Air Pollution And Human Health

TOXIC AIR POLLUTANTS

2.0 Toxic Air Pollutants

The air we breathe can become contaminated with pollutants viz. sulphur dioxide (SO2), nitrogen dioxide (NO2), carbon monoxide (CO), ozone (O3) and particulate matter from various natural and man made sources. In recent years, the focus of ambient air quality largely includes not only criteria air pollutants, but also other toxic air pollutants. Toxic air pollutants are also referred to as air toxics or hazardous air pollutants (HAP's) and are defined as those pollutants that are suspected of causing various diseases and other serious conditions such as reproductive effects or birth defects.

Toxic air pollutants may exist as particulate matter or aerosols. Examples of gaseous toxic air pollutants include benzene, toluene and xylene (BTX) which are found in gasoline. Air toxics typically associated with particulate matter include heavy metals such as chromium, cadmium, mercury and lead compounds; polycyclic aromatic hydrocarbons (PAHs), which are generally emitted from the combustion of wastes and fossil fuels.

2.1 Effects of Toxic Air Pollutants

The emission of toxic pollutants into the air has serious effects to human health and environment. Human exposure to these pollutants can include both short term (acute) and long term (chronic) effects. Many factors can dictate the nature and extent of impacts, including quantity, duration and frequency of the exposure, toxicity level of the pollutant , the person’s overall health and level of resistance or susceptibility. Short-term exposures can include effects such as eye irritation, nausea or difficulty in breathing. In addition, toxic air pollutants can have indirect effects on human health through deposition onto soil or into the nearby lakes and streams potentially affecting ecological systems and eventually human health through consumption of contaminated food.

Table 2 Community Sources of Specific Air Toxics

Toxic Air Pollutant

Major Sources

Benzene

Driving and personal activities associated with vehicles, pumping gasoline, direct and indirect tobacco exposure, lawn mowers and other small household combustion engines, household solvents and cleaners.

1,3 - Butadiene

Proximity to industrial sites and gasoline vapour

Formaldehyde

Combustion of hydrocarbons from incinerators and vehicle exhaust.

Tetrachloroethylene

Waste disposal sites and dry cleaning establishments.

Polychlorinated dibenzodioxins and polychlorinated dibenzofurans

(PCDD and PCDF)

Industrial sources (chemical synthesis and processing, manufacture of pesticides). Combustion sources (incineration of municipal and hazardous waste, sewage sludge, hospital waste, metal reclamation), diffused sources (automobile exhaust, private home heating, cigarettes, accidental fires, waste sites, dry cleaners and cigarette smoke.

Polycyclic aromatic compounds

Biomass combustion, internal combustion engines, municipal solid waste incineration and cigarette smoke.

Mutagenic heterocyclic amines

Diesel exhaust particles, cigarette smoke, cooking fumes, sewage water, incinerated ash and solid.

2.2 Environmental Pathways

The environmental pathways of various pollutants illustrated in Figure. 3 is one of the most basic set of relationships in environmental sciences, those among sources, emissions, concentrations, exposures and health effects. It is useful to understand the entire environmental pathway from source through health effects. In this way, the most important sources and best points for control can be determined and ill effects prevented before they occur. The environmental pathway of air pollution exposure are

Step 1: Source Emissions

The type of source, polluting versus clean fuels, gives some idea of hazard but a more valuable measure is the actual amount of pollutants released.

Step 2: Emission Concentrations

The most valuable measure, is the environmental concentrations of pollution, which depends not only on the emissions but also on the transportation and dilution of the pollutant in the environment.

Step 3: Concentration Exposure

Environmental contamination, is not as reliable an indicator of impact as some measure of exposure, which is the contact of the polluting material with the sensitive system, whether a human, a building or an ecosystem .

Step 4: Exposure Health Effect

All exposures will not create the same impact, because of differences in the vulnerability of different people or the competing risks that affect them.