A comprehensive assessment to offer optimized remediation method for mercury contamination in Musa Bay by using hybrid Fuzzy AHP-VIKOR approach.

Musa Bay, the largest wetland in Iran and one of the most important Hg-polluted media, plays a significant role in the ecosystem of the area and supports many forms of life. Mercury pollution has detrimental effects on the human body and at high levels leads to the loss of microorganisms in marine ecosystems. Hence, a comprehensive assessment for selecting an effective and sustainable remediation method is crucial to restoring the ecosystem promptly. The determination of a proper and practical treatment method not only is a case-based approach, but could be challenging due to its multi-criteria decision-making nature. Considering preferred crucial factors involved in the effectiveness of remedial actions, in this study a questionnaire is designed to assess the opinion of environmental experts, stakeholders, and some occupants of the area on remedial actions based on the importance weights of criteria. Subsequently, practical remediation and management strategies ranked by hybrid FVIKOR as a multi-criteria decision making (MCDM) method. Ranking results show that dredging and stabilization could offer a promising solution for the remediation of the case study. The results of the study demonstrate that the development of MCDM methods along with effective criteria and considering the analysis of the questionnaires, could offer the best remediation strategy for a specific contaminated site.

Electrocoagulation coupled with electrooxidation for the simultaneous treatment of multiple pollutants in contaminated sediments.

In situ and simultaneous remediation of a variety of pollutants in sediments remains a challenge. In this study, we report that the combination of electrocoagulation (EC) and electrooxidation (EO) is efficient in the immobilization of phosphorus and heavy metals and in the oxidation of ammonium and toxic organic matter. The integrated mixed metal oxide (MMO)/Fe anode system allowed the facile removal of ammonium and phosphorus in the overlying water (99% of 10 mg/L NH4+-N and 95% of 10 mg/L P disappeared in 15 and 30 min, respectively). Compared with the controls of the single Fe anode and single MMO anode systems, the dual MMO/Fe anode system significantly improved the removal of phenanthrene and promoted the transition of Pb and Cu from the mobile species to the immobile species. The concentrations of Pb and Cu in the toxicity characteristic leaching procedure extracts were reduced by 99% and 97% after an 8 hr operation. Further tests with four real polluted samples indicated that substantial proportions of acid-soluble fraction Pb and Cu were reduced (30%-31% for Pb and 16%-23% for Cu), and the amounts of total organic carbon and NH4+-N decreased by 56%-71% and 32%-63%, respectively. It was proposed that the in situ electrogenerated Fe(II) at the Fe anode and the active oxygen/chlorine species at the MMO anode are conducive to outstanding performance in the co-treatment of multiple pollutants. The results suggest that the EC/EO method is a powerful technology for the in situ remediation of sediments contaminated with different pollutants.

Molybdate effectively controls sulphide production in a shrimp pond model.

The production of shrimp is often performed in earthen outdoor ponds in which the high input of feed and faeces on the bottom can result in deterioration of the water quality, which negatively impacts the animals and the environment. Here, we investigate the potential of sodium molybdate (Na2MoO4·2H2O), sodium nitrate (NaNO3) and sodium percarbonate (Na2CO3·1.5H2O2) to control sulphide production in a simulated shrimp pond bottom system that included the sediment, overlaying artificial seawater and organic matter input in the form of shrimp feed and shrimp faeces. Sediment depth gradient measurements of oxygen, H2S and pH were obtained during 7 days of incubation using microelectrodes. The most significant impact in terms of H2S, was observed for 50 mg/L sodium molybdate. At the water-sediment interface, there was up to 73% less H2S detected for this treatment in comparison to a control treatment, while in the deeper layers of the sediment it was up to 47% less H2S. The residual sulphate concentrations in the molybdate treated samples were 16 ± 4% higher than the control, indicating an inhibition in sulphate reduction. Nitrate and sodium percarbonate treatments also showed a limited capacity to decrease H2S entering in the water column, yet no clear difference in H2S concentrations in the sediment compared to the control were observed. Molybdate treatment appears to work through the inhibition of sulphate reducing bacteria in situ for the control of H2S production better than the chemical oxygen boosters or nitrate treatment.

A microcosm study of microbial community profiles during sediment remediation using pyrolyzed oyster shells.

The accumulation of organic and inorganic components in sediments leads to a deterioration in the environment and an imbalance in the coastal ecosystem. Currently, capping is the most effective technology for remediating polluted sediment and restoring ecosystems. A microcosm experiment was designed using pyrolyzed oyster shell (POS). These were mixed in with coastal sediment or added as a capping layer. The results showed that POS effectively decreased pollutants, including PO4-P and NH4-N. Metagenomics analysis was performed using 16S rRNA gene sequencing and the most abundant phyla identified in the POS treated and untreated sediments were Proteobacteria, followed by Firmicutes, Bacteroidetes, Chloroflexi, Fusobacteria, Nitrospirae, and Spirochaetes. The relative abundance of Proteobacteria members of the Class Gammaproteobacteria significantly increased, but Deltaproteobacteria gradually decreased throughout the experiment in POS-covered sediment. This suggests that the POS effectively promoted a shift from anaerobic to facultative anaerobic or aerobic microbial communities in the sediment. Dominant species of facultative anaerobic or microaerophilic bacteria from the order Chromatiales and phylum Nitrospirae were observed in the POS-covered sediment. Based on these study results, it can be concluded that POS is an effective covering material for sediment remediation and restores the microbial communities in sediments.

Mechanisms and risks of joint control of nitrogen and phosphorus through sediment capping technology in a pilot-scale study.

Purpose: Nitrogen (N) and phosphorus (P) are the key elements leading to eutrophication, and it is important to jointly control N and P release from sediments into the water column. Methods: Different mixed materials including P sorbent, natural organic carbon (C), and an oxidizing agent were applied in a 1-year pilot-scale experiment. Results: The addition of iron-rich (IR) clay and Phoslock agent promoted the formation of iron bound P (Fe(OOH)~P) and calcium bound P (CaCO3~P) in sediments, respectively. IR clay offered more advantages in immobilization of phosphorus as refractory P, and the Phoslock agent more effectively reduced the risk of P release into water, which was expressed as a low equilibrium P concentration (EPC0). Mixtures of sugarcane (SU) detritus and IR clay exhibited high carbohydrate (CHO) contents, which further fuelled both denitrification and dissimilatory nitrate reduction to ammonium (DNRA). This indicated that the SU dosage should be controlled to avoid DNRA over denitrification. Attention should be given to the fact that SU introduction significantly promoted the generation of an anaerobic state, leading to the desorption and release of Fe(OOH)~P, which could be alleviated by using Oxone. Multienzyme activity analysis showed that P and N transformation shifted from P desorption to organic P hydrolysis and from ammonification to denitrification and DNRA, respectively. Conclusion: We recommend the use of P sorbent and organic C combined with oxidizing agents as effective mixed materials for sediment remediation, which could enhance P adsorption and provide electron donors for denitrification, while also avoiding the generation of anoxia.

Review on utilization of biochar for metal-contaminated soil and sediment remediation.

Biochar is a carbon-neutral or even carbon-negative material produced through thermal decomposition of plant- and animal-based biomass under oxygen-limited conditions. Recently, there has been an increasing interest in the application of biochar as an adsorbent, soil ameliorant and climate mitigation approach in many types of applications. Metal-contaminated soil remediation using biochar has been intensively investigated in small-scale and pilot-scale trials with obtained beneficial results and multifaceted effects. But so far, the study and application of biochar in contaminated sediment management has been very limited, and this is also a worldwide problem. Nonetheless, there is reason to believe that the same multiple benefits can also be realized with these sediments due to similar mechanisms for stabilizing contaminants. This paper provides a review on current biochar properties and its use as a sorbent/amendment for metal-contaminated soil/sediment remediation and its effect on plant growth, fauna habits as well as microorganism communities. In addition, the use of biochar as a potential strategy for contaminated sediment management is also discussed, especially as regards in-situ planning. Finally, we highlight the possibility of biochar application as an effective amendment and propose further research directions to ensure the safe and sustainable use of biochar as an amendment for remediation of contaminated soil and sediment.

New insights into the sustainable use of co-pyrolyzed dredged sediment for the in situ remediation of Cd polluted sediments in coastal rivers.

The remediation of Cd-polluted sediment in coastal rivers is essential because of its potential hazards to river and marine ecosystems. Herein, a co-pyrolysis product of contaminated dredged sediment (S@BC) was innovatively applied to cap and immobilize Cd-contaminated sediment in coastal rivers in situ, and their remediation efficiencies, mechanisms, and microbial responses were explored based on a 360 d incubation experiment. The results showed that although S@BC immobilization and capping restrained sediment Cd release to the overlying water, S@BC capping presented a high inhibitory efficiency (66.0% vs. 95.3% at 360 d). Fraction analysis indicated that labile Cd was partially transformed to stable fraction after remediation, with decreases of 0.5%- 32.7% in the acid-soluble fraction and increases of 5.0%- 182.8% in the residual fraction. S@BC immobilization and capping had minor influences on the sediment bacterial community structure compared to the control. S@BC could directly adsorb sediment mobile Cd (precipitation and complexation) to inhibit Cd release and change sediment properties (e.g., pH and cation exchange capacity) to indirectly reduce Cd release. Particularly, S@BC capping also promoted Cd stabilization by enhancing the sediment sulfate reduction process. Comparatively, S@BC capping was a priority approach for Cd-polluted sediment remediation. This study provides new insights into the remediation of Cd-contaminated sediments in coastal rivers.

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.

Thin-layer capping with granular activated carbon and calcium-silicate to remediate organic and metal polluted harbor sediment - A mesocosm study.

Sediments polluted with hydrophobic organic contaminants (HOCs) and metals can pose environmental risks, yet effective remediation remains a challenge. We investigated a new composite sorbent comprising granular activated carbon (GAC) and a calcium-silicate (Polonite®, PO) for thin-layer capping of polluted sediment, with the aim to sequester both HOCs and metals. Box cores were collected in polluted Oskarshamn harbor, Sweden, and the sediments were treated with GAC and/or Polonite in a 10-week mesocosm study to measure endpoints ranging from contaminant immobilization to ecological side effects on native fauna and biogeochemical processes. The GAC particle size was 300-500 µm to reduce negative effects on benthic fauna (by being non-ingestible) and of biogenic origin (coconut) to have a small carbon footprint compared with traditional fossil ACs. The calcium-silicate was a fine-grained industrial by-product used to target metals and as a carrier for GAC to improve the cap integrity. GAC decreased the uptake of dioxins (PCDD/Fs) in the bivalve Macoma balthica by 47 % and the in vitro bioavailability of PCB by 40 %. The composite cap of GAC + Polonite decreased sediment-to-water release of Pb < Cu < Ni < Zn < Cd by 42-98 % (lowest to highest decrease) and bioaccumulation of Cd < Zn < Cu in the worm Hediste diversicolor by 50-65 %. Additionally, in vitro bioavailability of Pb < Cu < Zn, measured using digestive fluid extraction, decreased by 43-83 %. GAC showed no adverse effects on benthic fauna while Polonite caused short-term adverse effects on fauna diversity and abundance, partly due to its cohesiveness, which, in turn, can improve the cap integrity in situ. Fauna later recovered and bioturbated the cap. Both sorbents influenced biogeochemical processes; GAC sorbed ammonium, Polonite decreased respiration, and both sorbents reduced denitrification. In conclusion, the side effects were relatively mild, and the cap decreased the release and bioavailability of both HOCs and metals effectively, thus offering a promising sustainable and cost-effective solution to remediating polluted sediments.

The impact of bottom water light exposure on electrical and sediment remediation performance of sediment microbial fuel cells.

Sediment microbial fuel cells (SMFCs) generate bioelectricity from benthic sediments and thus providing both bioelectricity generation and sediment remediation. However, the high internal resistance of the cathode leads to a low power output, which requires research on cathode treatment. In this study, we explored the influence of light irradiation on bioelectricity production and nutrient removal in the SMFC system. The microcosm experiment of the SMFC system was designed with artificial illumination of 500 lux (light-SMFC) and compared with dark conditions of 15 lux (dark-SMFC), which showed that the current increases during photoperiods. The study reveals that light-illuminated SMFC consistently produced the highest voltage, with the highest voltage (553 mV) being 1.3 times higher than the dark-SMFC (440 mV). The polarization curves show a significant reduction in internal cathodic resistance under light condition, resulting in increased voltage generation. The light-SMFC exhibits the highest maximum power density of 35.93 mW/m2, surpassing the dark SMFC of 31.13 mW/m2. It was found that light illumination in the SMFC system increases oxygen availability in the cathodic region, which supports the oxygen reduction reaction (ORR) process. At the same time, the high bioelectricity output contributes to the highest sediment remediation by greatly reducing the chemical oxygen demand (COD) and phosphate (PO4-P) concentrations. The study highlights the potential of light illumination in mitigating cathodic limitation to improve SMFC performance and nutrient removal.

Control of phosphorus release from sediment by iron/aluminum co-modified zeolite: efficiency, mechanism, and response of microbial communities in sediment.

The efficiency of iron/aluminum co-modified zeolite (FeAl-Z) covering and amendment for controlling the internal loading of phosphorus (P) from sediment to the overlying water (OW) and its controlling mechanism were explored. The response of the composition of sedimentary microbial communities in sediment and their function to the FeAl-Z capping and amendment was also examined. FeAl-Z showed good removal performance for phosphate in aqueous solution. The maximum phosphate adsorption quantity for FeAl-Z at pH 7 attained 11.2 mg P/g. The release of sediment endogenous phosphorus to OW can be successfully restrained by the FeAl-Z covering and amendment, and the suppression ability of FeAl-Z covering was stronger than that of FeAl-Z amendment. Under the capping or amendment condition, FeAl-Z can effectively inactivate the labile phosphorus measured by diffusion gradient in thin film (DGT-LP) in the overlying water and surface sediment. The added FeAl-Z transformed redox-sensitive phosphorus (BD-P) to metal oxide-bound phosphorus (NaOH-IP) and residual phosphorus (Res-P) in sediment, which increased the stability of inorganic phosphorus in the sediment. The passivation of soluble reactive phosphorus (SRP) and DGT-LP in the surface sediment by FeAl-Z significantly contributed to the inhibition of sediment endogenous phosphorus release to OW by the FeAl-Z capping, and the passivation of SRP, DGT-LP and mobile phosphorus in the surface sediment played a pivotal role in the control of sediment internal phosphorus release by the FeAl-Z amendment. The FeAl-Z amendment and capping did not increase the liberation risk of Fe from sediment, and the microorganisms in the sediments under the conditions of FeAl-Z amendment and covering still can perform good ecological functions. Results of this research demonstrate that FeAl-Z capping has high application potential in the control of phosphorus transfer from sediment to OW.

High performance self-assembled nano-chlorapatite in the presence of lactonic sophorolipid for the immobilization of cadmium in polluted sediment.

A novel lactonic sophorolipid (LS) self-assembled nano-chlorapatite (LS-nClAP) was prepared for the immobilization of severe cadmium (Cd) in sediment. The experimental results indicated that the introduction of LS not only improved the dispersed performance of chlorapatite, but also brought massive hydroxyl and carboxyl groups, which significantly improved the immobilization efficiency of Cd and reduced its eco-toxicity in sediment. LS can significantly increase the effective utilization rate of phosphorus in chlorapatite, and reduce the content of available phosphorus (AP) by half after remediation compared with ClAP. Additionally, the participation of LS possessed a significant impact on the enzyme activities in the sediment, especially for urease, which was closely related to the effective stability of Cd and the introduction of LS. All experimental results of this study provided new insights into the possible effects of Cd immobilization by chlorapatite in contaminated sediments, demonstrating great application potential for sediment remediation in the future.

Capping fiberbank sediments to reduce persistent organic pollutants (POPs) fluxes: A large-scale laboratory column experiment.

Deposits of contaminated wood fiber waste (fiberbanks), originating from sawmills and pulp and paper industries, have been found in the aquatic environment in boreal countries. In-situ isolation capping has been proposed as a remediation solution because it has the potential to prevent dispersal of persistent organic pollutants (POPs) from this type of sediment. However, knowledge about the performance of such caps when placed on very soft (unconsolidated), gaseous organic rich sediment is scarce. We investigated the effectiveness of conventional in-situ capping to limit POPs fluxes to the water column from contaminated fibrous sediments that produce gas. A controlled, large-scale laboratory column (40 cm diameter, 2 m height) experiment was performed over 8 months to study changes in sediment-to-water fluxes of POPs and particle resuspension before and after capping the sediment with crushed stones (≥4 mm grain size). Two different cap thicknesses were tested (20 and 45 cm) on two types of fiberbank sediment with different fiber type composition. Results showed that capping fiberbank sediment with a 45 cm gravel cap reduced the sediment-to-water flux by 91-95% for p,p'-DDD, o,p'-DDD, by 39-82% for CB-101, CB-118, CB-138, CB-153, CB-180 and by 12-18% for HCB, whereas for less hydrophobic PCBs, capping was largely ineffective (i.e. CB-28 and CB-52). Although cap application caused particle resuspension, the long-term effect of the cap was reduced particle resuspension. On the other hand, substantial sediment consolidation released large volumes of contaminated pore water into the overlying water body. Importantly, both sediment types produced large amount of gas, observed as gas voids forming inside the sediment and gas ebullition events, which increased pore water advection and affected the structural integrity of the cap. This may limit the practical applicability of this method on fiberbank sediments.

Using recoverable sulfurized magnetic biochar for active capping to remediate multiple heavy metal contaminated sediment.

Due to anthropogenic activities, heavy metals are discharged into the hydrosphere and deposit onto the sediment. Heavy metals remobilize through physical disturbance and change in environmental conditions, posing a risk to environments and human health. Among several remediation methods, active layer capping is considered to be more feasible due to its financial and technical advantages; however, its long-term effects remain unknown. To overcome this problem, this work applied a novel, recoverable amendment, sulfurized magnetic biochar (SMBC), to remediate multiple heavy metal (Cu, Ni, Zn, Cr, Hg, and MeHg) contaminated sediment. Physiochemical characterization shows magnetite (Fe3O4) crystalline in both magnetic biochar (MBC) and SMBC, with such characteristics resulting in a greater surface area (324.9 and 346.3 m2/g) than BC (39.6 m2/g) and SBC (65.0 m2/g). FeS crystalline was also observed in SMBC, which plays an important role in controlling heavy metal release from sediment. Microcosm experiments indicated the effectiveness of SMBC in lowering aquatic Cu, Ni, Zn, Hg, and MeHg releases was significantly greater than the other three biochar materials. Notably, the recovery of SMBC by magnetism was 87%, demonstrating the exceptional recoverability of SMBC from seawater and sediment. Based on its robust capability in lowering Cu, Ni, Zn, Hg, and MeHg release and excellent recoverability from seawater and sediment, this technique represents a practical alternative to conventional approaches for heavy metal immobilization from sediment.

Biochar Derived from Post-Adsorbent for Immobilizing Cu and Cd in Sediment: The Effect on Heavy Metal Species and the Microbial Community Composition.

Many biomass wastes or their modified forms have been investigated as heavy metal adsorbents. However, less emphasis has been placed on post-adsorbent management or possible further utilization. In this study, biochar (BC) derived from modified bamboo adsorbent after the adsorption of Cu from an aqueous solution was used for the in situ remediation of lake sediment contaminated with Cd and Cu. The results indicated that the Cu concentration was extremely low (≤0.015 mg/L), while Cd was not detected in the overlying water or the interstitial water after the 90-day BC treatment. The pH value (7.5-8.1) slightly increased, and the toxicity characteristic leaching procedure (TCLP) leachability of the Cu and Cd in the sediment decreased overall. Cu and Cd were preferentially transformed into more stable species. The findings highlighted the potential possibility of BC derived from post-adsorbent being used for sediment remediation. However, the BC addition produced significant effects on the sediment microbial activity and community structure. In general, with an increase in BC, the urease activity increased, while the alkaline phosphatase and invertase activity decreased, which could be attributed to the BC itself. In addition, significant changes in both bacterial and fungal genera were observed. Hence, a cautious approach should be taken in the practical application of BC.

Organic ligands activate the dark formation of hydroxyl radicals (HO•) in surface soil/sediment: Yields, mechanisms, and applications.

Soil is an important sink for various pollutants. Recent findings suggest that soil and sediment would spontaneously form HO• through Fenton or Fenton-like reactions under natural conditions. In this study, the effects and mechanisms of organic ligands (OLs) on the occurrence of HO• in surface soil/sediment were experimentally and computationally examined. Results confirmed that HO• generation was ND-12.92 nmol/g in surface soil/sediment, and the addition of EDTA-2Na would significantly enhance the yields of HO• by 1.4-352 times. Moisture was the decisive factor of soil HO• generation. The release of Fe(II) from solid into the aqueous phase was essential for the stimulation of HO• in EDTA-2Na suspensions. Furthermore, complexation reactions between Fe(II) and OLs would enhance single electron transfer (SET) reactions and the formation of O2•-. Interestingly, for specific OLs, their stimulations on SET and formation of O2•- would depress HO• generation. Provoking HO• generation by OLs could be efficiently used to degrade sulfamethoxazole in rice field sediment. The study provided new knowledge on how commonly synthetic OLs affect the HO• generation in surface soil/sediment, and it additionally shed light on the engineered stimulation of in-situ Fenton reactions in natural soil/sediment.

Degradation of atrazine in river sediment by dielectric barrier discharge plasma (DBDP) combined with a persulfate (PS) oxidation system: response surface methodology, degradation mechanisms, and pathways.

Single degradation systems based on dielectric barrier discharge plasma (DBDP) or persulfate (PS) oxidation cannot achieve the desired goals (high degradation efficiency, high mineralization rate, and low product toxicity) of degrading atrazine (ATZ) in river sediment. In this study, DBDP was combined with a PS oxidation system (DBDP/PS synergistic system) to degrade ATZ in river sediment. A Box-Behnken design (BBD) including five factors (discharge voltage, air flow, initial concentration, oxidizer dose, and activator dose) and three levels (- 1, 0, and 1) was established to test a mathematical model by response surface methodology (RSM). The results confirmed that the degradation efficiency of ATZ in river sediment was 96.5% in the DBDP/PS synergistic system after 10 min of degradation. The experimental total organic carbon (TOC) removal efficiency results indicated that 85.3% of ATZ is mineralized into CO2, H2O, and NH4+, which effectively reduces the possible biological toxicity of the intermediate products. Active species (sulfate (SO4•-), hydroxy (•OH), and superoxide (•O2-) radicals) were found to exert positive effects in the DBDP/PS synergistic system and illustrated the degradation mechanism of ATZ. The ATZ degradation pathway, composed of 7 main intermediates, was clarified by Fourier transform infrared spectroscopy (FTIR) and gas chromatography-mass spectrometry (GC-MS). This study indicates that the DBDP/PS synergistic system is a highly efficient, environmentally friendly, novel method for the remediation of river sediment containing ATZ pollution.

Long-Term Monitoring of an In Situ Activated Carbon Treatment to Reduce Polychlorinated Biphenyl Availability in an Active Harbor.

Activated carbon-based amendments have been demonstrated as a means of sequestering sediment-associated organic compounds such as polychlorinated biphenyls (PCBs). In a 2012 effort, an activated carbon amendment was placed at a 0.5-acre amendment area adjacent to and underneath Pier 7 at the Puget Sound Naval Shipyard and Intermediate Maintenance Facility, Bremerton, Washington, USA to reduce PCB availability. Multiple postplacement monitoring events over a 3-year period showed an 80%-90% reduction in PCBs, stability of activated carbon, and no significant negative impacts to the benthic community. To further evaluate the long-term performance, a follow-on to the approximately 7-year (82-month) postplacement monitoring event was conducted in 2019. The results of in situ porewater and bioaccumulation evaluations were consistent with previous observations, indicating overall PCB availability reductions of approximately 80%-90% from preamendment conditions. Multiple measurement approaches for quantifying activated carbon and amendment presence indicated that the amendment was present and stable in the amendment area and that the activated carbon content was similar to levels observed previously. As in the previous investigation, benthic invertebrate community metrics indicated that the amendment did not significantly impair benthic health. An application of carbon petrography to quantify activated carbon content in surface sediments was also explored. The results were found to correspond within a factor of 1.3 (on average) with those of data for the black carbon content via a black carbon chemical oxidation method, an approach that quantifies all forms of black carbon (including activated carbon). The results suggest that at sites with low soot-derived black carbon content in sediment (relative to the targeted activated carbon dose), the black carbon chemical oxidation method would be a reasonable method for measurement of activated carbon dosage in sediment at sites amended with activated carbon. Environ Toxicol Chem 2022;41:1568-1574. © 2022 SETAC.

Risk control and assessment of sulfide-rich sediment remediation by controlled-release calcium nitrate.

Nitrate stimulation is widely used in sediment remediation to eliminate sulfides, degrade organic pollutants and immobilize phosphorus. However, the environmental risks of nitrate escape and the subsequent release of pollutants (e.g. nitrite, ammonium and trace metals) to water bodies during its application has received less attention. In this study, controlled-release nitrate pellets (SedCaN pellets) were manufactured and applied at different sediment depths to examine their effectiveness in controlling the risk of nitrate escape and subsequent pollutant release. The germination of submerged plant was also analyzed to assess the ecological risks associated with the remediated sediment. The results showed that the SedCaN pellets slowly released calcium nitrate, which led to denitrifying sulfide oxidation, organic matter degradation and the immobilization of phosphorus as a calcium-bound species. Gas production by denitrification increased the sediment porosity (0.3-2.2%) and led to the concomitant release of nitrite, ammonium, and heavy metals, creating secondary risks. Application of the SedCaN pellets at depth decreased the nitrate escape and the secondary risks, presumably by means of a capping effect of the upper sediment. The release of nitrate, ammonium, Ni and Cu were partially limited by 91.6%, 19.0%, 61.6% and 57.4% when SedCaN pellets were incorporated into deeper sediments (7-9 cm). Moreover, the range of sulfide oxidation extended to the upper and lower sediments in the profile (column), while the sulfide oxidation efficiency reached 85.9-95.0%. Finally, increased germination of Bacopa monnieri (20.0-26%) demonstrated that in comparison to reference materials the ecological risks of the treated sediments was reduced and the habitat function of sediment was restored after nitrate-stimulating remediation. The results of this study provide valuable guidelines for nitrate-stimulating remediation of sulfide-rich (black-odor) sediments.

Evaluation of Capping Materials to Reduce Zinc Flux from Sediments in a Former Mining Pit Lake.

Wilson Mine is a former vanadium mine site located in the Ouachita Mountains near Hot Springs, Arkansas. The site, which drains via two streams to Lake Catherine, has undergone extensive reclamation to significantly reduce groundwater and surface water contact with mine spoils. One of the streams passes through a former mine pit forming East Wilson Pond, and flux from pit lake sediments can result in elevated metal, that is, zinc (Zn), concentrations in overlying water. To mitigate potential risks, an investigation was conducted to evaluate the efficacy of capping materials for partitioning Zn-contaminated sediments from overlying water in East Wilson Pond. A 28-day laboratory study compared the effectiveness of capping materials including combinations of limestone, bentonite clay, and gravel for mitigating Zn flux, including under reasonable worst-case conditions (pH 5.5) encountered in the hypolimnion. Dissolved Zn was monitored over time in overlying water and in sediment porewaters within untreated controls and within the capping layer of treated systems. The use of limestone and/or bentonite clay improved buffering capacity compared to the noncapped control, and pH declined gradually but only modestly in the overlying water and porewater of all treated systems. Concentrations of Zn in overlying water of the noncapped control increased from approximately 30 to 100 µg/L during the study period, while concentrations in the overlying water and porewater of systems containing capping materials remained low (10-30 µg/L). The results demonstrated the effectiveness of the capping materials for neutralizing pH and reducing Zn flux, and a three-layer cap consisting of limestone (top) + bentonite clay (middle) + gravel (bottom) was determined to be most effective. These results were used to inform the selection of materials for the application of a cap to reduce Zn flux from the pit lake sediments. Environ Toxicol Chem 2022;41:193-200. © 2021 SETAC.