Journal of Environmental Protection, 2011, 2, 11-20
doi:10.4236/jep.2011.21002 Published Online March 2011 (http://www.SciRP.org/journal/jep)
11
BTEX in Ambient Air of a Metropolitan City
D. Majumdar (née Som)1, A. K. Mukherjeea2, S. Sen1
1Department of Chemistry, Calcutta University, Kolkata, India; 2Regional Occupational Health Centre (Eastern), Kolkata, India.
Received September 29th, 2010; revised November 11th, 2010; accepted December 20th, 2010.
ABSTRACT
The environmental fate, global warming effect and human health risk from mono aromatic VOCs are of major concerns
among many consequences of their anthropogenic emission. In more than a yearlong study (November 2003 to Febru-
ary 2005) of the city air in Kolkata, India at different seasons in three different sites, the seasonal mean benzene and
toluene concentrations varied between 13.8 - 72.0 μg/m3 and 21.0 - 83.2 μg/m3 respectively along all the sites. The en-
vironmental distribution and load of BTEX (Benzene, Toluene, Ethylbenzene and isomers of Xylene) in different envi-
ronmental compartment was estimated using a multimedia mass balance model, TaPL3. The total environmental load of
BTEX together was estimated to be 9.7 × 104 kg. Contribution of Kolkata metropolitan city towards global warming due
to environmental emission of BTEX has been estimated as 1.9 × 105 tons of carbon dioxide equivalent per year which is
about 1.1% of yearly direct CO2 emission the city. The consequence of BTEX emission towards human health has been
estimated in terms of non-cancer and cancer risk in population due to their inhalation exposure. The cumulative lifetime
cancer risk for benzene and ethylbenzene was found to be higher than the acceptable value and range between 3.0 × 105
and 8.9 × 106 in three sites, although the non-cancer health risk was found to be within acceptable limit.
Keywords: Multimedia Mass Balance, Seasonal Variation, Global Warming, Health Risk, Kolkata
1. Introduction
The fate of a chemical in the environment is controlled
by its physico-chemical properties, the nature of intro-
duction of the chemical in the environment [1] and also
by the environmental conditions. Volatile organic com-
pounds (VOCs) are omnipresent in lower urban atmos-
phere. Various typical anthropogenic activities like in-
tense transportation, industrial and commercial activities
prevailing in urban areas particularly in metropolitan
cities [2-4] in addition to natural emissions are responsi-
ble for elevated VOC levels in urban air [5].
The mono-aromatic volatile compounds like benzene,
toluene, ethylbenzene, xylenes (BTEX), emitted to the
ambient air, constantly take part in partitioning and dis-
tribution between the major environmental compartments
like water, soil, vegetation etc. or it may entail partition-
ing between phases within an environmental compart-
ment [6].
Multimedia mass balance models are simple mathe-
matical descriptions of the natural environment designed
to gain qualitative and quantitative understanding of the
environmental distribution and fate of chemicals. These
models can be effectively used to describe the fate of the
chemicals such as VOCs in different subdivision of en-
vironmental compartments having homogeneous envi-
ronmental characteristics and chemical concentration by
integrating information of multiple and interacting proc-
ess of partitioning, transport and transformation [1,7-9].
Several models and software packages have been devel-
oped and efficiently used for assessing chemical fate in
the environment on a regional scale, e.g., EUSES and
ChemCAN in Japan [10]; QWASI in West Yorkshire,
United Kingdom [11]; TaPL3 in Mumbai, India [12].
Worldwide rapid urbanization, industrialization and
consumerism are resulting in increasing emission of CO2
and other Green House Gases (GHGs) along with VOCs.
The most significant increase of energy consumption and
GHG emissions are taking place in metropolitan cities
which have rapidly expanding populations enjoying
higher living standards and material affluence than the
people living in rural areas and smaller cities [13]. VOCs
are considered as contributors to global warming by In-
tergovernmental Panel for Climate Change (IPCC) be-
cause of their chemical reactivity and their potential to
produce tropospheric ozone and other photochemical
oxidant. Metropolitan cities thus have significant contri-
bution towards the total national as well as global emis-
sion of GHGs including CO2 and VOCs. Although the
yearly CO2 emission load for Kolkata is reported [13] but

BTEX in Ambient Air of a Metropolitan City 12
neither a comprehensive VOC emission inventory is
available nor the global warming consequences of VOC
emission of any city have ever been estimated.
Besides their environmental effects, VOCs also have
many harmful effects to human health even at lower
concentrations, affecting different target organs e.g. cen-
tral nervous systems, respiratory system, liver, kidney,
reproductive systems etc. [14,15]. The VOCs, in general,
have a positive correlation with severe symptoms of
asthma among children [16]. Many of these especially
benzene has been confirmed as human carcinogen both
by International Agency on Research on Cancer (IARC)
and American Conference of Governmental Industrial
Hygienist (ACGIH).
Risk assessments for the toxic pollutants are widely
used in different countries as a regulatory decision-
making processes to combat air pollution. In a risk as-
sessment, the extent to which a population is or may be
exposed to a certain chemical is determined, and the ex-
tent of exposure is considered in relation to the kind and
degree of hazard posed by the chemical, thereby permit-
ting an estimate of the potential health risk due to that
chemical for the population involved [17]. By perform-
ing non-cancer and cancer risk assessment, the extent of
the possible health damage of the general population due
to environmental exposure to VOCs can be assessed. The
human health risk assessment process includes exposure
assessment that determines the magnitude and duration
of the exposures and risk estimation. The likelihood of
adverse effects on direct human exposure via inhalation
is understood from risk estimation [18].
In the present study, the ambient seasonal concentra-
tion of BTEX in a metropolitan city, namely Kolkata,
India, have been measured to estimate the total elevated
environmental load of these target VOCs utilizing TaPL3
multimedia mass balance model. Contribution of Kolkata
metropolitan city towards global warming due to its en-
vironmental load of BTEX has been estimated as carbon
dioxide equivalent. Estimation of non-cancer health haz-
ard as well as integrated lifetime cancer Risk (ILCR) due
to the inhalation exposure of the general city population
towards BTEX was also made.
2. Methodology
2.1. Study Area
Three monitoring sites, was selected geographically for
ambient air sampling. All the sites were a combination of
commercial and residential area with several small-scale
industries scattered intermittently. The details of the
three sites, Site N in Northern Kolkata, Site C in Central
Kolkata and Site S in Southern Kolkata, are as follows:
Site N: Situated in North Kolkata at ~10 m away from
the main arterial road connecting North and South Kol-
kata at a height of 5 m. Mainly residential and some
commercial activities were prevailing in the surrounding
area.
Site C: Situated in the Central Kolkata at about 5m
height at a distance of ~5 m away from the major road
connecting Central Kolkata to the city railway station.
There was an open ground with greeneries in front of the
sampling site at other side of the road. The surrounding
areas were mainly used for commercial purposes along
with some residential activities. Minor small scale indus-
trial activity can also be noticed in the adjacent area.
Site S: Located in South Kolkata at a height of about 7
m and ~5 m away from a major road connecting southern
and eastern part of the megacity. The area around the
sampling site was populated with various small and me-
dium scale industries. Some commercial and residential
activities were also noticed in the adjacent area.
Transportation activity was prominent in all the three
sites same as in the rest of the city.
2.2. Sampling Period
Air sampling was performed at the selected sites (Site N,
C and S) in dry seasons during the period from Decem-
ber 2003 to February 2005. The monitoring were done in
winter (December ’03 - February ’04 & December ’04–
February ’05), summer (March ’04 - June ’04) and post
monsoon (September ’04 - November ’04). The moni-
toring was continued up to the next winter. 15-18 sam-
ples per season (except in winter ’03 - ’04; 9 samples)
were collected in each site with a total of 152 samples.
2.3. Sampling Procedure
Air sampling for VOCs were conducted at the selected
sites between 9:00 AM and 6:00 PM. VOCs were col-
lected in sorbent tubes containing activated charcoal (60-
80 mesh), spread in two compartments (100/50mg) by
drawing air through a constant flow low volume pump
(SKC, USA) at a rate of 0.1 LPM or less for about 4-5
hours each.
2.4. Determination of BTEX
The charcoal was desorbed in 1 ml of carbon disulfide
(CS2) for 1-1.5 hour and analysed for benzene, toluene,
ethylbenzene, and three isomers of xylenes. Quantifica-
tion was done on a Gas Chromatograph (Perkin Elmer,
Auto System XL GC) equipped with a Flame Ionization
Detector. Separation of the analytes was achieved by PE
624 (Perkin Elmer) capillary column, isothermally at
100˚C. Detector and injector temperature were main-
tained at 200˚C and 180˚C respectively.

BTEX in Ambient Air of a Metropolitan City13
The samples were quantified against five-point cali-
bration curve prepared from standard pure substances
(Aldrich, USA) at different dilutions in CS2 containing
each of the six analytes. Fluorobenzene was used as in-
ternal standard to avoid injection error and error from
trace benzene content in the solvent.
2.5. Quality Control
Duplicate measurements were done for 10% samples
using dual holders of which the analytical results were
highly correlated (r2 = 0.99). Sampling flow rates of all
the pumps were determined using Ultra-flo Calibrator
(SKC Inc. USA) before and after sampling. Field blank
test and breakthrough test were done to ensure quality
control.
3. Calculations
3.1. Determination of Multimedia Partitioning,
Persistence and LRT of BTEX
The percentage distribution of the target pollutant in five
well mixed environmental compartment namely air, wa-
ter, soil, sediment and vegetation can be predicted along
with their long-range transport (LRT) potential and over-
all environmental persistence using TaPL3 model (soft-
ware copyright 2000, version 3.0, Canadian Environ-
mental Modeling Centre). This simulation tool is a fuga-
city-based Level III multimedia mass balance model [16]
that uses a default value for the total emission of 1000
kg/h into a single mobile medium (air or water) and re-
turns the total environmental load in the system. The
probable emission of the target VOCs in the system un-
der examination is estimated from the actual environ-
mental load as calculated from measured concentration in
air assuming a linear relationship between the two. Re-
quired input for the model used in the simulation for the
target pollutant is given in Table 1.
3.2. Determination of Global Worming
Consequences of BTEX
BTEX are non methane volatile organic compounds
(NMVOC) and they have two fold contributions towards
climate change [25,26].
1) The primary contribution arises from their indirect
chemical effect on the atmosphere. VOCs influence cli-
mate through production of organic aerosols and their
involvement in photochemistry, i.e., production of O3 in
presence of NOx and sunlight [27].
2) The secondary contribution is due to the eventual
production of CO2 from the atmospheric degradation of
the VOC and determined by the amount of carbon pre-
sent therein.
The CO2 equivalent emissions arising from 1) is given
by:
2
CO
p
rimaryvoc voc
GWP m

 (1)
Where, CO2primary is CO2 equivalent in tons, mvoc is the
number of tons of the VOC emitted and GWPvoc is the
indirect Global Warming Potential (GWP) for the par-
ticular VOC species. The GWP of a VOC species com-
pares the radiative forcing of a ton of a GHG over a
given time period (say, 100 years) to a ton of CO2 [25].
Estimation of GWPs requires complicated calculation
involving powerful models and the values for many
VOCs have been reported by the Intergovernmental
Panel on Climate Change [27]. Unfortunately, the GWPs
of BTEX are not available and an indirect GWP value of
10 is assumed for each of them [26] in our calculation.
The secondary CO2 equivalent emissions arising from
(2) depends on the number of carbon atoms in the VOC,
its molecular weight and the mass of the VOC released.
2
CO 44
s
econdaryvoc vocvoc
nmMW

 (2)
Where, nvoc is the number of carbon atoms in a mole-
cule of the VOC, MWvoc is its molecular weight in g/mole
and CO2secondary is in tons of CO2 ‘44’ refers to the mo-
lecular weight of CO2.
Thus the total CO2 equivalent emissions (in tons) aris-
ing from the direct release of the VOC is
22 2
CO COCO
equivprimary secondary

 (3)
3.3. Determination of Inhalation Exposure and
Risk
In the current study, the non-cancer hazard and integrated
life time cancer risk (ILCR) due to the exposure to a few
VOCs at their prevailing level were estimated. The daily
exposure (E) of an individual due to intake process (con-
sidering inhalation only) was calculated from the Equa-
tion (1) [18]:
ECIRaEDaBWa

 (1)
The chronic non-cancer hazard index was estimated
using daily exposure E. The integrated lifetime cancer
risk (ILCR) upon an individual for residing in the area
for 15 years was estimated from the effective life time
exposure, EL (Equation (2)).




L
EED 7WK 52YE YL 

(2)
The description of the variables used here is tabulated
below.

BTEX in Ambient Air of a Metropolitan City 14
Table 1. Chemical and environmental par ame ters for running TaPL3 simulation.
Chemical parameters
VOC pollutant Benzene Toluene Ethylbenzene Xylene
molar mass (g mole-1) 78 92 106 106
Vapour Pressurea VP (Pa) 12672.2 3769.3 1276.7 1074.0
Octanol-carbon partition co-efficienta K
oc 55.1 139 228 271
Octanol-air partition co-efficientb K
oa 465 1471 3080 3245
Octanol-water partition co-efficienta K
ow 150 480 1300 1300
Dimensionless Henry’s law constantc K
h 0.289 0.325 0.422 0.357
Partition co-efficient (dimentionless)d water-air 4.35 3.76 3.02 3.61
soil-air 47.7 150.8 315.7 332.6
sediment-air 47.7 150.8 315.7 332.6
suspended particles-air473.5 1591.8 4699.6 5586.4
Fish-air 23.3 73.6 154.0 162.3
aerosol-air 473.5 1591.8 4699.6 5586.4
vegetation-air 6.0 12.4 23.2 27.4
Half life (h) ina Air 141.8 57.1 47.0 23.3
Water 267.6 312.0 156.0 420.0
Soil 4564.8 682.3 156.0 362.4
Sediment 5359.0 2568.0 2772.0 4404.0
vegetatione 1000 1997.12 1000 1000
Environmental parameters
System Areaf 1785.0 km2
Area of waterf 59.2 km2
Vegetation fraction of total areaf 0.35
Mixing height 400 m
Wind velocity 2.0 km h-1
Water velocity 0.5 km h-1
aDatabase available with CalTOX™, Version 1.5 [19]. b[20] c[21]. dCalculated [22]; except for fish-air partition coefficient (KFA), KFA = VL x
Koa, where VL is the volume fraction of lipid in fish. eDue to in non-availability of data, half life of 1000 hour has been assumed for benzene,
ethylbenzene and xylene in vegetation compartment. Value for toluene was calculated from Fostera et al. [23]. f[24].
Variable Description Value Units
E Daily Exposure mg/kg/day
C Concentration of the pollutant mg/m3
IRa Inhalation rate, adult 0.83* m3/hr
EDa Exposure Duration, adult 10 hr/d
Bwa Body Weight, adult 70 kg
D Days per Week Exposure 7 d
WK Weeks of Exposure 52 d
YE Years of Exposure 15 y
YL Years in Lifetime 75 y
3.3.1. Calculation of Chronic Non-Cancer Risk
Non-cancer risks were expressed as Hazard Quotient
(HQ), which is defined as the ratio between the yearly
average daily dose received, EY and the response dose,
RfD (a level below which adverse health effects are not
likely to occur).
This algorithm were used to calculate chronic non-
cancer risk (i.e., risk associated with long-term expo-
sures), using chronic RfDs. Summation of HQs for indi-
vidual contaminants gave Hazard Index (HI).
3.3.2. Calcul a t i on of Cancer Ri sk
Cancer risks was calculated from the Equation (3)


11 1
L
RiskEmgkgdSFmgkg d
 


  (3)
*Ref.: [18].

BTEX in Ambient Air of a Metropolitan City15
Where, SF is the slope factor or carcinogenic potency
slope.
4. Result & Discussion
4.1. Ambient Level of BTEX and Their Seasonal
Variation
Mean VOC concentrations at three monitoring sites dur-
ing December 2003 to February 2005 and their seasonal
variation are shown in Figure 1. There is hardly any de-
marcation of areas for distinct activities like residential,
industrial, commercial etc. in most part of the Kolkata
mega-city and the difference in concentration in all the
sites are thus not statistically significant. Toluene was
found to be the most abundant component followed by
benzene. Seasonal mean concentrations varied between
Figure 1. Seasonal levels of BTEX in three monitoring sites in Kolkata City.

BTEX in Ambient Air of a Metropolitan City 16
13.8 - 72.0 μg/m3 for benzene, 21.0 - 83.2 μg/m3 for tolu-
ene, 7.6 - 21.6 μg/m3 for ethyl benzene, 22.1 - 57.3 μg/m3
for m-& p-xylene (combined) and 7.8 - 21.2 μg/m3 for
o-xylene with overall geometric mean levels of 29.2,
45.4, 13.1, 32.9 and 11.9 μg/m3 respectively. The highest
values observed for benzene and toluene was 177.2 μg/m3
and 174.9 μg/m3 respectively during winter ’04 - ’05, at
site S. More than a decade ago, Samanta et al. [28] re-
ported enormously high values for BTX (benzene, 192 -
18,816 μg/m3; toluene, 98 - 3139 μg/m3 and xylene, 153 -
2037 μg/m3) in Kolkata atmosphere. Since then some
effective measure was taken by the State Pollution Con-
trol Board to wind up unauthorized small scale industries
responsible for VOC emission in and around Kolkata.
More over, the decrease of BTEX level is due to the di-
rectives of the Government of India in lowering the per-
missible limit of benzene up to 3% in metro cities in-
cluding Kolkata after 2001 and also the mandatory use of
Bharat Stage II (equivalent to EURO II) vehicles after
year 2002. An overall fairly good correlation (r2 = 0.62
to 0.83) among the BTEX were found except between
benzene and o-xylene (0.51) indicating a predominant
common source, namely vehicular emission. One way
analysis of variance (ANOVA) shows that except for
benzene, seasonal variation is significant (p ≤ 0.01). The
site-wise toluene to benzene ratio ranged from 1.3 - 2.2
with an overall average of 1.7 which is typical of urban
environment.
Table 2 gives a comparative account of the level and
seasonal trend obtained in the current study with a few
other urban areas worldwide. The city experiences a hu-
mid and tropical climate. The temperature measured at
different sites during the study period found to vary be-
tween 13.5˚C to 29.0˚C in winter months and 29.0˚C to
39.0˚C during summer months. Wind speed recorded in
all sites during winter months varied between 0.03 to
3.30 m/s and during summer months, 0.10 to 3.70 m/s.
Calm conditions prevail frequently during winter months,
and are more common in the evening hours. Relative
humidity remains quite high throughout the year. The
relative humidity varied from 34% to 89% during winter
months and 44% to 86% during summer months.
The target VOCs showed higher average level in most
cases in winter season compared to summer or post-
monsoon may be due to the lower mixing height and less
dispersion during winter. The photochemical reactivity of
toluene, ethylbenzene and xylenes which leads to the
formation of carbonyls through reaction with hydroxyl
radical plays important role in their removal during hot
tropical summer with bounty of sunlight. Relatively
lesser photochemical reactivity of benzene [37] may ex-
plain the higher level (though not statistically significant)
during winter caused by lowered mixing height and dis-
persion.
4.2. Environmental Distribution of BTEX
The percentage distribution and probable load of BTEX
in different environmental compartments for their direct
and continuous release in air was estimated using TaPL3
multimedia mass balance model (Table 3). Out of the
five segments, there was negligible partitioning in vege-
tation and thus not incorporated in table. Air is expect-
edly the most favorable compartment of residence for
principal part of all the target pollutants with dominant
load. A small amount of distribution of these compounds
was found in soil followed by water. Trace amount of
partitioning was observed in the sediment compartment.
The total environmental load is highest for toluene and
xylenes (3.3 × 104 kg both) followed by benzene (2.1 ×
104 kg) and ethylbenzene (9.5 × 103 kg). Considering the
target VOCs, the total environmental load was calculated
as 9.7 × 104 kg. Table 4 compares the emission rates of
the pollutants and their fate in the environment. Esti-
mated hourly emission rate was highest for xylenes fol-
lowed by toluene, ethylbenzene and benzene. The per-
sistence and long range transport (LRT) were highest for
benzene and lowest for xylenes which commensurate
with the relative reactivity of the mono-aromatics. The
persistence of benzene was found to be 2.5, 3.0 and 6.1
times higher than toluene, ethylbenzene and xylene re-
spectively. This is reflected in the observation that the
concentration ratios with respect to benzene i.e., T/B,
E/B and X/B emission ratio obtained from the model are
3.9, 1.4 and 9.5 respectively whereas the T/B, E/B and
X/B concentration ratio in air is only 1.7, 0.4 and 1.6.
The LRT denotes that at least for benzene this city acts as
an area source for surrounding suburban and rural areas
within 400 km radius. An estimation of yearly emission
for BTEX in Kolkata metropolitan city is presented in
Table 4.
The total estimated emission for BTEX is as high as
1.4 × 104 tons per year which is comparable to the esti-
mated evaporative emission of 1.1 × 105 tons per year for
total hydrocarbon reported for Kolkata in emission in-
ventories for VOCs in metro cities [38].
4.3. Global Warming Consequences of BTEX
Emission in City Air
The global warming consequences for BTEX emission in
the city environment, expressed as CO2 equivalent esti-
mated using Equations 1, 2 and 3, is also given in Table
4. Our study shows that 1.9 × 105 tons of CO2 equiva-
lents of only BTEX are being emitted per year from
Kolkata metropolitan city. The total yearly CO2 emission
of Kolkata city in the year 2000 has been estimated to be
1.7 × 107 tons, which is 2.2% of national CO2 emission

BTEX in Ambient Air of a Metropolitan City17
Table 2. Comparison of average level and seasonal trend with studies in other urban area.
Reported value (site characteristics)
City, country
Benzene (μg m−3) Toluene (μg m−3)
Comments
Hong Kong,
China [29]
4.9
(roadside)
28.8
(roadside) Different sources for total BTEX in different seasons are indicated.
Pearl River Delta,
China [3]
15.4-67.3
(urban-roadside)
28.6-106.9
(urban-roadside)
Autumn (November) BTEX level is 26-56% more than their sum-
mer (July) level. Meteorological conditions such as source and
characteristics of air mass are the reason for such massive seasonal
variation rather than variation in source input or photochemistry.
Delhi, India [30]
12-55
(urban-residential)
80-550
(urban-traffic crossing)
10-80
(urban-residential)
18-55
(urban-traffic crossing)
Winter VOC level is distinctly higher than summer or monsoon
level in general, B/T ratio ranged from 1.04-2.05.
Shizuoka, Japan
[31]
0.478 μg m-3 in summer
0.946 μg m-3 in winter
(industrial urban)
4.339 μg m-3 in summer
6.403 μg m-3 in winter
(industrial urban)
BTEX level in winter was higher than summer. Pollutants were
more homogeneously distributed in winter. Seasonal variation was
also influenced by emission sources.
Algiers city,
Algeria [32]
27.1 (roadside)
9.6 (urban)
39.2 (roadside)
15.2 (urban)
Minor seasonal variation with winter concentration 10% higher
than summer. T:B is 1.5-2.1
Hong Kong,
China [33]
417 pptv (urban)
(≈1.3 μg m-3)
2765 pptv (urban)
(≈10.4 μg m-3)
Winter levels of toluene and other VOCs were significantly higher
than the summer. A strong local/regional source during winter is
suggested. The VOC levels are affected by Asian monsoon circula-
tion, the clean maritime inflow air dilutes (reduces) them signify-
cantly during summer also resulting low annually averaged VOC
level.
United States [34] 1.03 (Urban) 2.38 (Urban)
Higher concentration in cooler season for BTEX. Changes in emis-
sion activity, removal rates, or dispersion/dilution/transport may
explain the seasonal variation
Delhi, India [35] 48-110
(metropolitan-urban)
85-204
(metropolitan-Urban)
Winter levels are higher than summer. Meteorology, variation in
source strength and availability of OH radical were identified to be
the controlling factors. T/B ratio varied between 1.8-2.5
São Paulo, Brazil
[36]
1.30-11.31
(metropolitan-urban)
2.05-16.92
(metropolitan-urban)
Higher VOC concentration in winter (August) than summer (De-
cember). Variation in sources is attributed to be the probable cause.
Kolkata, India
[present Study]
29.2
(metropolitan -urban)
45.4
(metropolitan -urban)
Significantly higher winter level due to meteorological factors like
lowered mixing height and lesser dispersion and also enhanced
photochemical removal of TEX in summer; insignificantly lower
summer level for benzene due to less photochemical reactivity,
only meteorological factors increases the winter level. T/B ratio
ranged from 1.3 to 2.2.
Table 3. Percentage distribution and estimated load of BTEX in environmental compartments.
Benzene Toluene Ethylbenzene Xylene
Environmental
compartment % load (kg) % load (kg) % load (kg) % load (kg)
Air 98.6 2.1 × 104 97.7 3.2 × 104 98.9 9.4 × 103 97.8 3.3 × 104
Water 0.2 5.0 × 101 0.2 7.0 × 101 0.1 1.2 × 101 0.2 7.3 × 101
Soil 1.2 2.5 × 102 2.1 6.9 × 102 1.0 9.0 × 101 1.9 6.4 × 102
Sediment <0.1 9.6 × 10-1 <0.1 4.2 <0.1 3.0 0.1 2.3 × 101

BTEX in Ambient Air of a Metropolitan City 18
Table 4. LRT, persistence and emissions of BTEX in environment.
Parameters Benzene Toluene Ethylbenzene Xylene
LRT (km) 409 164 135 67
Persistence (day) 8.6 3.5 2.9 1.4
Emission rate (kg h-1) 102 394 138 968
Yearly emission (tons year-1) 8.94 × 102 3.45 × 103 1.21 × 103 8.48 × 103
Emission CO2-eqivalant (tons year-1) 1.2 × 104 4.6 × 104 1.6 × 104 1.1 × 105
with only 1.6% of population [13]. Thus the CO2 equiva-
lent of BTEX only represents almost 1.1% of the total
emission of Kolkata and 0.002% of national CO2 emis-
sion in addition to the total CO2 load. It is expected that
the total hydrocarbon present in the city air has the po-
tential to increase the level of CO2 even more. This indi-
cates that the actual global warming consequence of
emissions in city air is reasonably higher than the direct
CO2 emission after considering the emission of VOCs.
4.4. Risk Assessment
The concentrations of the BTEX were found to be quite
high in the present study and their levels could be a real
threat to the health of the city inhabitants. Table 5 gives
the average daily exposure, average life time exposure,
Individual Hazard Quotient (HQ) and ILTCR (for 15
years residence time for an individual). Effective life
time exposure is maximum for xylene mixture and tolu-
ene because of their higher ambient concentration fol-
lowed by benzene and ethylbenzene.
According to WHO the lifetime risk of chronic leuke-
mia for benzene exposure of 1 µg/m3 is 4.4 – 7.6 × 10-6
[39] while ethylbenzene is classified as a group D car-
cinogen [40]. The cancer risk calculated in the current
study suggests the exposure level to be far from being
safe for population residing for 15 years in the city. In all
the three sites, the estimated cancer risk is more for ben-
zene due its high carcinogenicity. Estimated cancer risk
for all the individual components (except for ethyl ben-
zene in Site N) exceeded the threshold value of 1 × 10-6
indicating significant cancer risk. In general, residents of
Site S receive higher exposure from the pollutants in
comparison to the other two sites and as a result the
probability of cancer risk is higher in Site S. Assuming
that the carcinogenic effect from different pollutant is
additive, the cumulative cancer risk from benzene and
ethylbenzene is maximum (3.0 × 10-5) in Site S, followed
by Site C (1.9 × 10-5) and Site N (8.9 × 10-6).
In spite of its lower exposure value, benzene gives the
highest non-cancer HQ due to its low reference dose for
adverse non-cancer health effect. Benzene is closely fol-
lowed by xylenes in causing non-cancer health hazard.
Table 5. Estimate of individual pollutant exposure, associ-
ated non-cancer hazard and cancer risk.
Daily
exposure
Effective life
time exposure
Pollutant Site
(mg kg-1day-1) (mg kg-1day-1)
Individual
HQ ILCR
Site N1.5E-03 3.0E-04 1.8E-018.3E-06
Site C3.3E-03 6.6E-04 3.9E-011.8E-05Benzene
Site S5.2E-03 1.0E-03 6.0E-012.8E-05
Site N3.1E-03 6.2E-04 2.2E-03
Site C5.1E-03 1.0E-03 3.6E-03 Toluene
Site S6.0E-03 1.2E-03 4.2E-03
Site N8.2E-04 1.6E-04 2.9E-036.3E-07
Site C1.5E-03 3.0E-04 5.2E-031.2E-06Ethylbenzene
Site S1.7E-03 3.5E-04 6.1E-031.3E-06
Site N3.6E-03 7.1E-04 1.2E-01
Site C5.0E-03 1.0E-03 1.8E-01
Xylene
mixture
Site S5.7E-03 1.1E-03 2.0E-01
The individual HQs or the HI for BTEX did not exceed
anywhere indicating no serious threat of chronic non-
cancer health effect in pollutant specific target organs for
the city population.
5. Conclusions
Ambient concentration of Benzene, Toluene, Ethylben-
zene and isomers of Xylene (BTEX) have been found to
be appreciably high in Kolkata metropolitan city. After
air compartment, BTEX was found to be residing in soil
followed by water with the total environmental load of
BTEX as high as 9.7 × 104 kg.
The prevailing benzene and ethylbenzene level is es-
timated to pose significant cancer risk due to the inhala-
tion exposure to the general city population.
6. Acknowledgements
The authors’ sincerest thanks are due to Dr. Anjali Sri-

BTEX in Ambient Air of a Metropolitan City19
vastava, Scientist & Head, Kolkata Zonal Laboratory,
National Environmental Engineering Research Institute
for her interest in the work. Thank is also due to Dr. K.
Mukhopadhyay for his help during field work.
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