Observations of limited secondary effects to benthic invertebrates and macrophytes with activated carbon amendment in river sediments

Impaired benthic macrofauna function 4 years after sediment capping with activated carbon in the Grenland fjords, Norway

The sediments in the Grenland fjords in southern Norway are heavily contaminated by large emissions of dioxins and mercury from historic industrial activities. As a possible in situ remediation option, thin-layer sediment surface capping with powdered activated carbon (AC) mixed with clay was applied at two large test sites (10,000 and 40,000 m²) at 30-m and 95-m depths, respectively, in 2009. This paper describes the long-term biological effects of the AC treatment on marine benthic communities up to 4 years after treatment. Our results show that the capping with AC strongly reduced the benthic species diversity, abundance, and biomass by up to 90%. Vital functions in the benthic ecosystem such as particle reworking and bioirrigation of the sediment were also reduced, analyzed by using novel bioturbation and bioirrigation indices (BP_c, BIP_c, and IP_c). Much of the initial effects observed after 1 and 14 months were still present after 49 months, indicating that the effects are long-lasting. These long-lasting negative ecological effects should be carefully considered before decisions are made on sediment remediation with powdered AC, especially in large areas, since important ecosystem functions can be impaired.

Performance of an in situ activated carbon treatment to reduce PCB availability in an active harbor

In situ amendment of surface sediment with activated carbon is a promising technique for reducing the availability of hydrophobic organic compounds in surface sediment. The present study evaluated the performance of a logistically challenging activated carbon placement in a high-energy hydrodynamic environment adjacent to and beneath a pier in an active military harbor. Measurements conducted preamendment and 10, 21, and 33 months (mo) postamendment using in situ exposures of benthic invertebrates and passive samplers indicated that the targeted 4% (by weight) addition of activated carbon (particle diameter ≤74 µm) in the uppermost 10 cm of surface sediment reduced polychlorinated biphenyl availability by an average (± standard deviation) of 81 ± 11% in the first 10 mo after amendment. The final monitoring event (33 mo after amendment) indicated an approximate 90 ± 6% reduction in availability, reflecting a slight increase in performance and showing the stability of the amendment. Benthic invertebrate census and sediment profile imagery did not indicate significant differences in benthic community ecological metrics among the preamendment and 3 postamendment monitoring events, supporting existing scientific literature that this approximate activated carbon dosage level does not significantly impair native benthic invertebrate communities. Recommendations for optimizing typical site-specific assessments of activated carbon performance are also discussed and include quantifying reductions in availability and confirming placement of activated carbon. Environ Toxicol Chem 2018;37:1767-1777. Published 2018 Wiley Periodicals, Inc. on behalf of SETAC. This article is a US government work and, as such, is in the public domain in the United States of America.

A Combined Field and Laboratory Study on Activated Carbon-Based Thin Layer Capping in a PCB-Contaminated Boreal Lake

The in situ remediation of aquatic sediments with activated carbon (AC)-based thin layer capping is a promising alternative to traditional methods, such as sediment dredging. Applying a strong sorbent like AC directly to the sediment can greatly reduce the bioavailability of organic pollutants. To evaluate the method under realistic field conditions, a 300 m² plot in the PCB-contaminated Lake Kernaalanjärvi, Finland, was amended with an AC cap (1.6 kgAC/m²). The study lake showed highly dynamic sediment movements over the monitoring period of 14 months. This led to poor retention and rapid burial of the AC cap under a layer of contaminated sediment from adjacent sites. As a result, the measured impact of the AC amendment was low: Both the benthic community structure and PCB bioaccumulation were similar on the plot and in surrounding reference sites. Corresponding follow-up laboratory studies using Lumbriculus variegatus and Chironomus riparius showed that long-term remediation success is possible, even when an AC cap is covered with contaminated sediment. To retain a measurable effectiveness (reduction in contaminant bioaccumulation), a sufficient intensity and depth of bioturbation is required. On the other hand, the magnitude of the adverse effect induced by AC correlated positively with the measured remediation success.

Response of marine benthic fauna to thin-layer capping with activated carbon in a large-scale field experiment in the Grenland fjords, Norway

A field experiment with thin-layer capping was conducted in the Grenland fjords, Norway, for remediation in situ of mercury and dioxin-contaminated sediments. Experimental fields at 30 and 95 m depth were capped with (i) powdered activated carbon (AC) mixed with clay (AC+cla`y), (ii) clay, and (iii) crushed limestone. Ecological effects on the benthic community and species-feeding guilds were studied 1 and 14 months after capping, and a total of 158 species were included in the analyses. The results show that clay and limestone had only minor effects on the benthic community, while AC+clay caused severe perturbations. AC+clay reduced the abundance, biomass, and number of species by up to 90% at both 30 and 95 m depth, and few indications of recovery were found during the period of this investigation. The negative effects of AC+clay were observed on a wide range of species with different feeding strategies, although the suspension feeding brittle star Amphiura filiformis was particularly affected. Even though activated carbon is effective in reducing sediment-to-water fluxes of dioxins and other organic pollutants, this study shows that capping with powdered AC can lead to substantial disturbances to the benthic community.

Effect of PCB Bioavailability Changes in Sediments on Bioaccumulation in Fish

In situ sediment amendment with sorbents such as activated carbon (AC) can effectively reduce the bioavailability of hydrophobic organic chemicals such as polychlorinated biphenyls (PCBs). However, there is limited experimental or modeling assessment of how bioavailability changes in sediments impact bioaccumulation in fish - the primary risk driver for exposure to humans and top predators in the aquatic ecosystem. In the present study we performed laboratory aquarium experiments and modeling to explore how PCB sorption in sediments impacted exposure pathways and bioaccumulation in fish. Results showed that freely dissolved PCBs in porewater and overlying water measured by passive sampling were reduced by more than 95% upon amendment with 4.5% fine granular AC. The amendment also reduced the PCB uptake in fish by 87% after 90 days of exposure. Measured freely dissolved concentrations were incorporated in equilibrium and kinetic models for predicting uptake by fish. Predicted uptake using the kinetic model was generally within a factor of 2 for total PCBs measured in fish. The kinetic model output was most sensitive to overlying water PCBs, lipid fraction, and dissolved oxygen concentration (regulating gill ventilation). Our results indicate that by incorporating changes in freely dissolved PCB concentrations in bioaccumulation models it is possible to predict effectiveness of sediment remediation in reducing PCB uptake in fish.

In situ sediment treatment using activated carbon: a demonstrated sediment cleanup technology

This paper reviews general approaches for applying activated carbon (AC) amendments as an in situ sediment treatment remedy. In situ sediment treatment involves targeted placement of amendments using installation options that fall into two general approaches: 1) directly applying a thin layer of amendments (which potentially incorporates weighting or binding materials) to surface sediment, with or without initial mixing; and 2) incorporating amendments into a premixed, blended cover material of clean sand or sediment, which is also applied to the sediment surface. Over the past decade, pilot- or full-scale field sediment treatment projects using AC-globally recognized as one of the most effective sorbents for organic contaminants-were completed or were underway at more than 25 field sites in the United States, Norway, and the Netherlands. Collectively, these field projects (along with numerous laboratory experiments) have demonstrated the efficacy of AC for in situ treatment in a range of contaminated sediment conditions. Results from experimental studies and field applications indicate that in situ sequestration and immobilization treatment of hydrophobic organic compounds using either installation approach can reduce porewater concentrations and biouptake significantly, often becoming more effective over time due to progressive mass transfer. Certain conditions, such as use in unstable sediment environments, should be taken into account to maximize AC effectiveness over long time periods. In situ treatment is generally less disruptive and less expensive than traditional sediment cleanup technologies such as dredging or isolation capping. Proper site-specific balancing of the potential benefits, risks, ecological effects, and costs of in situ treatment technologies (in this case, AC) relative to other sediment cleanup technologies is important to successful full-scale field application. Extensive experimental studies and field trials have shown that when applied correctly, in situ treatment via contaminant sequestration and immobilization using a sorbent material such as AC has progressed from an innovative sediment remediation approach to a proven, reliable technology.

Biological responses to activated carbon amendments in sediment remediation

Sorbent amendment with activated carbon (AC) is a novel in situ management strategy for addressing human and ecological health risks posed by hydrophobic organic chemicals (HOCs) in sediments and soils. A large body of literature shows that AC amendments can reduce bioavailability of sediment-associated HOCs by more than 60-90%. Empirically derived biodynamic models can predict bioaccumulation in benthic invertebrates within a factor of 2, allowing for future scenarios under AC amendment to be estimated. Higher AC dose and smaller AC particle size further reduce bioaccumulation of HOCs but may induce stress in some organisms. Adverse ecotoxicity response to AC exposure was observed in one-fifth of 82 tests, including changes in growth, lipid content, behavior, and survival. Negative effects on individual species and benthic communities appear to depend on the characteristics of the sedimentary environment and the AC amendment strategy (e.g., dose and particle size). More research is needed to evaluate reproductive end points, bacterial communities, and plants, and to link species- and community-level responses to amendment. In general, the ability of AC to effectively limit the mobility of HOCs in aquatic environments may outshine potential negative secondary effects, and these outcomes must be held in comparison to traditional remediation approaches.