Human their chemical composition, reaction properties, emission, persistence

Humanhealth effects of air pollution  Abstract Hazardous chemicalsescape to the environment by a number of natural and/or anthropogenicactivities and may cause adverse effects on human health and the environment.Increased combustion of fossil fuels in the last century is responsible for theprogressive change in the atmospheric composition.

Air pollutants, such ascarbon monoxide (CO), sulfur dioxide (SO2), nitrogen oxides (NOx), volatileorganic compounds (VOCs), ozone (O3), heavy metals, and respirable particulatematter (PM2.5 and PM10), differ in their chemical composition, reactionproperties, emission, time of disintegration and ability to diffuse in long orshort distances. Air pollution has both acute and chroniceffects on human health, affecting a number of different systems and organs. Itranges from minor upper respiratory irritation to chronic respiratory and heartdisease, lung cancer, acute respiratory infections in children and chronicbronchitis in adults, aggravating pre-existing heart and lung disease, orasthmatic attacks. In addition, short- and long-term exposures have also beenlinked with premature mortality and reduced life expectancy. 1.

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    IntroductionAlthough a number ofphysical activities (volcanoes, fire, etc.) may release different pollutants inthe environment, anthropogenic activities are the major cause of environmentalair pollution. Hazardous chemicals can escape to the environment by accident,but a number of air pollutants are released from industrial facilities and otheractivities and may cause adverse effects on human health and the environment.By definition, an air pollutant is any substance which may harm humans,animals, vegetation or material. As far as humans are concerned an airpollutant may cause or contribute to an increase in mortality or seriousillness or may pose a present or potential hazard to human health. The determination ofwhether or not a substance poses a health risk to humans is based on clinical,epidemiological, and/or animal studies which demonstrate that exposure to asubstance is associated with health effects.

In the context of human health,”risk” is the probability that a noxious health effects may occur. 2.     Pollutant categories Themain change in the atmospheric composition is primarily due to the combustionof fossil fuels, used for the generation of energy and transportation. Variantair pollutants have been reported, differing in their chemical composition,reaction properties, emission, persistence in the environment, ability to betransported in long or short distances and their eventual impacts on humanand/or animal health. However, they share some similarities and they can begrouped to four categories:  1.     Gaseouspollutants (e.g.

SO2, NOx, CO, ozone, Volatile Organic Compounds). Gaseous pollutants contribute to a greatextent in composition variations of the atmosphere and are mainly due tocombustion of fossil fuels (Katsouyanni, 2003). Nitrogen oxides are emitted asNO which rapidly reacts with ozone or radicals in the atmosphere forming NO2.

The main anthropogenic sources are mobile and stationary combustion sources.Moreover, ozone in the lower atmospheric layers is formed by a series ofreactions involving NO2 and volatile organic compounds, a process initiated bysun light. CO, on the other hand, is a product of incomplete combustion. 2.     Persistentorganic pollutants (e.

g. dioxins).     Persistentorganic pollutants form a toxic group of chemicals. They persist in the   environment for long periods of time, andtheir effects are magnified as they move up  through the food chain (bio-magnification).They include pesticides, as well as dioxins, furans and PCBs. 3.

     Heavymetals (e.g. lead, mercury).

4. Particulate Matter.Heavy metals include basic metalelements such as lead, mercury, cadmium silver nickel, vanadium, chromium andmanganese. They are natural components of the earth’s crust; they cannot bedegraded or destroyed, and can be transported by air, and enter water and humanfood supply.

 3.Health effects Sporadic air pollutionevents, like the historic London fog in 1952 and a number of short and longterm epidemiological studies investigated the effects of air quality changes onhuman health. A constant finding is that air pollutants contribute to increasedmortality and hospital admissions (Brunekreef and Holgate, 2002). The differentcomposition of air pollutants, the dose and time of exposure and the fact thathumans are usually exposed to pollutant mixtures than to single substances, canlead to diverse impacts on human health. Human health effects can range fromnausea and difficulty in breathing or skin irritation, to cancer. They alsoinclude birth defects, serious developmental delays in children, and reduced activityof the immune system, leading to a number of diseases. Moreover, there existseveral susceptibility factors such as age, nutritional status and predisposingconditions.

Health effects can be distinguished to acute, chronic not includingcancer and cancerous. Epidemiological and animal model data indicate thatprimarily affected systems are the cardiovascular and the respiratory system 4.Cellular mechanisms involved in air pollutants actions Common cellular mechanism by which most airpollutants exert their adverse effects is their ability to act directly asprooxidants of lipids and proteins or as free radicals generators, promotingoxidative stress and the induction of inflammatory responses (Menzel, 1994;Rahman and MacNee, 2000). Free radicals (reactive oxygen and nitrogen species)are harmful to cellular lipids, proteins, and nuclear- or mitochondrialDNA,inhibiting their normal function (Valko et al.

, 2006). In addition, they caninterfere with signaling pathways within cells (Valko et al., 2006). Ineukaryotic aerobic organisms including humans, free radicals are continuouslygenerated during normal metabolism and in response to exogenous environmentalexposures (e.g. irradiation, cigarette smoke, metals and ozone).

When freeradical concentration increases, due to an overwhelming of organism’s defense,a state of oxidative stress occurs. This oxidative state has been implicated ina wide variety of degenerative diseases such as atherosclerosis, heart attacks,stoke, chronic inflammatory diseases (rheumatoid arthritis), cataract, centralnervous system disorders (Parkinson’s, and Alzheimer’s disease), age relateddisorders and finally cancer.            4.1Impact of air pollutionA basic and simplecriterion for assessing the importance of the health risk related to indoorpollution makes reference to the severity of the effect concerned and to thesize of the population affected. The resulting 2 x 2 matrix is shown in Table1. Important issues for the community may come from severe health impacts,particularly when affecting a large segment of the population.

Minor impacts,such as those related to discomfort or annoyance may, however, become importantwhen a large number of individuals in the community are concerned.     5.Classification of environmental pollutants:   6.Toxicology of air pollutantsNot all air pollutantshave the same capacity for producing toxic effects, nor do they cause the samedamage. It is a logical conclusion that the differences are due to the physicaland chemical properties of these components. This report will briefly mentionthe properties as they relate to toxicity. Beginning with the molecularaggregation state, substances in aerosol form have been shown to be more toxicthan compounds in gaseous state. This is due to the fact that gaseous compoundsare eliminated by the respiratory system much more easily than aerosols, whichare rapidly deposited or absorbed.

The particle size of an aerosol, between 1nm and 2 µm, is easily deposited in the respiratory system (Wilson et al.1996). Particle size determines the extent to which the particles can penetrateinto the respiratory system. Table 2 shows penetration ability of particles asa function of size. Once particles have entered the respiratory tract, dependingon their size they can accumulate in different sites within the respiratorysystem. 7.Toxic effects of air pollutants Chemical compoundsemitted into the atmosphere due to human activity or those compounds that arebyproducts of the interaction of chemical emissions have been shown to haveadverse effects on health. These effects, as discussed in this report, dependfundamentally on the nature of the compound in question, the concentration inthe air and the time of individual exposure.

Noxious health effects caused byair pollution can be classified as due to either chronic or acute exposure.2.4.1 Health effects due to acute exposure to air pollutants Toxic effectsattributable to acute exposure to air pollutants vary widely and have beenreported practically since the beginning of the industrial revolution whereepisodes of high levels of pollutants were associated with increases in diverserespiratory and heart diseases and death. These episodes have occurred on morethan a single occasion in different parts of the world, especially in highlyindustrialised and/or populated areas . The most studied toxic effect due to acuteexposure to environmental pollutants is mortality.

Many reports describe anincrease in total mortality (not including accidental death) associated mainlywith exposure to particulate matter (PM), ozone and sulphates. This associationcan be disputed, however, since the cause of death should be related to theroute of exposure (Schwartz 1994a , Dockery and Pope 1994). Air pollution exposurefactors The major sources of human exposure to air pollution are, as mentionedabove, those produced by human activity. Pollutants can enter the organism invarious ways such as ingestion, absorption through the skin and inhalation (Mölleret al. 1994, Wilson et al.

1996). Inhalation is the major route of entry forexposure to air pollution. An important aspect of inhalation that is oftenignored is oral breathing. When individuals breath through the mouth, thephysical and mechanical barriers of nasal breathing are absent, and oralbreathing has been shown to decrease the ability to eliminate particlesdeposited in the respiratory tract, mainly in the upper air ways (Wilson et al.

1996). Until recently, only outdoor areas (exterior) were considered asexposure sites since that was where an individual would contact the majority ofair pollutants. We now know that this is true only for certain types ofpollutants such as metals, which due to their particle size are foundessentially only outdoors (this is true for any particulate pollutant with aparticle diameter greater than 10 µm). Carbon monoxide (CO) and nitrogendioxide (NO2), on the other hand are found in greater quantity indoors (Mölleret al. 1994, Maynard 1999). A study in the United States showed thatindividuals spend an average of 87.2% of their time indoors, 5.

6% of their timeoutdoors and 7.2% in transit (Wilson et al. 1996), and values for Mexico are83.7%, 11.

50% and 0.05% correspondingly (Rojas-Bracho 1994). These data demonstratethe importance of determining indoor, as well as outdoor, exposure whenprecisely defining an individual’s true exposure.      References1  .Berglund B, Berglund U, Lindvall T, SpenglerJ, Sundell J. lndoor air quality – containing papers from the Thirdlnternational Conference on lndoor Air Quality and Climate, Stockholm, Sweden,1984.

Environment lnternational 12 (1 986) (special issue).2. Berglund B,Grimsrud DT, Seifert B.

lndoor Air Quality – A special issue of EnvironmentInternational. Environment lnternational 15 (1 989) ,3.     Abbey, D.Petersen, F. Mills, P. Beeson, W.

(1993). Long-term ambient concentrations of total suspend particulates, ozone,and sulfur dioxide and respiratory symptoms in a nonsmoking population.Archives of Environmental Health 48 (1): 33-46. 4.     Anderson, H., Ponce de León, A.

Bland, J. Bower,J. Strachan, J. (1996).

Air pollution and daily mortality in London: 1987-92.BMJ. March 16; 312:665-669.

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