Bioaerosols Handbook

Christopher S. Cox, Christopher M. Wathes, Christopher S. Cox, Christopher M. Wathes

• Publisher: CRC Press
• Year: 2020
• eBook ISBN: 9781000157840
• Edition: 1
• Topic: Biological Sciences
• Subtopic: Environmental Management
• Index: Biological Sciences

This comprehensive handbook provides up-to-date knowledge and practical advice from established authorities in aerosol science. It covers the principles and practices of bioaerosol sampling, descriptions and comparisons of bioaerosol samplers, calibration methods, and assay techniques, with an emphasis on practicalities, such as which sampler to use and where it should be placed. The text also offers critiques concerning handling the samples to provide representative and meaningful assays for their viability, infectivity, and allergenicity. A wide range of microbes-viz., viruses, bacteria, fungi and pollens, and their fragments-are considered from such perspectives.Bioaerosols Handbook is divided into four parts, providing a wide-ranging reference work, as well as a practical guide on how best to sample and assay bioaerosols using current technology.

CHAPTER 1

Editors’ Introduction

Many processes generate bioaerosols of diverse forms ranging from submicron allergens to much larger fungi, pollens, droplet nuclei, and dust rafts. Humans and animals are disseminators, e.g., during sneezing, while acting too as reservoirs and amplifiers. Indoor bioaerosol particles comprise respiratory pathogens, contaminated skin squames, dust mite fragments/faeces, fungal spores, hyphae and products, etc. Residential environments may present more serious risk through infection and allergy than those of lower bioaerosol concentration as occur outdoors. Reduced house ventilation rates may benefit energy conservation but concomitantly result in higher bioaerosol concentrations and risks of associated diseases. Offices, schools, hospitals and industrial workplaces, similarly are contaminated, while practices conducted therein contribute to bioaerosol burdens. Industrial workplaces provide further sources owing to contamination by, and the biological activity of, materials being handled, such as microbial and food allergens/toxins, industrial scale fermentation microbes and products, e.g., insulin. In animal houses, bioaerosols are produced from animals themselves, their foodstuffs, bedding and faeces. Within all buildings, particle diffusion and air currents ensure bioaerosols become distributed throughout and reach the most inaccessible places. But, during this process their biochemical properties (e.g., viability, infectivity, allergenicity) can be modified so that allergenic/immunological properties change and viability declines, while physical parameters such as size and shape alter.

Outdoors many processes cause bioaerosol liberation including air turbulence, spray irrigation, sewage treatment plants, breaking of waves, bursting of bubbles, and crop spraying. The purposeful release of pollen and spores provides a further example. The use and deliberate release of biological pesticides/genetically engineered microorganisms also represent potential hazards both during their application as well as manufacture in industrial fermenters. Our ability to successfully monitor and control any associated leaks seems essential while environmental impacts of these processes through colonization by released microbes, competition with indigenous species and genetic exchange through transformation also may present a hazard. Of concern too, is contamination via bioaerosols of food and pharmaceutical products especially where vaccines are concerned.

Bioaerosol hazards to man primarily arise from exposure to high concentrations or to unfamiliar forms, and comprise respiratory distress, microbial infection, allergenic reaction, respiratory sensitization, and toxicological reaction. Changing patterns of work and leisure have raised risks, while outdoors air pollution (particulate and gaseous) levels generally are increasing. Respiratory hazards, or our awareness of them, show an upsurge, one example being asthma in the UK. The costs to society of bioaerosol hazards are great, e.g., in the USA each year currently there are 250 million episodes of respiratory infection, i.e., 75 million physician visits/year, 150 million days lost from work with medical care costs of ca. $10 billion, plus loss of income of ca. $10 billion. There are too airborne plant and animal diseases, both causing substantial economic losses, e.g., respiratory diseases in pigs, exacerbated by poor air hygiene in animal houses with associated reduced feed efficiency, depressed growth rate and increased veterinary treatment, at an annual estimated cost in the UK of £20 million.

Exposure limits may be set for environments in which bioaerosols are found. In the UK, the Public Health Act (1936) and Control of Pollution Act (1990) are relevant, while in the USA, the Food and Drug Administration (FDA) sets stringent limits on levels of bioaerosols in pharmaceutical industries for example, especially when concerned with vaccine production. But, how are such limits to be monitored? Assessment requires the meaningful collection of representative samples, and their characterization. However, cursory examination of the aerosol literature often leads to confusing and conflicting perspectives on sampler choice, methodology and analytical procedures. In addition, what is the sampling efficiency and very importantly, how are samplers calibrated?

Even when these matters have been settled there are further questions concerning handling the catch to determine biological and physical characteristics, all of which can change in time and space. Microbial bioaerosols present additional special difficulties because of potential conflicts between their efficient sampling as particles and as viable entities. Furthermore, biological effects can be modified/exacerbated by simultaneous inhalation of other particles and/or pollutants, e.g., sulphur and nitrogen oxides.

Clearly, no single sampler/sampling protocol is likely to be adequate for all bioaerosols in their diverse environments. Two alternative strategies have been proposed: (1) a reference sampler (or protocol) can be specified with the advantage of consistency though there will be limitations to any one sampler; (2) performance standards may be set for a particular sampling objective against which alternative samplers (or protocols) can be tested. The latter encourages development of better, generic samplers/sampling procedures though gradual improvements may take time. Ultimately establishing performance standards for bioaerosol samplers/sampling is essential. The UK Department of Trade initiative in this area, as well as the UK Calibration Forum for Aerosol Analysis (NCFAA), are noteworthy.

The main objectives of the “Bioaerosols Handbook” are to provide up-to-date detailed descriptions, comparisons and calibration methods for bioaerosol samplers with appropriate sampling methodologies and analytical procedures. Physical and biological properties are considered from both practical and theoretical viewpoints. The Handbook represents a compilation of relevant, up-to-date knowledge and expertise of leading bioaerosol and aerosol scientists from six different countries in Europe and North America. The authors and editors are aware that there are other texts dealing with aerosols and measurement techniques. However, often these are theoretical and may fail to include essential practicalities of sampling, calibration or sample assay methodologies. This Handbook attempts to deal with the subject of bioaerosols on a broad yet in-depth basis, and provide guidance based on firm physical and biological principles plus practical experience of meaningful catching, assessing and monitoring bioaerosols encountered in many environments.

After two introductory chapters, the Handbook is divided into four parts. Chapters 3, 6 examine the principles of bioaerosol sampling while emphasizing the essential foundations upon which good practice is built. Comprehensive descriptions of modern bioaerosol samplers, including direct reading instruments, are given in Chapters 7, 10: many of the described calibration techniques are common to other aerosols samplers. Bioaerosols may be analyzed chemically, physically, and biologically, and current techniques are described in Chapters 11, 15. Finally, Chapters 16, 21 proffer the varied experiences of current practitioners of the ‘art’ of bioaerosol sampling in the workplace, home, specialized settings, e.g., laboratories and hospitals, and outdoors.

CHAPTER 2

Bioaerosols: Introduction, Retrospect and Prospect

J.M. Hirst¹

THE FOUNDATIONS

‘Bioaerosol’ and the comparable term ‘aerobiology’ are compound words that describe studies relying on the interplay of disciplines primarily physical, chemical and biological. Neither the order of the syllables nor the history of the studies gives any guidance as to the precedence of the living or atmospheric component and attempts to identify which ‘was the chicken and which the egg’ would be fruitless; they must always be interactive and interdependent!

However, studies of how particles enter and travel in air are so characterized by diversity and diffusion that contributors and readers of the Handbook will need to recognize the same boundaries. The specialist will have no difficulty in distinguishing the scientific meaning of the word ‘aerosol’ from that thrust into common parlance by advertisements that lead the public to believe an ‘aerosol’ is the can bought at the chemist or supermarket and used to generate an aerosol of fly-spray, deodorant or the like. Scientists will support the definitions provided by the editors:

An aerosol consists of material finely divided and suspended in air or other gaseous environment, with compositions as varied as matter itself.

A bioaerosol is an aerosol comprising particles of biological origin or activity which may affect living things through infectivity, allergenicity, toxicity, pharmacological or other processes. Particle sizes may range from aerodynamic diameters of ca. 0.5 to 100 μm.

These definitions show how an aerosol can qualify to be a bioaerosol, yet they permit the great flexibility required to accommodate enormous biological diversity and to allow the subject to develop. Thus, life is not essential but the particles must have biological origin or activity. Also, sizing particles by aerodynamic diameter (see page 180) specifies airborne properties but allows the inclusion of great diversity in the dimensions and shape of biological propagules or fragments of organisms or their products formed mechanically

Inflexible definitions could also inhibit inclusion of desirable additions, for example, novel ‘product allergens’ comparable to those in the faeces of the house dust mite, or greater need for simultaneous study of biological and abiotic components that seem synergistic to biological activity.

Among the earliest recorded effects of aerosols and bioaerosols must have been types of occupational pneumoconioses that were mentioned in ancient Greek literature. Understanding grew slowly until the late 17th century when microscopic recognition became a reality. Thereafter study of airborne transmission accelerated, but erratically, for instance when important pathogens were shown to be transmitted by water or vectors rather than by dispersal in air. During the late 19th and 20th centuries the rate of development has become exponential, fostered by scientific progress, increased industrialization, and population growth (differentially causing either wealth or poverty), not to mention the consequences of international trade and conflicts. Later chapters show how all aspects of human activity are affected and exemplify the roles of viruses, bacteria, fungi, algae, plant microspores and many products with biological activity. The roles of many in causing the various plagues that afflict plants, animals and man are justifiably stressed in the Handbook as are the increasing concerns with the contamination of food, pharmaceutical products and effects related to environmental pollution. Currently these are the effects that most attract both interest and support. The hazard list (as exemplified in Chapter 1) is of course prodigious and very costly but judgement will not be balanced unless we also consider what may be receiving less attention than it should; has anything been neglected? In time, science will suffer if it forgets that bioaerosols are probably as beneficial as they are hazardous. Most of the benefits operate so effectively yet so surreptitiously that they are easy to overlook and although the costs of the hazards have to be met and so can usefully be estimated the same would not be possible or useful for the benefits. Nevertheless, life on earth could not survive for long without the re-mineralization of organic matter by the essential organisms of decay, many of which arrive by air. The mosses, ferns, and grasses (and many other plants and trees) could neither reproduce nor spread properly without airborne propagules. Surely not only ‘green ecologists’ should be concerned that there is so little attention (other than in polar regions) to the colonization of barren or environmentally altered substrates or in spreading genetic diversity (existing or engineered) through existing populations.

The real work of the Handbook begins in Chapters 3, 6, each of which helps set the rules for studying bioaerosols and together they provide firm foundations, based on the wealth of knowledge and methods of aerosol science for understanding how particles behave in air and the ‘ideals’ of sampling. Some of these chapters may not be bed-time reading for biologists but they must persevere with the study because it is worth repeating that only thus can they build a better understanding of the proven behavior of particles in air. These chapters provide vital clues (if not always prescriptions) as to how physical principles may be applied to generate or to capture airborne particles. They not only explain the great diversity of forces that may operate but also how important it is to understand which may operate, when and on what. For example, even Brownian movement is shown to be important on sub-micron particles within the strict confines of the alveoli of the lungs. More familiar will be roles of gravitational settling, eddy diffusion, inertial impaction, filtration and other processes, here described separately but usually variously interacting in experimental conditions and during sampling both within buildings and in outdoor weather.

Gradually, but sometimes a bit erratically, principle gives way to practice with the introduction of less idealistic conditions. It is probably helpful and certainly realistic that this transfer cannot be seamless. Complex interactions between physical factors affecting sampling and deposition often make the path difficult to follow as complications of weather, topography and vegetation are introduced as modifiers of both liberation and deposition, and how samplers should be designed to try to match these circumstances. Consideration of how to attempt to bring some ordered measurement to the complexity of composite bioaerosols illustrates how difficult this process is, yet how necessary where total aerosol content may be important. The introduction of the concept of ‘dispersal unit’ raises the problem of when and what is the effective unit to estimate. When is one particle sufficient, or may a clump be required for effect or infection? How much are clumps fragmented on capture? When and in what circumstances is number most important? When should it be replaced by mass, surface area or other parameters from among those now often so much easier to measure electronically? Fortunately, perhaps, biological requirements can often be more precisely defined by selective trapping methods or catch treatment allowing cultural or visual identification. These chapters foreshadow some of the myriad complications inevitable with living things, for example, the difficulty of measuring effects of dispersal and the stresses of capture on viability, which form essential knowledge to many investigations but are of no consequence to others.

It is inescapable that the Bioaerosols Handbook, having stressed the importance of aerosol science, must gradually confront the no less difficult problems posed by the biotic components. Biologists must realize that the innumerable further complexities their target organisms will present in bioaerosol studies can only, as a last resort, justify any departure from the principles of good sampling. However, I fear that later chapters will confirm that in reality such ‘last resorts’ are all too common. It would also be wise for biologists to recall how often history has shown that methods first used in biology and medicine were later replaced by more capable and accurate instruments borrowed or developed from work by physicists, chemists or engineers engaged in industry, military studies, aerodynamics or meteorology. This is a point in the Handbook and in research where both biologists and physicists need, yet again, to remind themselves that their disciplines must interact and be interdependent. Success depends on both groups of discipline generating a common language and understanding of mutual aims and problems. Even when this is achieved the battle may not be won without joint attention to the problems and design of experimental sampling and of manufacture. Practitioners studying bioaerosols are often remarkably dependent on anecdotal episodes and on which instruments are available. Nevertheless, experiments should be designed to permit statistical analysis whenever possible. Also some teams need to forge close cooperative links with manufacturers jointly to develop and market convenient, reliable, robust, but accurate samplers that are well matched to biological techniques yet suited to use in laboratories, factories, forests, crops, poultry houses or patients’ homes.

THE TOOLS OF THE TRADE

The diversity of particles, of aims and techniques involved in sampling bioaerosols ensures that there never will be one perfect, all-purpose sampler. That allows no excuse to abandon attempts to get as close as possible. The initial chapters indicated the enormous range of particle sizes and showed how differently their behavior is affected by the many forces active and the prevailing environment.

Chapters 7, 10 examine how that information has been or could be used for sampling and measurement. Freely exposed surface samplers are often much more complex in action than their simple structure suggests. For those who seek it there is information to guide when and for what purposes they may reliably be used. Suction samplers are as difficult to calibrate; the first hurdle is to collect a known volume of the aerosol containing a representative sample of all airborne particles. By sampling uniform spherical mono-dispersed particles isokinetically in laminar air flow this perfection can be approached and there are many specialized circumstances for which it can and must remain the aim. However, in practice assorted shapes, sizes, densities, turbulent flow and gustiness create many problems, especially when suspected interactions between aerosol components seem increasingly to demand the simultaneous measurement of all. Wide ranges of size, shape and density make this difficult enough but when, in bioaerosols, they defy recognition unless grown, need to be measured over months or years, or are rele...

Table of contents

• Cover
• Title Page
• Copyright Page
• Acknowledgments
• About the Editors
• About the Authors
• Table of Contents
• Chapter 1 Editor’s Introduction
• Chapter 2 Bioaerosols: Introduction, Retrospect and Prospect
• Chapter 3 Physical Aspects of Bioaerosol Particles
• Chapter 4 Physical Aspects of Bioaerosol Sampling and Deposition
• Chapter 5 Bioaerosol Particle Statistics
• Chapter 6 Stability of Airborne Microbes and Allergens
• Chapter 7 Aerosol Generation for Instrument Calibration
• Chapter 8 Particle Size Analyzers: Practical Procedures and Laboratory Techniques
• Chapter 9 Inertial Samplers: Biological Perspectives
• Chapter 10 Non-Inertial Samplers: Biological Perspectives
• Chapter 11 Modern Microscopic Methods of Bioaerosol Analysis
• Chapter 12 Chemical Analysis of Bioaerosols
• Chapter 13 Biological and Biochemical Analysis of Bacteria and Viruses
• Chapter 14 Biological Analysis of Fungi and Associated Molds
• Chapter 15 Aerobiology of Pollen and Pollen Antigens
• Chapter 16 Outdoor Air Sampling Techniques
• Chapter 17 Safety Cabinets, Fume Cupboards and Other Containment Systems
• Chapter 18 Problem Buildings, Laboratories and Hospitals
• Chapter 19 Industrial Workplaces
• Chapter 20 Bioaerosols in Animal Houses
• Chapter 21 Bioaerosols in the Residential Environment
• Index