Sediment Remediation Using Activated Carbon: Effects of Sorbent Particle Size and Resuspension on Sequestration of Metals and Organic Contaminants.

Thin-layer capping using activated carbon has been described as a cost-effective in situ sediment remediation method for organic contaminants. We compared the capping efficiency of powdered activated carbon (PAC) against granular activated carbon (GAC) using contaminated sediment from Oskarshamn harbor, Sweden. The effects of resuspension on contaminant retention and cap integrity were also studied. Intact sediment cores were collected from the outer harbor and brought to the laboratory. Three thin-layer caps, consisting of PAC or GAC mixed with clay or clay only, were added to the sediment surface. Resuspension was created using a motor-driven paddle to simulate propeller wash from ship traffic. Passive samplers were placed in the sediment and in the water column to measure the sediment-to-water release of polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs), and metals. Our results show that a thin-layer cap with PAC reduced sediment-to-water fluxes of PCBs by 57% under static conditions and 91% under resuspension. Thin-layer capping with GAC was less effective than PAC but reduced fluxes of high-molecular weight PAHs. Thin-layer capping with activated carbon was less effective at retaining metals, except for Cd, the release of which was significantly reduced by PAC. Resuspension generally decreased water concentrations of dissolved cationic metals, perhaps because of sorption to suspended sediment particles. Sediment resuspension in treatments without capping increased fluxes of PCBs with log octanol-water partitioning coefficient (KOW ) > 7 and PAHs with log KOW of 5-6, but resuspension reduced PCB and PAH fluxes through the PAC thin-layer cap. Overall, PAC performed better than GAC, but adverse effects on the benthic community and transport of PAC to nontarget areas are drawbacks that favor the use of GAC. Environ Toxicol Chem 2022;41:1096-1110. © 2022 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Biological Effects of Activated Carbon on Benthic Macroinvertebrates are Determined by Particle Size and Ingestibility of Activated Carbon.

The application of activated carbon (AC) to the surface of contaminated sediments is a promising technology for sediment remediation in situ. Amendment with AC has proved to be effective in reducing bioavailability and sediment-to-water release of hydrophobic organic contaminants. However, AC may cause positive or negative biological responses in benthic organisms. The causes of these effects, which include changes in growth, reproduction, and mortality, are unclear but are thought to be related to the size of AC particles. The present study investigated biological response to AC ranging from ingestible powdered AC to noningestible granular AC in two benthic deposit feeders: the polychaete Marenzelleria spp. and the clam Limecola balthica (syn. Macoma balthica). In the polychaete, exposure to powdered AC (ingestible) reduced both dry weight and carbon assimilation, whereas exposure to granular AC (noningestible) increased both dry weight and carbon assimilation. Responses in the clam were similar but less pronounced, indicating that response levels are species-specific and may vary within a benthic community. In addition, worms exposed to the finest ingestible AC particles had reduced gut microvilli length and reduced gut lumen, indicating starvation. These results strongly suggest that biological responses to AC depend on particle ingestibility, whereby exposure to ingestible particles may cause starvation through reduced bioavailability of food coingested with AC or due to rejection of AC-treated sediment as a food source. Environ Toxicol Chem 2021;40:3465-3477. © 2021 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Sediment Remediation with New Composite Sorbent Amendments to Sequester Phosphorus, Organic Contaminants, and Metals.

This study tested two sediment amendments with active sorbents: injection of aluminum (Al) into sediments and thin-layer capping with Polonite (calcium-silicate), with and without the addition of activated carbon (AC), for their simultaneous sequestration of sediment phosphorus (P), hydrophobic organic contaminants (HOCs), and metals. Sediment cores were collected from a eutrophic and polluted brackish water bay in Sweden and incubated in the laboratory to measure sediment-to-water contaminant release and effects on biogeochemical processes. We used diffusive gradients in thin-film passive samplers for metals and semi-permeable membrane devices for the HOC polychlorinated biphenyls and polycyclic aromatic hydrocarbons. Al injection into anoxic sediments completely stopped the release of P and reduced the release of cadmium (Cd, -97%) and zinc (Zn, -95%) but increased the sediment fluxes of PAH (+49%), compared to the untreated sediment. Polonite mixed with AC reduced the release of P (-70%), Cd (-67%), and Zn (-89%) but increased methane (CH4) release. Adding AC to the Al or Polonite reduced the release of HOCs by 40% in both treatments. These results not only demonstrate the potential of innovative remediation techniques using composite sorbent amendments but also highlight the need to assess possible ecological side effects on, for example, sedimentary microbial processes.

Capping with activated carbon reduces nutrient fluxes, denitrification and meiofauna in contaminated sediments.

Sediment capping with activated carbon (AC) is an effective technique used in remediation of contaminated sediments, but the ecological effects on benthic microbial activity and meiofauna communities have been largely neglected. This study presents results from a 4-week experiment investigating the influence of two powdered AC materials (bituminous coal-based and coconut shell-derived) and one control material (clay) on biogeochemical processes and meiofauna in contaminated sediments. Capping with AC induced a 62-63% decrease in denitrification and a 66-87% decrease in dissimilatory nitrate reduction to ammonium (DNRA). Sediment porewater pH increased from 7.1 to 9.0 and 9.7 after addition of bituminous AC and biomass-derived AC, respectively. High pH (>8) persisted for at least two weeks in the bituminous AC and for at least 24 days in the coconut based AC, while capping with clay had no effect on pH. We observed a strong impact (nitrate fluxes being halved in presence of AC) on nitrification activity as nitrifiers are sensitive to high pH. This partly explains the significant decrease in nitrate reduction rates since denitrification was almost entirely coupled to nitrification. Total benthic metabolism estimated by sediment oxygen uptake was reduced by 30 and 43% in presence of bituminous coal-based AC and coconut shell-derived AC, respectively. Meiofauna abundances decreased by 60-62% in the AC treatments. Taken together, these observations suggest that AC amendments deplete natural organic carbon, intended as food, to heterotrophic benthic communities. Phosphate efflux was 91% lower in presence of bituminous AC compared to untreated sediment probably due to its content of aluminum (Al) oxides, which have high affinity for phosphate. This study demonstrates that capping with powdered AC produces significant effects on benthic biogeochemical fluxes, microbial processes and meiofauna abundances, which are likely due to an increase in porewater pH and to the sequestration of natural, sedimentary organic matter by AC particles.

Environmental risk assessment of pesticides in the River Madre de Dios, Costa Rica using PERPEST, SSD, and msPAF models.

This study assesses the ecological risks (ERA) of pesticides to aquatic organisms in the River Madre de Dios (RMD), which receives surface runoff water from banana, pineapple, and rice plantations on the Caribbean coast of Costa Rica. Water samples collected over 2 years at five sites in the RMD revealed a total of 26 pesticides. Their toxicity risk to aquatic organisms was assessed using three recent ERA models. (1) The PERPEST model showed a high probability (>50 %) of clear toxic effects of pesticide mixtures on algae, macrophytes, zooplankton, macroinvertebrates, and community metabolism and a low probability (<50 %) of clear effects on fish. (2) Species sensitivity distributions (SSD) showed a moderate to high risk of three herbicides: ametryn, bromacil, diuron and four insecticides: carbaryl, diazinon, ethoprophos, terbufos. (3) The multi-substance potentially affected fraction (msPAF) model showed results consistent with PERPEST: high risk to algae (maximum msPAF: 73 %), aquatic plants (61 %), and arthropods (25 %) and low risk to fish (0.2 %) from pesticide mixtures. The pesticides posing the highest risks according to msPAF and that should be substituted with less toxic substances were the herbicides ametryn, diuron, the insecticides carbaryl, chlorpyrifos, diazinon, ethoprophos, and the fungicide difenoconazole. Ecological risks were highest near the plantations and decreased progressively further downstream. The risk to fish was found to be relatively low in these models, but water samples were not collected during fish kill events and some highly toxic pesticides known to be used were not analyzed for in this study. Further sampling and analysis of water samples is needed to determine toxicity risks to fish during peaks of pesticide mixture concentrations. The msPAF model, which estimates the ecological risks of mixtures based on their toxic modes of action, was found to be the most suitable model to assess toxicity risks to aquatic organisms in the RMD. The PERPEST model was found to be a strong tool for screening risk assessments. The SSD approach is useful in deriving water quality criteria for specific pesticides. This study, through the application of three ERA models, clearly shows that pesticides used in plantations within the RMD watershed are expected to have severe adverse effects on most groups of aquatic organisms and that actions are urgently needed to reduce pesticide pollution in this high biodiversity ecosystem.

Toward a conceptual approach for assessing risks from chemical mixtures and other stressors to coastal ecosystem services.

Growth of human populations and increased human activity, particularly in coastal areas, increase pressure on coastal ecosystems and the ecosystem services (ES) they provide. As a means toward being able to assess the impact of multiple stressors on ES, in the present study we propose an 8-step conceptual approach for assessing effects of chemical mixtures and other stressors on ES in coastal areas: step A, identify the relevant problems and policy aims; step B, identify temporal and spatial boundaries; step C, identify relevant ES; step D, identify relevant stressors (e.g., chemicals); step E, translate impacts into ES units; step F, assess cumulative risk in ES units; step G, rank stressors based on their contribution to adverse effects on ES; and step H, implement regulation and management as appropriate and necessary. Two illustrative case studies (Swedish coastal waters and a coastal lagoon in Costa Rica) are provided; one focuses on chemicals that affect human food supply and the other addresses pesticide runoff and trade-offs among ES. The 2 cases are used to highlight challenges of such risk assessments, including use of standardized versus ES-relevant test species, data completeness, and trade-offs among ES. Lessons learned from the 2 case studies are discussed in relation to environmental risk assessment and management of chemical mixtures. Integr Environ Assess Manag 2017;13:376-386. © 2016 SETAC.

Assessing and managing multiple risks in a changing world-The Roskilde recommendations.

Roskilde University (Denmark) hosted a November 2015 workshop, Environmental Risk-Assessing and Managing Multiple Risks in a Changing World. This Focus article presents the consensus recommendations of 30 attendees from 9 countries regarding implementation of a common currency (ecosystem services) for holistic environmental risk assessment and management; improvements to risk assessment and management in a complex, human-modified, and changing world; appropriate development of protection goals in a 2-stage process; dealing with societal issues; risk-management information needs; conducting risk assessment of risk management; and development of adaptive and flexible regulatory systems. The authors encourage both cross-disciplinary and interdisciplinary approaches to address their 10 recommendations: 1) adopt ecosystem services as a common currency for risk assessment and management; 2) consider cumulative stressors (chemical and nonchemical) and determine which dominate to best manage and restore ecosystem services; 3) fully integrate risk managers and communities of interest into the risk-assessment process; 4) fully integrate risk assessors and communities of interest into the risk-management process; 5) consider socioeconomics and increased transparency in both risk assessment and risk management; 6) recognize the ethical rights of humans and ecosystems to an adequate level of protection; 7) determine relevant reference conditions and the proper ecological context for assessments in human-modified systems; 8) assess risks and benefits to humans and the ecosystem and consider unintended consequences of management actions; 9) avoid excessive conservatism or possible underprotection resulting from sole reliance on binary, numerical benchmarks; and 10) develop adaptive risk-management and regulatory goals based on ranges of uncertainty. Environ Toxicol Chem 2017;36:7-16. © 2016 SETAC.