Exponent scientists are nationally recognized for their work on evaluating the bioavailability of organic chemicals and metals to humans and ecological receptors. Understanding the bioavailability of a chemical is critical to understanding risks and for informing decisions about products in the workplace or general commerce, and on the proper management of contaminated soils or sediments. Bioavailability studies determine how much of a chemical is absorbed by a human or ecological receptor following exposure. Often, the actual absorption from environmental media, such as soils or sediments, is lower than the absorption measured in the laboratory studies that form the basis of regulatory values. Therefore, incorporating bioavailability adjustments into human or ecological risk assessments can provide important insight into the safety of products and the risks posed by contaminated media. The insights gained can lead to better-informed decisions for companies and regulators.
Exponent is at the forefront of this emerging scientific specialty, having studied the bioavailability of many chemicals under widely varying site conditions. We have used the information gained from this work to support the use of site-specific cleanup goals for soil and sediments that adequately protect human health and the environment. Our studies have served as benchmarks for others and have helped develop a better understanding of exposures within affected communities and within industry and the regulatory agencies. Exponent has been involved in developing and applying site-specific oral bioavailability values for inorganic chemicals (antimony, arsenic, beryllium, cadmium, chromium, lead, mercury, and vanadium) and organic compounds (polycyclic aromatic hydrocarbons, dioxins and furans). Specific contributions in this area include:
- Conducting field sampling of sediment pore water that successfully demonstrated reduced bioavailability of chromium in sediments
- Implementing the use of semi-permeable membrane devices (SPME) to demonstrate reduced bioavailability of PAHs in sediments
- Conducting laboratory experiments that document reduced oral bioavailability of metals in soils that are ingested by small mammals or humans
Human health and ecological risk assessments are conducted to evaluate the potential for people, wildlife, or plants to be adversely affected by exposures to chemicals in the environment. Risk assessments are a critical component of environmental regulatory decision-making and are used to determine the need for, and nature of, remedial actions and to support the derivation of cleanup levels at hazardous waste facilities and sites. However, default methodologies used in risk assessments to estimate exposure to chemicals frequently overestimate exposure by assuming that a chemical will be equally bioavailable in all media, irrespective of the properties of the environmental media or the chemical form of the contaminant.
In many cases, exposure from environmental media is much less than predicted, because organic and inorganic chemicals in soil or sediment are less bioavailable than in water or food. A site-specific evaluation of bioavailability may be used to produce more realistic estimates of exposure and risk to establish cleanup goals that are scientifically defensible and protective of human health and the environment.
Two Ways to Determine Oral Bioavailability
In vivo — Studies of oral bioavailability conducted in animal models. Commonly used animals include rats, mice, rabbits, swine, and monkeys. These studies are relatively expensive and time consuming, but when properly designed are generally considered by the regulatory community to provide a reliable estimate of absorption in a biological receptor.
In vitro — “Test-tube” or “bench-top” studies designed to estimate oral bioavailability. These methods can vary depending on the contaminant, receptor, and environmental media of interest. Emerging methods that have met with scientific and regulatory approval include the use of physiologically-based extraction procedures for soil, or solid-phase microextraction (SPME) of sediment pore water. These studies are less expensive than animal studies and can provide an estimate of bioavailability that is based on the fraction of a contaminant that would be available for absorption. For human health risk assessment, the U.S. EPA has recently approved the use of an extraction method for assessing the relative oral bioavailability of lead from soils and sediments. For PAHs in sediments, several regulatory agencies have made site-specific remedial decisions based in part on the use of SPME to measure the bioavailability of organic contaminants in sediment.
Results of these studies produce site-specific relative absorption factors and uptake factors that can be used to adjust estimates of exposure to the contaminants in soil or sediments. These improved estimates of exposure have served as the basis for technical refinements to risk-based cleanup goals for residential and industrial soils. Several states have accepted Exponent’s methods and resulting data in making precedent-setting decisions.
Exponent continues to be at the forefront of nation-wide efforts to demonstrate the value of incorporating information on bioavailability into environmental decision-making. We take a multidisciplinary approach to such studies and routinely involve biologists, ecologists, chemists, risk assessors, and modelers in or work. We publish frequently in peer-reviewed journals, regularly give invited talks at national conferences and regulatory workshops, and often arrange symposia and conference sessions on bioavailability issues. This level of involvement in ongoing research and policy programs, both our own and those of other firms and institutions across the country, often allows us access to study results before they reach the scientific literature, giving our clients the advantage of using the very latest data in evaluating their sites.
Budinsky RA, Rowlands JC, Casteel S, Fent G, Cushing CA, Newsted J, Giesy JP, Ruby MV, Aylward LL. A pilot study of oral bioavailability of dioxins and furans from contaminated soils: Impact of differential hepatic enzyme activity and species differences. Chemosphere 2008; 70(10):1774–1786.
Lowney YW, Wester RC, Schoof RA, Cushing CA, Edwards M, Ruby MV. Percutaneous absorption of arsenic from soils as measured in the Rhesus Monkey. Toxicol Sci 2007; 100(2):381–392.
Shock SS, Bessinger BA, Lowney YW, Clark JL. Assessment of the solubility and bioaccessibility of barium and aluminum in soils affected by mine dust deposition. Environ Sci Technol 2007; 41(13):4813–4820.
Kane Driscoll SB, Burgess RM. An overview of the development, status, and application of equilibrium partitioning sediment benchmarks for PAH Mixtures. Hum Ecol Risk Assess 2007; 13:2:286–301.
Menzie CA, Coleman AJ. Debate & commentary. Polycyclic aromatic hydrocarbons in sediments: An overview of risk-related issues. Hum Ecol Risk Assess 2007; 13(2):269–275.
Nico PS, Ruby MV, Lowney YW, Holm SE. Chemical speciation and bioaccessibility of arsenic and chromium in CCA-treated wood and soils. Environ Sci Technol 2006; 40(1):402–408.
Kane Driscoll SB, McElroy AE. Bioaccumulation and metabolism of benzo[a]pyrene in three species of polychaete worms. Environ Toxicol Chem 2006; 15:1401–1410.
Lowney YW, Ruby MV, Wester RC, Schoof RA, Holm SE, Hui X, Barbadillo S, Maibach HI. Percutaneous absorption of arsenic from environmental media. Toxicol Indust Health 2005; 21(1):1–14.
Kane Driscoll SB, Amos CB, McArdle ME, Southworth B, Menzie CA, Coleman A. Use of Equilibrium Partitioning Sediment Benchmarks (ESBs) to predict toxicity of PAH contaminated sediments. Electric Power Research Institute (EPRI), Palo Alto, CA, 1010371, 2005.
Menzie CA, Efroymson RA, Ells SJ, Henningsen GM, Hope BK. Risk assessment and risk management. Chapter 2. In: Pellston Workshop on Contaminated Soils: From Soil-Chemical Interactions to Ecosystems Management. Lanno RP (ed), SETAC Publications. Pensacola, FL, 2003.
Shatkin JA, Wagle M, Kent S, Menzie CA. Development of a biokinetic model to evaluate dermal absorption of polycyclic aromatic hydrocarbons from soil. Hum Ecol Risk Asses 2002; 8(4):713–734.
Cura, JJ, Kane Driscoll SB, Lacey R, McArdle M, Menzie CA. Assessing ecological risks of PAH-contaminated sediments. In: Sediments Guidance Compendium. Electric Power Research Institute (EPRI), Palo Alto, CA, 2001.
Menzie CA, Burke AM, Grasso D, Harnois M, Magee B, McDonald D, Montgomery C, Nichols A, Pignatello J, Price B, Price R, Rose J, Shatkin J, Smets B, Smith J, Svirsky S. An approach for incorporating information on chemical availability in soils into risk assessment and risk-based decision making. Hum Ecol Risk Assess 2000; 6(3):479–510.
Lowney Y, Ruby MV, Hook GC, Nelson RR. Biological interactions: Human health considerations. In: Metals-Contaminated Soils: In Situ Inactivation and Phytorestoration. Vangronsveld J, Cunningham SD (eds), Landes Bioscience, Austin, TX, 1998.
Kane Driscoll SB, Schaffner SC, Dickhut RM. Toxicokinetics of fluoranthene to the amphipod, Leptocheirus plumulosus, in water-only and sediment exposures. Environ Res 1998; 45(3):269-284.
Kane Driscoll SB, McElroy AE. Elimination of sediment-associated benzo[a]pyrene and its metabolites by polychaete worms exposed to 3-methylcholanthrene. Aquat Toxicol 1997; 39(1):77-91.
Kane Driscoll SB, Landrum PF. A comparison of equilibrium partitioning and critical body residue approaches for predicting toxicity of sediment associated fluoranthene to freshwater amphipods. Environ Toxicol Chem 1997; 16(10):2179-2186.
Kane Driscoll SB, Harkey GA, Landrum PF. Accumulation and toxicity of fluoranthene in sediment bioassays with freshwater amphipods. Environ Toxicol Chem 1997; 16(4):742-753.
Kane Driscoll SB, Landrum PF, Tigue EA. Accumulation and toxicity of fluoranthene in water only bioassays with freshwater amphipods. Environ Toxicol Chem 1997; 16(4):754-761.
Menzie CA, Heiger-Bernays WJ, Montgomery CR, Linz DG, Nakles DV. Development of an ecological risk assessment framework based on contaminant availability. In: Ecotox—Environmental Contaminants through the Macroscope. Wuerz Publishing Ltd., Winnipeg, MB, Canada, 1996.