Environmental Risk Assessment

A Toxicological Approach

Ted W. Simon

• Publisher: CRC Press
• Year: 2019
• ISBN:
  9781000754377
• Edition: 2
• Topic: Médecine
• Subtopic: Toxicologie

The purpose of risk assessment is to support science-based decisions about how to solve complex societal problems. Indeed, the problems humankind faces in the 21st century have many social, political, and technical complexities. Environmental risk assessment in particular is of increasing importance as health and safety regulations grow and become more complicated.

Environmental Risk Assessment: A Toxicological Approach, 2nd Edition looks at various factors relating to exposure and toxicity, human health, and risk. In addition to the original chapters being updated and expanded upon, four new chapters discuss current software and platforms that have recently been developed and provide examples of risk characterizations and scenarios.

Features:

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• Introduces the science of risk assessment—past, present, and future

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• Provides environmental sampling data for conducting practice risk assessments

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• Considers how bias and conflict of interest affect science-based decisions in the 21st century

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• Includes fully worked examples, case studies, discussion questions, and suggestions for additional reading

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• Discusses new software and computational platforms that have developed since the first edition

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Aimed at the next generation of risk assessors and students who need to know more about developing, conducting, and interpreting risk assessments, the book delivers a comprehensive view of the field, complete with sufficient background to enable readers to probe for themselves the science underlying the key issues in environmental risk.

CHAPTER 1

An Introduction to Risk Assessment with a Nod to History

What a piece of work is a man! how noble in reason! how infinite in faculty! in form and moving how express and admirable! in action how like an Angel!

William Shakespeare, Hamlet, Act II, Scene 2

At the outset of the 21st century, technology and industrialization have provided advantages for much of the world’s population—but technology is a double-edged sword. Twenty-first-century technology affords us many benefits, including advances in medical care and pharmaceutical products, cell phones, microwave ovens, and mass transit—but, as a downside, industrialization creates a legacy of waste and unintended consequences. Humans enjoy the benefits of technology, but must also deal with accompanying and often unforeseen hazards.

The purpose of risk assessment and the underlying science of risk analysis is to support societal decision-making. Risk assessment is the means by which democratic societies attempt to understand the adverse and unintended consequences of technology. Risk management is the use of risk assessment information to control or abate these consequences.

Ideally, both the risk assessment and risk management will be conducted in a way that takes into account the interests of all stakeholders—this is no more than fair! In risk assessment, the central issue embodied in the ideal is how we as a society take into account both the variation in human exposures to environmental hazards or stressors and the variation in human susceptibility to injury or illness.

1.1 Risk Assessment: Does Consistency Achieve the Goal of Fairness?

One way to be fair in risk assessment is consistency. Risk assessment sits at the uneasy interface of science and policy. Almost all decisions about risk assessment methods require considerations of issues in both policy and science. Science is constantly changing, whereas the pace of policy change at times seems glacial in comparison. Tension between the old and the new in the science of risk analysis will always exist. Risk analysis is an applied science useful for decision support of various activities, including exposure to chemicals, medical procedures, finance as well as other human endeavors; risk analysis can also be considered a pure science producing knowledge about means to assess, characterize, communicate, and manage risk.¹

Some risk assessment practitioners have come to see this tension between old and new as a scientific culture war—a battle between those who would preserve the status quo, clinging to old ways for consistency’s sake, and those who heartily embrace new ideas and new information. Since the field of risk assessment began with 17th-century mathematician Blaise Pascal’s development of probability theory to ameliorate his winnings at games of chance,^* there has been tension between those who view the best available science as a new and challenging opportunity and those who view change as an anathema. This conflict between new and old lies at the heart of modern environmental risk assessments. Ralph Waldo Emerson noted that “a foolish consistency is the hobgoblin of little minds.”² Consistency, however, is a way to create the perception of fairness.

If the goal of consistency were achieved by nothing more than using the same default values for exposure and the same toxicity criteria in every environmental risk assessment, then this consistency would indeed be foolish and likely unfair. This makes the job of a risk assessor tough—one must understand not only the science but also the policy goals, and use this knowledge of both in an honest and forthright manner. A commitment to rigorous intellectual honesty in the evaluation of the data and scientific knowledge used in a risk assessment allow one move away from “foolish consistency” while still achieving fairness.

Two types of ethics are at play in risk assessment—ethics of the mind that justifies an action by reference to intention, and ethics of the consequence that justifies an action by reference to the results or consequences. The commitment to intellectual honesty involves the ethics of intention, whereas the actual goal of the risk assessment is clearly associated with the ethics of consequence. Speaking truth regardless of the consequences is an example of the ethics of intention. Philosopher Immanuel Kant’s categorical imperative arises from the decision to act morally, to do good, as a compelling moral obligation. Kant noted that people may perform good deeds for bad reasons (e.g., egotism, attaining social prominence, etc.), and, based on the ethics of intention, the deeds would have no moral worth.³

On the other hand, the ethics of consequence is expressed as utilitarianism that supports material benefit (e.g., money, pleasure, food, survival) as an appropriate end. In Leviathan, Thomas Hobbes opined that utilitarianism requires man to recognize and accede to a sovereign authority. Utilitarianism on an individual level gives every man or woman the right to anything in the world. The resulting conflict would result in lives that are “solitary, poor, nasty, brutish and short.” The social contract underlying a democratic society is based on surrendering individual utilitarianism for that of the larger society.⁴

The ethics of consequence seems the basis of environmental regulation—there is no intrinsic common good in setting a maximum contaminant level in drinking water at a particular level; instead, the common good arises from the protection inherent in the regulation. Often, environmental regulation seeks democratic balance between competing agendas using risk assessment as one of many sources of decision support information. However, many view the risk assessment process as obfuscating, antagonistic to environmental protection, and inimical to stakeholders who lack sufficient expertise. The result is the two types of ethics have become tightly woven in an oft-confusing fashion in the practice of risk analysis.⁵

* Success at poker requires skills in both risk assessment and risk management.

Scientific knowledge is constantly increasing, maybe 5% per year, maybe more.⁶ Changes in policy occur more slowly, thus science will always be ahead of policy. For example, knowledge of the genetic code and the structure of DNA led not only to use of forensic DNA analysis, but also to the growing field of genomics and its use in medicine. Epigenetics is another growing area of biological knowledge that is just beginning to be incorporated in human health risk analysis. Such information is relevant to differences in susceptibility to the health effects of environmental chemicals; to date, most risk assessments have not attempted to incorporate consideration of genomics or epigenetics.

These genomic studies reveal the remarkable ability of humans and other species to modulate gene expression in a subtle and context-dependent way and thus produce biologically appropriate responses to the ever-changing internal and external stimuli living organisms experience.^7,8 A similarly large degree of variation manifests in the range of human behavior and resulting exposure characteristics; this variation is clearly evident in time–activity studies in children.^9–11

Epigenetics refers to potentially heritable alterations in DNA structure, chromosome structure, and modifications of gene/protein expression without a change in the DNA sequence. These changes fall into three broad categories—DNA methylation, histone modifications, and non-coding microRNAs (miRNAs) that alter gene expression and nucleosome positioning.^12,13 Epigenetic regulation can also be influenced by environmental exposures.^14–17 Epigenetic alterations associated with environmental exposures may play a causal role in disease; however, as noted, the use of epigenetic data in risk assessment remains a subject of investigation, and the value of such data has yet to be determined.^13–15

Given the range of human variability, how can one account for this range in the exposure and toxicity assessments in an honest way that is fair to all stakeholders? The amelioration of the scientific knowledge base underpinning risk assessment is inevitable—why would one not want to avail oneself of all this information?

Of course, some risk assessments are better than others, and some risk-based decisions are better than others. As scientists and risk assessment practitioners, we use the tools provided by toxicologists, chemists, statisticians, and others to understand the exposures and effects of environmental stressors and account for human variability in both these aspects. Our efforts inform decision-makers so that they can balance the competing interests of many stakeholders and hold the ideal...