Ex situ determination of freely dissolved concentrations of hydrophobic organic chemicals in sediments and soils: basis for interpreting toxicity and assessing bioavailability, risks and remediation necessity

Principles of passive sampling for ex situ measurement of hydrophobic organic compounds in sediment: Key considerations on dilution, depletion, and equilibrium

Passive sampling techniques have undoubtedly proven effective for determining freely dissolved concentrations (Cfree) in sediment. However, the absence of a rationale-based, hands-on protocol for guiding practitioners in conducting ex situ exposure of passive samplers in sediment underscores the need for research and development in this area. The goal of this study was to address three critical issues for passive sampling in sediment ex situ: sediment dilution, depletion, and nonequilibrium. Polyethylene (PE) and polymethyl methacrylate (PMMA) film samplers were utilized in experiments involving hydrophobic organic compounds (HOCs, including PAHs, PCBs, PBDEs, and pesticides) spiked sediments. The results indicated that the influence of sediment dilution could be safely disregarded for HOCs with a larger Kd value (i.e., > 140) when moisture content of 80 % was selected for the exposure. Given some data deviations stemming from sample analysis, the depletion extent could significantly vary within a wide range (up to 36.4 %) rather than being fixed at a specific level (e.g., 5 %). Most HOCs reached equilibrium in a 10-d exposure for the PE sampler, and compounds with a log Kow value <7.12 did not need correction for nonequilibrium. An equation for estimating the nonequilibrium correction factor and an approach for correcting nonequilibrium exposure were introduced. The passive sampling method with PE was applied to a set of field-contaminated sediments under the depletion extents ranged from 7.1 % to 77 %. Based on the relatively comprehensive understanding of the passive sampling in sediment ex situ, a practical and standardized protocol was provided for Cfree measurement of HOCs.

Improving Sediment Toxicity Testing for Very Hydrophobic Chemicals: Part 2-Exposure Duration, Upper Limit Test Concentrations, and Distinguishing Actual Toxicity from Physical Effects

Sediment toxicity testing with very hydrophobic organic chemicals (VHOCs) is challenging because of the chemicals' low aqueous solubilities and slow kinetics. The present study presents the results of experiments investigating whether the standard exposure duration of 28 days with benthic invertebrates is sufficient for VHOCs; above which concentrations in sediment VHOCs are present as "free phase," that is, crystals or non-aqueous-phase liquids (NAPLs); and whether it is possible to discriminate between actual VHOC toxicity and physical effects caused by NAPLs through fouling of the test organisms. The results suggest that the standard sediment toxicity test duration is sufficient for obtaining steady-state VHOC concentrations in Hyalella azteca and Lumbriculus variegatus, provided that spiking and equilibration are performed properly (i.e., no free phase present). Under these conditions, transient (days 3-20) peak-shaped toxicokinetics were observed, with steady-state concentrations reached at approximately 28 days. The concentration above which NAPLs are present, the so-called critical separate phase concentration (CSPC), was determined for several VHOCs by modeling and two experimental methods. Modeling resulted in unrealistic and variable data and therefore should be applied with caution. Experimentally determining CSPCs was successful and yielded values of approximately 1000 (400-2000) mg/kg dry weight, depending on the chemical. Finally, it was demonstrated that distinguishing actual toxicity from physical effects is possible by applying a well-considered test setup, combining toxicity tests with multiple invertebrates (including Lumbriculus, which serves as a negative control for fouling); a broad test concentration range, preferably up to at least 30 000 mg/kg; and passive sampling to localize the CSPC. Applying this setup, false-positive effects due to fouling, as well as false-negative results due to testing at too low concentrations (trying to stay below the CSPC), can be avoided. Environ Toxicol Chem 2024;43:1728-1739. © 2023 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Improving Sediment Toxicity Testing for Very Hydrophobic Chemicals: Part 1-Spiking, Equilibrating, and Exposure Quantification

Sediment toxicity tests have applications in ecological risk and chemical safety assessments. Despite the many years of experience in testing and the availability of standard protocols, sediment toxicity testing remains challenging with very hydrophobic organic chemicals (VHOCs; i.e., chemicals with a log octanol/water partition coefficient of more than 6). The challenges primarily relate to the chemicals' low aqueous solubilities and slow kinetics, due to which several experimental artifacts may occur. To investigate the potential artifacts, experiments were performed, focusing on spiking and equilibrating (aging) sediments, as well as exposure quantification with passive sampling. The results demonstrated that generally applied, Organisation for Economic Co-operation and Development-recommended spiking (coating) methods may lead to significant chemical losses and the formation of nondissolved, nonbioavailable VHOCs. Direct spiking appeared to be the most optimal, provided that intensive mixing was applied simultaneously. Passive dosing was tested as a novel way of spiking liquid VHOCs, but the approach proved unsuccessful. Intensive postspiking mixing during sediment equilibration for 1 to 2 weeks was shown to be essential for producing a homogeneous system, minimizing the presence of nondissolved chemical (crystals or nonaqueous phase liquids; NAPLs), and creating a stable toxicological response in subsequent toxicity tests. Finally, exposure quantification of VHOCs in sediments through passive sampling was found to be feasible with different polymers, although prolonged equilibration times may be required, and determining sampler/water partition coefficients can be extremely challenging. The results of additional experiments, focusing on toxicity test exposure duration, concentrations above which NAPLs will occur, and ways to distinguish actual toxicity from false-positive results, are presented in Part 2 of this publication series. Environ Toxicol Chem 2024;43:1717-1727. © 2024 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Sediment Toxicity Tests: A Critical Review of Their use in Environmental Regulations

Sediments are an integral component of aquatic systems, linking multiple water uses, functions, and services. Contamination of sediments by chemicals is a worldwide problem, with many jurisdictions trying to prevent future pollution (prospective) and manage existing contamination (retrospective). The present review assesses the implementation of sediment toxicity testing in environmental regulations globally. Currently, the incorporation of sediment toxicity testing in regulations is most common in the European Union (EU), North America, and Australasian regions, with some expansion in Asia and non-EU Europe. Employing sediment toxicity testing in prospective assessments (i.e., before chemicals are allowed on the market) is most advanced and harmonized with pesticides. In the retrospective assessment of environmental risks (i.e., chemicals already contaminating sediments), regulatory sediment toxicity testing practices are applied inconsistently on the global scale. International harmonization of sediment toxicity tests is considered an asset and has been successful through the widespread adoption and deployment of Organisation for Economic Co-operation and Development guidelines. On the other hand, retrospective sediment assessments benefit from incorporating regional species and protocols. Currently used toxicity testing species are diverse, with temperate species being applied most often, whereas test protocols are insufficiently flexible to appropriately address the range of environmental contaminants, including nanomaterials, highly hydrophobic contaminants, and ionized chemicals. The ever-increasing and -changing pressures placed on aquatic resources are a challenge for protection and management efforts, calling for continuous sediment toxicity test method improvement to insure effective use in regulatory frameworks. Future developments should focus on including more subtle and specific toxicity endpoints (e.g., incorporating bioavailability-based in vitro tests) and genomic techniques, extending sediment toxicity testing from single to multispecies approaches, and providing a better link with ecological protection goals. Environ Toxicol Chem 2024;43:1697-1716. © 2024 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

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.

Understanding of Co-boiling between Organic Contaminants and Water during Thermal Remediation: Effects of Nonequilibrium Heat and Mass Transport

In situ thermal desorption (ISTD) provides an efficient solution to remediation of soil and groundwater contaminated with nonaqueous phase liquids (NAPLs). Establishing a relationship between the subsurface temperature rise and NAPL removal is significant to reduce energy consumption of ISTD. However, the co-boiling phenomenon between NAPL and water poses a great challenge in developing this relationship due to the nonequilibrium heat and mass transport effects. We performed a systematic experimental investigation into the local temperature rise patterns at different distances from a NAPL pool and under different degrees of superheat by selecting four representative NAPLs (i.e., trichloroethylene, tetrachlorethylene, n-hexane, and n-octane) according to their density and boiling point relative to water. The patterns of temperature rise indicated that the underground temperature field can be divided into three zones: the zone of local thermal equilibrium, the nonequilibrium zone affected by co-boiling, and the zone unaffected by co-boiling. We developed a pattern-recognition-based approach, which considers the effects of local heat and mass transport to establish a qualitative correlation between the temperature rise and NAPL removal. Our results give deeper insights into the understanding of subsurface temperatures in ISTD practice, which can serve as the guideline for more accurate and sustainable remediation.

Avoiding artifacts in the determination of per- and polyfluoroalkyl substance sorbent-water distribution

Characterizing sorbent affinity for a target compound (described by sorbent-water distribution coefficient, Ksw) is a necessary step in the sorbent selection and performance-testing process in the process of capturing aquatic contaminants. However, no standardized procedure exists to measure Ksw, and studies display significant variations in set-up and performance. For per- and polyfluoroalkyl substances (PFAS), most Ksw determinations employ batch experiments with small-scale water-sorbent mixtures, methanol-based spike of target compound(s), and analysis after assumed equilibrium, but methodological details of the above procedure differ and might cause artifacts in the determination of Ksw. We conducted several batch experiments systematically varying a general procedure to characterize effects of sub-optimal experimental design. Using a selection of PFAS (6-carbon fluorinated chain length with differing functional groups) and two sorbents, we tested variations of solution:sorbent ratio, methanol content, and PFAS initial concentration, and compared derived Ksw values. Each methodological component affected log(Ksw), usually by suppressing the value (by 0-48%) when compared with a "best design" procedure. Thus, we suggest (1) a reference procedure for PFAS and sorbents used here, and (2) general guidelines for batch experiment design with different compounds and sorbents. Additionally, we report well-constrained Ksw values for 23 PFAS and two sorbents.

Passive Sampling-Based versus Conventional-Based Metrics for Evaluating Remediation Efficacy at Contaminated Sediment Sites: A Review

Passive sampling devices (PSDs) are increasingly used at contaminated sites to improve the characterization of contaminant transport and assessment of ecological and human health risk at sediment sites and to evaluate the effectiveness of remedial actions. The use of PSDs after full-scale remediation remains limited, however, in favor of evaluation based on conventional metrics, such as bulk sediment concentrations or bioaccumulation. This review has three overall aims: (1) identify sites where PSDs have been used to support cleanup efforts, (2) assess how PSD-derived remedial end points compare to conventional metrics, and (3) perform broad semiquantitative and selective quantitative concurrence analyses to evaluate the magnitude of agreement between metrics. Contaminated sediment remedies evaluated included capping, in situ amendment, dredging and monitored natural recovery (MNR). We identify and discuss 102 sites globally where PSDs were used to determine remedial efficacy resulting in over 130 peer-reviewed scientific publications and numerous technical reports and conference proceedings. The most common conventional metrics assessed alongside PSDs in the peer-reviewed literature were bioaccumulation (39%), bulk sediments (40%), toxicity (14%), porewater grab samples (16%), and water column grab samples (16%), while about 25% of studies used PSDs as the sole metric. In a semiquantitative concurrence analysis, the PSD-based metrics agreed with conventional metrics in about 68% of remedy assessments. A more quantitative analysis of reductions in bioaccumulation after remediation (i.e., remediation was successful) showed that decreases in uptake into PSDs agreed with decreases in bioaccumulation (within a factor of 2) 61% of the time. Given the relatively good agreement between conventional and PSD-based metrics, we propose several practices and areas for further study to enhance the utilization of PSDs throughout the remediation of contaminated sediment sites.

Recalibrating polyparameter linear free energy relationships and reanalyzing mechanisms for partition of nonionic organic compounds to low-density polyethylene passive sampler

Equilibrium passive sampling techniques based on the low-density polyethylene (LDPE) film are increasingly used for determining the concentration of contaminants in water and air. Reliable models capable of predicting LDPE-water and LDPE-air partition coefficients (K_iLDPEw and K_iLDPEa) would be very useful. In previous studies, polyparameter linear free energy relationships (PP-LFERs) based on Abraham's solute descriptors were calibrated for LDPE-water and LDPE-air systems. Unfortunately, a portion of unreliable partition coefficients and solute descriptors were included in the calibration sets of these previous studies, leading to unexpected system parameters and predictive performance in the regression results. In this study, more reliable PP-LFERs were recalibrated for LDPE-water and LDPE-air systems (20‒25 °C) using carefully collected reliable partition coefficients and solute descriptors of various polar and nonpolar compounds (over one hundred and with low redundancy) from the literature, as well as the robust regression method. The PP-LFERs performed well with root-mean-square errors of 0.15-0.25 log units and successfully predicted K_iLDPEw and K_iLDPEa values spanning over 10 orders of magnitude for compounds with reliable descriptors. The partitioning mechanisms of compounds to LDPE were also reanalyzed and compared in detail with n-alkanes (C₆-C₁₆). Generally, LDPE is more prone to form dispersion interactions with solutes than n-alkanes, while it is more difficult to form cavities in LDPE. In addition, the crystallinity of LDPE is not the sole reason for the distinct constant terms presenting in PP-LFERs for LDPE-water and n-hexadecane-water systems.

Long-term monitoring and modeling of PAHs in capped sediments at the Grand Calumet River

The assessment of a cap for remediation of sediments requires long-term monitoring because of the slow migration of contaminants in porous media. In this study, coring and passive sampling tools were used to assess the transport and degradation of polycyclic aromatic hydrocarbons (PAHs) in an amended cap (sand + Organoclay® PM-199) in the Grand Calumet River (Indiana, USA) during four sampling events from 2012 to 2019. Measurements of three PAHs (phenanthrene (Phe), pyrene (Pyr) and benzo[a]pyrene (BaP), representing low, medium, and high molecular weight compounds, respectively) showed a difference of at least two orders of magnitude between bulk concentrations in the native sediments and the remediation cap. Averages of pore water measurements also showed lower levels in the cap respective to the native sediments by a factor of at least 7 for Phe and 3 for Pyr. In addition, between the baseline (BL), which corresponds to observations from 2012 to 2014, and the measurements in 2019, there was a decrease in depth-averaged pore water concentrations of Phe (C₂₀₁₉/C_BL=0.20_-0.07^+0.12 in sediments and 0.27_-0.10^+0.15 in cap) and Pyr (C₂₀₁₉/C_BL=0.47_-0.12^+0.16 in sediments and 0.71_-0.20^+0.28 in the cap). In the case of BaP in pore water, no change was observed in native sediments (C₂₀₁₉/C_BL=1.0_-0.24^+0.32) and there was an increase in the cap (C₂₀₁₉/C_BL=2.0_-0.54^+0.72). Inorganic anions and estimates of pore water velocity along with measurements of PAHs were used to model the fate and transport of contaminants. The modeling suggested that degradation of Phe (t_1/2=1.12_-0.11^+0.16 years) and Pyr (t_1/2=5.34_-1.8^+5.3 years) in the cap is faster than migration, thus the cap is expected to be protective of the sediment-water interface indefinitely for these constituents. No degradation was noted in BaP and the contaminant is expected to reach equilibrium in the capping layer over approximately 100 years if there exists sufficient mass of BaP in the sediments and there is no deposition of clean sediment at the surface.

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.

Scientific concepts and methods for moving persistence assessments into the 21st century

The evaluation of a chemical substance's persistence is key to understanding its environmental fate, exposure concentration, and, ultimately, environmental risk. Traditional biodegradation test methods were developed many years ago for soluble, nonvolatile, single-constituent test substances, which do not represent the wide range of manufactured chemical substances. In addition, the Organisation for Economic Co-operation and Development (OECD) screening and simulation test methods do not fully reflect the environmental conditions into which substances are released and, therefore, estimates of chemical degradation half-lives can be very uncertain and may misrepresent real environmental processes. In this paper, we address the challenges and limitations facing current test methods and the scientific advances that are helping to both understand and provide solutions to them. Some of these advancements include the following: (1) robust methods that provide a deeper understanding of microbial composition, diversity, and abundance to ensure consistency and/or interpret variability between tests; (2) benchmarking tools and reference substances that aid in persistence evaluations through comparison against substances with well-quantified degradation profiles; (3) analytical methods that allow quantification for parent and metabolites at environmentally relevant concentrations, and inform on test substance bioavailability, biochemical pathways, rates of primary versus overall degradation, and rates of metabolite formation and decay; (4) modeling tools that predict the likelihood of microbial biotransformation, as well as biochemical pathways; and (5) modeling approaches that allow for derivation of more generally applicable biotransformation rate constants, by accounting for physical and/or chemical processes and test system design when evaluating test data. We also identify that, while such advancements could improve the certainty and accuracy of persistence assessments, the mechanisms and processes by which they are translated into regulatory practice and development of new OECD test guidelines need improving and accelerating. Where uncertainty remains, holistic weight of evidence approaches may be required to accurately assess the persistence of chemicals. Integr Environ Assess Manag 2022;18:1454-1487. © 2022 The Authors. Integrated Environmental Assessment and Management published by Wiley Periodicals LLC on behalf of Society of Environmental Toxicology & Chemistry (SETAC).

Comparing biochar and hydrochar for reducing the risk of organic contaminants in polluted river sediments used for growing energy crops

In Europe alone, >200 million m³ of river sediments are dredged each year, part of which are contaminated to such an extent that they have to be landfilled. This study compares the use of biochar and hydrochar for the remediation of sediment contaminated with pentachlorobenzene, hexachlorobenzene, lindane, trifluralin, alachlor, simazine, and atrazine with the motivation to make sediments contaminated by such priority substances usable as arable land for growing energy crops. Biochar and hydrochar originating from Miscanthus giganteus and Beta vulgaris shreds were compared for their potential to reduce contaminant associated risk in sediments. Specifically, by investigating the effects of sorbent amendment rate (1, 5, and 10 %) and incubation time (14, 30, and 180 d) on contaminant bioaccessibility, toxicity to the bacteria Vibrio fischeri, as well as toxicity and plant uptake in Zea mays. Biochar reduced contaminant bioaccessibility up to five times more than hydrochar. The bioaccessibility of contaminants decreased up to sevenfold with increasing incubation time, indicating that the performance of carbonaceous sorbents may be underestimated in short-term lab experiments. Biochar reduced contaminants toxicity to Vibrio fischeri, whereas hydrochar was itself toxic to the bacteria. Toxicity to Zea mays was determined by contaminant bioaccessibility but also sorbent feedstock with cellulose rich Beta vulgaris based sorbents exhibiting toxic effects. The plant uptake of all contaminants decreased after sorbent amendment.

Estimating the bioavailability of acetochlor to wheat using in situ pore water and passive sampling

The intensive use of acetochlor in China leads to its extensive existence in soil which may result in contamination of crops and commodities. Therefore, it is vital to assess the bioavailability and phytotoxicity of acetochlor to crops. In this study, four measurements involved in in situ pore water extraction (C_IPW), passive sampling extraction (C_free), ex situ pore water extraction (C_EPW), and organic solvent extraction (C_soil) were conducted to assess the bioavailability and phytotoxicity of acetochlor to wheat plant plants in five soils. The results showed that the acetochlor concentrations accumulated in wheat foliage and roots were in the range of 0.11-0.87 mg/kg and 0.09-2.02 mg/kg in the five tested soils, respectively, and had a significant correlation with the acetochlor values analyzed by C_IPW (R² = 0.83-0.90, p < 0.0001) or the C_free method (R² = 0.86-0.92, p < 0.0001). The acetochlor concentrations in the five soils measured by these two methods were also correlated with the IC₅₀ values of acetochlor in wheat foliage and roots (R² > 0.69, p ≤ 0.05). The results indicated that the C_IPW and C_free methods were effective in evaluating acetochlor toxicity to wheat and the acetochlor concentrations in wheat. The effects of soil physical and chemical properties including pH, organic matter content (OMC), clay content, and cation exchange capacity (CEC) on the acetochlor toxicity to wheat were analyzed, and soil OMC was found to be the dominant factor affecting the toxicity of acetochlor in the soil-wheat system.

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.

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.

pH-Dependent Partitioning of Ionizable Organic Chemicals between the Silicone Polymer Polydimethylsiloxane (PDMS) and Water

The silicone polymer polydimethysiloxane (PDMS) is a popular passive sampler for in situ and ex situ sampling of hydrophobic organic chemicals. Despite its limited sorptive capacity for polar and ionizable organic chemicals (IOC), IOCs have been found in PDMS when extracting sediment and suspended particulate matter. The pH-dependent partitioning of 190 organics and IOCs covering a range of octanol-water partition constants log K _ow from -0.3 to 7.7 was evaluated with a 10-day shaking method using mixtures composed of all chemicals at varying ratios of mass of PDMS to volume of water. This method reproduced the PDMS-water partition constant K _PDMS/w of neutral chemicals from the literature and extended the dataset by 93 neutral chemicals. The existing quantitative structure-activity relationship between the log K _ow and K _PDMS/w could be extended with the measured K _PDMS/w linearly to a log K _ow of -0.3. Fully charged organics were not taken up into PDMS. Thirty-eight monoprotic organic acids and 42 bases showed negligible uptake of the charged species, and the pH dependence of the apparent D _PDMS/w(pH) could be explained by the fraction of neutral species multiplied by the K _PDMS/w of the neutral species of these IOCs. Seventeen multiprotic chemicals with up to three acidity constants pK _a also showed a pH dependence of D _PDMS/w(pH) with the tendency that the neutral and zwitterionic forms showed the highest D _PDMS/w(pH). D _PDMS/w(pH) of charged species of more hydrophobic multiprotic chemicals such as tetrabromobisphenol A and telmisartan was smaller but not negligible. Since these chemicals show high bioactivity, their contribution to mixture effects has to be considered when testing passive sampling extracts with in vitro bioassays. This work has further implications for understanding the role of microplastic as a vector for organic micropollutants.

Passive-Sampler-Based Bioavailability Assessment of PCB Congeners Associated with Aroclor-Containing Paint Chips in the Presence of Sediment

This is the first investigation of the bioavailability of PCBs associated with paint chips (PC) dispersed in sediment. Bioavailability of PCB-containing PC in sediment was measured using ex situ polyethylene passive samplers (PS) and compared to that of PCBs from field-collected sediments. PC were mixed in freshwater sediment from a relatively uncontaminated site with no known PCB contamination sources and from a contaminated site with non-paint PCB sources. PC < 0.045 mm generated concentrations in the PS over one order of magnitude higher than coarser chips. The bioavailable fraction was represented by the polymer-sediment accumulation factor (PSAF), defined as the ratio of the PCB concentrations in the PS and organic carbon normalized sediment. The PSAF was similar for both field sediments. The PSAFs for the field sediments were ~ 50-60 and ~ 5 times higher than for the relatively uncontaminated sediment amended with PC for the size fractions 0.25-0.3 mm and < 0.045 mm, respectively. These results indicate much lower bioavailability for PCBs associated with PC compared to PCBs associated with field-collected sediment. Such information is essential for risk assessment and remediation decision-making for sites where contamination from non-paint PCBs sources is co-located with PCB PC.

Bioavailability and toxicity of imazethapyr in maize plant estimated by four chemical extraction techniques in different soils

The bioavailability and toxicity of herbicides on the crop depend on its uptake efficiency from the soil, and thus the assessment of the bioavailable fraction of herbicides in soil is a crucial work. In this study, we investigated the uptake concentration and toxicity of imazethapyr in maize plant using four chemical measurements, including the extraction of in situ pore water (C_IPW), ex situ pore water (C_EPW), organic solvent (C_soil) and passive sampling (C_free) in five soils. The results obtained that the C_IPW in a specific soil had the most significant correlation with the uptake concentration of imazethapyr in maize plant (R² = 0.8851-0.9708), followed by C_EPW (R² = 0.8911-0.9565) and C_free (R² = 0.7881-0.9673). However, C_free showed a higher correlation when considering all five soils, and thus C_free can describe the bioavailability beyond the types of soil. Additionally, the median inhibition concentrations (IC₅₀) of imazethapyr to maize plant ranged from 5.0 to 6.9 mg/kg in five soils, and the C_IPW, C_EPW and C_free had better relationships with the IC₅₀ (R² > 0.8681) than the C_soil (R² = 0.6782). The effects of soil properties on the phytotoxicity of imazethapyr, including pH, organic matter content, cation exchange capacity and clay content, were studied, and the soil pH was shown to be a main factor. This study demonstrated that the freely dissolved fraction and soil pore water concentration of imazethapyr in soil can be used to evaluate its bioavailability and toxicity to maize.

Stochastic Framework for Addressing Chemical Partitioning and Bioavailability in Contaminated Sediment Assessment and Management

Passive sampling to quantify net partitioning of hydrophobic organic contaminants between the porewater and solid phase has advanced risk management for contaminated sediments. Direct porewater (Cfree) measures represent the best way to predict adverse effects to biota. However, when the need arises to convert between solid-phase concentration (Ctotal) and Cfree, a wide variation in observed sediment-porewater partition coefficients (KTOC) is observed due to intractable complexities in binding phases. We propose a stochastic framework in which a given Ctotal is mapped to an estimated range of Cfree through variability in passive sampling-derived KTOC relationships. This mapping can be used to pair estimated Cfree with biological effects data or inversely to translate a measured or assumed Cfree to an estimated Ctotal. We apply the framework to both an effects threshold for polycyclic aromatic hydrocarbon (PAH) toxicity and an aggregate adverse impact on an assemblage of species. The stochastic framework is based on a "bioavailability ratio" (BR), which reflects the extent to which potency-weighted, aggregate PAH partitioning to the solid-phase is greater than that predicted by default, KOW-based KTOC values. Along a continuum of Ctotal, we use the BR to derive an estimate for the probability that Cfree will exceed a threshold. By explicitly describing the variability of KTOC and BR, estimates of risk posed by sediment-associated contaminants can be more transparent and nuanced.

Suspended Particulate Matter-A Source or Sink for Chemical Mixtures of Organic Micropollutants in a Small River under Baseflow Conditions?

Suspended particulate matter (SPM) plays an important role in the fate of organic micropollutants in rivers during rain events, when sediments are remobilized and turbid runoff components enter the rivers. Under baseflow conditions, the SPM concentration is low and the contribution of SPM-bound contaminants to the overall risk of organic contaminants in rivers is assumed to be negligible. To challenge this assumption, we explored if SPM may act as a source or sink for all or specific groups of organic chemicals in a small river. The concentrations of over 600 contaminants and the mixture effects stemming from all chemicals in in vitro bioassays were measured for river water, SPM, and the surface sediment after solid-phase extraction or exhaustive solvent extraction. The bioavailable fractions of chemicals and mixture effects were estimated after passive equilibrium sampling of enriched SPM slurries and sediments in the lab. Dissolved compounds dominated the total chemical burden in the water column (water plus SPM) of the river, whereas SPM-bound chemicals contributed up to 46% of the effect burden even if the SPM concentration in rivers was merely 1 mg/L. The equilibrium between water and SPM was still not reached under low-flow conditions with SPM as a source of water contamination. The ratios of SPM-associated to sediment-associated neutral and hydrophobic chemicals as well as the ratios of the mixture effects expressed as bioanalytical equivalent concentrations were close to 1, suggesting that the surface sediment can be used as a proxy for SPM under baseflow conditions when the sampling of a large amount of water to obtain sufficient SPM cannot be realized.

Evaluation of a rapid biosensor tool for measuring PAH availability in petroleum-impacted sediment

Decades of research have shown that the concentration of freely dissolved PAH (C_free) in sediment correlates with PAH bioavailability and toxicity to aquatic organisms. Passive sampling techniques and models have been used for measuring and predicting C_free, respectively, but these techniques require weeks for analytical chemical measurements and data evaluation. This study evaluated the performance of a portable, field-deployable antibody-based PAH biosensor method that can provide measurements of PAH C_free within a matter of minutes using a small volume of mechanically-extracted sediment porewater. Four sediments with a wide range of PAHs (ΣPAH 2.4 to 307 mg/kg) derived from petroleum, creosote, and mixed urban sources, were analyzed via three methods: 1) bulk chemistry analysis; 2) ex situ sediment passive sampling; and 3) biosensor analysis of mechanically-extracted sediment porewater. Mean ΣPAH C_free determined by the biosensor for the four sediments (3.1 to 55 μg/L) were within a factor of 1.1 (on average) compared to values determined by the passive samplers (2.0 to 52 μg/L). All mean values differed by a factor of 3 or less. The biosensor was also useful in identifying sediments that are likely to be non-toxic to benthic invertebrates. In two of the four sediments, biosensor results of 20 and 55 μg/L exceeded a potential risk-based screening level of 10 μg/L, indicating toxicity could not be ruled out. PAH Toxic Units (ΣTU) measured in these two sediments using the passive sampler C_free results were also greater than the ΣTU threshold of 1 (6.7 and 5.8, respectively), confirming the conclusions reached with the biosensor. In contrast, the other two sediments were identified as non-toxic by both the biosensor (3.1 and 4.3 μg/L) and the passive sampler (ΣTUs of 0.34 and 0.039). These results indicate that the biosensor is a promising tool for rapid screening of sediments potentially-impacted with PAHs.

Assessment of marine sediment remediation efficiency with SPME-based passive sampling measurement

Passive sampling has been shown to be a suitable procedure to assess the risk of contaminated sediments through the measurement of freely dissolved concentrations (C_Free) and remedial actions involving amendments such as activated carbon (AC). Here we report results of the application of simple, solvent-free solid phase micro extraction methodology (SPME) to assess the performance of different materials for the remediation of selected Norwegian harbour sediments contaminated with polycyclic aromatic hydrocarbons (PAHs) and polychlorinated biphenyls (PCBs). AC amendments enabled a reduction of the availability of PAHs and/or PCBs by a factor of ten to over one hundred in Aker Brygge sediments (Oslo) and sediments from Elkembukta, impacted by industrial emissions of PAHs with/from coal tar pitch. Another material, anthracite, slightly less effective in this set of experiment than AC, showed nonetheless great promise as capping material. The SPME data are put in perspective with equilibrium measurements of C_Free for PAHs and organochlorines with silicone rubber in other Elkembukta sediments collected in the vicinity of those used for the remediation experiments. A reduction of sediment C_free for pyrene, benzo[a]pyrene and benzo[ghi]perylene in inner Elkembukta sediment from on average 407, 6.3 and 0.82 ng L^-1 to values of/or below 1.3, 0.15 and 0.076 ng L^-1, respectively can be expected upon remediation with AC. For the outer, less contaminated Elkembukta sediment, Cfree would reduce from 36, 0.81 and 0.13 ng L^-1 to value of or below 0.06, 0.03 and 0.005 ng L^-1 for these three compounds, respectively. Differences in pattern of PAH and organochlorine contamination of inner and outer Elkembukta sediments are discussed.

Effects of sediment manipulation on freely dissolved concentrations of hydrophobic organic chemicals

The freely dissolved concentration (C_free) of hydrophobic organic chemicals (HOCs) in pore water is an important parameter in the risk assessment and management of contaminated sediments and soils. It can be determined most conveniently through ex situ passive sampling, i.e., in the laboratory. For this purpose, samples are taken from the field and transported to the laboratory, where they are stored and possibly manipulated by sieving, freezing, drying and/or grinding. Although the objective of ex situ passive sampling often is to determine a C_free that reflects the metric under in situ conditions, hardly any information is available on possible effects of sample manipulation. Hence, the present study investigated the impact of freezing, freeze-drying, and grinding on C_free of HOCs in field sediments, as determined with solid phase microextraction (SPME). Freezing increased the C_free of 3- and 4-ring polycyclic aromatic hydrocarbons (PAHs) with up to a factor of 4, whereas for 5- and 6-ring PAHs hardly any effects were observed. Generally, additional freeze-drying did not further increase C_free, but subsequently grinding the samples (further) increased C_free of all PAHs with up to a factor of 4, leading to an overall maximum observed increase in C_free of a factor of 16. Probably, these effects are caused by a structural change in the sorption matrix, enhancing PAH availability. The results indicate that freezing, freeze-drying, and grinding prior to ex situ C_free determinations should be avoided, as these treatments may considerably increase the C_free of HOCs, leading to an overestimation of risks.

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.

Mixture Risk Drivers in Freshwater Sediments and Their Bioavailability Determined Using Passive Equilibrium Sampling

The identification of mixture risk drivers is a great challenge for sediment assessment, especially when taking bioavailability into consideration. The bioavailable portion, which comprises the organic contaminants in pore water and the ones bound to organic carbon, was accessed by equilibrium partitioning to polydimethylsiloxane (PDMS). The exhaustive solvent and PDMS extracts were toxicologically characterized with a battery of in vitro reporter gene assays and chemically analyzed with liquid and gas chromatography coupled to high-resolution mass spectrometry. The bioavailable fractions of mixture effects and individual chemicals were mostly lower than 0.1, indicating that more than 90% of the substances are strongly bound and would not pose an immediate risk but could potentially be remobilized in the long term. Despite 655 organic chemicals analyzed, only 0.1-28% of the observed biological effects was explained by the detected compounds in whole sediments, while 0.009-3.3% was explained by bioavailable chemicals. The mixture effects were not only dominated by legacy pollutants (e.g., polycyclic aromatic hydrocarbons (PAHs) in the bioassay for activation of the aryl-hydrocarbon receptor (AhR) and oxidative stress response (AREc32)) but also by present-use chemicals (e.g., plastic additives for binding to the peroxisome proliferator-activated receptor γ (PPARγ)), with different fingerprints between whole sediments and bioavailable extracts. Our results highlight the necessity to involve different bioassays with diverse effect profiles and broader selection of contaminants along with bioavailability for the risk assessment of chemical mixtures in sediments.

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.