Reference Manual on Scientific Evidence Third Edition (2011) / Chapter Skim
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Reference Guide on Exposure Science--Joseph V. Rodricks
Reference Guide on Exposure Science--Joseph V. Rodricks
Pages 503-548
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From page 503... ...
508 C. Organization of the Reference Guide, 508 III. Contexts for the Application of Exposure Science, 509 A. Consumer Products, 509 B. Environmental and Product Contaminants, 510 C. Chemicals in Workplace Environments, 511 D. Claims of Disease Causation, 511 IV.
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Reference Manual on Scientific Evidence Appendix A: Presentation of Data -- Concentration Units, 541 Appendix B: Hazardous Waste Site Exposure Assessment, 543 Glossary of Terms, 545 References on Exposure, 548 504
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2. See Bernard D Goldstein & Mary Sue Henifin, Reference Guide on Toxicology, in this manual.
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Although some schools of public health may offer courses in exposure assessment, there are no academic degrees offered in exposure science. When regulatory and public health agencies began in the 1970s to examine toxicological risks in a quantitative way, it became apparent that quantitative exposure assessments would become necessary.
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8 chemicals that may be present in various environmental media (air, water, food, soil, consumer products of all types) and of the amounts of those chemicals that enter the body as a result of these contacts.9 Exposure scientists also study whether and how those amounts change over time.
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C Organization of the Reference Guide The reference guide begins with a discussion of the various contexts in which exposure science is applied (Section III)
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This last topic comprises the interface between exposure science and the sciences of epidemiology and toxicology. Traditionally, exposure scientists have described their work as ending with the description of dose to the body (exposure dose)
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. Human exposure assessments are central to the regulatory approval of these products.13 Many other consumer products require risk assessments, but premarket approvals are not generally required under our current laws.
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Specifically, they allege that some existing medical condition has been caused by exposures occurring in the past, whether in the workplace, the environment, or through the use of various consumer products.20 16. National Research Council, Air Quality Management in the United States (2004)
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Green et al., Reference Guide on Epidemiology, in this manual.
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The primer also introduces some technical terms that frequently arise in exposure science.
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There are also inorganic chemicals -- the inerals -- m present in living organisms, many essential to life. But the principal natural source of inorganic chemicals is the nonliving part of the Earth that humans have learned how to mine.
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, limestone (calcium carbonate) , sulfuric acid, and phosphates, and various compounds of the metals, have hundreds of different uses, as strictly industrial chemicals and as consumer products.
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Human Exposures to Chemicals As noted earlier, this section is entirely descriptive, rather than quantitative. It describes all the various physical processes that lead to human exposures to chemicals and introduces the terms that exposure scientists apply to those processes.
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Examples of Sources Potential Exposures Occupational Exposures Emissions to Air Manufacture Wastewater Effluents Storage Leaks to soil Spills water, air, and Accidents biota Transportation Application of Pesticides Consumption of Pesticide Residues Use Consumption of Food Additives Dermal Exposure to Cosmetics Inhalation of Gasoline Vapors Hazardous Waste Incinerator Emissions Evaporation to Air Disposal Surface Runoff Leaching to Ground Water Figure 9-1.eps difficult to identify and quantify than are intended exposures.31 In the case of the intended exposures, the pathway from source to humans is direct; in the case of unintended exposures, the pathway is indirect, sometimes highly so. Thus, the most important distinction for purposes of exposure assessment concerns the directness of the pathway from source to people.
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Understanding the dose is the necessary first step in understanding these processes; for purposes of this reference guide, the boundary of exposure science is set at understanding dose. However, some 32. See, e.g., Hackensack Riverkeeper, Inc.
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Cal 35. See reference guides on epidemiology and toxicology in this manual.
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Thus, in the case of certain personal care products that are applied to the skin, there is a possibility of inhalation exposures to any substance in those products that can readily volatilize at room temperatures. One physical characteristic of chemicals that exposure scientists need to understand is their capacity to move from a liquid to a gaseous state (to volatilize)
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45. In the context of exposure science, the term "final" refers to the medium through which people become exposed. A chemical may in fact continue to move to other media after that human exposure has occurred.
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D Exposure Routes Pathways analysis leads to the identification of the environmental media in which the chemical of interest comes to be present and with which human contact can occur -- the media of human exposure.
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Point B Exposure Point C Surface Exposure Point D Water Well Water Drinking Runoff Ru Runoff Leak E Exposure Vapor Intrusion Point E Leaching ng Waste Dump Groundwater transport to o (Source) surface water Groundwater Flow Direction Exposures at Point A could include: drinking water ingestion, dermal contact with water, and inhalation Exposures at Point B could include: incidental soil ingestion, inhalation, dermal contact, and consumption of local produce and meat Exposures at Point C could include: incidental soil ingestion, dermal contact, and consumption of game Exposures at Point D could include: dermal contact and consumption of fish Exposures at Point E could include: incidental water ingestion and dermal contact Source: Graphic created by Jason Miller.
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The pathways analysis concludes with a description of what chemicals will be present in the various environmental media with which the exposed populations were, are, or could become exposed (air, water, foods, soils and dusts, consumer products)
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. 54. See Appendix A for a discussion of units used in exposure science.
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Goldstein & Mary Sue Henifin, Reference Guide on Toxicology, Section I.A.1.c, in this manual. 58. The 24-hour inhalation rate outside the workplace setting is ca.
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, determining the concentrations of the chemical in the media of exposure becomes difficult.62 Such a situation is clearly different from that in which a specific amount of an additive is directly added to a specific amount of food. The challenge faced by exposure scientists when the chemical comes to be present in the medium of human exposure not by direct and intentional addition, but by indirect means, through movement from source through the environment, is to find a reliable 60. See, e.g., Northwest Coalition for Alternatives to Pesticides (NCAP)
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Environmental sampling and analysis is under way all over the world, at and near contaminated waste sites, in the vicinity of facilities emitting chemicals to air and water, and in many other circumstances.64 One purpose of such sampling and analysis is to determine whether products and environmental media contain substances at concentrations that meet existing regulatory requirements. In many circumstances, regulators have established limits on the concentrations of certain chemicals in foods, other products, water, air, and even soils.
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2008) (MCLs for public drinking water)
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In the matters at hand, a model refers to a mathematical description of the quantitative relationship between the amount of a chemical emitted from some source, usually over a specified period of time, to the concentrations of that chemical in the media of human exposure, again over some specified time period.66 66. See, e.g., NCAP v.
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Typically, a model is developed by first constructing a flow diagram to illustrate the theoretical pathways of environmental contamination, as shown in Figure 2 and for a hazardous waste site in Appendix B These models can be used to estimate concentrations in the relevant media based on several factors related to the nature of the site and the chemicals of interest.
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Much effort has been put into developing and validating air dispersion models.68 Similar models are available to track the movement of contaminants in both surface and ground waters. The fate and transport modeling issue becomes more complex when attempts are made to follow a chemical's movement from air, water, and soils into the food chain and to estimate concentrations in the edible portions of plants and animals.69 Most of the effort in this area involves the use of empirical data (e.g., What does the scientific literature tell us about the quantitative relationships between the concentration of cadmium in soil and its concentration in the edible portions of plants grown in that soil?
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But numerous variations on this basic scenario are possible: one chemical in several products or environmental media, many chemicals in one product or environmental medium, or many chemicals in many environmental media. Even though some exposure situations can be complex and involve multiple chemicals through both direct and indirect pathways, the exposure assessment methods and principles described here can be applied.
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For several reasons, truly accurate prediction of risk is difficult to achieve (see Bernard D Goldstein & Mary Sue Henifin, Reference Guide on Toxicology, in this manual)
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To understand these relationships, pharmacokinetic studies typically are carried out in conjunction with toxicity studies in animals, and their results are used to assess possible toxic risk in humans.75 Pharmacokineticists do not ordinarily characterize themselves as exposure scientists; more often they are toxicologists or pharmacologists. But they are in fact extending the usual work of exposure scientists into the body, and it is here that we see the interface between exposure science and toxicology and epidemiology.
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Currently, we can measure only a few thousand chemicals in the body, a large share of them pharmaceuticals, nutrients, and substances of abuse. Some standards for occupational exposures are expressed as allowable blood or urine concentrations, and their measurement is a useful supplement to air monitoring.76 The environmental chemical that has perhaps received the most attention in this area of exposure science is lead (chemical symbol Pb)
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For a discussion of the routes of exposure to toxic substances, see Bernard D Goldstein & Mary Sue Henifin, Reference Guide on Toxicology, Section III.A, in this manual.
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If the exposure scientist is also an epidemiologist or toxicologist,84 he or she may offer additional testimony on the health risks associated with those exposures or even regarding the question of whether such exposures have actually caused disease. For purposes of this reference guide, it is assumed that questions regarding disease risk and causation are beyond the bounds of exposure science.
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IX. Qualifications of Exposure Scientists Exposure science is not yet a true academic discipline.
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There are currently no certification programs available for exposure scientists, but increasingly exposure science research appears in publications such as Environmental Health Perspectives, Risk Analysis, and the Journal of Exposure Science and Environmental Epidemiology. Certification programs do exist in occupational exposure science.
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, or as unit weight of the chemical per weight or volume of environmental media, such as milligrams per kilogram (mg/kg) or milligrams per cubic meter (mg/m3)
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Reference Manual on Scientific Evidence Table 2. Weight of Chemical per Unit Volume of Medium Water Air mg/L = ppm mg/m3 ≠ ppm µg/L = ppb mg/m3 ≠ ppb ng/L = ppt ng/m3 ≠ ppt 542
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From page 543... ...
Testing in 1978 confirmed the presence of toxic chemicals in domestic wells, and by January 1979 all uses of the contaminated well water had been discontinued. Among the chemicals of concern detected in the ground water were benzene, carbon tetrachloride, chlordane, chlorobenzene, chloroform, and several other pesticides or chemicals associated with pesticide production.
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The concentration of carbon tetrachloride in air during showering was calculated assuming that it would quickly reach equilibrium with carbon tetrachloride in the shower water. In Table 3, carbon tetrachloride exposure estimates for the infant and adult are compared with the minimum daily exposure producing liver damage in guinea pigs and the lifetime cumulative exposure producing liver cancer in mice.
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Examples include exposures mediated by cosmetics, other consumer products, some food and beverage additives, medical devices, over-the-counter drugs, and single-medium environmental exposures. dose.
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Often defined as an exposure involving multimedia transport of chemicals from source to exposed individual. Examples include exposures to chemicals deposited onto soils from the air, chemicals released into the ground water beneath a hazardous waste site, or consumption of fruits or vegetables with pesticide residues.
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source. The activity or entity from which the chemical is released for potential human exposure.
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P Lioy, Exposure Science: A View of the Past and Milestones for the Future, 118 Envtl.
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