Environmental Impacts of Hurricane Harvey on the Neches-Brakes Bayou River System in Beaumont, Texas.

Hurricane Harvey caused unprecedented floods across large regions of Southeast Texas resulting in several infrastructural issues. One of the notable failures was of a drinking water source pump in Beaumont, Texas, that necessitated the emergency use of a temporary pump intake station in the Neches River system. This study examines the environmental consequences of Harvey-induced flooding in the Neches River system by focusing on sensitive locations, including a Superfund site (International Creosoting, IC) and adjacent to the temporary pump intake. Post-Harvey water samples showed greater than two orders of magnitude increase in polycyclic aromatic hydrocarbons (PAH) about 3 weeks after Harvey (350-420 µg L-1 on September 22) at locations adjacent to IC and the temporary water pump intake, which by that time was no longer in use. The organic carbon normalized PAH measurements in the heavily contaminated water samples from both locations (~3% w/w) agreed well with surficial soil/sediment samples collected at the east bank adjacent to the IC site (0.7-5.2% w/w). Furthermore, molecular diagnostic ratios of select PAHs supported the contribution of PAHs from the IC site into the surface waters. PAH measurements were consistent with sediment resuspension by floodwaters that were initially diluted by large flows but became more significant as the flood subsided. Overall, our data showed that flooding can cause high levels of contamination weeks after the initial flooding event, with potential for cascading risks through mobilization of pollutants from source areas and impacts to critical water infrastructure systems.

Seasonal trends of mercury bioaccumulation and assessment of toxic effects in Asian clams and microbial community from field study of estuarine sediment.

This study investigated seasonal trends in bioaccumulation potential and toxic effects of mercury (Hg) in Asian clams (Corbicula fluminea) and microbial community. For this, a clam-exposure experiment was performed during summer, fall, and winter seasons in four different sites (HS1: control/clean site; HS2, HS3, and HS4: contaminated sites) of Hyeongsan River estuary, South Korea. Total mercury (THg) and methylmercury (MeHg) in whole sediments were highest at HS4 site during fall, sustained similar levels during winter, but decreased during summer. Unlike whole sediment, pore water reported higher levels in summer, and gradually declined during fall and winter. Asian clams from HS4 site collected during summer presented highest bioaccumulations of THg (521.52 µg/kg, dry weight) and MeHg (161.04 µg/kg, dry weight), which also correlated with the higher levels of Hg present in pore water in the same season. Moreover, biota-sediment-pore water accumulation factor (BSpAF) were comparatively greater in clams collected from HS2∼HS4 compared to HS1 sites, suggesting that porewater was a better indicator of accumulation of Hg. Upregulation of biomarker genes responsible for detoxifying process (gsts1), scavenging oxidative stress (cat), and protein reparation (hsp70 and hsp90) were observed in clams collected from HS2∼HS4. The overexpression of these biomarkers implied that Asian clams can be considered as promising warning tools for Hg-contamination. Both bacterial and metabolic diversities were negatively affected by higher levels of THg and MeHg. Phylum Proteobacteria was enriched in HS2∼HS4 compared to HS1. In contrast, phylum Bacteroidetes showed a reverse trend. The metabolic profile was highest in HS1 and lowest in HS4, revealing higher stress of Hg in HS4 site. Overall, the outcomes of this field study broaden the information on seasonal trends of bioaccumulation of Hg and its toxic effects. These findings may be helpful in Hg monitoring and management programs in other river systems.

Impacts of Sediment Particle Grain Size and Mercury Speciation on Mercury Bioavailability Potential.

Particle-specific properties, including size and chemical speciation, affect the reactivity of mercury (Hg) in natural systems (e.g., dissolution or methylation). Here, terrestrial, river, and marine sediments were size-fractionated and characterized to correlate particle-specific properties of Hg-bearing solids with their bioavailability potential and measured biomethylation. Marine sediments contained ∼20-50% of the total Hg in the <0.5 µm size fraction, compared to only 0.5 and 3.0% in this size fraction for terrestrial and river sediments, respectively. X-ray absorption spectroscopy (XAS) analysis indicated that metacinnabar (ß-HgS) was the main mercury species in a marine sediment, whereas organic Hg-thiol (Hg(SR)2) was the main mercury species in a terrestrial sediment. Single-particle inductively coupled plasma time-of-flight mass spectrometry analysis of the marine sediment suggests that half of the Hg in the <0.5 µm size fraction existed as individual nanoparticles, which were ß-HgS based on XAS analyses. Glutathione-extractable mercury was higher for samples containing Hg(SR)2 species than ß-HgS species and correlated well with the amount of Hg biomethylation. This particle-scale understanding of how Hg speciation and particle size affect mercury bioavailability potential helps explain the heterogeneity in Hg methylation in natural sediments.

Combined Effects of Plant Cultivation and Sorbing Carbon Amendments on Freely Dissolved PAHs in Contaminated Soil.

We report freely dissolved concentrations ( Cfree) of PAHs in soils amended with 2.5% biochar and activated carbon (AC) during a long-term (18-months) field experiment. The study evaluates also the impact of different plants (clover, grass, willow) on Cfree PAHs. The cumulative effect of treatments on nitrogen and available forms of phosphorus, potassium, and magnesium is also assessed. The direct addition of biochar to soil did not cause any immediate reduction of the sum of 16 Cfree PAHs, while AC resulted in a slight reduction of 5- and 6 ring compounds. The efficiency of binding of Cfree PAHs by biochar and AC increased with time. For biochar, the maximum reduction of 4-6-ring PAHs (18-67%) was achieved within 6 months. For 2- and 3-ring PAHs, a gradual decrease of Cfree was observed which reached 60-66% at 18 months. AC proved to be better in reducing Cfree PAHs than biochar, though for 2- and 3-ring PAHs, the differences in AC and biochar performances were smaller than those for 4-6-ring PAHs. After 18 months, a significantly lower content of Cfree PAHs was observed in the soil with plants compared to the unplanted soil. Except for potassium, AC or biochar did not negatively impact nutrient availability.

Advancing the Use of Passive Sampling in Risk Assessment and Management of Sediments Contaminated with Hydrophobic Organic Chemicals: Results of an International Ex Situ Passive Sampling Interlaboratory Comparison.

This work presents the results of an international interlaboratory comparison on ex situ passive sampling in sediments. The main objectives were to map the state of the science in passively sampling sediments, identify sources of variability, provide recommendations and practical guidance for standardized passive sampling, and advance the use of passive sampling in regulatory decision making by increasing confidence in the use of the technique. The study was performed by a consortium of 11 laboratories and included experiments with 14 passive sampling formats on 3 sediments for 25 target chemicals (PAHs and PCBs). The resulting overall interlaboratory variability was large (a factor of ∼10), but standardization of methods halved this variability. The remaining variability was primarily due to factors not related to passive sampling itself, i.e., sediment heterogeneity and analytical chemistry. Excluding the latter source of variability, by performing all analyses in one laboratory, showed that passive sampling results can have a high precision and a very low intermethod variability (

Electro-bioremediation of contaminated sediment by electrode enhanced capping.

In-situ capping often eliminates or slows natural degradation of hydrocarbon due to the reducing conditions in the sediments. The purpose of this research was to demonstrate a reactive capping technique, an electrode enhanced cap, to produce favorable conditions for hydrocarbon degradation and evaluate this reactive capping technique for contaminated sediment remediation. Two graphite electrodes were placed horizontally at different layers in a cap and connected to external power of 2 V. Redox potentials increased and pH decreased around the anode. Phenanthrene concentration decreased and PAH degradation genes increased in the vicinity of the anode. Phenanthrene concentrations at 0-1 cm sediment beneath the anode decreased to ∼50% of initial concentration over ∼70 days, while phenanthrene levels in control reactor kept unchanged. A degradation model of electrode enhanced capping was developed to simulate reaction-diffusion processes, and model results show that a reaction-dominated region was created in the vicinity of the anode. Although the degradation dominated region was thin, transport processes in a sediment cap environment are typically sufficiently slow to allow this layer to serve as a permeable reactive barrier for hydrocarbon decontamination.

Significant spatial variability of bioavailable PAHs in water column and sediment porewater in the Gulf of Mexico 1 year after the Deepwater Horizon oil spill.

One year after the Deepwater Horizon oil spill accident, semipermeable membrane devices (SPMDs) and polyethylene devices (PEDs) were deployed in wetland areas and coastal areas of the Gulf of Mexico (GOM) to monitor polycyclic aromatic hydrocarbons (PAHs). The measured PAH levels with the PEDs in coastal areas were 0.05-1.9 ng/L in water and 0.03-9.7 ng/L in sediment porewater. With the SPMDs, the measured PAH levels in wetlands (Barataria Bay) were 1.4-73 ng/L in water and 3.3-107 ng/L in porewater. The total PAH concentrations in the coastal areas were close to the reported baseline PAH concentrations in GOM; however, the total PAH concentrations in the wetland areas were one or two orders of magnitude higher than those reported in the coastal areas. In light of the significant spatial variability of PAHs in the Gulf's environments, baseline information on PAHs should be obtained in specific areas periodically.

Regional variation in water-related impacts of shale gas development and implications for emerging international plays.

The unconventional fossil fuel industry is expected to expand dramatically in coming decades as conventional reserves wane. Minimizing the environmental impacts of this energy transition requires a contextualized understanding of the unique regional issues that shale gas development poses. This manuscript highlights the variation in regional water issues associated with shale gas development in the U.S. and the approaches of various states in mitigating these impacts. The manuscript also explores opportunities for emerging international shale plays to leverage the diverse experiences of U.S. states in formulating development strategies that minimize water-related impacts within their environmental, cultural, and political ecosystem.

Application of ß-Cyclodextrin Adsorbents in the Removal of Mixed Per- and Polyfluoroalkyl Substances.

The extensive use of per- and polyfluoroalkyl substances (PFASs) in industrial consumer products has led to groundwater contamination, raising concerns for human health and the environment. These persistent chemicals exist in different forms with varying properties, which makes their removal challenging. In this study, we assessed the effectiveness of three different ß-cyclodextrin (ß-CD) adsorbents at removing a mixture of PFASs, including anionic, neutral, and zwitterionic compounds, at neutral pH. We calculated linear partition coefficient (Kd) values to quantify the adsorption affinity of each PFAS. ß-CD polymers crosslinked with hexamethylene diisocyanate (ß-CD-HDI) and epichlorohydrin (ß-CD-EPI) displayed some adsorption of PFASs. Benzyl chloride ß-CD (ß-CD-Cl), an adsorbent that had not been previously reported, was also synthesized and tested for PFAS adsorption. ß-CD-Cl exhibited higher PFAS adsorption than ß-CD-HDI and ß-CD-EPI, with log Kd values ranging from 1.9 L·g-1 to 3.3 L·g-1. ß-CD-Cl displayed no affinity for zwitterionic compounds, as opposed to ß-CD-HDI and ß-CD-EPI, which removed N-dimethyl ammonio propyl perfluorohexane sulfonamide (AmPr-FHxSA). A comparison between Kd values and the log Kow of PFAS confirmed the significant role of hydrophobic interactions in thee adsorption mechanism. This effect was stronger in ß-CD-Cl, compared to ß-CD-HDI and ß-CD-EPI. While no effect of PFAS charge was observed in ß-CD-Cl, some influence of charge was observed in ß-CD-HDI and ß-CD-EPI, with less negative compounds being more adsorbed. The adsorption of PFASs by ß-CD-Cl was similar in magnitude to that of other adsorbents proposed in literature. However, it offers the advantage of not containing fluorine, unlike many commonly proposed adsorbents.

Evaluating the Sorption Kinetics of Polychlorinated Biphenyls in Powdered and Granular Activated Carbon.

Activated carbon (AC) has been applied widely in water treatment as a strong sorbent for organic contaminants and, more recently, in-situ treatment and capping for remediating legacy contaminants. In some sediment environments, the sorption kinetics onto AC may significantly impact remedial performance, particularly for large, highly hydrophobic contaminants such as PCBs, but there is limited kinetic data on such compounds. In this study, batch experiments were conducted over 52 weeks to measure PCB adsorption kinetics on 2 ACs in granular (1.1 mm diameter) and powdered (0.02 mm) form using polydimethylsiloxane (PDMS) fibers to measure aqueous concentrations over time. The experiment was conducted in glass containers with water at known PCB concentration and containing 10 mg/L natural organic matter (NOM) and activated carbon. Blanks without activated carbon were used to estimate kinetics and equilibrium uptake to PDMS and NOM. The PDMS measured aqueous concentration in AC containing slurries was then used to estimate kinetics and equilibrium uptake of the various PCBs onto the AC. Achieving equilibration of PCBs onto the powdered activated carbon (PAC) was accomplished in days to weeks, but granular activated carbon (GAC) uptake was not complete for some high molecular weight congeners in a year. The data were used to fit linear driving force models with both linear and Freundlich models of equilibrium. The models were then used to predict uptake onto powdered and granular AC during in-situ capping and treatment using the CapSim model. Slow kinetics can significantly limit the performance of granular AC in high upwelling (> 1-10 cm/day) environments. This study demonstrates the usage of polymeric passive samplers to explore sorption kinetics and equilibrium for low solubility compounds as well as the differences in performance of granular and powdered forms of AC for remediation of PCB contaminated sediment.

Inhibition of sediment erosion and phosphorus release by remediation strategy of contaminated sediment backfilling.

The management of sediment-water interfaces, especially bed stability, is essential for controlling accumulated contaminants in the sediment. In this study, the relationship between sediment erosion and phosphorus (P) release under the remediation strategy of contaminated sediment backfilling (CSBT) was explored through a flume experiment, i.e. the dredged sediment was calcined into ceramsite after dewatering and detoxification and then backfilled to the dredged area for sediment capping, thus avoiding the introduction of foreign materials via in-situ remediation and the large-scale land occupation associated with ex-situ remediation. Acoustic Doppler velocimeter (ADV) and optical backscatter sensor (OBS) were used to measure the vertical distributions of flow velocity and sediment concentration in the overlying water, respectively, and diffusive gradients in thin films (DGT) was used to measure the P distribution in the sediment. The results revealed that improving bed stability from CSBT can considerably improve the robustness of sediment-water interface and reduce sediment erosion by more than 70%. The corresponding P release from the contaminated sediment could be inhibited with an inhibition efficiency as high as 80%. CSBT is a potent strategy for managing contaminated sediment. This study provides a theoretical reference for controlling sediment pollution, further supporting river and lake ecological management and environmental restoration.

Assessment and Management of Mercury Leaching from a Riverbank.

The South River located in the city of Waynesboro, Virginia, contains mercury (Hg) contamination due to historical releases from an industrial facility operating between 1929 and 1950. In 2015, two sampling events were conducted in two of the contaminated bank regions (Constitution Park and North Park) to evaluate non-particulate total mercury (THg) and methylmercury (MeHg) concentrations in bank interstitial waters during river base flows and during bank drainage after flooding events. Porewater THg and MeHg at the bank-water interface were measured using diffusive gradient in thin-film devices (DGTs). The results showed THg mercury concentrations during bank drainage were approximately a factor of 3 higher than during base flow conditions. To have a better understanding of the parameters that control Hg leaching, a series of laboratory experiments were designed using South River sediments. The field and laboratory assessment showed that drainage/inundation cycles can lead to high THg concentration leachate from contaminated sediment due to increased partitioning from solids under oxic bank conditions and mobilization by the drainage waters. The results also demonstrated that methyl mercury concentrations at the bank-water interface are highest under base flow when conditions are more reduced due to the absence of oxic water exchange with the surface water. A remedial approach was implemented involving partial removal of surficial sediments and placement of biochar (to reduce non-particulate THg) and an armoring layer (to reduce erosion). DGT Measurements after bank stabilization showed THg decreased by a factor of ~200 and MeHg concentration by a factor of more than 20.

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/CBL=0.20-0.07+0.12 in sediments and 0.27-0.10+0.15 in cap) and Pyr (C2019/CBL=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/CBL=1.0-0.24+0.32) and there was an increase in the cap (C2019/CBL=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 (t1/2=1.12-0.11+0.16 years) and Pyr (t1/2=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.

Effect of applied voltage, initial concentration, and natural organic matter on sequential reduction/oxidation of nitrobenzene by graphite electrodes.

Carbon electrodes are proposed in reactive sediment caps for in situ treatment of contaminants. The electrodes produce reducing conditions and H(2) at the cathode and oxidizing conditions and O(2) at the anode. Emplaced perpendicular to seepage flow, the electrodes provide the opportunity for sequential reduction and oxidation of contaminants. The objectives of this study are to demonstrate degradation of nitrobenzene (NB) as a probe compound for sequential electrochemical reduction and oxidation, and to determine the effect of applied voltage, initial concentration, and natural organic matter on the degradation rate. In H-cell reactors with graphite electrodes and buffer solution, NB was reduced stoichiometrically to aniline (AN) at the cathode with nitrosobenzene (NSB) as the intermediate. AN was then removed at the anode, faster than the reduction step. No common AN oxidation intermediate was detected in the system. Both the first order reduction rate constants of NB (k(NB)) and NSB (k(NSB)) increased with applied voltage between 2 V and 3.5 V (when the initial NB concentration was 100 µM, k(NB) = 0.3 h(-1) and k(NSB) = 0.04 h(-1) at 2 V; k(NB) = 1.6 h(-1) and k(NSB) = 0.64 h(-1) at 3.5 V) but stopped increasing beyond the threshold of 3.5 V. When initial NB concentration decreased from 100 to 5 µM, k(NB) and k(NSB) became 9 and 5 times faster, respectively, suggesting that competition for active sites on the electrode surface is an important factor in NB degradation. Presence of natural organic matter (in forms of either humic acid or Anacostia River sediment porewater) decreased k(NB) while slightly increased k(NSB), but only to a limited extent (∼factor of 3) for dissolved organic carbon content up to 100 mg/L. These findings suggest that electrode-based reactive sediment capping via sequential reduction/oxidation is a potentially robust and tunable technology for in situ contaminants degradation.

PAH degradation and redox control in an electrode enhanced sediment cap.

Capping is typically used to control contaminant release from the underlying sediments. However, the presence of conventional sediment caps will often eliminate or slow natural degradation that might otherwise occur at the surface sediment. The objective of this study was to explore the potential of a novel reactive capping, an electrode enhanced cap for the remediation of PAH contaminated sediment. The study on electrode enhanced biodegradation of PAH in slurries showed that naphthalene concentration decreased from ~1000 µg/L to ~50 µg/L, and phenanthrene decreased from ~150 µg/L to ~30 µg/L in ElectroBioReactor within 4 days, and the copy numbers of PAH degrading genes increased by almost 2 orders of magnitude. In a cap microcosm, two carbon electrodes were emplaced within a sediment cap with an applied potential of 2 V. The anode was placed at the sediment-cap interface encouraging oxidizing conditions. Oxidation and Reduction Potential (ORP) profiles showed redox potential approximately 60-100 mV higher at the sediment-cap interface with the application of voltage than in controls. Vertical profiles of phenanthrene porewater concentration were obtained by PDMS-coated fiber, and results showed that phenanthrene at the depth of 0-0.5 cm below the anode was degraded to ~70% of the initial concentration within 10 weeks. PAH degrading genes showed an increase of approximately 1 order of magnitude at the same depth. The no power controls showed no degradation of PAH. These findings suggest that electrode enhanced capping can be used to control redox potential, provide microbial electron acceptor, and stimulate PAH degradation.

The development of diffusive equilibrium, high-resolution passive samplers to measure perfluoroalkyl substances (PFAS) in groundwater.

Per- and poly-fluoroalkyl substances (PFAS) are a group of anthropogenic, highly recalcitrant organic compounds consisting of thousands of individual species that are of increasing importance as groundwater contaminants. In-situ measurements of PFAS would be useful to better understand vertical profiles and mobility, contamination in partially saturated media, and to reduce sampling artifacts associated with groundwater collection and analysis. Diffusive equilibrium, high-resolution passive samplers (HRPPs) can be directly driven (>10 m) in sediments or groundwater. The samplers equilibrate with porewater through diffusion across the sampler membrane, providing high spatial resolution (sample every 20 cm) porewater concentrations of dissolved species. The objective of this study was to develop an HRPP to measure PFAS in contaminated groundwater and saturated media. To achieve this objective, a screening study was conducted to demonstrate quantitative measurement of selected PFAS as well as the kinetics of uptake into a sampler using both nylon and stainless steel membranes. Utilizing the results of the screening study, a prototype sampler was demonstrated in a laboratory flow box. Over a deployment period of 28 days, concentrations of several perfluoroalkyl carboxylic acids (PFCAs), a perfluoroalkyl sulfonate (PFSA), and a precursor PFAS reached equilibrium with porewater (sampler concentration >90 percent of porewater concentration). Application of these samplers could provide improved understanding of the behavior of PFAS in saturated or partially saturated groundwater systems and allow better assessment of fate and transport in the subsurface. Reliable subsurface site characterization will yield robust site assessments, conceptual models, and improve remediation designs as well as increase confidence in post remedial assessments at PFAS-impacted locations.

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

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

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 (Cfree ) 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 Cfree 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 Cfree 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 Cfree 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 Cfree results were similar for academic and private sector laboratories. The accuracy and precision that we demonstrate for determination of Cfree 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.

Assessing the effectiveness of thin-layer sand caps for contaminated sediment management through passive sampling.

The effectiveness of thin-layer sand capping for contaminated sediment management (capping with a layer of thickness comparable to the depth of benthic interactions) is explored through experiments with laboratory-scale microcosms populated with the deposit-feeding oligochaete, Ilyodilus templetoni. Passive sampling of pore water concentrations in the microcosms using polydimethylsiloxane (PDMS)-coated fibers enabled quantification of high-resolution vertical concentration profiles that were used to infer contaminant migration rates and mechanisms. Observed concentration profiles were consistent with models that combine traditional contaminant transport processes (sorption-retarded diffusion) with bioturbation. Predictions of bioaccumulation based on contaminant pore water concentrations within the surface layer of the cap correlated well with observed bioaccumulation (correlation coefficient of 0.92). The results of this study show that thin-layer sand caps of contaminated sediments can be effective at reducing the bioaccumulation of polycyclic aromatic hydrocarbons (PAHs) provided the thickness of the cap layer exceeds the depth of organism interaction with the sediments and the pore water concentrations within the biologically active zone remain low (e.g., when molecular diffusion controls transport from the underlying sediment layer).

Theoretical Analysis of Constant Voltage Mode Membrane Capacitive Deionization for Water Softening.

Water softening is desirable to reduce scaling in water infrastructure and to meet industrial water quality needs and consumer preferences. Membrane capacitive deionization (MCDI) can preferentially adsorb divalent ions including calcium and magnesium and thus may be an attractive water softening technology. In this work, a process model incorporating ion exclusion effects was applied to investigate water softening performance including ion selectivity, ion removal efficiency and energy consumption in a constant voltage (CV) mode MCDI. Trade-offs between the simulated Ca2+ selectivity and Ca2+ removal efficiency under varying applied voltage and varying initial concentration ratio of Na+ to Ca2+ were observed. A cut-off CV mode, which was operated to maximize Ca2+ removal efficiency per cycle, was found to lead to a specific energy consumption (SEC) of 0.061 kWh/mole removed Ca2+ for partially softening industrial water and 0.077 kWh/m3 removed Ca2+ for slightly softening tap water at a water recovery of 0.5. This is an order of magnitude less than reported values for other softening techniques. MCDI should be explored more fully as an energy efficient means of water softening.