Sediment Cap Research Articles

Assessment of the calcium-silicate Polonite as a sorbent for thin-layer capping of metal contaminated sediment

Sediments contaminated with hazardous metals pose risks to humans and wildlife, yet viable management options are scarce. In a series of laboratory experiments, we characterized Polonite® – an activated calcium-silicate – as a novel sorbent for thin-layer capping of metal-contaminated sediments. We tested a fine-grained by-product from the Polonite production as a cheap and sustainable sorbent. First, Polonite was reacted with solutions of Cu, Pb, and Zn, and the surface chemistry of the Polonite was examined using, e.g., scanning electron microscopy to investigate metal sorption mechanisms. Batch experiments were conducted by adding Polonite to industrially contaminated harbor sediment to determine sorption kinetics and isotherms. Importantly, we measured if the Polonite could reduce metal bioavailability to sediment fauna by performing digestive fluid extraction (DFE). Finally, a cap placement technique was studied by applying a Polonite slurry in sedimentation columns.The results showed rapid metal sorption to Polonite via several mechanisms, including hydroxide and carbonate precipitation, and complexation with metal oxides on the Polonite surface. Isotherm data revealed that the sediment uptake capacity (Kf) for Cu, Pb, and Zn increased by a factor of 25, 21, and 14, respectively, after addition of 5% Polonite. The bioavailability of Cu, Pb, and Zn was reduced by 70%, 65%, and 54%, respectively, after a 25% Polonite addition. In conclusion, we propose that sediment treatment with low doses of the Polonite by-product can be a cheap, sustainable, and effective remediation method compared to other more intrusive methods such as dredging or conventional isolation capping.

Combined measures in lake restoration – A powerful approach as exemplified from Lake Groote Melanen (the Netherlands)

Controlling lake eutrophication is a challenge. A case-specific diagnostics driven approach is recommended that will guide to a suite of measures most promising in restoration of eutrophic lakes as exemplified by the case of the shallow lake Groote Melanen, The Netherlands. A lake system analysis identified external and internal nutrient load as main reasons for poor water quality and reoccurring cyanobacterial blooms in the lake. Based on this analysis, a package of restoration measures was implemented between January 2015 and May 2016. These measures included fish removal, dredging, capping of peat rich sediment with sand and an active barrier (lanthanum-modified bentonite), diversion of two inlet streams, reconstruction of banks, and planting macrophytes. Dredging and sand capping caused temporarily elevated turbidity and suspended solids concentrations, while addition of the lanthanum-modified clay caused a temporary exceedance of the Dutch La standard for freshwaters. Diversion of inflow streams caused 35 % less water inflow and larger water level fluctuations, but the lake remained water transporting with strongly improved water quality as was revealed by comparing five years pre-intervention water quality data with five years’ post-intervention data. Total phosphorus concentration in the water column was reduced by 93 % from 0.47 mg P l-1 before the intervention to 0.03 mg P l-1 after the intervention, total nitrogen by 66 % from 1.27 to 0.21 mg N l-1, total chlorophyll-a by 75 % from 68 to 16 µg l-1, cyanobacteria chlorophyll-a by 88 % from 32 to 4 µg l-1. Turbidity had declined by 58 % from 23.5 FTU to on average 9.9 FTU. No cyanobacteria blooms were recorded over the entire post-intervention monitoring period (2016–2021). Submerged macrophytes increased from complete absence before intervention to around 10 %–15 % coverage after intervention. Repeated fish removal lowered the fish stock to below 100 kg ha-1 with 12 % of bream and carp remaining. Hence, the package of cohesive measures that was based on a thorough diagnosis resulted in rapidly, strongly and enduringly improved water quality. This case provides evidence for the power of combining measures in restoring eutrophic lakes.

Combined amendment and capping of sediment with ferrihydrite and magnetite to control internal phosphorus release

This study developed novel active capping systems with recycling convenience using ferrihydrite (Fh) combined with magnetite (Mag), and investigated the effectiveness and mechanism for the restriction of endogenous phosphorus movement from sediment into overlying water (OW) by the combined use of Fh and Mag. The Fh/Mag combined amendment effectively hindered endogenous phosphorus release from sediment to OW in dissolved oxygen (DO)-deficit environment, and the immobilization of diffusion gradient in thin film-labile phosphorus (LPDGT) and mobile phosphorus in the sediment played a key role in the control of endogenous phosphorus liberation by the Fh/Mag combined amendment. Combined capping sediment with Fh and Mag effectively hindered endogenous phosphorus release from sediment to OW in anoxic environment, and the inactivation of LPDGT in the upper sediment played a key part in the control of sediment phosphorus release by the Fh/Mag mixture capping. The stability of phosphorus immobilized by the Fh/Mag combined covering layer was related to its construction way, and the majority (around 90%) of P immobilized to the Fh/Mag mixture covering layer had low risk of release in common pH (5–9) and DO-deficit environments. The Fh/Mag mixture amendment or capping did not increase the risk of sediment iron release, and it also did not produce a large impact on the diversity and richness of bacterial community in the sediment. The combined utilization of Fh and Mag as a composite amendment or capping material to prevent the internal phosphorus from being moved to OW can make full use of their respective advantages. The Fh/Mag mixture capping wrapped by permeable fabric has high potential to reduce the risk of endogenous phosphorus from sediment into OW due to its advantages of high internal phosphorus release suppression efficiency, environmental friendliness, application convenience and sustainability.

Sand-capping stabilizes muddy sediment and improves benthic light conditions in eutrophic estuaries: Laboratory verification and the potential for recovery of eelgrass (Zostera marina)

Decades of eutrophication have increased water turbidity in Danish estuaries and led to light limitation of eelgrass (Zostera marina) growth. Former eelgrass areas are now denuded and consist of organic-rich muddy sediment with frequent resuspension events that maintain a high turbidity state. In addition, low anchoring capacity of eelgrass in the soft organic-rich sediments has contributed to eelgrass loss. When navigation channels in Danish estuaries are dredged, large amounts (~100.000 m3) of sandy sediment are shipped to remote dumping sites. Instead, we suggest that the dredged sand is used to consolidate adjacent muddy areas. We demonstrate in the present laboratory study that capping of fluid muddy sediment with 10 cm of sand is feasible without any vertical mixing and that this marine restoration approach potentially can lower the magnitude and frequency of resuspension events. Erosion of suspended solids change from 5 g m−2 min−1 above muddy sediment as to about 0.2 g m−2 min−1 after sand-capping, implying that the application of sand can improve light conditions. Moreover, since erosion thresholds increase from about 10–12 cm s−1 for mud to 40 cm s−1 for sand-capped mud the anchoring capacity of rooted vegetation is increased. However, the full potential of sand-capping to facilitate restoration of otherwise lost eelgrass habitats requires verification by large-scale field experiments.

The effects of adsorptive materials on microbial community composition and PAH degradation at the sediment cap–water interface

Capping with layers of inert or adsorptive materials is used to control the release of polycyclic aromatic hydrocarbons (PAH) in sediment but little is known about microbial degradation processes in these materials. A rich native microbial community inhabits the sediment bed, and capping media can influence enrichment and biodegradation activity of benthic microorganisms. The aim of this study was to evaluate the effects of capping media (sand, organoclay, and powdered activated carbon [PAC]) on microbial communities under oxic conditions typical of the cap–water interface, where naphthalene degradation (model PAH) is likely to be maximized. Bench scale experiments compared naphthalene concentrations, nahAc biomarker abundance, microbial community composition, and cellular attachment in systems amended with adsorptive and non-adsorptive capping materials. Results indicate that activated carbon promoted and enhanced bioactivity; PAC treatments showed high biodegradation rates, nahAc biomarker levels, and attached biological growth consistent with enrichment of the PAH-degrading genus Pseudomonae. In contrast, sand did not enhance biological activity compared to media-free systems. Naphthalene strongly influenced microbial community composition at the species level in all treatments except organoclay, which promoted biological signatures commonly associated with impeding degradation activity. Data overall suggest that adsorptive capping materials can both promote (PAC) and inhibit (organoclay) bioactivity in the surficial layer of caps, indicating that media selection is critical to the design of bioactive capping systems.

Contaminated aquatic sediments.

The remediation of contaminated aquatic sediments requires a range of expertise from assessment (investigation, risk evaluations, modeling, and remedy selection) to design and construction. Research in 2019 has added to knowledge on optimizing the use of passive samplers for assessing chemical concentrations in sediment porewater. The porewater and black carbon appear to be better predictors of contaminant bioaccumulation than total organic carbon alone. This has led to better characterization of potential risk at sediment sites. Tools to identify and model sources of chemicals have been developed and used particularly for some metals, polynuclear aromatic hydrocarbons and polychlorinated biphenyls. There is great emphasis on beneficially using dredged sediment, treating it as a resource rather than a waste. Amendments used in sediment caps continue to be refined including the use of activated carbon within the caps and by itself. A technique involving 16S rRNA has been established as a means of identifying microbiological composition that naturally degrade contaminants. © 2020 Water Environment Federation PRACTITIONER POINTS: Sediment capping technology continues to advance Sampling and testing methods continue to be refined Natural processes such as biodegradation are being better understood Beneficial use of dredged sediment continue to be emphasized.

Effectiveness of dredging on internal phosphorus loading in a typical aquacultural lake

Intensive aquaculture significantly affects the global phosphorus (P) cycle and enhances eutrophication in inland waters. Sediment dredging efficiently removes P-rich sediments from shallow-water eutrophic lakes. However, studies on the effects of sediment dredging on the internal P loading of aquacultural lakes are still lacking. Moreover, the migration and transformation processes of labile P and the mechanisms of sediment P release are unclear. To evaluate dredging effectiveness, we employed two in situ high-resolution sampling techniques to simultaneously measure sediment labile P and porewater soluble reactive P (SRP) and Fe (II) at the millimeter scale. Dredging effectively reduced surface sediment CaP contents and organic matter (OM) below the sediment-water interface (SWI). Moreover, dredging decreased the SRP diffusion flux across the SWI in summer. After dredging, FeP (P bound to Fe, Al, and Mn oxides and hydroxides) and OP (organic P) contents increased by 136% and 48% in the newly formed deposited layer (140 mm thick), respectively. The increased bioavailable P content significantly enhanced the capability of sediment solids to resupply labile P to porewater SRP. The stronger positive correlation between porewater soluble Fe (II) and SRP suggests that Fe redox cycling regulated internal P release. Our results suggest that dredging effectiveness will weaken over time due to the re-deposition of active P, which in turn increases the risk of sediment P release. To curb the release of sediment P, we recommend the implementation of additional in situ restoration techniques that improve the oxide layer of surface sediments and reduce sediment suspension.

Biological Natural Attenuation and Contaminant Oxidation in Sediment Caps: Recent Advances and Future Opportunities

Capping represents an efficient and well-established remediation practice to contain pollutants in sediments. Coupling capping amendments with biodegradation is an emerging technology with great potential to promote simultaneous sequestration and oxidation of contaminants in situ. Capping materials alter the native sediment environment and affect the biodegradation potential of benthic microbial communities. The placement of materials specifically influences (i) porewater pH and composition, (ii) nutrient fluxes, (iii) electron accepting processes, (iv) bioavailability of contaminants, and (v) biofilm formation. This review summarizes current literature documenting the impact of these alterations on microbial ecology and biodegradation activity, describes recent advances in bioactive sediment caps, and identifies areas where additional research is warranted.

First attempt for in situ capping with lanthanum modified bentonite (LMB) on the immobilization and transformation of organic phosphorus at the sediment-water interface

LMB is a widely utilized material for the management of sediment-derived phosphorus (P) in eutrophic lakes. However, the properties of organic P at the sediment-water interface and the effect of LMB on organic P fractions in sediments are still unclear. The batch studies reported here indicate that LMB has good adsorption properties toward organic P (Glucose-6-phosphate), and the tentative adsorption mechanism relies on chemisorption. Laboratory microcosmic experiments were conducted to study the immobilization effect of LMB on the organic P in water and sediments. The results indicated that the concentration of total P, labile P and organic P in overlying water and pore water could be effectively reduced by LMB capping of sediments. After treatment, the optimal immobilization effects appeared on the 7th day and until the 60th day. However, the fractions of organic P change during the capping time. Active organic P eluted with NaHCO3 transforms into moderately labile or non-labile P through the physical and chemical processes, as well as microbial action. Microbial community analysis showed that the addition of LMB had inhibitory effect on the phosphorus-solubilizing bacteria, which also affected the transformation between various forms of organic P. This study provided new insights of LMB in situ capping of organic P and the mechanisms of the migration and cycling of internal organic P, which is beneficial for the management of eutrophic lakes.

Utilization of zirconium-modified granular zeolite as capping and mixing materials to suppress phosphorus release from sediment in landscape water body

A zirconium-modified granular zeolite (ZMGZ) was created and investigated for the suppression of the internal P loading in shallow landscape water bodies in this study. Results showed that the as-synthesized ZMGZ possessed high phosphate sorption capacity with a Langmuir maximum monolayer uptake capacity of 6.87 mg PO43−/g. Capping of landscape water body sediments with ZMGZ reduced the releasing rate of soluble reactive P (SRP) from the sediments into the overlying water, and it significantly reduced the SRP releasing rate under anoxic condition. Furthermore, the sediment capping decreased the pore water SRP concentration, and it was difficult for most of P trapped by the ZMGZ covering layer to be re-released into the water column. When the ZMGZ in the covering layer was mixed with the sediment, the ZMGZ became a sediment amendment. Mixing of landscape water body sediments with ZMGZ also resulted in the reduction of the SRP concentrations in the overlying and pore waters under the conditions of low and high dissolved oxygen, and it was also hard for most of P adsorbed by the added ZMGZ to be released back into the water column. Additionally, the addition of sediments with ZMGZ led to the decrease of the amounts of mobile and bioavailable P in the sediments. To sum up, we conclude that the capping/mixing combination method, which involves sediment capping with ZMGZ at first and then gradual mixing of ZMGZ with sediment via various natural disturbances (e.g., physical disturbance and bioturbation), is a very promising strategy for inhibiting the release of SRP from shallow landscape water body sediments into the overlying water.

Efficient recycling of nutrients in modern and past hypersaline environments

The biogeochemistry of hypersaline environments is strongly influenced by changes in biological processes and physicochemical parameters. Although massive evaporation events have occurred repeatedly throughout Earth history, their biogeochemical cycles and global impact remain poorly understood. Here, we provide the first nitrogen isotopic data for nutrients and chloropigments from modern shallow hypersaline environments (solar salterns, Trapani, Italy) and apply the obtained insights to δ15N signatures of the Messinian salinity crisis (MSC) in the late Miocene. Concentrations and δ15N of chlorophyll a, bacteriochlorophyll a, nitrate, and ammonium in benthic microbial mats indicate that inhibition of nitrification suppresses denitrification and anammox, resulting in efficient ammonium recycling within the mats and high primary productivity. We also suggest that the release of 15N-depleted NH3(gas) with increasing salinity enriches ammonium 15N in surface brine (≈34.0‰). Such elevated δ15N is also recorded in geoporphyrins isolated from sediments of the MSC peak (≈20‰), reflecting ammonium supply sufficient for sustaining phototrophic primary production. We propose that efficient nutrient supply combined with frequent bottom-water anoxia and capping of organic-rich sediments by evaporites of the Mediterranean MSC could have contributed to atmospheric CO2 reduction during the late Miocene.

Effects of Pollution on Freshwater Organisms.

The scientific literature review in this paper includes research papers published in 2017 on issues related to pollutants from human activity and its effects on organisms of freshwater reported from the different parts of the world. The fist part of the literature review highlights on two broad sections that are focused on research conducted at the field level as well as surveys based on field experiments. A number of sections categorized in order to reflect the different class of pollutants follows the first part of literature review. Sections in this part of review includes non-point source pollution, stormwater, wastewater, nutrients, sediment cap materials and suspended clays, botanical extracts, surfactants, metals, persistent organic pollutants, pharmaceuticals, endocrine disruptors, pesticides, petroleum hydrocarbons and polycyclic aromatic hydrocarbons, nanomaterials and ionic liquids. The final part of the literature review highlights the published research on recent innovations of recent in addressing problem of pollution in the freshwater and its management.

Bioturbation facilitates DDT sequestration by activated carbon against recontamination by sediment deposition

We evaluated bioturbation as a facilitator for in situ treatment with a thin layer of activated carbon to treat dichlorodiphenyltrichloroethane (DDT)-contaminated sediment and contaminant influx by sediment deposition. Using the freshwater worm Lumbriculus variegatus as a bioturbator, microcosm time-series studies were conducted for 4 mo and monitored for DDT flux and porewater concentration profiles by polyethylene passive samplers. With bioturbators present, the thin-layer activated carbon amendment reduced DDT flux by >90% compared with the same simulated scenario without activated carbon amendment. In contrast, a clean sediment cap without activated carbon was ineffective in reducing flux when bioturbation was present. In simulated scenarios with contaminant influx through deposition of contaminated sediment, bioturbation facilitated in situ activated carbon treatment, reducing 4-mo DDT flux by 77% compared with the same scenario without bioturbation. Porewater concentration profiles and activated carbon dose profiles confirmed effective mixing of activated carbon particles down to 1-cm depth. A mass transfer model was developed to predict flux with consideration of bioturbation and sediment deposition processes. Predicted flux values were consistent with experimental results and confirm that bioturbation activity helps reduce DDT sediment-to-water fluxes in activated carbon-treated sediment with recontamination by contaminated sediment deposition. To our knowledge, this is the first study to combine experimental and modeling results showing how bioturbation enhances activated carbon amendment effectiveness against ongoing contaminant influx by sediment deposition. Environ Toxicol Chem 2018;37:2013-2021. © 2018 SETAC.

Capping of marine sediments with valuable industrial by-products: Evaluation of inorganic pollutants immobilization

In-situ capping of polluted sediment is considered as an inexpensive and effective treatment technology to immobilize contaminants in a short time. In this remediation technique sediments are capped by placing a layer of sand, clean sediment or other materials over sediments in order to mitigate risk. In this study, low cost industrial by products (bauxaline, steel slag, and mixture of the two products) were applied as capping agents. A bench scale laboratory experiment in aquariums was performed to evaluate their effects on Cd, Zn, As, and Cr mobility from an artificially contaminated marine sediment. Without capping, all the contaminants are constantly released with various kinetic depending of mineral oxidation or dissolution or leaching. Nevertheless, release did not exceed 31% of the initial amount of pollutant. Capping sediment with steel slag, bauxaline and their mixture totally captured Cd, Zn, and As. In the case of Cr, only steel slag actively blocked its release. A kinetic model was developed to model As and Cr release, with and without capping. The release times for Cr and As from the sediment were close to 6 days. In the presence of capping agents, the capture time for Cr was found to be 57 days for steel slag, and 7 days for bauxaline. Despite a high capture time, steel slag was the best capping agent since bauxaline matrix was a source of Cr and rapidly released it (release time = 1 day). The results indicated that steel slag and its mixture additive can be used as potential capping materials for the remediation of contaminated sites due to their significant entrapping of Cd, Zn, As, and Cr.

Seismic stratigraphy of the Shatsky Rise sediment cap, northwest Pacific, and implications for pelagic sedimentation atop submarine plateaus

Pelagic sediments accumulated atop Shatsky Rise since Early Cretaceous time provide a valuable record of Pacific paleoceanography. The accepted sedimentation model invokes relatively continuous pelagic sediment accumulation punctuated by four regional hiatuses caused by changes in oceanic chemistry. That framework was proposed more than two decades in the past and based on low-quality single channel seismic profiles. It was developed at the center of Tamu Massif, the main topographic high of Shatsky Rise, and extended to other highs with uncertainty owing to sparse data. The availability of high-quality seismic data and additional coring by the Ocean Drilling Program and Integrated Ocean Drilling Program allows a re-examination. Seismic and core data indicate that sedimentation atop Shatsky Rise has been complex, with regional and local variability. Four major hiatuses were previously defined and tentatively correlated to nearby topographic highs. These breaks occurred approximately during the Aptian-Barremian and Cenomanian-Coniacian ages of the Cretaceous and during the Paleocene and Oligocene epochs of the Cenozoic. They are of variable length and tend to be of shorter duration at the summit of Tamu Massif, but of longer durations elsewhere. All produced erosional unconformities that may be related to mass wasting of the sediment cap edges. Each hiatus is approximately correlated with global falls of sea level, suggesting a connection, perhaps to intensified bottom currents at those times. Local variability is observed in the form of discontinuous layering, non-uniform sedimentation, thinning of the sediment caps at their edges, and local erosion near topographic highs. These variations are likely the result of shifting bottom currents, possibly resulting from interactions of internal tides with topography. Shatsky Rise sedimentation is inherently punctuated and non-uniform and the sedimentary record includes significant lateral variability. Other large oceanic plateaus are likely to exhibit similar sedimentary cap complexities.

Analysis of factors controlling sediment phosphorus flux potential of wetlands in Hulun Buir grassland by principal component and path analysis method.

Phosphorus (P) flux potential can predict the trend of phosphorus release from wetland sediments to water and provide scientific parameters for further monitoring and management for phosphorus flux from wetland sediments to overlying water. Many studies have focused on factors affecting sediment P flux potential in sediment-water interface, but rarely on the relationship among these factors. In the present study, experiment on sediment P flux potential in sediment-water interface was conducted in six wetlands in Hulun Buir grassland, China and the relationships among sediment P flux potential in sediment-water interface, sediment physical properties, and sediment chemical characteristics were examined. Principal component analysis and path analysis were used to discuss these data in correlation coefficient, direct, and indirect effects on sediment P flux potential in sediment-water interface. Results indicated that the major factors affecting sediment P flux potential in sediment-water interface were amount of organophosphate-degradation bacterium in sediment, Ca-P content, and total phosphorus concentrations. The factors of direct influence sediment P flux potential were sediment Ca-P content, Olsen-P content, SOC content, and sediment Al-P content. The indirect influence sediment P flux potential in sediment-water interface was sediment Olsen-P content, sediment SOC content, sediment Ca-P content, and sediment Al-P content. And the standard multiple regression describing the relationship between sediment P flux potential in sediment-water interface and its major effect factors was Y=5.849-1.025X 1-1.995X 2+0.188X 3-0.282X 4 (r=0.9298, p<0.01, n=96), where Y is sediment P flux potential in sediment-water interface, X 1 is sediment Ca-P content, X 2 is sediment Olsen-P content, X 3 is sediment SOC content, and X 4 is sediment Al-P content. Therefore, future research will focus on these sediment properties to analyze the interrelation among sediment properties factors, main vegetable factors, and environment factors which influence the sediment P flux potential in sediment-water interface.

Effects of Pollution on Freshwater Organisms.

This review covers research papers and scientific literature published in the year 2016 on the effects of anthropogenic pollutants on freshwater organisms. In the first, the review begins with two broad sections thate are mainly focused on research reviews and broad field studies and surveys. This is followed by reviews of research categorized in sections to reflect the pollutant class. These sections include wastewater, stormwater and non-point source pollution, nutrients, sediment cap materials and suspended clays, botanical extracts, surfactants, metals, persistent organic pollutants, pharmaceuticals, endocrine disruptors, pesticides, petroleum hydrocarbons and polycyclic aromatic hydrocarbons (PAHs), ionic liquids, and nanomaterials. The final section of the review highlights the research published on describing innovations in the field of freshwater pollution research.

Adsorption performance of modified bentonite granular (MBG) on sediment phosphorus in all fractions in the West Lake, Hangzhou, China

Modified bentonite granulars (MBGs) were prepared by acidification, natrification, calcination, and combined modification methods, and evaluated as effective in-situ adsorption materials to remove sediment phosphorus (P) in all fractions. The morphology and microstructure of MBG were characterized by scanning electron microscope (SEM), X-ray fluorescence (XRF), fourier transform infrared (FTIR) and X-ray diffraction (XRD). Results showed that the P removal capacity of CMBG-Na10-450 treated with 10% (g/g) Na2CO3 and calcined at 450°C exhibited the highest P removal capacity. Under the optimal conditions of stirring tests, the removal rates of sediment TP, OP, IP, Fe/Al-P and Ca-P by CMBG-Na10-450 were 35.5%, 29.1%, 54.5%, 44.6% and 10.7%, respectively. The adsorption mechanism analysis found that MBG adsorbed sediment P mainly by anionic coordination exchange adsorption. These results indicated that modification enhanced the P adsorption capacity of bentonite, and the MBG can be further applied to control and reduce sediment P in eutrophication remediation.

Diffusive flux of PAHs across sediment–water and water–air interfaces at urban superfund sites

Superfund sites may be a source of polycyclic aromatic hydrocarbons (PAHs) to the surrounding environment. These sites can also act as PAH sinks from present-day anthropogenic activities, especially in urban locations. Understanding PAH transport across environmental compartments helps to define the relative contributions of these sources and is therefore important for informing remedial and management decisions. In the present study, paired passive samplers were co-deployed at sediment-water and water-air interfaces within the Portland Harbor Superfund Site and the McCormick and Baxter Superfund Site. These sites, located along the Willamette River (Portland, OR, USA), have PAH contamination from both legacy and modern sources. Diffusive flux calculations indicate that the Willamette River acts predominantly as a sink for low molecular weight PAHs from both the sediment and the air. The sediment was also predominantly a source of 4- and 5-ring PAHs to the river, and the river was a source of these same PAHs to the air, indicating that legacy pollution may be contributing to PAH exposure for residents of the Portland urban center. At the remediated McCormick and Baxter Superfund Site, flux measurements highlight locations within the sand and rock sediment cap where contaminant breakthrough is occurring. Environ Toxicol Chem 2017;36:2281-2289. © 2017 SETAC.

Pathogen reduction co-benefits of nutrient best management practices.

BackgroundMany of the practices currently underway to reduce nitrogen, phosphorus, and sediment loads entering the Chesapeake Bay have also been observed to support reduction of disease-causing pathogen loadings. We quantify how implementation of these practices, proposed to meet the nutrient and sediment caps prescribed by the Total Maximum Daily Load (TMDL), could reduce pathogen loadings and provide public health co-benefits within the Chesapeake Bay system.MethodsWe used published data on the pathogen reduction potential of management practices and baseline fecal coliform loadings estimated as part of prior modeling to estimate the reduction in pathogen loadings to the mainstem Potomac River and Chesapeake Bay attributable to practices implemented as part of the TMDL. We then compare the estimates with the baseline loadings of fecal coliform loadings to estimate the total pathogen reduction potential of the TMDL.ResultsWe estimate that the TMDL practices have the potential to decrease disease-causing pathogen loads from all point and non-point sources to the mainstem Potomac River and the entire Chesapeake Bay watershed by 19% and 27%, respectively. These numbers are likely to be underestimates due to data limitations that forced us to omit some practices from analysis.DiscussionBased on known impairments and disease incidence rates, we conclude that efforts to reduce nutrients may create substantial health co-benefits by improving the safety of water-contact recreation and seafood consumption.