Chapter 16 Indoor Environmental Quality and Health

John B. Sullivan, Jr., MD, MBA, Mark D. Van Ert, PhD, CIH, Gary R. Krieger, MD, MPH, Michael E. Peterson, DVM, MS

Of the 71 million employees that work indoors in the United States, the Bureau of Statistics estimates that more than 21 million are exposed to some degree of poor indoor air quality.¹ The Occupational Safety and Health Administration (OSHA) estimates that 69,000 persons reporting severe headaches and 105,000 persons reporting respiratory problems in the workplace may be suffering from poor indoor environmental quality.¹ Similar environmental quality problems exist in homes, possibly at a more severe degree, since no regulatory agency monitors indoor home environments. The impact of these indoor home conditions on the companion small animal population is unknown. However, it is reasonable to hypothesize that the impact may be greater in that group than in their human counterparts, particularly in view of the fact that many animals never leave the indoor environment in which they live and in certain instances may come into closer contact with specific sources, such as contaminated carpeting or pesticides.

The goal of this chapter is to familiarize the veterinary practitioner with the conditions and issues involved in indoor environmental quality problems. The magnitude of the problem in human medicine has not yet been fully elucidated, and the field has been practically unaddressed by the veterinary community. It is hoped that information shared in this chapter may begin to define a possible problem that the veterinary practitioner may consider in patients with nebulous clinical signs. It is not the purpose of this chapter to make the veterinarian an indoor air specialist but only to make him or her conversant in the field. Any attempts to characterize the suspected environmental problem and to remedy the problem should be left to a trained environmental specialist, such as an industrial hygienist.

SOURCES AND CAUSES OF POOR ENVIRONMENTAL QUALITY

Changing energy use strategies in the 1970s resulted in construction of buildings with improved energy efficiency and tighter sealing to prevent energy loss. As a consequence, human health complaints relating to indoor environments began to increase, and the terms tight building syndrome and sick building syndrome (SBS) were adopted to describe this problem. Complaints relating to the environment had previously been attributed to either poor working conditions or psychological factors. It soon became apparent, however, that health complaints could also be attributed to inadequate ventilation, mold overgrowth, lack of fresh air exchange, excess biological and chemical contaminants, and dampness or inadequate dilution of indoor contaminants.¹^–⁹ The phrase poor indoor air quality is used to describe indoor environmental conditions that can result in clinical signs attributable to the buildup of airborne contaminants. However, such illnesses are often multifactorial. Increased incidences of allergic diseases, coughing, wheezing, shortness of breath, asthma, bronchitis, headaches, eye irritation, muscle aches, fever, chills, nausea, vomiting, and diarrhea are reported among children and adults exposed to indoor biological contaminants; these substances encompass a wide array of contaminants and biochemical byproducts.

The World Health Organization (WHO) characterized SBS in 1983. Since then health complaints associated with poor indoor air quality have been classified as either SBS or building-related illness (BRI). This classification, although lacking refinement, serves to categorize this type of illness as traceable or untraceable to a defined cause or source.

The term SBS defines a set of clinical signs and, in humans, symptoms whose origin is uncertain or is related to ill-defined factors in the environment (Box 16-1). Affected individuals experience multiple and sometimes vague health complaints. In such cases, health complaints tend to cease when the individual leaves the site and recur when the individual reenters the site.

The term BRI applies to a definable medical condition that can be traced to a single source and is documented by specific signs consistent with a known disease. Examples include Legionella pneumonia, hypersensitivity pneumonitis caused by organic dusts and bioaerosols, carbon monoxide (CO) poisoning, and allergy-mediated asthma caused by identifiable allergens. The seriousness of BRI became apparent in the infection of 182 members of the American Legion who attended a convention in 1976 in Philadelphia; they were infected with Legionella pneumophila, which resulted in 29 fatalities. Dissemination of this bacteria from contaminated ventilation systems emphasizes the contribution of the multiple factors of humidity, biological growth, and ventilation in the cause of illness.

Vague complaints relating to mucous membrane irritation, respiratory signs, and headache commonly occur in indoor environments.^3,^4,^9,¹⁰ But sources and causes of such health complaints are multiple and can be difficult to identify. Investigations of the sites involved show that deterioration of indoor environmental quality is most often due to problems with airborne contaminants that are chemical, biological, or physical in nature.

A dynamic mixture of chemical, biological, and particulate pollutants arising from a variety of sources circulates in indoor air (Box 16-2). These pollutants are influenced by air movement, ventilation, temperature, and humidity. Most of the chemical sources of indoor contaminants are volatile organic chemicals (VOCs). Analyses of indoor air samples have demonstrated that between 50 and 300 different VOCs can be present at low levels in nonindustrial environments, such as offices, homes, shopping centers, and malls.¹¹^–¹³

Biological sources of indoor pollution include mold, fungus, pollen, spores, bacteria, viruses, and insects, such as dust mites and roaches. Water reservoirs and damp areas provide nutrient sources for the growth of microorganisms. Relatively high levels of humidity and moisture allow biological agents to increase to levels that, when disseminated indoors, can trigger illness and allergies. Reports indicate that indoor dampness and mold growth are associated with increased respiratory illness in adults and children.^5,^7,⁸ High relative humidity also encourages growth of the dust mite population, which can cause allergies and asthma. More attention is being focused on biochemical products of microorganisms as potential causes of indoor-related respiratory illness. These include endotoxin, 1,3-β-glucan, mycotoxins, peptidoglycan, and VOCs emitted from fungi.⁹

Physical factors, the third source of indoor-related illness, include dusts, fibers, particulates, and overall comfort factors, such as ventilation, lighting, temperature, humidity, noise, and vibration. Dust and particulate matter are always present indoors. Each cubic meter of air contains small concentrations of millions of particulates, of which 99% are invisible to the eye.⁹

Energy conservation strategies dating from the 1970s have contributed to declining indoor air quality. Building design and operational changes have focused on decreasing energy consumption to comply with the goal of reducing American dependency on foreign energy sources. But energy-efficient buildings may sacrifice ventilation effectiveness to reduce overall energy costs.¹⁴^–¹⁷ Such efforts may result in better insulated buildings but reduced performance of ventilation systems. The overall result is often inadequate fresh air exchange for building occupants that allows concentration of airborne chemical contaminants and pollutants.

Building materials and furnishings

Products used in construction contain chemicals that can offgas into the indoor environment. Building materials are constantly changing, and new products are entering the market, so it is difficult to keep track of the large variety of volatile chemicals contained in these products. Building products ranging from structural materials to coatings contain chemicals that are emitted indoors.¹¹^–¹³ ¹⁸ Emissions of VOCs from building materials depend on the nature of the material, the chemicals involved, and the location of the material in the structure (Table 16-1). Emission rates can vary from an initial high release in minutes or hours to long-term offgassing that occurs over weeks, months, or even years. Such products include wood, insulation, plastics, sealers, caulking, adhesives, paints, varnishes, waxes, finishes, lacquers, fabrics, and carpets.

Table 16-1 Common Sources of Volatile Organic Chemicals (VOCs)

Source	Volatile Organic Chemicals
*Building Materials*
Plywoods	Formaldehyde, terpenes, methylacetate, n-butanol, tetrachloroethylene, toluene, nonanol, n-undecane, tetradecane, naphthalene, p-dichlorobenzene, xylenes
Polystyrene foam	Styrene, ethylbenzene, aromatics
Rubber-backed nylon carpet	Toluene, benzene, n-decane, 4-phenylcyclohexane
New vinyl flooring	Isoalkanes, methylbenzenes, xylenes, ethylbenzene, toluene, 2-ethylhexanol, formaldehyde
Rubber floor covering	1,1,1-Trichloroethane, styrene, indane, 1,3/1,4-diisopropylbenzene, isodecane, acetophenone
*Solvents and Adhesives*
Solvent-based adhesives	Toluene, styrene, n-decane, n-undecane, cyclohexane, methylcyclopentane, alcohols
Water-based adhesives	Nonane, decane, undecane, octane
Wall/flooring adhesives	Toluene, benzene, ethyl acetate, styrene, ethylbenzene
Sealants	Methylethyl ketone, butyl propionate, 2-butoxyethanol, butanol, benzene, toluene
Wood stains	Nonane, decane, undecane, methyloctane, dimethylnonane, trimethylbenzene
Polyurethane varnish	Nonane, decane, undecane, methylethyl ketone, ethylbenzene, xylene
Solvent-based waxes/detergents	Alkanes, alkenes, terpenes
Water-based waxes/detergents	Alcohols, esters, alkoxy alcohols, terpenes, alcohols/acetates
Deodorizers	Nonane, decane, undecane, ethylheptane, limonene
Liquid cleaners/disinfectants	Limonene, p-cymene, undecane, α-pinene, heptene, decane, nonane, heptane

Wood furnishings purchased for use in homes are rarely solid wood anymore; rather, they may have a wood facing on a product mainly composed of particleboard or plywood. Formaldehyde and other contaminants that are “outgassing” from these products into energy-efficient “tight” homes can result in significantly elevated indoor air exposures.

Furnishings and fabrics can act as “sinks” that absorb airborne chemicals, releasing them slowly back into the indoor environment depending on temperature, humidity, and ventilation. In general, warmer temperatures and higher humidity increase the rate of emission of VOCs.

Human factors

Human activity contributes to indoor contamination by introducing irritating cleaning agents, pesticides, solvents, tobacco smoke, particulates, dust, fibers, mold, and allergens. Humans also shed millions of skin particles and microbes indoors. Cooking and other combustion sources introduce carbon dioxide (CO₂), CO, nitrogen dioxide (NO₂), sulfur dioxide (SO₂), and particulates into indoor air.^19,²⁰ Computers, copiers, fax machines, laser printers, and other office machines emit volatile chemicals and ozone (O₃).

Smokers contribute to the indoor chemical and particulate pollutant load with many of the ingredients of cigarette smoke adsorbing to porous surfaces, such as fabrics and carpeting. Although environmental tobacco smoke (ETS) has previously been considered a nuisance by most nonsmokers, the Environmental Protection Agency (EPA) considers it a substantive risk factor for cancer and heart disease.^21,²² The EPA classifies ETS as a group A carcinogen, meaning that it causes human cancer. Although the EPA’s cancer conclusions are being questioned, ETS remains a prime contributor to cough, shortness of breath, and chest tightness in exposed human asthmatics.²³ ETS also contributes to significant formaldehyde exposure indoors.^24,²⁵

Ventilation system

Up to 50% of cases involving poor indoor air quality can be traced to a ventilation problem.^16,¹⁷ A properly functioning ventilation system provides adequate fresh air and dilutes and removes pollutants. It also balances indoor air quality with comfort. Ventilation is a dominant cost of building maintenance and energy use, and decreasing ventilation is sometimes employed as a cost-saving measure. However, such approaches can lead to the buildup of pollutants indoors. Improperly maintained ventilation systems can also serve as a source of indoor contaminants. Air ducts contaminated with dirt, dust, and moisture can provide sources for microbial growth that may cause illness. The 1976 discovery of legionnaires’ disease in Philadelphia underscores the fact that serious illness and death can result from a contaminated ventilation system.

Breathing produces CO₂ as a byproduct, and its concentration indoors is a useful measure of air freshness. Accumulation of CO₂ concentrations above 800 parts per million (ppm) of air indicates an inadequate fresh air supply and in humans can be associated with health complaints, such as fatigue, headache, lethargy, and general discomfort. The American Society of Heating, Refrigeration and Air-Conditioning Engineers (ASHRAE) recommends that indoor CO₂ concentrations not exceed 1000 ppm.^16,^26,²⁷ However, elevated CO₂ concentrations of more than 800 ppm may signal the buildup of other indoor pollutants caused by their inadequate removal or dilution. Direct reading instruments are available to track CO₂ levels in various environments to ensure that adequate fresh air is available to occupants.

Temperature

Thermal comfort is usually achieved between a temperature range of 68° F to 79° F (20° C to 26° C). Illness caused by airborne chemicals can be exacerbated by higher temperatures.²⁸ Warmer temperatures also enhance chemical emissions from building materials and furnishings. Formaldehyde release from particleboard or other sources increases in warm, humid environments. Copier machines release more volatile chemicals into the air in warmer temperatures. Turning the thermostat down about 5° to 10° can help to alleviate some of the irritant symptoms caused by poor indoor air quality.

Humidity

In humans excessive dampness indoors increases the risk of childhood asthma and other respiratory symptoms.^5,^7,⁸ Relative indoor humidity values more than 60% are associated with overgrowth of fungus and bacteria that can contaminate ventilation systems, carpet, wall spaces, insulation, ceiling tiles, window seals, and other areas of the indoor environment. Humidity below 20% can cause drying of skin and mucous membranes, leading to irritation. High relative humidity increases upper airway moisture, allowing dusts and water-soluble toxic chemicals to dissolve more easily, thus contributing to upper airway irritation, inflammation, and cough. A humidity range of 45% to 50% is recommended by ASHRAE and the EPA.²¹ Properly functioning ventilation systems help to maintain the relative humidity between 20% and 60%.¹⁷