Environmental Toxicants

Human Exposures and Their Health Effects

Morton Lippmann, George D. Leikauf, Morton Lippmann, George D. Leikauf

• Publisher: Wiley
• Year: 2020
• ISBN:
  9781119438915
• Edition: 4
• Topic: Medicine
• Subtopic: Occupational & Industrial Medicine

An Updated Reference on Human Exposure to Environmental Toxicants and A Study of Their Impact on Public Health

With the 4th edition of Environmental Toxicants: Human Exposures and Their Health Effects, readers have access to up-to-date information on the study and science of environmental toxicology and public health worldwide. Practitioners and professionals can use this resource to understand newly discovered information on the adverse health effects of toxins and pollutants in air, water, and occupational and environmental environments on large human populations.

The 4th edition of this book is updated to reflect new knowledge and research on:

? Performing risk assessments on exposed individuals

? Assessing the effects of toxicants and substances on large populations for health and medical professionals

? Patterns of human exposure to select chemical toxicants

? World Trade Center dust, agents for chemical terrorism, and nanoparticles

For health professionals, including health authorities, public health officials, physicians, and industrial managers, who are seeking new research and techniques for managing environmental substances, this invaluable reference will guide you through in a thorough, easy- to-read manner.

1
INTRODUCTION AND BACKGROUND

Morton Lippmann and George D. Leikauf

This book identifies and critically reviews current knowledge on the health effects of human exposure to selected chemical agents and physical factors in the ambient environment. It provides a state‐of‐the‐art knowledge base essential for risk assessment for exposed individuals and populations to guide public health authorities, primary care physicians, and industrial managers having to deal with the consequences of environmental exposure.

Aside from professionals in public health, medicine, and industry who may use this book to guide their management functions, the volume can also be used in graduate and postdoctoral training programs in universities and by toxicologists, clinicians, and epidemiologists in research as a resource for the preparation of research proposals and scientific papers.

The subject is focused on those environmental toxicants, that is, chemical or physical agents released into the general environment that produce adverse health effects among large numbers of people. Such effects are usually subclinical, except when cumulative changes lead to chronic effects after long exposure. Short‐term responses following acute exposures are often manifest as transient alterations in physiological function that may, in some sensitive members of the population, be of sufficient magnitude to be considered adverse. Each of the specific topic chapters has a thorough discussion of the extent of human exposure as well as of toxic responses. The four chapters on the uses of the data for risk assessment, risk management, clinical applications, and industrial operations provide guidance for those performing individual and/or collective population hazard evaluations. The first provides individuals and public agency personnel with a basis for decisions on risk avoidance and relative risk assessment. The second outlines the operational philosophies and techniques used by environmental engineers in scoping and managing environmental risks. The third enables the primary care physician to recognize diseases and symptoms associated with exposures to environmental toxicants and to provide counsel to patients. The fourth assists decision makers in industry in evaluating the potential impacts of their plant operations and products on public health.

Although many books provide brief reviews of hundreds of chemicals encountered in the work environment at levels that can cause demonstrable health effects, both acute and chronic, they contain relatively little information on the effects of low‐level exposures on large populations of primary interest in environmental health and risk assessment. This book is designed to provide in‐depth, critical reviews of the environmental toxicants of contemporary public health concern.

1.1 CHARACTERIZATION OF CHEMICAL CONTAMINANTS

1.1.1 Concentration Units

In environmental science, confusion often arises from the use of the same or similar sounding terms having different meanings in different contexts. This is especially true in describing the concentrations of water or air contaminants. For water contaminants, solutes are expressed frequently in parts per million (ppm) or parts per billion (ppb). However, when used for air contaminants, the units are molar or volume fractions, whereas when used for water contaminants, they are weight fractions. This problem can be avoided by expressing all water contaminant concentrations as the weight of contaminant per unit volume (e.g., m³ or L) of fluid. In air, the units generally used are mg/m³ or μg/m³, whereas in water they are most often mg/L or μg/L.

1.1.2 Air Contaminants

At normal ambient temperatures and pressures, chemical contaminants are dispersed in air in gaseous, liquid, or solid forms. The latter two represent suspensions of particles in air and were given the generic term “aerosols” by Gibbs (1924) based on analogy to the term “hydrosol,” used to describe disperse systems in water. On the contrary, gases and vapors, which are present as discrete molecules, form true solutions in air. Particles consisting of moderate‐ to high‐vapor‐pressure materials tend to evaporate rapidly, since those small enough to remain suspended in air for more than a few minutes (i.e., those smaller than about 10 μm) have large surface‐to‐volume ratios. Some materials with relatively low vapor pressures can have appreciable fractions in both vapor and aerosol forms simultaneously.

1.1.2.1 Gases and Vapors

Once dispersed in air, contaminant gases and vapors generally form mixtures so dilute that their physical properties, such as density, viscosity, enthalpy, and so on, are indistinguishable from those of clean air. Such mixtures may be considered to follow ideal gas law relationships. Vapors are not practically difference than gases, except that vapors are generally considered the gaseous phase of a substance that is normally a solid or liquid at room temperature. While dispersed in the air, all molecules of a given compound are essentially equivalent in their size and probabilities of contact with ambient surfaces, respiratory tract surfaces, and contaminant collectors or samplers.

1.1.2.2 Aerosols

Aerosols, being dispersions of solid or liquid particles in air, have the very significant additional variable of particle size. Size affects particle motion and, hence, the probabilities for physical phenomena such as coagulation, dispersion, sedimentation, impaction onto surfaces, interfacial phenomena, and light‐scattering properties. It is not possible to characterize fully a given particle by a single size parameter. For example, a particle's aerodynamic properties depend on density and shape as well as linear dimensions, and the effective size for light scattering is dependent on refractive index and shape.

FIGURE 1.1 Particle size distribution data. (a) Plotted on linear coordinates. (b) Plotted on a logarithmic size scale. (c) In practice, logarithmic probability coordinates are used to display the percentage of particles less than a specific size versus that size. The geometric standard deviation (s_g) of the distribution is equal to the 84.1% size/50% size.

In some special cases, all of the particles are essentially the same in size. Such aerosols are considered monodisperse. Examples are natural pollens and some laboratory‐generated aerosols. More typically, aerosols are composed of particles of many different sizes and hence are called heterodisperse or polydisperse. Different aerosols have different degrees of size dispersion. Therefore, it is necessary to specify at least two parameters in characterizing aerosol size: a measure of central tendency, that is, the mean or median diameter, and a measure of dispersion, that is, the arithmetic or geometric standard deviation.

Particles generated by a single source or process generally have diameters following a lognormal distribution; that is, the logarithms of their individual diameters have a Gaussian distribution. In this case, the measure of dispersion is the geometric standard deviation, which is the ratio of the 84.16 percentile size to the 50th percentile size (Fig. 1.1c). When more than one source of particles is significant, the resulting mixed aerosol will usually not follow a single lognormal distribution, and it may be necessary to describe it by the sum of several distributions.

1.1.3 Particle Characteristics

Many properties of particles, other than their linear size, can greatly influence their airborne behavior and their effects on the environment and health. These include the following:

• Surface: For spherical particles, the surface area (A) varies as the square of the radius (r...