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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

Frontiers of Membrane Desalination Processes for Brackish Water Treatment: A Review.

Climate change, population growth, and increased industrial activities are exacerbating freshwater scarcity and leading to increased interest in desalination of saline water. Brackish water is an attractive alternative to freshwater due to its low salinity and widespread availability in many water-scarce areas. However, partial or total desalination of brackish water is essential to reach the water quality requirements for a variety of applications. Selection of appropriate technology requires knowledge and understanding of the operational principles, capabilities, and limitations of the available desalination processes. Proper combination of feedwater technology improves the energy efficiency of desalination. In this article, we focus on pressure-driven and electro-driven membrane desalination processes. We review the principles, as well as challenges and recent improvements for reverse osmosis (RO), nanofiltration (NF), electrodialysis (ED), and membrane capacitive deionization (MCDI). RO is the dominant membrane process for large-scale desalination of brackish water with higher salinity, while ED and MCDI are energy-efficient for lower salinity ranges. Selective removal of multivalent components makes NF an excellent option for water softening. Brackish water desalination with membrane processes faces a series of challenges. Membrane fouling and scaling are the common issues associated with these processes, resulting in a reduction in their water recovery and energy efficiency. To overcome such adverse effects, many efforts have been dedicated toward development of pre-treatment steps, surface modification of membranes, use of anti-scalant, and modification of operational conditions. However, the effectiveness of these approaches depends on the fouling propensity of the feed water. In addition to the fouling and scaling, each process may face other challenges depending on their state of development and maturity. This review provides recent advances in the material, architecture, and operation of these processes that can assist in the selection and design of technologies for particular applications. The active research directions to improve the performance of these processes are also identified. The review shows that technologies that are tunable and particularly efficient for partial desalination such as ED and MCDI are increasingly competitive with traditional RO processes. Development of cost-effective ion exchange membranes with high chemical and mechanical stability can further improve the economy of desalination with electro-membrane processes and advance their future applications.

Phosphorus adsorption by sediment considering mineral composition and environmental factors.

Sediment, composed of a complex assemblage of minerals, controls the fate and behaviour of P in aqueous environments and affects trophic status. In this study, P adsorption was studied on minerals including quartz, hematite, potassium feldspar, montmorillonite, kaolin, and calcite (i.e., the main components of sediment) and sediment from the Guanting Reservoir. A general formula for P adsorption was proposed that considers mineral composition through the component additivity method, also incorporating the effects of environmental factors, including the aqueous P concentration (Ce), pH, sediment concentration (S), and ionic strength (IS). The P adsorption capacity gradually decreased with increasing particle size, and the contributions from kaolin and montmorillonite to P adsorption were significant despite representing only a small fraction of sediment (with a maximum amount of P adsorption of 0.92 and 0.36 mg/g, respectively). The content of quartz accounted for approximately 40-60% of sediment; however, its P adsorption capacity was only 0.13 mg/g. These minerals exhibited different adsorption characteristics due to their different surface morphologies and lattice structures. Multivariable regression analysis was used to show that the amount of P adsorption was strongly correlated with Ce, followed by S, IS, and pH.

Application of polyoxymethylene passive air sampler to monitor hydrophobic organics in air around a confined disposal facility.

Volatile losses of hydrophobic organic contaminants from a confined disposal facility (CDF) containing dredged contaminated sediments is of substantial concern to surrounding communities. A partitioning passive sampling approach using polyoxymethylene (POM) was applied to measure long-term average (weeks to months) air concentrations resulting from evaporation at a CDF. Measurements at 10 locations surrounding the CDF using the POM air samplers indicated that the highest concentrations of ΣPCBs∼13 ng/m3 and ΣPAHs ∼65 ng/m3 were measured during an active dredge material placement period when the average temperature was 23 °C. The measurements were dominated by the more volatile, lower molecular weight compounds of each type. Partitioning to the POM during the post dredge material placement period with average temperature of 5 °C was corrected for temperature and the measured ∑PCBs and ∑PAHs were ∼3 ng/m3 and 45 ng/m3 respectively. The partitioning passive sampling measurements agreed well with the available weekly 24-h high-volume air samples (HVAS) averaged over the POM equilibration time for lower congener number PCBs (15, 18, 20/28 and 31) and naphthalene but were as much as 10 times lower than HVAS for high molecular weight PAHs. The difference was likely the result of the greater association of these PAHs with particulates and sources other than evaporation from the CDF. The POM air sampler achieved the goal of providing a long-term average air concentration without having to collect, analyze and average multiple HVAS samples although the technique is largely limited to the lower molecular weight PAHs and PCBs and different equilibration times for different compounds complicate its use and analysis.

Powdered activated carbon (PAC) amendment enhances naphthalene biodegradation under strictly sulfate-reducing conditions.

Capping represents an efficient and well-established practice to contain polycyclic aromatic hydrocarbons (PAHs) in sediments, reduce mobility, and minimize risks. Exposure to PAHs can encourage biodegradation, which can improve the performance of capping. This study investigates biodegradation of naphthalene (a model PAH) in highly reducing, sediment-like environments with amendment of different capping materials (PAC and sand). Microcosms were prepared with sediment enrichments, sulfate as an electron acceptor, and naphthalene. Results show that PAC stimulates naphthalene biodegradation and mineralization, as indicated by production of 14CO2 from radiolabeled naphthalene. Mineralization in PAC systems correlates with the enrichment of genera (Geobacter and Desulfovirga) previously identified to biodegrade naphthalene (Spearman's, p < 0.05). Naphthalene decay in sand and media-free systems was not linked to biodegradation activity (ANOVA, p > 0.05), and microbial communities were correlated to biomass yields rather than metabolites. Naphthalene decay in PAC systems consists of three stages with respect to time: latent (0-88 days), exponential decay (88-210 days), and inactive (210-480 days). This study shows that PAC amendment enhances naphthalene biodegradation under strictly sulfate-reducing conditions and provides a kinetic and metagenomic characterization of systems demonstrating naphthalene decay.

Assessing Biota Accumulation Due to Contamination of Sediments by Storm Water Heavy Metals.

Evaluating sediment recontamination due to storm water discharges is important when evaluating the long-term effectiveness of sediment remediation efforts at reducing biological impacts. The bioaccumulation of the heavy metals zinc, nickel, copper, cadmium, mercury, and lead and the metalloid arsenic in a clam (Macoma nasuta) was studied in surficial sediments before and after storm water inputs from Paleta Creek, California, USA, during wet seasons in 2015 to 2016 and 2016 to 2017. The bioaccumulation was compared with bulk sediment concentrations and porewater concentrations measured by diffusion gradient in thin film devices. Significant reductions in biota accumulation and porewater concentrations were observed in samples collected after storm seasons compared with before storm seasons despite bulk sediment concentrations remaining the same or increasing. This was apparently the result of the deposition of storm water contaminants in low bioavailable forms. The bioaccumulation of all the measured contaminants showed a positive significant correlation with porewater concentrations (p < 0.1, α = 0.1) and weak or no correlations with bulk sediment concentration. In conclusion, observed bulk sediment recontamination due to storm water should not be assumed to lead directly to greater biota accumulation without bioavailability assessment. Environ Toxicol Chem 2020;39:2475-2484. © 2020 SETAC.

Bioavailability assessment in activated carbon treated coastal sediment with in situ and ex situ porewater measurements.

Passive sampling and bioaccumulation assessments were used to evaluate the performance of activated carbon (AC) remediation of polychlorinated biphenyl (PCB) contaminated sediment offshore in Parcel F of the former Hunters Point Naval Shipyard (HPNS) (San Francisco, California). Two different composite AC materials, AquaGate+PAC™ (86 tons) and SediMite™ (24 tons) were placed on the sediment surface covering an area of 3200 m2. PCB tissue concentrations in the clam Macoma nasuta were reduced 75 to 80% in pilot amendment areas after 8 months and 84-87% in non-lipid normalized tissues after 14 months during in situ monitoring, confirming the effectiveness of the AC at reducing bioavailability of the PCBs. Polydimethylsiloxane (PDMS) passive samplers were applied to evaluate and monitor freely dissolved concentrations (Cfree) of PCBs in sediment porewater before AC placement (i.e., during baseline) and at 8 months, 14 months and 26 months following placement. Although AC composite materials were placed only at the surface, 80% reductions were observed to a depth of 16 cm after 8 months and up to 26 cm after 26 months in AquaGate+PAC treatment area. Total PCB porewater concentrations in surface sediments (1-6 cm) were reduced 89 and 91% in the AquaGate+PAC and SediMite areas during final sampling. Ex situ passive sampling showed porewater concentrations 2-5 times larger than in situ measurements due to the absence of hyporheic exchange in laboratory measurements and near equilibration between sediment and porewater. Estimated post placement ex situ porewater concentrations were more consistent with a model of bioaccumulation using the octanol-water partition coefficient (KOW) as a bioaccumulation factor leading to a hypothesis that the bioaccumulation factor in the deposit feeding clam is better estimated by equilibrium ex situ porewater measurements.

Evaluating the transport of Hg(II) in the presence of natural organic matter through a diffusive gradient in a thin-film passive sampler.

The effects of a model natural organic matter (NOM) on the transport of Hg(II) into diffusive gradient in thin-film devices (DGTs) was evaluated in order to better understand their ability to measure colloidal Hg species in porewater. The presence of NOM significantly reduced the diffusivity of the Hg(II) species and the reduction was dependent upon NOM to Hg(II) ratio. This relationship was modeled by determining the Hg(II) partition coefficients (Kd) of size fractionated NOM obtained by ultrafiltration and estimating the Hg diffusivity through the DGT for the different NOM size fractions across a range of Hg-NOM ratios. The estimated diffusivities were consistent with experimental observations of uptake into the DGT. Overall, this study indicated that Hg(II) associated with NOM passes into a DGT, however the transport is slowed in accordance with the diffusivity of the NOM to which the Hg(II) is associated. Thus, the Hg-NOM association and complex diffusivities need to be considered when relating DGT uptake to Hg porewater concentration. The results also suggest that Hg(II) associated with colloidal or larger particles of negligible diffusivity are unlikely to contribute significantly to DGT measurements.

Assessing sediment recontamination from metals in stormwater.

Recontamination of sediments by stormwater is a major concern when evaluating the potential effectiveness of sediment remediation. Stormwater and sediment sampling were conducted in a mixed-use watershed at Paleta Creek in San Diego, CA to evaluate methods for assessing sediment recontamination by metals. Size-segregated stormwater contaminant loads with simultaneous receiving water and sediment measurements were used to identify dominant sources and contaminants with respect to their impact on sediment recontamination. Most of the stormwater contaminant loads of Cd, Cu, Pb, and Zn were associated with residential and highway sources from the upstream portions of the watershed and As, Ni and Hg were more significantly influenced by the downstream area of the watershed. Cd was strongly associated with large particles (>63 µm) and observed to settle in near shore areas with some attenuation due to mixing and dilution. Cu, in contrast, was associated more with the filtered fraction (<0.45 µm) and clay fraction (0.45-5 µm), resulting in less near shore sediment recontamination. Depositing sediment and other metals, particularly Cu and Hg, exhibited greater accumulation in settling traps than could be attributed to stormwater loads indicating the importance of other sources or resuspension of bay sediments on surficial sediment concentrations. Pb, Zn, Ni, and As showed influences of both stormwater and other sources. The study showed that measurement of size-segregated stormwater contaminant mass and concentrations combined with simultaneous measurements of deposition in sediment traps could differentiate between recontamination by stormwater and that of other sources.