Comparative Environmental Risk Assessment

C. Richard Cothern

• Publisher: CRC Press
• Year: 2018
• Print ISBN: 9781315891705
• eBook ISBN: 9781351087704
• Topic: Technology & Engineering
• Subtopic: Environmental Management
• Index: Technology & Engineering

What data is needed to complete a quantitative risk assessment for environmental and public health? How accurate does a quantitative risk assessment have to be? How confident does a risk assessor need to be when presenting risk estimates to a decision maker? Find out the answers to these questions and more with Comparative Environmental Risk Assessment, the first major commercial publication that describes the current state of the art in comparative environmental risk assessment. This book examines the problems involved in such analyses and offers ideas and thoughts for future development. The book examines major problems in this area and covers all aspects of the environment, including human and ecological health. Comparative Environmental Risk Assessment is an excellent guide for risk assessment experts, environmentalists, regulators, planners, legislators, scientists in industry, instructors, and students.

Quantitative Risk Assessment Problem Areas and Issues

Introduction

Morton Lippmann

Overview

The first two sessions of this symposium addressed the nature of ecological and health risks and how they were addressed and defined. In this session, attention turns to approaches for the quantification of risk, in order to provide a framework for the ranking of risks. A first order of business is to define the risks to be ranked. When they are defined in the manner used by Unfinished Business (UB),¹ i.e., according to EPA’s programmatic and regulatory authorities, then it is virtually impossible to make quantitative distinctions among them. For example, some significant risks, such as environmental exposure to lead, cannot be identified within the list of 31 UB categories. Sources of exposure to lead come under various categories, e.g., criteria air pollutants; indoor air pollutants; drinking water; consumer products; worker exposure; waste sites; etc., along with myriad other chemicals of greater or lesser toxicity and levels. As described in Reducing Risk:²

‘’At this time EPA does not have an effective, consistent way of identifying environmental problems in a manner that neither fragments nor aggregates sources of risk to an extent that renders comparisons untenable. EPA’s current framework of statutory mandates and program structure helps to maintain artificial distinctions among environmental problems, and those distinctions are conducive neither to sound evaluation of relative risk nor to selection of the most effective actions to risk.”

The Science Advisory Board (SAB), in its report Reducing Risk,² concluded that:

‘’Improved methodologies for comparing different human health risks also are needed. A new approach to ranking risks, one that uses a matrix of data on sources, exposures, agents, and endpoints, is needed to help identify specific agents and mixtures for quantitative risk assessments. Risk rankings should be based on risk assessments for specific toxic agents, or definable mixtures of agents, and on the total human exposure to such agents. When possible, risks should be assigned to persons in target or more sensitive populations, as well as to the population as a whole.”

Issues

Among the key issues that need to be addressed are the needs for and purposes of quantitative risk assessments, how quantitative they need to be, and how the risks to be assessed are to be described and addressed.

Needs and Purposes

There are at least three different needs for risk assessments. One is for developers and manufacturers of new chemicals and products. They need risk assessments to help guide decisions about occupational exposures, labeling, and product liability, and have the luxury of dealing with one or, at most, a few chemicals at a time.

A second need is related to regulatory requirements. Legislation may mandate that either manufacturers and/or regulatory agencies conduct risk assessments, and may also require that they be reviewed by governmental personnel and/or advisory bodies. For example, the 1990 Clean Air Act (CAA) amendments mandate risk assessments for 189 “air toxics”. It is difficult to imagine how EPA can effectively address the mandate without an enormous increase in staff and effort. If such an effort was undertaken it might well divert resources that could have achieved a greater risk reduction if committed elsewhere.

A third need is for research planning. The risk assessment framework can be used to identify critical gaps in knowledge as well as summarize available knowledge, and a compilation of critical knowledge gaps can provide valuable input into the research planning process.

Level of Quantitation Needed

For some regulatory purposes, such as premarketing approvals, where large safety factors (orders of magnitude) are applied, relatively large quantitative uncertainties are tolerable. On the other hand, for ubiquitous chemicals of natural as well as anthropogenic origin, such as lead, radon, and ozone, large safety factors cannot be built in, and margins of safety, if they exist, are much less than an order of magnitude. Thus, the level of quantitation needed is dependent on the purposes to which the risk assessment is applied.

Kinds of Risks Addressed

The kinds of risks addressed can be broadly (poorly) defined, as in Unfinished Business, or they can be specific. In the latter case, the specificity can be according to chemical or physical class as recommended by the Science Advisory Board in Reducing Risk for health effects or, alternatively, by the risk to be prevented. The health risks could be by disease category, such as cancer, birth defects, asthmatic attacks, etc. The risks can also be specified by major impacts, such as habitat alteration, species extinction, or global warming, as recommended for ecological effects by the Science Advisory Board in Reducing Risk. When taking the risk to be prevented approach, it is important to explicitly address the contribution made by anthropogenic activity to the change in risk from that unusually present at a baseline level.

Thus, there are many and varied issues that need to be addressed in quantitating risks, and the papers that follow address the concepts and problems in ways that are interesting and innovative. They provide some valuable inputs for a topic of increasing importance in environmental protection.

References

1. U.S. EPA. Unfinished Business: a Comparative Assessment of Environmental Problems. U.S. Environmental Protection Agency, Office of Policy, Planning and Evaluation, Washington, D.C. (1987).

2. Science Advisory Board (SAB): Reducing Risk: Setting Priorities and Strategies for Environmental Protection. SAB-EC-90-021, Science Advisory Board, U.S. EPA, Washington, D.C. 1990).

Chapter 10
Atmospheric Nitrogen Oxides: a Bridesmaid Revisited

John Bachmann

Introduction

The relative risk ranking in both the Environmental Protection Agency’s Unfinished Business study¹ and the Science Advisory Board report, Reducing Risk² placed ambient air pollution among the highest priority environmental problems. The subjective judgments leading to this ranking almost certainly accorded great weight to the risk to public health and the environment from problems such as tropospheric ozone (smog), acid deposition, particulate matter, and airborne toxins. Few, however, would have listed nitrogen oxides as a high-risk, high-priority category of air pollution problems.

Indeed, air pollution control programs have tended to assign a lower priority to nitrogen oxides than to other prevalent air pollutants. The lack of impressive direct effects of nitrogen dioxide, the belief that volatile organic chemical controls were favored for ozone reductions, that sulfur oxides were more important in acidification, the role of nitrates as a beneficial nutrient for crops, and the relative high cost of significant control technology are all partly responsible for the lesser emphasis on nitrogen oxide control. The Clean Air Act Amendments of 1990, for example, call for a 10 million-ton reduction in emissions of sulfur oxides³ and mandate controls that will reduce anthropogenic volatile organic chemicals by an equivalent amount.⁴ Despite being far more aggressive with respect to nitrogen oxides than previous legislation, however, the controls specified in these amendments over the next 20 years would hardly offset projected emissions growth (see below). In loose terms, nitrogen oxide control seems to have been “always a bridesmaid”.

It is only recently that nitrogen oxides or, more broadly, atmospheric nitrogen compounds, have begun to be recognized as a significant contributor to multiple environmental problems.⁵ While past scientific assessments have catalogued potential effects and interactions,⁶ quantitative assessments of combined multiple effects have been lacking. This paper attempts to take an integrated view of nitrogen oxides and related nitrogen compounds, beginning with an overview of the effects associated with nitrogen. The paper also outlines past and projected trends in nitrogen oxide emissions, taking into account the provisions of the Clean Air Act Amendments of 1990, and summarizes some of the key uncertainties that limit our ability to conduct an integrated assessment of cumulative risk and to develop alternative strategies for reducing those risks.

Multiple Environmental Effects

Direct Effects of NO₂

Traditionally, the nitrogen species of concern in air pollution regulations are nitric oxide (NO) and nitrogen dioxide (NO₂).⁶ These are formed and emitted during combustion of fuels. In the atmosphere, NO — the major component in emissions — is oxidized to NO₂, while NO₂ reacts with ozone to form NO. EPA has established a primary (health-based) National Ambient Air Quality Standard for NO₂ of 0.05 ppm (100 μg/m³) annual mean.⁷ Currently, this standard is violated only in the Los Angeles basin.

The NO₂ standard is based on scientific criteria as reviewed and revised through 1985. The major quantitative evidence suggesting the need for this standard comes from studies showing a relationship between NO₂ exposure in homes using natural gas and respiratory symptoms in children.⁸ These and other studies suggest that single or repeated peak exposures of shorter duration are most likely to be responsible for these and other respiratory responses, but several studies raise doubts about the link between significant effects and NO₂ at levels prevalent in most U.S. cities. The most recent standard review found no basis in the direct environmental effects of NO₂ for a tighter secondary or welfare standard to protect vegetation, materials, or other values.⁷

Indirect Effects

By contrast, the indirect effects associated with nitrogen oxides and their transformation products are many and varied. A case can be made that, through atmospheric reactions, NO_x (to which we now add nitrous oxide, N₂O) plays at least a secondary role in all of the most important air pollution problems mentioned in Reducing Risk. A brief qualitative synopsis of the major pollutant/effects categories follows.

Tropospheric Ozone

Ozone and other photochemical oxidants form in the troposphere through reactions of nitrogen oxides and volatile organic compounds (VOCs) in the presence of sunlight and high temperature. On a local/urban scale, increased nitrogen oxides can actually decrease ozone concentrations, but at t...

Table of contents

• Cover
• Half Title
• Title Page
• Copyright Page
• Table of Contents
• Overview
• Ecological Health Risks
• Human Health Risks
• Quantitative Risk Assessment Problem Areas and Issues
• Thoughts for the Future
• Index