Exposure profiles, seasonal variation and health risk assessment of BTEX in indoor air of homes at different microenvironments of a terai province of northern India
Introduction
The impact of air pollution on human health has become a major issue of concern worldwide for various scientific communities. Present human lifestyle has forced us to spend most of our time in enclosed spaces like classrooms, offices and our homes. Thus we are more susceptible to exposure to indoor air. Level of pollutants in the indoor air is far more dangerous than that in outdoor air. According to USEPA’s total exposure assessment methodology (TEAM) study, the concentration of contaminants found in indoor environment is significantly higher than that found in outdoors (Wallace, 1986, Guo et al., 2003). At outdoors, pollutants get diluted in air due to dispersion. However in indoor environment, due to lack of proper ventilation and high humidity, the concentration of pollutants increases exceedingly. Amongst the wide variety of organic and inorganic air pollutants which have been recognized, volatile organic compounds (VOCs) deserve special consideration, because of their ability to affect human health as well as the environment. Many studies have shown that exposure to elevated levels of VOCs can cause several adverse health effects such as irritation in mucous membrane, physical and mental weakness, difficulty in concentrating, nausea, discomfort and headache (Pouli et al., 2003, Cometto-Muniz et al., 2004, Wolkoff et al., 2006, Bernstein et al., 2008). VOCs which are predominantly found in indoor environment include benzene, toluene, ethylbenzene and isomers of xylene (BTEX) (Ilgen et al., 2001a, Ilgen et al., 2001b, Guo et al., 2003). Even at very low concentrations of microgram per cubic meter, BTEX can cause serious health problems (Ueno et al., 2001, Badjagbo et al., 2010). Thus, a proper and systematic study of these monoaromatic pollutants is necessary for monitoring the indoor air quality.
Contamination of indoor air by BTEX can be attributed to various emission sources. The major sources include the combustion processes like cooking, heating and burning. In most of the religious rituals, burning of scented candles and incense is quite common. Similarly, some of the occupant activities such as smoking, use of air fresheners, deodorants and insect repellants may also release BTEX in indoor air. It can be easily noticed that even a single house contains numerous synthetic chemical products such as cleansers, stain removers, paints, adhesives, solvents, oils and various plastic products. These products continuously emit many harmful VOCs including BTEX in air and hence deteriorate the quality of indoor air. Certain building materials such as furnishings, wood finishings, furniture foam, floorings and carpets also have a major contribution. In addition to these, BTEX from outdoor air may also enter indoor air through various vents present in the building (Batterman et al., 2007).
According to USEPA, benzene has been proved to be carcinogenic for both humans as well as other animals (USEPA, 1998). IARC has placed benzene in group 1 carcinogens (IARC, 2002). Toluene is a potent human teratogen (Hersh, 1989, Donald et al., 1991). Ethylbenzene has been categorized as a possible human carcinogen and has been placed in group 2B by IARC (IARC, 2000). BTEX also act as sensitizers and cause irritation in upper respiratory tract. They can even cause lung cancer and leukemia (Rezazadeh et al., 2012). BTEX slows down the brain activity and is toxic at high doses. Among BTEX, benzene and toluene have the highest toxicity (Molhave, 2003).
In India, several studies have been conducted on ambient levels of BTEX (Srivastava et al., 2005a, Srivastava et al., 2005b, Hoquea et al., 2008, Saxena and Ghosh, 2012). However, despite of so many adverse health effects of BTEX, only a limited number of studies have been conducted on indoor levels of BTEX particularly in this part of India. The aim of this study is to investigate the exposure levels of BTEX in indoor microenvironments of different sites as well as estimate the related human health risk. Moreover, the effect of temperature as well as seasonal variation on the indoor concentration of BTEX has also been discussed.
Section snippets
Description of sampling sites
Gorakhpur (26°45′32″N 83°22′11″E) is located in the terai region of eastern Uttar Pradesh in northern India, near the border of Nepal, in the foothills of the Shiwalik Himalayas. Gorakhpur city is surrounded by the rivers Rapti, Rohini and other small streams from three sides. River Rapti is interconnected through many other small rivers. The present district of Gorakhpur, 265 km east of capital Lucknow, on National Highway (NH-28), covers geographical area of 3483.8 km2 having total population
Concentration of BTEX in indoor air
The statistical data for BTEX concentrations at Gorakhpur has been represented in Table 3. The concentration of benzene ranged from 1.74 μg m−3 to 181.92 μg m−3 with mean value of 40.67 μg m−3. Concentration of toluene was found in the range 2.97 μg m−3 to 123.68 μg m−3 with mean value of 38.06 μg m−3. Ethylbenzene ranged from 0.13 μg m−3 to 29.50 μg m−3 with a mean value of 5.69 μg m−3 whereas xylene had mean concentration of 4.88 μg m−3 with a range of 0.22 μg m−3 to 18.97 μg m−3. Thus the
Conclusion
The indoor levels of BTEX were measured at homes located at selected sites of the city. The mean concentrations of BTEX at residential, roadside, industrial and agricultural sites were found to be 6.1, 12.3, 18.2 and 54.3 μg m−3 respectively. Seasonal variation was also observed in BTEX levels at all the sites. The mean concentration of BTEX was highest in winter season (32.56 μg m−3) followed by monsoon (19.90 μg m−3) and summer (14.44 μg m−3) at all the sites. Toluene was found to be dominant
Acknowledgement
Financial support from Department of Science and Technology (DST), New Delhi, India in Project No. SR/FTP/ES-77/2013 is duly acknowledged. Authors gratefully acknowledge Revd. Prof. J. K. Lal (Principal) and Dr. S. D. Sharma (Head) Chemistry Department, St Andrew’s College, Gorakhpur, UP, India, for providing necessary facilities. Authors are also thankful to Mr. Jay Patel, ERT, USEPA for providing technical support during the analysis of samples.
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