Quantitative Risk Assessment for Environmental and Occupational Health

William H. Hallenbeck

• Publisher: CRC Press
• Year: 2018
• Print ISBN: 9781315897066
• eBook ISBN: 9781351093064
• Edition: 1
• Topic: Technology & Engineering
• Subtopic: Industrial Engineering
• Index: Technology & Engineering

Many individuals and groups need a usable treatment of the methodology required to assess the human health risks caused by toxicant exposure. This need is shared by industrial hygienists, environmental, occupational and public health professionals, toxicologists, epidemiologists, labor unions, attorneys, regulatory officials, and manufacturers and users of chemicals. The reader needs only a basic knowledge of biology adn algebra in order to utilize the methodology presented. In addition, a basic knowledge of toxicology, epidemiology, and statistics is derisrable for a full understanding of some aspects of risk assessment. Sophisticated computer programs are not required. All the computations can be carried out with a pocked calculator.

CHAPTER 1

Introduction

W. H. Hallenbeck

In recent years, the need to quantify the health risks associated with exposure to environmental and occupational toxicants has generated a new interdisciplinary methodology referred to as risk assessment. For given conditions of exposure, risk assessment (as defined in this volume) provides:

• a characterization of the types of health effects expected

• an estimate of the probability (risk) of occurrence of these health effects

• an estimate of the number of cases with these health effects

• a suggested acceptable concentration of a toxicant in air, water, or food

The outputs of risk assessment are necessary for informed regulatory decisions regarding worker exposures, plant emissions and effluents, ambient air and water exposures, chemical residues in foods, waste disposal sites, consumer products, and naturally occurring contaminants.

Risk assessment and risk management are an integral part of the contemporary regulatory activities of federal (FDA, 1979, 1985a, 1985b; OSHA, 1980, 1983, 1985; USEPA, 1980, 1984, 1985) and state agencies and the industries with which these agencies interact. This book is concerned only with risk assessment. Risk management refers to the selection and implementation of the most appropriate regulatory action based upon the results of risk assessment, available control technology, cost-benifit analysis, acceptable risk, acceptable number of cases, policy analysis, and social and political factors.

The major impetus for conducting risk assessments comes from federal legislation. Since 1972, federal health and safety statutes have adopted a general safety standard of “unreasonable risk” (e.g., Consumer Product Safety Act of 1972, the Federal Environmental Pesticide Control Act of 1972, and the Toxic Substances Control Act. of 1976). These statutes do not contain a definition of the critical phrase “unreasonable risk” (Hutt, 1984). Recently several court decisions have helped to clarify the meaning of “unreasonable risk.” U.S. courts recognize the legal doctrine referred to as de minimus non curat lex, or simply de minimus. This maxim holds that the law does not concern itself with trifling matters and that courts should be reluctant to apply the literal terms of a statute to mandate pointless results (FDA, 1985a). Courts have upheld this principle in their interpretations of the Food Additives Amendment, the Clean Air Act, the PCB provisions in the Toxic Sub-stances Control Act, and the Occupational Safety and Health Act (FDA, 1985a; Hutt, 1984; OSHA, 1985). In its benzene decision, the U.S. Supreme Court indicated when a reasonable person might consider a risk significant (or unreasonable) and take steps to decrease it. The court stated:

It is the Agency’s [OSHA] responsibility to determine in the first instance what it considers to be a “significant” risk. Some risks are plainly acceptable and others are plainly unacceptable. If, for example, the odds are one in a billion that a person will die from cancer by taking a drink of chlorinated water, the risk clearly could not be considered significant. On the other hand, if the odds are one in a thousand that regular inhalation of gasoline vapors that are 2% benzene will be fatal a reasonable person might well consider the risk significant and take appropriate steps to decrease or eliminate it (OSHA, 1985).

Thus, OSHA is using an acceptable working lifetime risk of one in a thousand as a guide in determining permissible exposure levels for carcinogens (OSHA, 1985). In addition to the Supreme Court decision, OSHA is being guided in its determination of significant risk by the lifetime (45 years) work-related death rates for various occupations (OSHA, 1985):

• high-risk occupations (fire fighting and mining/quarrying): 27.45 per 1000 and 20.16 per 1000, respectively

• average-risk occupations (all manufacturing and all service employment): 2.7 per 1000 and 1.62 per 1000, respectively

• low-risk occupations (electrical equipment and retail clothing): 0.48 per 1000 and 0.07 per 1000, respectively

An acceptable risk of 10^–3 is excessive. OSHA’s overall goal should be to reduce the work-related death rates of all occupational sectors to that of the sector with the lowest work-related mortality, i.e., retail clothing at 0.07/1000 = 10^–4. Also, it appears that OSHA is ignoring the additive effects caused by exposure to multiple carcinogens. (Synergistic effects are mentioned in Chapter 4.) For example, if a worker is exposed to 10 carcinogens each of which conveys a risk of 10^–3, the additive risk is 10^–2. Hence, it is recommended that OSHA use an acceptable risk of 10^–5 or less as its goal. Of course, the attainment of this goal is subject to technological feasibility.

The FDA has interpreted several recent court decisions (excluding the benzene decision) to mean that a lifetime risk of one in a million is a de minimus level of cancer risk (i.e., insignificant and therefore acceptable) and is of no public health consequence (FDA, 1985a, 1985b). This level of risk translates into three excess cases per year (10^–6 • 227 • 10⁶/74) in a population of 227 million people with a life expectancy of 74 years. The USEPA also uses an acceptable risk of one in a million (USEPA, 1985). It appears that the FDA and USEPA would permit a lifetime risk of 10^–6 for each contaminant. For example, if the general population has lifetime exposure to 100 carcinogenic chemicals, each of which conveys a lifetime acceptable risk of 10^–6, the additive lifetime risk is 10^–4, not 10^–6. Thus, an acceptable lifetime risk of 10^–6 may not actually be as conservative as intended.

The Nuclear Regulatory Commission (NRC) has proposed higher acceptable lifetime risks than any other federal agency. NRC’s acceptable lifetime risks (due to cancer mortality and serious hereditary effects) are 4 • 10^–2 for occupational exposure and 5 • 10^–3 for general population exposure (NRC, 1986).

Acceptable risks for the general population are frequently compared to the relatively higher lifetime risks of death which exist for many activities in the U.S. (Crouch and Wilson, 1984):

• selected occupational risks range from 0.004 (manufacturing) to 0.04 (mining and quarrying)

• selected accident risks range from 10^–5 (bite/sting) to 0.02 (motor vehicle) and 0.04 (all types of accidents combined)

• selected sports risks range from 10^–4 (ski racing) to 0.04 (parachuting) and 0.2 (professional stunting)

It must be remembered that there is a large component of individual discretion involved in the selection of one’s occupation, sports activities, and living environment (the latter largely controls the probability of non-work related accidents). The presence of a toxicant in community air, water, or food usually constitutes an involuntary risk. It is important to distinguish between voluntary and involuntary risks. Most people would consider that these are two entirely separate classes of risk. People usually assume they are breathing risk-free air, drinking risk-free water, and eating risk-free food. Thus, the level of risk associated with breathing air, drinking water, and eating food is expected by most people to be far less than the risks involved in, for example, a career in mining, or professional stunting, or a sport like parachuting.

Another impetus for conducting risk assessments resulted from President Reagan’s Executive Order 12291 (issued February 19, 1981). This order requires that certain agencies cannot undertake regulatory action unless:

• A need for regulation is adequately demonstrated.

• The potential benefits outweigh the potential costs and adverse effects.

• The most cost-effective and least burdensome approach is established (Zentner, 1984).

Thus, it can be appreciated that many individuals and groups need a usable treatment of the methodology required to assess the human health risks caused by toxicant exposure. This need is shared by industrial hygienists, environmental, occupational and public health professionals, toxicologists, epidemiologists, labor unions, attorneys, regulatory officials, and manufacturers and users of chemicals. Most interested parties do not have the expertise to evaluate risk(s) due to toxicant exposure. Furthermore, many of the published treatments of risk assessment are confusing due to impenetrable mathematics. This leaves interested parties suspicious of each other and with no recourse except to let the “experts” arrive at some acceptable level of exposure for the general population and/or workers. There is no justification for basing public policy on obscure methodology.

This book is designed to be readable and useful to those who need to assess the human health consequences of toxicant exposure. It will be especially valuable to those involved in the process of establishing acceptable concentrations of contaminants in air, water, and food. In order to reduce controversy and broaden the utilization of this work, every effort has been made to blend the overriding need to protect public and worker health with the need to use consensus-oriented methodologies.

A basic knowledge of biology and algebra is needed in order to utilize the methodology presented. In addition, a basic knowledge of toxicology, epidemiology, and statistics is desirable for a full understanding of some aspects of risk assessment. Sophisticated computer programs are not required. All the computations can be carried out with a pocket calculator.

1.1 CONTENTS

The chapters of this book are ordered in the same sequence of steps as one would use in performing an actual risk assessment: characterization of the exposure of a risk group, evaluation of experimental studies, calculation of risks and cases, and calculation of an acceptable concentration. “Risk group” refers to the actual or hypothetical exposed group for whom the risk assessment is being conducted. This group is composed of members of the general population and/or workers. “Experimental studies” refers to experimental animal or human epidemiology studies used to assess the significance of the risk group exposure.

Exposure characterization (Chapter 2) involves the definition of the chemical and physical properties of the toxicant, the routes of exposure, the environmental fate, the conditions of exposure (concentration and duration), and the nature of the risk group (age distribution, sex, size, and location). It is especially important to determine the exposure conditions of the risk group so that the most pertinent experimental studies can be selected for risk assessment. One of the primary goals of risk assessment is to match risk group and experimental group dose ranges in order to obviate the need to extrapolate beyond the experimental dose range. The health effects associated with exposure of any duration, up to and including lifetime, can be assessed.

The qualitative and quantitative evaluation of human and animal studies (Chapters 3 and 4) involves the weighing of many aspects of experimental studies. Many important concepts are presented in Chapter 3. Among the most important is the distinction between classes of toxicants which are known or assumed to have a threshold of response (sometimes referred to as nonzero threshold toxicants) and classes of toxicants which are known or assumed to have no threshold of response (sometimes referred to as zero threshold toxicants). A threshold toxicant is known or assumed to have no adverse effects below a certain dose; a nonthreshold toxicant is known or assumed to incur some risk of adverse response at all doses above zero.

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Table of contents

• Cover
• Half Title
• Title Page
• Copyright Page
• Dedication
• Preface
• Acknowledgments
• Table of Contents
• 1.0 Introduction
• 2.0 Exposure Characterization
• 3.0 Qualitative Evaluation of Human and Animal Studies
• 4.0 Quantitative Evaluation of Human and Animal Studies
• 5.0 Risk Analysis
• 6.0 Acceptable Concentrations
• 7.0 Example: Environmental and Occupational Exposure to a Hypothetical Industrial Toxicant
• 8.0 Example: Environmental Exposure to a Natural Toxicant, Radon-222 and Its Daughters
• References
• Appendices
• Index