and 7.92 × 10^-2 mg/L for PE. This implies that exposure to raw PW was more toxic than exposure to PE extracts. This toxicity was attributed both to the presence of contaminants as well as PW salinity. Passive samplers are able to detect very low freely dissolved pollutant concentrations which is important for assessing the spatial dilution of PW releases. Bioassays provide complimentary information as they account for all toxic compounds including those that are not taken up by passive samplers.

Silicone-water partition coefficients determined by cosolvent method for chlorinated pesticides, musks, organo phosphates, phthalates and more

To further support implementation of monitoring by passive sampling, robust sampler-water partition coefficients (K_pw) are required to convert data from passive sampler into aqueous phase concentrations. In this work silicone-water partition coefficients were determined for ∼80 hydrophobic organic contaminants using the cosolvent method. Partition coefficients (K_pm) were measured in pure water and water-methanol mixtures up to a methanol mole fraction of 0.3 (50% v/v). Subsequently, logK_pw in pure water was determined as the intercept of linear regression of the logK_pm with the corresponding methanol mole fractions. LogK_pw were determined for phthalates, musks, organo phosphorus flame-retardants, chlorobenzenes, pesticides, some PCBs and a number of miscellaneous compounds. The median standard error and 95% confidence interval of the measured logK_pw was 0.06 and 0.13, respectively. The overall relationship between K_pw and K_ow seems insufficient to predict K_pw for unknown compounds. Prediction may work within a group of compounds with similar nature, e.g. homologues but HCH isomers having the same K_ow exhibit K_pw ranging over an order of magnitude. Long alkyl-chain phthalates and tris(2-ethylhexyl) phosphate; all having a molecular volume >400 ų, deviated the most from the K_pw-K_ow relationship.

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 (K_pw) 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 200 pg/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.

Partitioning of Chlorinated Paraffins (CPs) to Daphnia magna Overlaps between Restricted and in-Use Categories

Chlorinated paraffins (CPs) are high-production volume industrial chemicals consisting of n-alkanes (with 10 to 30 carbon atoms in the chain) with chlorine content from 30 to 70% of weight. In Europe, the use of short chain chlorinated paraffins (SCCPs) has been restricted by the Stockholm Convention on POPs due to their PBT (persistent, bioaccumulative and toxic) properties. Medium (MCCPs) and long chain (LCCPs) chlorinated paraffins are used as substitution products. In this work we studied the partitioning behavior of five different CP technical mixtures from the established categories (2 SCCPs, 1 MCCP, 1 LCCP and 1 CP technical mixture covering all categories) using passive dosing, by determining the partitioning coefficient of CP technical mixtures between silicone and water ( K_{silicone-water}) as well as between organic matter and water ( K_oc-water). We show that both silicone-water and organic carbon-water partition coefficients overlap between different categories of CP technical mixtures. These results indicate that in-use MCCPs and LCCPs may be equally or more bioaccumulative than restricted SCCPs. For the tested mixtures, both chlorine content and carbon chain length showed a significant correlation with both K_{silicone-water} and K_oc-water.

Applying no-depletion equilibrium sampling and full-depletion bioaccessibility extraction to 35 historically polycyclic aromatic hydrocarbon contaminated soils

Assessing the bioaccessibility of organic pollutants in contaminated soils is considered a complement to measurements of total concentrations in risk assessment and legislation. Consequently, methods for its quantification require validation with historically contaminated soils. In this study, 35 such soils were obtained from various locations in Switzerland and Cuba. They were exposed to different pollution sources (e.g., pyrogenic and petrogenic) at various distance (i.e., urban to rural) and were subject to different land use (e.g., urban gardening and forest). Passive equilibrium sampling with polyoxymethylene was used to determine freely dissolved concentrations (C_free) of polycyclic aromatic hydrocarbons (PAHs), while sorptive bioaccessibility extraction (SBE) with silicone rods was used to determine the bioaccessible PAH concentrations (C_bioacc) of these soils. The organic carbon partition coefficients of the soils were highest for skeet soils, followed by traffic, urban garden and rural soils. Lowest values were obtained from soil exposed to petrogenic sources. Applicability of SBE to quantify C_bioacc was restricted by silicone rod sorption capacity, as expressed quantitatively by the Sorption Capacity Ratio (SCR); particularly for soils with very high K_D. The source of contamination determined bioaccessible fractions (f_bioacc). The smallest f_bioacc were obtained with skeet soils (15%), followed by the pyrogenically influenced soils, rural soils, and finally, the petrogenically contaminated soil (71%). In conclusion, we present the potential and limitations of the SBE method to quantify bioaccessibility in real soils. These results can be used for additional development of this and similar bioaccessibility methods to guarantee sufficient sorption capacity to obtain reliable results.

The presence and partitioning behavior of flame retardants in waste, leachate, and air particles from Norwegian waste-handling facilities

Flame retardants in commercial products eventually make their way into the waste stream. Herein the presence of flame retardants in Norwegian landfills, incineration facilities and recycling sorting/defragmenting facilities is investigated. These facilities handled waste electrical and electronic equipment (WEEE), vehicles, digestate, glass, combustibles, bottom ash and fly ash. The flame retardants considered included polybrominated diphenyl ethers (∑BDE-10) as well as dechlorane plus, polybrominated biphenyls, hexabromobenzene, pentabromotoluene and pentabromoethylbenzene (collectively referred to as ∑FR-7). Plastic, WEEE and vehicles contained the largest amount of flame retardants (∑BDE-10: 45,000-210,000μg/kg; ∑FR-7: 300-13,000μg/kg). It was hypothesized leachate and air concentrations from facilities that sort/defragment WEEE and vehicles would be the highest. This was supported for total air phase concentrations (∑BDE-10: 9000-195,000pg/m³ WEEE/vehicle facilities, 80-900pg/m³ in incineration/sorting and landfill sites), but not for water leachate concentrations (e.g., ∑BDE-10: 15-3500ng/L in WEEE/Vehicle facilities and 1-250ng/L in landfill sites). Landfill leachate exhibited similar concentrations as WEEE/vehicle sorting and defragmenting facility leachate. To better account for concentrations in leachates at the different facilities, waste-water partitioning coefficients, K_waste were measured (for the first time to our knowledge for flame retardants). WEEE and plastic waste had elevated K_waste compared to other wastes, likely because flame retardants are directly added to these materials. The results of this study have implications for the development of strategies to reduce exposure and environmental emissions of flame retardants in waste and recycled products through improved waste management practices.

Assessing the influence of confounding biological factors when estimating bioaccumulation of PCBs with passive samplers in aquatic ecosystems

Passive samplers are promising surrogates for organisms, mimicking bioaccumulation. However, several biological characteristics disturb the passive partitioning process in organisms by accelerating or restraining bioaccumulation, resulting in species-specific body residues of hydrophobic organic contaminants (HOCs). In addition to site-specific characteristics and HOC concentrations, age, sex, diet, biotransformation capability and habitat-specific characteristics may affect body residues. Two passive sampler types, polyethylene (PE) and polydimethylsiloxane (PDMS) were deployed in a PCB-contaminated freshwater lake water and sediment, respectively, to assess their bioaccumulation prediction capacity. In order to understand the importance of biological characteristics in the bioaccumulation process, we explored bioaccumulation in biota from plants and plankton to mussels and fish. The PCB concentrations in the PE sheet reflected the bioavailable concentration of PCBs slightly better than those in the PDMS samplers. Passive samplers were good predictors of PCB concentrations in fish, whereas concentrations in algae and invertebrates were overestimated. When comparing the measured concentrations in biota to the estimated concentrations using the PE samplers, the average regression slope was 0.87 for all biota and 1.22 for fish, and average modeling efficiency (EF) was 3.02 for all biota and 0.6 for fish. The best model performance was achieved for fish in trophic levels 3-4. Bioaccumulation was species-specific and dependent on the trophic level and diet. Closer examination revealed that metabolic capability changes during the life span, and source of nutrition determined the biomagnification of HOCs, which differed between the fish species. Thus, species composition and available prey selection compose a unique bioaccumulation scenario and the resulting body residues. Due to the existing variation in body residues derived from passive samplers, extrapolating the results from one to another ecosystem must be done with caution. Passive samplers, however, offer a very powerful tool for risk assessment on the ecosystem level.

Transferring mixtures of chemicals from sediment to a bioassay using silicone-based passive sampling and dosing

Environmental mixtures of chemicals consist of a countless number of compounds with unknown identity and quantity. Yet, chemical regulation is mainly built around the assessment of single chemicals. Existing frameworks for assessing the toxicity of mixtures require that both the chemical composition and quantity are known. Quantitative analyses of the chemical composition of environmental mixtures are however extremely challenging and resource-demanding. Bioassays may therefore serve as a useful approach for investigating the combined toxicity of environmental mixtures of chemicals in a cost-efficient and holistic manner. In this study, an unknown environmental mixture of bioavailable semi-hydrophobic to hydrophobic chemicals was sampled from a contaminated sediment in a coastal Baltic Sea area using silicone polydimethylsiloxane (PDMS) as an equilibrium passive sampler. The chemical mixture was transferred to a PDMS-based passive dosing system, and its applicability was demonstrated using green algae Tetraselmis suecica in a cell viability assay. The proportion of dead cells increased significantly with increasing exposure level and in a dose-response manner. At an ambient concentration, the proportion of dead cells in the population was nearly doubled compared to the control; however, the difference was non-significant due to high inter-replicate variability and a low number of replicates. The validation of the test system regarding equilibrium sampling, loading efficiency into the passive dosing polymer, stability of the mixture composition, and low algal mortality in control treatments demonstrates that combining equilibrium passive sampling and passive dosing is a promising tool for investigating the toxicity of bioavailable semi-hydrophobic and hydrophobic chemicals in complex environmental mixtures.

Can solid-phase microextraction replace solvent extraction for water analysis in fish bioconcentration studies with highly hydrophobic organic chemicals?

With the aim to refine water analysis in fish bioconcentration studies, automated solid-phase microextraction (SPME) was used as an alternative approach to conventional solvent extraction (liquid-liquid extraction [LLE]) for the extraction of 3 hydrophobic organic chemicals (HOCs; log K_OW 5.5-7.8) from flow-through studies with rainbow trout (Oncorhynchus mykiss). The results showed that total concentrations extracted by SPME combined with internal standards and LLE are equal. The results further verify the possibility of simultaneous extraction of total and freely dissolved HOC concentrations by SPME. Freely dissolved concentrations allow the assessment of sorption and bioavailability of HOCs in bioconcentration studies and their potential impact on resulting bioconcentration factors (BCFs). Reduction in freely dissolved water concentrations can result in an underestimation of BCFs if they are calculated based on total water concentrations. For polychlorinated biphenyl (PCB) 153, a significant increase in BCF value was observed when freely dissolved concentrations were taken into account. However, log BCF values calculated based on freely dissolved concentrations did not correlate linearly with log K_OW values above 5 to 6. This pointed to further influences besides a reduction in freely dissolved water concentrations by sorption to organic matter. The results can aid in assessment of the factors that influence bioconcentration systems and also give important information regarding the possible replacement of LLE by SPME for water analysis of highly HOCs in fish bioconcentration studies. Environ Toxicol Chem 2017;36:2887-2894. © 2017 The Authors. Environmental Toxicology and Chemistry Published by Wiley Periodicals, Inc. on behalf of SETAC.

Partitioning of hydrophobic organic contaminants between polymer and lipids for two silicones and low density polyethylene

Polymers are increasingly used for passive sampling of neutral hydrophobic organic substances (HOC) in environmental media including water, air, soil, sediment and even biological tissue. The equilibrium concentration of HOC in the polymer can be measured and then converted into equilibrium concentrations in other (defined) media, which however requires appropriate polymer to media partition coefficients. We determined thus polymer-lipid partition coefficients (K_PL) of various PCB, PAH and organochlorine pesticides by equilibration of two silicones and low density polyethylene (LDPE) with fish oil and Triolein at 4 °C and 20 °C. We observed (i) that K_PL was largely independent of lipid type and temperature, (ii) that lipid diffusion rates in the polymers were higher compared to predictions based on their molecular volume, (iii) that silicones showed higher lipid diffusion and lower lipid sorption compared to LDPE and (iv) that absorbed lipid behaved like a co-solute and did not affect the partitioning of HOC at least for the smaller molecular size HOC. The obtained K_PL can convert measured equilibrium concentrations in passive sampling polymers into equilibrium concentrations in lipid, which then can be used (1) for environmental quality monitoring and assessment, (2) for thermodynamic exposure assessment and (3) for assessing the linkage between passive sampling and the traditionally measured lipid-normalized concentrations in biota. LDPE-lipid partition coefficients may also be of use for a thermodynamically sound risk assessment of HOC contained in microplastics.

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 (C_free) 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 C_free 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 C_free values.

Cross Validation of Two Partitioning-Based Sampling Approaches in Mesocosms Containing PCB Contaminated Field Sediment, Biota, and Activated Carbon Amendment

The Gold Standard for determining freely dissolved concentrations (C_free) of hydrophobic organic compounds in sediment interstitial water would be in situ deployment combined with equilibrium sampling, which is generally difficult to achieve. In the present study, ex situ equilibrium sampling with multiple thicknesses of silicone and in situ pre-equilibrium sampling with low density polyethylene (LDPE) loaded with performance reference compounds were applied independently to measure polychlorinated biphenyls (PCBs) in mesocosms with (1) New Bedford Harbor sediment (MA, U.S.A.), (2) sediment and biota, and (3) activated carbon amended sediment and biota. The aim was to cross validate the two different sampling approaches. Around 100 PCB congeners were quantified in the two sampling polymers, and the results confirmed the good precision of both methods and were in overall good agreement with recently published LDPE to silicone partition ratios. Further, the methods yielded C_free in good agreement for all three experiments. The average ratio between C_free determined by the two methods was factor 1.4 ± 0.3 (range: 0.6-2.0), and the results thus cross-validated the two sampling approaches. For future investigations, specific aims and requirements in terms of application, data treatment, and data quality requirements should dictate the selection of the most appropriate partitioning-based sampling approach.

Enhanced Accessibility of Polycyclic Aromatic Hydrocarbons (PAHs) and Heterocyclic PAHs in Industrially Contaminated Soil after Passive Dosing of a Competitive Sorbate

To assess the exposure to polycyclic aromatic hydrocarbons (PAHs) it is important to understand the binding mechanisms between specific soil constituents and the organic pollutant. In this study, sorptive bioaccessibility extraction (SBE) was applied to quantify the accessible PAH fraction in industrially contaminated soil with and without passive dosing of a competitive sorbate. SBE experiments revealed an accessible PAH fraction of 41 ± 1% (∑16 US EPA PAHs + 5 further PAHs). The passive dosing of toluene below its saturation level revealed competitive binding and resulted in an average increase of the accessible fraction to 49 ± 2%, whereby primarily the accessibility of higher molecular weight PAHs (log K_ow > 6) was affected. Competitive binding was verified using the same soil with only desorption-resistant PAHs present. In this experiment, passive dosing of toluene resulted in desorption of 13 ± 0.4% PAH. We explain increased PAH desorption after addition of toluene by competitive adsorption to high-affinity sorption sites while acknowledging that toluene could additionally have increased PAH mobility within the soil matrix. Findings suggest that the presence of copollutants at contaminated sites deserves specific considerations as these may increase accessibility and thereby exposure and mobility of PAHs.

Biodegradation testing of chemicals with high Henry's constants - Separating mass and effective concentration reveals higher rate constants

During simulation-type biodegradation tests, volatile chemicals will continuously partition between water phase and headspace. This study addressed how (1) this partitioning affects test results and (2) can be accounted for by combining equilibrium partition and dynamic biodegradation models. An aqueous mixture of 9 (semi)volatile chemicals was first generated using passive dosing and then diluted with environmental surface water producing concentrations in the ng/L to μg/L range. After incubation for 2 h to 4 weeks, automated Headspace Solid Phase Microextraction (HS-SPME) was applied directly on the test systems to measure substrate depletion by biodegradation relatively to abiotic controls. HS-SPME was also applied to determine air to water partitioning ratios. Biodegradation rate constants relating to the chemical in the water phase, k_water, were generally a factor 1 to 11 times higher than biodegradation rate constants relating to the total mass of chemical in the test system, k_system, with one exceptional factor of 72 times for a long chain alkane. True water phase degradation rate constants were found (i) more appropriate for risk assessment than test system rate constants, (ii) to facilitate extrapolation to other air-water systems and (iii) to be better defined input parameters for aquatic exposure and fate models.

Aquatic Global Passive Sampling (AQUA-GAPS) Revisited: First Steps toward a Network of Networks for Monitoring Organic Contaminants in the Aquatic Environment

Organic contaminants, in particular persistent organic pollutants (POPs), adversely affect water quality and aquatic food webs across the globe. As of now, there is no globally consistent information available on concentrations of dissolved POPs in water bodies. The advance of passive sampling techniques has made it possible to establish a global monitoring program for these compounds in the waters of the world, which we call the Aquatic Global Passive Sampling (AQUA-GAPS) network. A recent expert meeting discussed the background, motivations, and strategic approaches of AQUA-GAPS, and its implementation as a network of networks for monitoring organic contaminants (e.g., POPs and others contaminants of concern). Initially, AQUA-GAPS will demonstrate its operating principle via two proof-of-concept studies focused on the detection of legacy and emerging POPs in freshwater and coastal marine sites using both polyethylene and silicone passive samplers. AQUA-GAPS is set up as a decentralized network, which is open to other participants from around the world to participate in deployments and to initiate new studies. In particular, participants are sought to initiate deployments and studies investigating the presence of legacy and emerging POPs in Africa, Central, and South America.

Aquatic toxicity testing of liquid hydrophobic chemicals - Passive dosing exactly at the saturation limit

The aims of the present study were (1) to develop a passive dosing approach for aquatic toxicity testing of liquid substances with very high K_ow values and (2) to apply this approach to the model substance dodecylbenzene (DDB, Log K_ow = 8.65). The first step was to design a new passive dosing format for testing DDB exactly at its saturation limit. Silicone O-rings were saturated by direct immersion in pure liquid DDB, which resulted in swelling of >14%. These saturated O-rings were used to establish and maintain DDB exposure exactly at the saturation limit throughout 72-h algal growth inhibition tests with green algae Raphidocelis subcapitata. Growth rate inhibition at DDB solubility was 13 ± 5% (95% CI) in a first and 8 ± 3% (95% CI) in a repeated test, which demonstrated that improved exposure control can lead to good precision and repeatability of toxicity tests. This moderate toxicity at chemical activity of unity was higher than expected relative to a reported hydrophobicity cut-off in toxicity, but lower than expected relative to a reported chemical activity range for baseline toxicity. The present study introduces a new effective approach for toxicity testing of an important group of challenging chemicals, while providing a basis for investigating toxicity cut-off theories.

A passive dosing method to determine fugacity capacities and partitioning properties of leaves

The capacity of leaves to take up chemicals from the atmosphere and water influences how contaminants are transferred into food webs and soil. We provide a proof of concept of a passive dosing method to measure leaf/polydimethylsiloxane partition ratios (K_leaf/PDMS) for intact leaves, using polychlorinated biphenyls (PCBs) as model chemicals. Rhododendron leaves held in contact with PCB-loaded PDMS reached between 76 and 99% of equilibrium within 4 days for PCBs 3, 4, 28, 52, 101, 118, 138 and 180. Equilibrium K_leaf/PDMS extrapolated from the uptake kinetics measured over 4 days ranged from 0.075 (PCB 180) to 0.371 (PCB 3). The K_leaf/PDMS data can readily be converted to fugacity capacities of leaves (Z_leaf) and subsequently leaf/water or leaf/air partition ratios (K_leaf/water and K_leaf/air) using partitioning data from the literature. Results of our measurements are within the variability observed for plant/air partition ratios (K_plant/air) found in the literature. Log K_leaf/air from this study ranged from 5.00 (PCB 3) to 8.30 (PCB 180) compared to log K_plant/air of 3.31 (PCB 3) to 8.88 (PCB 180) found in the literature. The method we describe could provide data to characterize the variability in sorptive capacities of leaves that would improve descriptions of uptake of chemicals by leaves in multimedia fate models.

Utilizing the partitioning properties of silicone for the passive sampling of polychlorinated biphenyls (PCBs) in indoor air

The former use of polychlorinated biphenyls (PCBs) in construction materials can lead to elevated indoor air concentrations. We studied the partitioning of PCB congeners between indoor air and silicone with a view to establish passive sampling of PCBs. The release of PCB congeners from silicone followed first order kinetics and confirmed air-side rate-limited mass transfer. Logarithmic elimination rate constants decreased linearly with the logKOA values of the PCB congeners, but varied in a non-linear way with air velocity. Linear uptake of PCBs was found for silicone disks (0.5 mm thickness) in a petri dish, while PCBs reached equilibrium in silicone-coated paper sheets (0.001 mm silicone on each side) exposed to indoor air for 1-2 weeks. The ratios of equilibrium concentrations in silicone and conventionally measured air concentrations were roughly comparable with silicone-air partition coefficients, but further research is required for the determination of silicone-air partition coefficients. Avoiding performance reference compounds (PRCs) because of the indoor setting, the two formats were calibrated against conventional active measurements. Comparisons of air concentrations derived from active and kinetic passive sampling showed a divergence by factors of 2.4 and 2.0 (median values) for the petri dishes and the silicone-coated paper, respectively. With promising results for sensitivity and precision, the calibration of kinetic passive samplers remains the main challenge and will need suitable, non-hazardous PRCs. Equilibrium sampling indicated promising alternatives.

Passive Dosing in Chronic Toxicity Tests with the Nematode Caenorhabditis elegans

In chronic toxicity tests with Caenorhabditis elegans, it is necessary to feed the nematode with bacteria, which reduces the freely dissolved concentration (Cfree) of hydrophobic organic chemicals (HOCs), leading to poorly defined exposure with conventional dosing procedures. We examined the efficacy of passive dosing of polycyclic aromatic hydrocarbons (PAHs) using silicone O-rings to control exposure during C. elegans toxicity testing and compared the results to those obtained with solvent spiking. Solid-phase microextraction and liquid-liquid extraction were used to measure Cfree and the chemicals taken up via ingestion. During toxicity testing, Cfree decreased by up to 89% after solvent spiking but remained constant with passive dosing. This led to a higher apparent toxicity on C. elegans exposed by passive dosing than by solvent spiking. With increasing bacterial cell densities, Cfree of solvent-spiked PAHs decreased while being maintained constant with passive dosing. This resulted in lower apparent toxicity under solvent spiking but an increased apparent toxicity with passive dosing, probably as a result of the higher chemical uptake rate via food (CUfood). Our results demonstrate the utility of passive dosing to control Cfree in routine chronic toxicity testing of HOCs. Moreover, both chemical uptake from water or via food ingestion can be controlled, thus enabling the discrimination of different uptake routes in chronic toxicity studies.