Sediments

Valence state: The combining capacity of an atom or radical determined by the number of electrons that it will lose, add, or share when it reacts with other atoms.

Source: The American Heritage™ Dictionary of the English Language, Fourth Edition
Copyright © 2000 by Houghton Mifflin Company.

free product: A NAPL found in the subsurface in sufficient quantity that it can be partially recovered by pumping or gravity drain.

aerobic: Direct aerobic metabolism involves microbial reactions that require oxygen to go forward. The bacteria uses a carbon substrate as the electron donor and oxygen as the electron acceptor. Degradation of contaminants that are susceptible to aerobic degradation but not anaerobic often ceases in the vicinity of the source zone because of oxygen depletion. This can sometimes be reversed by adding oxygen in the form of air (air sparging, bioventing), ozone, or slow oxygen release compound (e.g., ORC(r)).

Aerobic dechlorination may also occur via cometabolism where the dechlorination is incidental to the metabolic activities of the organisms. In this case, contaminants are degraded by microbial enzymes that are metabolizing other organic substrates. Cometabolic dechlorination does not appear to produce energy for the organism. At pilot- or full-scale treatment, cometabolic and direct dechlorination may be indistinguishable, and both processes may contribute to contaminant removal. For aerobic cometabolism to occur there must be sufficient oxygen and a suitable substrate which allows the microbe to produce the appropriate enzyme. These conditions may be present naturally but often in the presence of a source area oxygen and a substrate such as methane or propane will need to be introduced.

Adapted from US. EPA 2006 Engineering Issue: In Situ and Ex Situ Biodegradation Technologies for Remediation of Contaminated Sites

anaerobic: Direct anaerobic metabolism involves microbial reactions occurring in the absence of oxygen and encompasses many processes, including fermentation, methanogenesis, reductive dechlorination, sulfate-reducing activities, and denitrification. Depending on the contaminant of concern, a subset of these activities may be cultivated. In anaerobic metabolism, nitrate, sulfate, carbon dioxide, oxidized metals, or organic compounds may replace oxygen as the electron acceptor.

Anaerobic dechlorination also may occur via cometabolism where the dechlorination is incidental to the metabolic activities of the organisms. In this case, contaminants are degraded by microbial enzymes that are metabolizing other organic substrates. Cometabolic dechlorination does not appear to produce energy for the organism. At pilot- or full-scale treatment, cometabolic and direct dechlorination may be indistinguishable, and both processes may contribute to contaminant removal.

Quoted from US. EPA 2006 Engineering Issue: In Situ and Ex Situ Biodegradation Technologies for Remediation of Contaminated Sites

architecture: "Architecture" refers to the physical distribution of the contaminant in the subsurface. Residuals that take the form of long thin ganglia or small dispersed globules provide a larger surface area that will dissolve much faster than if the same amount of liquid were concentrated in a competent pool.

Sources: For purposes of this discussion, a DNAPL source zone includes the zone that encompasses the entire subsurface volume in which DNAPL is present either at residual saturation or as "pools" of accumulation above confining units. In addition, the DNAPL source zone includes regions that have come into contact with DNAPL that may be storing contaminant mass as a result of diffusion of DNAPL into the soil or rock matrix.

source zone: For purposes of this discussion, a DNAPL source zone includes the zone that encompasses the entire subsurface volume in which DNAPL is present either at residual saturation or as "pools" of accumulation above confining units. In addition, the DNAPL source zone includes regions that have come into contact with DNAPL that may be storing contaminant mass as a result of diffusion of DNAPL into the soil or rock matrix.

focal ulceration: The process or fact of a localized area being eroded away.

metaplasia of the glandular stomach: A change of cells to a form that does not normally occur in the tissue in which it is found.

hyperplasia of the glandular stomach: A condition in which there is an increase in the number of normal cells in a tissue or organ.

histiocytic: Degenerative.

duodenum: First part of the small intestine.

microcytic: Any abnormally small cell.

squamous cell papillomas: A small solid benign tumor with a clear-cut border that projects above the surrounding tissue.

squamous cell carcinomas: Cancer that begins in squamous cells-thin, flat cells that look under the microscope like fish scales. Squamous cells are found in the tissue that forms the surface of the skin, the lining of hollow organs of the body, and the passages of the respiratory and digestive tracts. Squamous cell carcinomas may arise in any of these tissues.

jejunum: The middle portion of the small intestine, between duodenum and ileum. It represents about 2/5 of the remaining portion of the small intestine below duodenum.

ileum: The distal and narrowest portion of the small intestine.

squamous: Flat cells that look like fish scales.

metaplasia: A condition in which there is a change of one adult cell type to another similar adult cell type.

ossification: The process of creating bone, that is of transforming cartilage (or fibrous tissue) into bone.

clastogenesis: Any process resulting in the breakage of chromosomes.

neoplastic: Abnormal and uncontrolled growth of cells.

ulceration: The process or fact of being eroded away.

leucocytosis: An elevation of the total number of white cells in blood.

neutrophils: A type of white blood cell.

chromodulin: A small protein that binds four trivalent chromium ions.

biomagnification: The increased accumulation and concentration of a contaminant at higher levels of the food chain; organisms higher on the food chain will have larger amounts of contaminants than those lower on the food chain, because the contaminants are not eliminated or broken down into other chemicals within the organisms.

exencephaly: Cerebral tissue herniation through a congenital or acquired defect in the skull.

everted viscera: Rotated body organs in the chest cavity.

To Be Considered: Documents, such as federal or state guidances, that are not legally binding but may be relevant to the topic in question.

gaining: A gaining surface water body is one where groundwater flows into it.

losing: A surface water body is losing when there is a permeable sediment bed that is not in contact with the groundwater allowing the surface water to seep through it.

fluvial: Of or pertaining to flow in rivers and streams.

lacustrine: Of or pertaining to a lake as in lacustrine sediments—sediments at the bottom of a lake.

lipid: Any class of fats that are insoluble in water.

lipophilic: Able to dissolve in lipids—in this case fatty tissue.

organelles: A part of a cell such as mitochondrion, vacuole, or chloroplast that plays a specific role in how the cell functions and membranes.

RfD: The RfD is an estimate of a daily exposure of the human population (including sensitive sub-groups) to a substance that is likely to be without "the appreciable risk of deleterious effects during a lifetime." An RfD is expressed in units of mg/kg-day.

autonomic: That part of the nervous system that controls non-conscious actions such as heart rate, perspiration and digestion.

ataxia: Lack of muscle coordination.

funnel-and-gate configuration: A system where low-permeability walls (the funnel) placed in the saturated zone direct contaminated ground-water toward a permeable treatment zone (the gate)

References: ATSDR (Agency for Toxic Substances and Disease Registry). 2015. Draft Toxicological Profile for Perfluoroalkyls. 574 pp.

EFSA (European Food Safety Authority). 2008. Opinion of the scientific panel on contaminants in the food chain on perfluorooctane sulfonate (PFOS) and perfluorooctanoic acid (PFOA) and their salts. EFSA Journal 653:1-131.

Hekster, F.M., R.W.P.M. Laane, and P. de Voogt. 2003. Environmental and toxicity effects of perfluoroalkylated substances. Reviews of Environmental Contamination and Toxicology 179:99-121.

Higgins, C. and R. Luthy. 2006. Sorption of perfluorinated surfactants on sediments. Environmental Science & Technology 40(23):7251-7256.

HSDB (Hazardous Substances Data Bank). 2012 Update. Perfluorooctanoic acid.

Kaiser, M.A., B.S. Larsen, C-P.C. Kao, and R.C. Buck. 2005. Vapor pressures of perfluorooctanoic, -nonanoic, -decanoic, -undecanoic, and -dodecanoic acids. Journal of Chemical and Engineering Data 50(6):1841-1843.

Kauck, E.A. and A.R. Diesslin. 1951. Some properties of perfluorocarboxylic acids. Industrial and Engineering Chemical Research 43(10):2332-2334.

Lewis, R.J., Sr., ed. 2004. Sax's Dangerous Properties of Industrial Materials. 11th ed. Wiley-Interscience, Hoboken, NJ. V3:2860.

Lide, D.R. 2007. CRC Handbook of Chemistry and Physics. 88th ed. CRC Press, Boca Raton, FL. 3-412.

SRC (Syracuse Research Corporation). 2016. PHYSPROP Database. SRC Scientific Databases, Accessed May 2016.

UNEP (United Nations Environmental Program). 2015. Proposal to List Pentadecafluorooctanoic Acid (CAS No: 335-67-1, PFOA, Perfluorooctanoic Acid), Its Salts and PFOA-Related Compounds in Annexes A, B and/or C to the Stockholm Convention on Persistent Organic Pollutants. UNEP/POPS/POPRC.11/5.

USEPA (U.S. Environmental Protection Agency). 2016. Drinking Water Health Advisory for Perfluorooctanoic Acid (PFOA).#pdfsmall# Office of Water, EPA 822-R-16-005, 103 pp

• Overview
• Policy and Guidance
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• Fate and Transport of Contaminants
• Site Characterization
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Bioaccumulation

Sediment and Bioavailability

The Terminology Reference Section of the USEPA Web site defines bioavailability as "A measure of the physicochemical access that a toxicant has to the biological processes of an organism. The less the bioavailability of a toxicant, the less the toxic effect on the organism." This broad definition provides a foundation for understanding this complex topic, as it applies to organisms of varying complexity, from bacteria to human beings.

Incorporating Bioavailability Considerations into the Evaluation of Contaminated Sediment Sites
Interstate Technology & Regulatory Council (ITRC) Contaminated Sediments Team, Web-based resource, Feb 2011

This Web-based ITRC technical and regulatory guidance is intended to help state regulators and practitioners understand and incorporate bioavailability concepts in contaminated freshwater or marine sediment management practices. The website is constructed to help the user identify the most relevant places within an exposure assessment where bioavailability can be assessed using the tools and methods that are most appropriate. Case studies are provided.

Bioturbation

The bioavailability of organic and inorganic contaminants in sediment is affected by bioturbation, a dynamic, biotic process that brings about the constant mixing of the top layer of sediment. Both plants and animals contribute to bioturbation, but usually benthic invertebrates, the annelid (segmented) worms, insect larvae, and bivalve mollusks, such as clams and mussels, are the major contributors to the process. As these animals construct galleries and burrow into sediment they can drag contaminated particles down from the sediment�s surface into the deeper layers. However, these actions can also bring contaminants in the deeper layers to the surface. Burrowing animals release fine, contaminant-containing fecal material to the surface of the sediment, where the contaminants may become bioavailable. The benthic invertebrates represent an important link between contaminated sediments and higher-tier receptors, such as waterfowl (Meysman 2006).

Bioturbation: A Fresh Look at Darwin's Last Idea
Meysman, F.J., J.J. Middleburg, and C.H. Help.
Trends in Ecology and Evolution, Vol 21, No 12, p 688-695, 2006

This article on bioturbation contains general information on the role of bioturbation in sediments.

Metals

Sediments play a pivotal role in controlling the bioavailability of metallic and organic contaminants of concern. The release of bioavailable mercury from contaminated lake sediment provides one example. Sulfate reducing bacteria (SRB) are present in the surficial sediments and the anoxic (oxygen deprived) waters that immediately cover them. SRB in the first few centimeters of anoxic lake sediment convert mercury stored in the sediment to its most common organic form, methyl mercury (MeHg). MeHg�s high solubility and capacity to rapidly pass through cell membranes makes it readily bioavailable (USEPA 1997).

Although analysis of a particular sediment may indicate elevated concentrations of a toxic metal, or a mixture of toxic metals, this does not necessarily mean the metals are biologically available to benthic organisms. The geochemistry of a particular sediment governs the bioavailability of metals, such as cadmium, copper, lead, nickel, silver, and zinc. Generally, heavy metals are present as sulfide complexes in the deeper layers of sediment, and are minimally bioavailable due to their near-total insolubility. The oxidation state of a metal may affect its bioavailability. For example, the reduced form of the element chromium, chrome III (Cr^III), is less readily available then the highly oxidized form, chromium VI (Cr^VI). Sediment geochemistry will determine the oxidation state of chromium and metals that have multiple valence states. (WHO 2006).

The concept of bioavailability is used to generate protective benchmark concentrations such as equilibrium partitioning sediment benchmarks (ESBs). An ESB is a point of reference concentration below which adverse effects to benthic organisms are not expected, and can be used by environmental managers to provide a level of protection for these organisms. However, if site-specific sediment contaminant levels exceed the benchmark, this should prompt a decision to gather additional data to further evaluate potential toxicity and bioavailability (USEPA 2005).

When considering the magnitude of toxic risk from the ingestion of contaminated sediment in a HHRA or ERA, the concept of bioavailability is important. In this instance, bioavailability refers to the fraction of the ingested amount of a contaminant that passes through the wall of the gut and becomes available for distribution to other parts of the body. The size of this fraction is therefore of great importance when determining the magnitude of the health risk from ingested, contaminated sediment (USEPA 2007).

Acid Volatile Sulfide and Simultaneously Extracted Metals in the Sediment Cores of the Pearl River Estuary in South China
Fang, T., X. Li, and G. Zhang.
Ecotoxicology and Environmental Safety, Vol 61, p 420-431, 2005 (abstract)

Appendix A: Adjustments for Absorption Efficiency
In Risk Assessment Guidance for Superfund (RAGS) Part A.
USEPA, Office of Solid Waste and Emergency Response, EPA 540/1-89/002, 4 pp, 1989

Bioavailability of Contaminants in Soils and Sediments: Processes, Tools and Applications
National Academy of Sciences, 432 pp, 2003

Environmental Health Criteria 234: Elemental Speciation in Human Health Risk Assessment
World Health Organization, 256 pp, 2006

Guidance for Evaluating the Oral Bioavailability of Metal in Soils for Use in Human Health Risk Assessment
USEPA, Office of Solid Waste and Emergency Response, OSWER Directive 9285.7-80, 20 pp, 2007

Mercury Study Report to Congress, Volume III: Fate and Transport of Mercury in the Environment
USEPA, Office of Air Quality Planning and Standards and Office of Research and Development, EPA 452/R-97/005, 376 pp, 1997

Mercury Study Report to Congress, Volume IV: An Assessment of Exposure to Mercury in the United States
USEPA, Office of Air Quality Planning and Standards and Office of Research and Development, EPA 452/R-97/006, 293 pp, 1997

Procedures for the Derivation of Equilibrium Partitioning Sediment Benchmarks (ESBs) for the Protection of Benthic Organisms: Metal Mixtures (Cadmium, Copper, Lead, Nickel, Silver and Zinc)
USEPA, Office of Research and Development, EPA 600/R-02/011, 121 pp, 2005

Organic Compounds

Sediments are frequently contaminated by organic pollutants, such as chlorinated pesticides, PCBs, PAHs, PCDDs, PCDFs, and petroleum derived fuel oils. The USEPA has published procedures (USEPA 2003) that derive ESBs for the two organochlorine pesticides, dieldrin and endrin, and for PAH mixtures. USEPA also has derived second tier (Tier 2) ESBs for 32 nonionic organic compounds (USEPA 2008). An ESB for an organic compound is not based on a relationship between relatively insoluble sulfide-complexed and a more readily soluble form. However, organic ESBs still employ the concept of partitioning between freely available and less bioavailable forms. An organic ESB assumes steady-state equilibrium between pore water, sediment, and benthic organism tissue concentrations. If one of these concentrations is known, the others can be calculated. An aqueous toxicity value (expressed as a concentration) can therefore be used to predict the toxicity of a compound in sediment. A non-polar organic ESB is obtained by multiplying an aqueous toxicity value (such as its Water Quality Criteria) for the compound with its organic carbon-water partition coefficient (K_OC). Compounds with high K_OC values partition to the organic carbon fraction of sediment and become less bioavailable to benthic organisms. Less rigorous inputs may be used to derive a Tier 2 ESB than for a Tier 1 ESB. For example, a secondary chronic toxicity value may be used for a Tier 2 ESB derivation, and the resulting value may have greater uncertainty.

Bioavailability of Organic Compounds: Methods and Case Studies
National Institutes of Health, National Institute of Environmental Health Sciences, Superfund Basic Research Program.

This is an audio and slide presentation on the bioavailability of PAHs from sediment.

Developing Sediment Remediation Goals at Superfund Sites Based on Pore Water for the Protection of Benthic Organisms from Direct Toxicity to Nonionic Organic Contaminants
Burkhard, L.P., D.R. Mount, and R.M. Burgess.
EPA 600-R-15-289, 75 pp, 2017

This document provides a technical approach and basis for setting the pore water remediation goals (RGs) for contaminants in sediments. Contaminant concentrations in the sediment pore water measured using passive sampling directly incorporate bioavailability of the chemicals at the site into the development of site-specific sediment RGs. Also discussed is how to evaluate the consistency between passive sampling measurements and sediment toxicity testing results.

Ecological Risk Assessment of Polycyclic Aromatic Hydrocarbons in Sediments: Identifying Sources and Ecological Hazard
Neff, J.N., S.A. Stout, and D.G. Gunster.
Integrated Environmental Assessment and Management, Vol 1, No 1, 2005 (abstract)

Estimation of Biota Sediment Accumulation Factor (BSAF) from Paired Observations of Chemical Concentrations in Biota and Sediment
Burkhard, L.
EPA 600-R-06-047, 35 pp, 2009

BSAF is a parameter describing bioaccumulation of sediment-associated organic compounds or metals into tissues of ecological receptors. The report provides information on methodologies to estimate BSAF for nonionic organic chemicals. It is applicable to fish and benthic organisms, e.g., crabs and bivalves.

Evaluating Ecological Risk to Invertebrate Receptors from PAHs in Sediments at Hazardous Waste Sites
Burgess, Robert M.
EPA, Office of Research and Development, EPA/600/R-06/162F, 23 pp, 2009

Procedures for the Derivation of Equilibrium Partitioning Sediment Benchmarks (ESBs) for the Protection of Benthic Organisms: Dieldrin
USEPA, Office of Research and Development, EPA 600/R-02/010, 75 pp, 2003

Procedures for the Derivation of Equilibrium Partitioning Sediment Benchmarks (ESBs) for the Protection of Benthic Organisms: Endrin
USEPA, Office of Research and Development, EPA 600-R-02-009, 73 pp, 2003

Procedures for the Derivation of Equilibrium Partitioning Sediment Benchmarks (ESBs) for the Protection of Benthic Organisms: PAH Mixtures
USEPA, Office of Research and Development, EPA 600/R-02/013, 175 pp, 2003

Procedures for the Derivation of Equilibrium Partitioning Sediment Benchmarks (ESBs) for the Protection of Benthic Organisms: Compendium of Tier 2 Values for Nonionic Organics
USEPA, Office of Research and Development, EPA 600/R-02/016, 75 pp, 2008

Metals Assessment Issue Paper: Bioavailability and Bioaccumulation
Lanno, R.P.
USEPA Bioavailability Workshop, 15-16 April 2003, 27 slides, PowerPoint presentation, 2003

Sediment and Bioaccumulation

The bioaccumulation of contaminants can be defined generally as the accumulation of organic compounds, such as chlorinated pesticides, PAHs, and PCBs, or heavy metals in an animal or plant. Bioaccumulation requires the sequestration of contaminants that enter the organism through diet, water intake, respiration, and skin or root contact, resulting in contaminant concentrations that are greater than those of the organism's environment. In contrast, accumulation of a substance only through contact with water is known as bioconcentration. The contaminant concentration achieved by bioaccumulation is governed by many factors, such as rate of uptake, rate of elimination, metabolic transformation of the contaminant, lipid content of the organism, and integrity and health of the organism.

Contaminants in sediment represent a crucial first step toward passage into the food chain. The bioavailability of contaminants in surficial sediments and contaminants released into the pore water and water column by biotic and abiotic processes in the sediment layer provides an opportunity for bioaccumulation. Contaminants in bed sediments transfer to benthic organisms by direct contact with or ingestion of sediment particles and from sediment pore water. The relative contributions of these three pathways are difficult to predict. They vary with the particle size and composition of the sediment, the species of organism, and the physical chemistry of the contaminant. Once transferred to biota, contaminants may accumulate if no mechanism exists for their elimination. Non-ionic organic contaminants accumulate usually in the lipid-rich tissues of an organism. Some metals accumulate due to binding to protein. Bioaccumulated contaminants can exert toxic effects on the organism containing them and on the subsequent trophic levels that acquire them in prey.

As contaminants (MeHg, cadmium, PCBs, and chlorinated pesticides, such as DDT) move up the food chain from one trophic level to the next, biomagnification can occur. Biomagnification is the progressive accumulation of contaminants such that the concentration in a predator�s tissues exceeds the level in its prey by a large factor. Biomagnification occurs as a contaminant moves from one trophic level to the next higher level in the food chain. As successive trophic levels require greater amounts of prey, great increases in contaminant concentration can be seen (ATSDR Toxicological Profiles).

Toxicological Profiles
Agency for Toxic Substances and Disease Registry (ATSDR).

ATSDR publishes toxicological profiles for organic and inorganic chemicals. Information on the chemical's bioaccumulation potential is given in each profile.

Bioaccumulation Models: State of the Application at Large Superfund Sites
Gustavson, K., T. von Stackelberg, I. Linkov, and T. Bridges.
ERDC TN-DOER-R17, 31 pp, 2011

Food web bioaccumulation models are important in determining remedial actions as they often are used to establish sediment cleanup levels and compare the effect of various remedial scenarios on fish tissue concentrations. Model application can differ markedly from site to site owing to the absence of prescribed methods for selecting and applying the models to contaminated areas. This technical note reviews the application of bioaccumulation models at four large contaminated-sediment Superfund sites to document the state of the practice and to draw conclusions and recommendations from that combined experience.

Biological Processes Affecting Bioaccumulation, Transfer, and Toxicity of Metal Contaminants in Estuarine Sediments
Chen, C.Y., N.S. Fisher, and J.R. Shaw.
SERDP Project ER-1503, 94 pp, 2011

Comparison of stable isotope values between taxa within a particular site was used to link metal bioaccumulation in natural food webs to bioaccumulation and assimilation of metals by sentinel species. Results indicate that metal concentrations of Cd, Zn, As, Pb, and Se in sediments do not predict concentrations in biota, whereas sediment concentrations of Hg and MeHg do determine biotic exposures. Pelagic fauna bioaccumulate more MeHg than benthic feeding fauna, suggesting that chemical flux from contaminated sediments is important in determining bioaccumulation in pelagic food webs.

BSAF (Biota-Sediment Accumulation Factor)

A data set of approximately 20,000 biota-sediment accumulation factors (BSAFs) from 20 locations (mostly Superfund sites) for nonionic organic chemicals, e.g., PCBs, PCDDs, PCDFs, DDTs, PAHs, and pesticides. Fresh, tidal, and marine ecosystems are included in the data set, and species in the data set include fish and benthic species (e.g., lobster, crayfish, and benthic invertebrates). The purpose of the data set is fivefold: i) provides tools for evaluating the reasonableness of BSAFs from other locations, ii) provides a tool for building a BSAF data set for a specific location, iii) provides data for performing bounding assessments of risks for locations where limited or no bioaccumulation data are available, iv) permits inquiry into underlying relationships and dependences of BSAFs upon ecosystem conditions and parameters, and v) allows comparison of PCB, PCDD, and PCDF residues to residue-effects data download from PCBRes.

Biotransformation

The potential for bioaccumulation, biomagnification, and toxicity vary within closely related groups of chemicals, such as PCBs and PCDDs/PCDFs. For example, the uptake, metabolism, elimination, and bioaccumulation of the PCB congeners differ among species. These differences can result in top-tier predators in a food web having different congener profiles to the sediment dwelling, benthic organisms at the base of the food web. This process is generally referred to as biotransformation, and may result in the concentration of a PCB congener in a species that is particularly sensitive to its toxic effects (USEPA 2005).

Memorandum: Response to Ecological Risk Assessment Forum Request for Information on the Benefits of PCB Congener Specific Analysis
Cleverly, D.
USEPA, Office Research and Development, NCEA-C-1315 ERASC-002F, 21 pp, 2005

TrophicTrace: Tool for Assessing Risks from the Trophic Transfer of Sediment-Associated Contaminants
USACE

Trophic Trace is an Excel^™-based spreadsheet tool that allows the user to calculate the potential ecological and human health risks (child and adult) associated with the bioaccumulation of contaminants in dredged sediments.

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