Indoor environmental quality and health (Proceedings)

*these proceedings used with permission from Western Veterinary Conference 2007.

The Occupational Safety and Health Administration (OSHA) estimates that 69,000 people reporting severe headaches and 105,000 people reporting respiratory problems in the workplace may be suffering from poor indoor environmental quality. Similar environmental quality problems exist in homes, possibly at a more severe degree. The impact of these indoor home conditions on the small companion 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 may come into closer contact with specific sources such as contaminated carpeting or pesticides.

The goal of this lecture 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.

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 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 biologic and chemical contaminants, and dampness or inadequate dilution of indoor contaminants. 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 biologic contaminants; these substances encompass a wide array of contaminants and biochemical byproducts.

A dynamic mixture of chemical, biologic, and particulate pollutants arising from a variety of sources circulates in indoor air. 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 volatile organic chemicals can be present at low levels in nonindustrial environments such as offices, homes, shopping centers, and malls.

Biologic sources of indoor pollution include mold, fungus, pollen, spores, bacteria, viruses, and insects, such as dust mites and roaches. Relatively high levels of humidity and moisture allow biologic agents to increase to levels that, when disseminated indoors, can trigger illness and allergies. 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-beta-glucan, mycotoxins, peptidoglycan, and volatile organic chemicals emitted from fungi.

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.

Building Materials and Furnishings

Products used in construction contain chemicals that can off gas into the indoor environment. Emissions of volatile organic chemicals from building materials depend on the nature of the material, the chemicals involved, and the location of the material in the structure. Such products include wood, insulation, plastics, sealers, caulking, adhesives, paints, varnishes, waxes, finishes, lacquers, fabrics, and carpets.

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 volatile organic chemicals.

Ventilation System

Up to 50% of cases involving poor indoor air quality can be traced to a ventilation problem. 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. 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.

Breathing produces carbon dioxide (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 for Heating, Refrigeration and Air-Conditioning Engineers (ASHRAE) recommends that indoor CO2 concentrations not exceed 1000 ppm. However, elevated CO2 concentrations of over 800 ppm may signal the buildup of other indoor pollutants due to their inadequate removal or dilution.

Temperature

Thermal comfort is usually achieved between a temperature range of 68° to 79° Fahrenheit (20°–26° Centigrade). Illness caused by airborne chemicals can be exacerbated by higher temperatures. Warmer temperatures enhance chemical emissions from building materials and furnishings.

Humidity

In humans, excessive dampness indoors increases the risk of childhood asthma and other respiratory symptoms. Relative indoor humidity values over 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.

Biologic Mechanisms Of Indoor Environment-Related Illness

Pollutants, thermal comfort, humidity, adequacy of ventilation, and air movement play interacting roles in the quality of home environments. Establishing a cause-effect relationship between the indoor environment and illness is often difficult because of the numerous variables involved. However; there are patterns of illness that can be correlated with environmental clues. Poor indoor environmental quality should at least be considered if typical clinical signs occur in a site characterized by one or more of the following: presence of chemical odors, recent remodeling, newly constructed building, presence of moisture or water damage, heavy use of cleaning agents, indoor combustion sources, mold contamination and discoloration of walls and ceilings, musty or stale odors, excess dust or particulates on walls or other surfaces, new carpet odors, and office machines in unventilated areas or in direct sunlight.

Affected persons or animals show improvement of signs when they are away from the suspected indoor environment and recurrence of signs when they return. In humans the duration of exposure seems to be important in determining how quickly symptoms resolve in anecdotal cases. The longer the exposure, the slower the resolution of symptoms. The search for biologic models to explain the causes of these signs and symptoms has focused on the following mechanisms: inflammation involving upper and lower airways, mucous membrane irritancy, neurobehavioral and neurologic effects of volatile organic chemicals, allergic reactions and hypersensitivity to chemicals and biologic agents, stress and psychological reactions, infections, and effects of chemicals and biologic toxins on the immune system.

Xenobiotic-Induced Inflammation And Immune Responses

A xenobiotic is any substance foreign to the body. Xenobiotics include chemicals, infectious agents, bioaerosols, dusts, and other agents such as proteins and allergens to which the body responds. Host defense against airborne toxins, low molecular weight chemicals, and allergens includes nonspecific (passive) and specific (immune-mediated) defenses. Once the passive airway defense barriers are breached by a chemical or allergen, subsequent respiratory defense is either immune-mediated or nonimmune-mediated, or a combination of these.

Irritation and Pungency Caused By Airborne Contaminants

Airborne contaminants include particulates, bioaerosols or chemicals, and respirable airborne particles of 10 μm in diameter or less that can penetrate the airways. Detection of airborne chemicals and particulates by the nasal passages and upper airways involves the common chemical senses (CCS), a specialized network of nerves emanating from the trigeminal nerve with endings located in the face, eyes, and nasal passages. Activation of these chemical sensory pathways by airborne hazards serves to warn of danger by producing an irritancy reaction. If this CCS interaction with irritants is unregulated or if a constant activation occurs, inflammation can result.

The CCS responds quantitatively and qualitatively to stimulation by chemical vapors and airborne particulates. Small changes in molecular structure among volatile organic chemicals lead to large differences in chemical potencies. It may be significant that small companion animals have relatively larger nasal surface areas and therefore an increase in the size of the CCS apparatus.

Volatile organic chemicals and low molecular weight chemicals can activate the CCS nerve receptors by either physical or chemical reactions. Those that bind chemically produce a more potent reaction. Examples of such chemicals are formaldehyde, acrolein, chlorine, ozone, sulfur dioxide, and aldehydes.

The nerves of the CCS release neuropeptides in response to environmental irritants. This type of inflammatory response is termed neurogenic inflammation. Neuropeptides (also called neurokinins) are found in nerve fibers of the nose, dental pulp, and eyes and can be released by lung tissue. Therefore, volatile chemicals can produce irritant effects and release inflammatory neuropeptides at nerve sites in various locations in the body and throughout the nasal mucosa, lungs, and other sites that store such mediators. Neuropeptide release results in a cascade of events leading to more inflammation, swelling, pain, and release of other inflammatory mediators from tissues, amplifying the effects and producing clinical signs. Desensitization of these sensory nerves may also occur, causing the irritation response to fade. No single predictor dictates which response may occur in a given individual.

Respiratory Irritation, Bronchial Hyperresponsiveness, and Asthma

The lungs also respond to airborne chemicals and hazards through inflammation. The surface epithelial cell layer of the lungs forms a physical barrier against inhaled toxins and hazards. Besides epithelial cells that can release cytokines and other mediators of inflammation, nerve endings can be stimulated by irritants to cause bronchoconstriction. If the cell layer lining the airway is damaged by an inhaled hazard, nerve endings can react by constricting the airway. This reaction may result from a high-level acute exposure or chronic low-level exposure. Also, pulmonary macrophages and epithelial cells release mediators in response to stimuli by irritants, causing an inflammatory cascade resulting in an acute or chronic response.

The term reactive airways or nonspecific bronchial hyperresponsiveness is used to describe nonimmune-mediated asthma caused by inhaled respiratory irritants. Once an individual has developed reactive airways, exposure to chemically unrelated airborne irritants may trigger the onset of symptoms through inflammation. Signs of respiratory irritation occur quickly following such an exposure with coughing, chest tightness, and a burning sensation in the throat. Another inflammatory syndrome in humans of a nonallergic nature attributed to airborne pollutants is reactive upper airways dysfunction (RUDS). This syndrome is manifested by signs and symptoms of rhinitis (runny nose), nasal stuffiness, eye burning, sinus congestion, facial pain, and severe headache almost of a migraine nature.

Irritant Vocal Cord Dysfunction

Irritant vocal cord dysfunction (IVCD) is a newly recognized human medical disorder that is often misdiagnosed as asthma. Cases of irritant vocal cord dysfunction have occurred following acute high-level occupational or environmental exposures. Vocal cord dysfunction is a disorder of the larynx in which the vocal cords adduct inappropriately during inspiration or expiration. Signs and symptoms of irritant vocal cord dysfunction include wheezing, cough, shortness of breath, throat tightness, and chest pain. The abnormality can occur during inspiration or expiration or in both phases of the respiratory cycle.

Indoor Pollutants

Chemical Emissions From Office Products

Chemical Emissions From Building Materials

New Carpet

Cleaning Agents and Disinfectants

Indoor Combustion Sources

Formaldehyde

Environmental Tobacco Smoke

Nitrogen Oxides

Sulfur Dioxide (SO2)

Ozone

Biology Of The Indoor Environment

Biologic contamination of the indoor environment has increasingly become a major focus of indoor environmental quality investigations. Biologic contaminants are complex mixtures of microorganisms and particulates that may circulate indoors as bioaerosols or contaminate moisture-damaged areas. Biologic contaminants consist of one or a combination of the following: bacteria, fungi, spores, hyphal elements, viruses, amoebae, insects, dust mites, insect droppings, plant particles, pollens, chemical byproducts of microorganisms (beta-glucan, enzymes, ergosterol, mycotoxins), and animal proteins.

Evaluating Indoor Environment-Related Health Problems

Evaluation of indoor environmental quality-related illness requires a systematic approach because of the complexity of the potential causes. The objectives of the investigation are to gather information about the building, identify the signs and symptoms of those with health complaints, locate and identify potential causes, determine the work-relatedness of any illness, and remedy the cause by removing or isolating the source. For these reasons a qualified environmental specialist such as a trained industrial hygienist should be used to evaluate the indoor environment.