The Concept of Exposure Pattern

When we are predisposed to situations of pollution certain traits or factors in us and the period of time and concentration of the pollutant in question determine our response.

Determination of exposure pattern is a highly technical issue which involve complex processes in which the result varying from one individual to the other.

However, there are certain generally acceptable responses of exposure to specific pollutants. In this unit we are going to learn about the exposure pattern of certain pollutants common to our environment.

The Concept of Exposure Pattern

Because human activities impact the timing, location, and degree of pollutant exposure, they play a key role in explaining exposure variation.

This fact has motivated the collection of activity pattern data for their specific use in exposure assessments.

In the United States (US), the National Human Activity Pattern Survey (NHAPS), a 2-year probability-based telephone survey (n=9386) of exposure-related human activities is an effort towards exposure assessment.

The primary purpose of NHAPS was to provide comprehensive and current exposure information over broad geographical and temporal scales, particularly for use in probabilistic population exposure models.

NHAPS was conducted on a virtually daily basis from late September 1992 through September 1994 by the University of Maryland’s Survey Research Centre using a Computer-Assisted Telephone Interview instrument (CATI) to collect 24-h retrospective diaries and answers to a number of personal and exposure-related questions from each respondent.

The resulting diary records contain beginning and ending times for each distinct combination of location and activity occurring on the diary day (i.e., each microenvironment).

Between 340 and 1713 respondents of all ages were interviewed in each of the 10 EPA regions across the 48 contiguous states. Interviews were completed in 63 per cent of the households contacted.

NHAPS respondents reported spending an average of 87 per cent of their time in enclosed buildings and about six per cent of their time in enclosed vehicles. These proportions are fairly constant across the various regions of the US.

However, the number of people exposed to environmental tobacco smoke (ETS) in California seems to have decreased over the same time period, where exposure is determined by the reported time spent with a smoker. In both California and the entire nation, the most time spent exposed to ETS was reported to take place in residential locations.

National-level exposure assessments are required for major policy decisions. The importance of activity pattern data has increased with the realization that many types of exposure to environmental pollutants occur indoors and stem, in large part, from indoor pollutant sources such as cigarettes.

Read Also: Assessment of Pollutants and Risk Assessment in Public Health

Exposure monitoring studies have demonstrated how people’s locations and activities can explain the variation in exposure to benzene, tetrachloroethylene, and other volatile organic compounds. Human activity data are major inputs to human exposure models.

Sociological Study of Human Activity

The long history of studies on human activities in the sociological literature contains frequent use of the term “time budget” (also known as “zeitbudget” or “budget de temps”). A time budget is conceptually similar to a person’s money budget in that it summarizes the amount of time an individual spends in each of many activities over some time period (e.g., a day or a week).

According to Michelson (1973), a time budget is a record, presented orally or on paper, of what a person has done during the course of a stated period of time. It usually covers a 24- hour day or multiples thereof.

The record is taken down with precision and detail, identifying what people have done with explicit reference to exact amounts of time. It is usually presented chronologically through the day, beginning with the time that a person gets up in the morning.

The information that is normally gathered in a time budget consists of the time an activity began, the time it ended, the nature of the activity per se, the persons who were present and active in the given activities, and, not the least, the exact location where the activity took place.

Read Also: Food Contamination/Pollution and Sources of Food Contamination

Health and Human Activity

As alluded to above, the critical problem with activity pattern studies found in the sociological literature is that they do not include many aspects of daily life that are important for environmental pollution exposure assessment, such as storing chemicals in the home, driving an automobile on crowded highways, living with a smoker, using gas appliances, visiting a dry cleaner, using solvents in the home, or filling a gas tank. Nor do they provide sufficient detail on the locations that people visit.

Using methods similar to those of the social scientists, researchers in the environmental health sciences in the 1980s began to collect activity pattern data as part of exposure and health research. For example, the following studies appeared in the literature of this period.

Exposure Patterns

Air pollution is a significant risk factor for multiple health conditions including respiratory infections, heart disease, and lung cancer, according to the WHO. The health effects caused by air pollution may include difficulty in breathing, wheezing, coughing and aggravation of existing respiratory and cardiac conditions.

These effects can result in increased medication use, increased doctor or emergency room visits, more hospital admissions and premature death. The human health effects of poor air quality are far reaching, but principally affect the body‘s respiratory system and the cardiovascular system.

Individual reactions to air pollutants depend on the type of pollutant a person is exposed to, the degree of exposure, the individual‘s health status and genetics.

Both indoor and outdoor air pollution have caused approximately 3.3 million deaths worldwide. Children aged less than five years that live in developing countries are the most vulnerable population in terms of total deaths attributable to both indoor and outdoor air pollution.

The WHO states that2.4 million people die each year from causes directly attributable to air pollution, with 1.5 million of these deaths attributable to indoor air pollution.

Epidemiological studies suggest that more than 500,000 Americans die each year from cardiopulmonary disease linked to breathing fine particle air pollution.

A study by the University of Birmingham has shown a strong correlation between pneumonia related death and air pollution from motor vehicles. Another study suggests that 310,000 Europeans die from air pollution annually. Causes of death include aggravated asthma, emphysema, lung and heart diseases, and respiratory allergies.

The worst short term civilian pollution crisis in India was the 1984 Bhopal Disaster. Leaked industrial vapors from the Union Carbide factory, belonging to the Union Carbide, Inc., U.S.A., killed more than 25,000 people outright and injured anywhere from 150,000 to 600,000.

The United Kingdom suffered its worst air pollution event when the December 4 Great Smog of 1952 formed over London. In six days more than 4,000 died, and 8,000 more died within the following months. An accidental leak of anthrax spores from a biological warfare laboratory in the former USSR in 1979 near Sverdlovsk is believed to have been the cause hundreds of civilian deaths.

Diesel Exhaust (DE) is a major contributor to combustion derived particulate matter air pollution. A study from around the years 1999 to 2000, by the University of Washington, showed that patients near and around particulate matter air pollution had an increased risk of pulmonary exacerbations and decrease in lung function. Air pollution is also emerging as a risk factor for stroke, particularly in developing countries where pollutant levels are highest.

Respiratory Tract Mode

Pollutants in the air find their way into human body through exposure/inhalation of polluted air. In an industry for example producing asbestos, the fibres of asbestos released into the air are easily inhaled by the exposed workers which might become responsible for asbestosis condition in the exposed worker.

The same exposure pattern goes for gases like carbon monoxide, sulphur and other occupational dusts for example. Indoor pollution by cigarette smokers exposes non-smokers to the dangers of inhaling dangerous air pollutants like tar, nicotine etc.

Respiratory tract exposure is one of most common exposures to pollutants in the air. The exposure patterns exhibit in the form of cough, difficulty in breathing to symptoms like inflamed lungs and cancerous cells in the lungs.

Alimentary Tract Mode

This is by means of ingestion of pollutants and contaminants through the mouth. It happen both through pollutants in the air, water or ingestion of contaminants in food. Toxic gases or solids can be ingested through the mouth.

Read Also: Sources and Types of Water Pollution

Contaminants such as bacteria, viruses and fungi can also be taken into the body through food. Examples include streptococci, staphylococci, salmonella etc. These bacteria may be toxin producing and present as acute gastro-enteritis like staphylococcus food poisoning or infection like salmonella typhi (typhoid fever).

Skin and the Eyes Mode

Essentially what happens is that pollutants are absorbed through the skin by contact. Examples include exposure to solvents, acids and bases. Exposure patterns include contact dermatitis, headache, and nausea and also chronic effects may result into permanent injury to the nervous system.

Exposure to light pollution (excessive lighting) may present as eye irritation, temporary loss of sight or permanent loss of sight depending on the degree of exposure and other individual resistance factors.

Auditory Mode

Noise pollution from machines, engines and heavy traffic affect the auditory system. Exposure to decibels above the tolerable levels has negative impact on human health.

Patterns indicate that exposure to traffic noise could lead to higher risk of having a heart attack. A new study shows a clear relationship between traffic noise and heart attack risk with a 12 per cent higher risk per 10 decibels of noise.

In conclusion, exposure pattern is all about trying to ascertain the outcome of exposure to pollutants determined by complex human disposition based on body resistance, time of exposure, period of exposure and the amount of pollutants involved.