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Study of mutagenic pollution in Bombay
The Science o f the Total Environment, 38 (1984) 275--281 Elsevier Science Publishers B.V., Amsterdam -- Printed in The Netherlands
275
STUDY OF MUTAGENIC POLLUTION IN BOMBAY
C.N. SHENOY and K.A. CHAUBAL Biophysics Division, Cancer Research Institute, Tata Memorial Centre, Parel, Bombay-400 012 (India)
(Received October 18th, 1983; accepted November 30th, 1983)
ABSTRACT Airborne suspended particulate matter (SPM) from seven areas in and around Bombay city were collected over glass fibre filters (0.8 pm porosity). The chemicals from the SPM were extracted in dimethylsulfoxide and distilled water and were further tested for mutagenicity by Ames' test using five mutants of Salmonella typhimurium. Of the seven areas studied, only four exhibited mutagenicity, which was confirmed by dose--response assays using the mutant strain TA 100. The very high mutagenicity observed in central Bombay correlates with the higher incidence of respiratory tract diseases in the resident population.
INTRODUCTION T h e i n c i d e n c e o f lung c a n c e r a n d c a n c e r m o r b i d i t y r a t e s are o n t h e increase all o v e r t h e w o r l d . A n u m b e r o f n e w c h e m i c a l s are b e i n g s y n t h e s i z e d a n d r e a c h h u m a n p o p u l a t i o n t h r o u g h f o o d , w a t e r a n d air. Several o f t h e s e c h e m i c a l s m a y b e c a p a b l e o f p r o d u c i n g c a n c e r o u s c o n d i t i o n s a n d an increase in t h e i r n u m b e r a p p e a r s u n a v o i d a b l e , c o n s i d e r i n g t h e a c c e l e r a t i n g t e c h n o l ogical g r o w t h y e a r a f t e r y e a r . T h e u r b a n air c o n t a i n s a large v a r i e t y o f p o l l u t a n t s [ 1 - - 9 ] , b o t h gaseous a n d p a r t i c u l a t e , o r i g i n a t i n g m a i n l y f r o m industrial c h i m n e y s , a u t o m o b i l e e x h a u s t s a n d d o m e s t i c sources. A s t u d y o f air p o l l u t a n t s a n d h e a l t h m o r b i d i t y in B o m b a y , I n d i a [3] s e e m s to c o n f i r m c o r r e l a t i o n b e t w e e n higher levels o f p o l l u t a n t s ( s u s p e n d e d p a r t i c u l a t e m a t t e r (SPM), s u l p h u r d i o x i d e a n d n i t r o g e n o x i d e ) a n d higher i n c i d e n c e o f r e s p i r a t o r y diseases. In a n o t h e r s t u d y in B o m b a y , e m p l o y i n g c h e m i c a l analysis [ 2 ] , a higher c o n c e n t r a t i o n o f t h e c a r c i n o g e n b e n z o [a] p y r e n e (BaP) was n o t i c e d in t h e area w h i c h i n d i c a t e d higher m o r b i d i t y . P r o m p t e d b y t h e s e o b s e r v a t i o n s , it was d e c i d e d t o c o l l e c t SPM in several areas (industrial a n d residential) in a n d a r o u n d t h e c i t y o f B o m b a y , a n d t o a n a l y s e t h e s e f o r t h e i r m u t a g e n i c p o t e n t i a l . T h e s e studies c o u l d be e x t e n d e d in o r d e r t o v e r i f y w h e t h e r m u t a g e n i c i t y is d u e t o o n e c h e m i c a l or a c o m b i n a t i o n o f c h e m i c a l s . This a s p e c t has t o be e m p h a s i s e d i n
276
13-
3ool
LOCALITY: L A L B A G STRAIN : TA 1OO
®
200 W > 0----0 0---0 .C.. -', A,---.A
100 .,./
tl
~
0,1
0.2 AMOUNT
300
DMSO + DMSOWATER WATER
0,5 OF
O- 4
EXTRACT
LOCALITY
: PAREL
STRA, N
: TA 100
$9 $9 + $9 - $9
IN
ML
@
o.
~ =
~°° F
~oDMSO 4- S9 ~j~______..~ ,,,ATER + S9
I look
~ _ _ . - o OMSO - S9 .~.-::-:::----,
F
,',ATE.-
S.
;2-"'I 0.2
0,1 AMOUNT
u,I
300 ,.I a. n,.
OF
I 0'3
EXTRACT
LOCALITY
:
STRAIN
: TA I 0 0
I 0,4
(ml)
SANTACRUZ
ImJ
a.
200 z I,,t¢
DMSO + $9 OMSO
--
S9
WATER -- $9 . ~ : 2 - ~ 2 2 - - -~-AI
0-1 AMOUNT
0'2 OF
EXTRACT
0'3 (ml)
0-4
277 laJ I--
<
..I Q.
300
LOCALITY
: CHEMBUR
STRAIN
: TA
IOO
a* r,
co 2 0 0 Iz
w
h,
D M S O + S~,) W A T E R -4- S 9
100
OMSO
j-~'.-~
0.1
0.2 AMOUNT
OF
0.3 EXTRACT
--
$9
W A T E R -- $ 9
0.4
(ml)
Fig. 1. Dose--response graphs of SPM extracts from four areas in Bombay: (a) Lalbag, (b) Parel, (c) Santacruz, (d) Chembur. The n u m b e r of revertants per plate with DMSO and water (155 + 20 and 150 + 20, respectively) were subtracted. Each graph is representative of three independent experiments.
air pollution studies as there is more possibility of chemicals occurring in the complex form than as individual ones [ 1 ].
MATERIALS AND METHODS
It is k n o w n t h a t SPM of size < 3 . 5 p m contains a greater a m o u n t of mutagenic activity/unit sample mass [1]. It is also known that SPM of size > 0 . 8 # m is respirable [11]. Hence, SPM of size > 0 . 8 p m was collected for 24 h on glass fibre filter paper (BARC, Bombay, India) with a vacuum pump having a suction rate of about 16 m3/min. The samples were collected from surroundings which were about 10--12 ft from the ground level and about 20 ft from the nearest road. The different areas selected for this study are shown in Fig. 2.
Extraction o f mutagens The filter paper, with its deposit of SPM, was cut into two halves, each half being further cut into smaller bits and ground in a pestle and mortar using d i m e t h y l sulfoxide (DMSO) as solvent for one half and distilled water for the other. It was then sonicated in cold and centrifuged to remove glass fibre residues. The two supernatants, containing chemicals soluble in DMSO and water, respectively, were t h e n filtered through filters of porosity 0.45 pm (Millipore) to remove microbial contamination.
Mutagenicity test The mutagenicity of the extracts was tested following the procedure of Ames et al. [10]. In the initial screening all five strains, namely TA 1535, TA 1537, TA 1538, TA 98 and TA 100, were studied. The criterion of
278 comparing the number of revertant colonies, corrected to background, was e m p l o y e d to check the sensitivity of the five strains. The dose--response relationships were obtained using the strain TA 100, which showed m a x i m u m activity, and were confined to the extracts from the areas Lalbag, Parel, Chembur and Santacruz, which gave high to very high mutagenicity.
Microsomal activation system Wistar rats weighing 150--200g were injected with Aroclor 1254 to elevate the microsomal enzyme activity, which is an essential step in achieving m a x i m u m activation of mutagens to their ultimate electrophilic form. Positive controls 3,4-Benzo[a]pyrene (BaP) and N-methyl-N-nitro-N-nitrosoguanidine (MNNG) were used as positive controls in these experiments. RESULTS Calculations made after considering the rate of pumping air through the filter paper have shown that 0.1 ml of extract, in the present work, is equivalent to 0.5 m 3 of air sample. The DMSO and water extracts of samples from all the areas studied in this work exhibited mutagenicity. It was highest for Lalbag, followed by Parel, Chembur, Santacruz and Peddar Road, Vidyavihar, Borivli. In both DMSO and water extracts the number of revertants increased with the addition of $9 mixture. With 2 pg of MNNG alone, i.e., w i t h o u t the $9 fraction, the number of revertants per. 2 × 10 s bacteria of TA 100 was 550; while the similar number for 4 pg (BaP) with the $9 fraction was 1600. The extracts from Peddar Road, Vidyavihar and Borivli, studied initially with all five strains, showed marginal activity in preliminary tests and hence the dose--response relationship for SPM from these areas was not obtained. The graphs shown in Fig. l a d are representative of three independent experiments. These show that the extracts from Lalbag, Parel, Chembur and Santacruz exhibit high to very high mutagenicity and that it is due to the water/DMSO soluble fraction of SPM. Several other factors such as location of industries, air-port, open areas with trees, flow of air currents, for which no measurements were made, are compared with the mutagenic pollution studied in this work and are shown in Fig. 2. The + signs in Fig. 2 have been chosen arbitrarily to give a rough estimate of the a m o u n t of air pollution in terms of (BaP) activity.
DISCUSSION As mentioned in the Results, 0.1ml of extract from the Lalbag area is from 0.5 m 3 of air and corresponds to 287 revertants. Extrapolation of this
279
SANTACRUZ (+ -t- + )
BORIVLI (+)
/9"'" ~
eeo
~
o°
~
t
...
VIDYAVIHAR (+)
i oo
,A/
~ eo
J/
oeo
i
c~ °
/
-'"
PAREL (+
I
1ODe
,/J
~ ~
ooo
...
CHEMBUR (-t--t--I" )
000
~
LALBAUG (++++-I-)
~'~/
°"
[~
ool
~
•
~'~%.~)'
JJ° '~
* *
0
"-
*
PEDDAR Rd.(+]
~-~j-
TEXTILE
MILLS
¢~_.~-- VEHICULAR
...
TRAFFIC
-- P O P U L A T I O N
JJ
•
,,/,/ . . . '~
(+)
INDICATES MUTAGENS EOUIVALENT TO 1-2/Jgms OF B (o)P/tSm 3 AIR
DENSITY
-- PETROCHEMICALS - - COAL
UTILIZATION
-- A I R I.
TRAFFIC
I -- O P E N
SPACE
,~
-- T R E E S eee
HiGH 1
ee
MEOIUMp
•
LOW #//~v/
-- AIR
CURRENTS
Fig. 2. A map of Bombay showing the location of zones where SPM samples were collected. The other factors in the Figure (see Results), represented for comparison, are from general observation.
n u m b e r o f 15 m 3 o f air, which is a b o u t the q u a n t i t y a man breathes per day, means ar o u n d 2870 revertants. Earlier studies carried out in the same area [2] have shown the mean BaP value is 4 0 p g per 1 0 0 m 3 of air, i.e., 6 p g of BaP per 15 m 3 o f air. The positive c o n t r o l e xpe r i m e nt s described in t he present w o r k have shown th at 4 pg o f BaP produces 1600 revertants. If this n u m b e r is extrap o lated to 6 #g, we obtain ar ound 2400 revertants. The facts that: (a) 2 8 7 0 revertants cor r es pond t o an ext ract from a 15-m 3 air sample, (b) 15 m 3 o f air contain a b o u t 6 pg of BaP, (c) 6/~g o f BaP gives a b o u t 2400 revertants, as shown by these studies, imply t hat the air samples f r o m Lalbag contain mutagens whose c o m b i n e d activity is detectable with the present bioassay. In similar studies, G or da n et al. [5] emphasise t hat BaP alone c a n n o t be considered as the index of air pollution.
280 In another study in the Lalbag area, the presence of gases such as NO2 and SO2 and a higher incidence of respiratory-tract disease were reported [3]. Independent experiments employing fumigation with the two gases, separately and together, have shown that higher toxicity towards the plant Poa pratensis was noted when the two gases were present together [4]. The Lalbag area is located in central Bombay and is known for its high population density, large number of textile mills, closely spaced buildings, a coal gas plant and heavy vehicular traffic through three main traffic arteries. Hence, the observed higher morbidity in this area is self-explanatory and agrees with the higher experimental value of mutagenicity given here due to the SPM from this region. For the Chembur, Santacruz and Parel areas, the number of revertants of TA 100 per 1 5 m 3 of air sample are 1570, 1380 and 1280, respectively, indicating moderately high mutagenicity. There are fewer sources of air pollution in Parel and Chembur than in Lalbag. Santacruz is devoid of textile mills and coal gas plants and has a smaller, diffuse population, but international and domestic airports are located in this region. The only source of air pollution in the other areas Vidyavihar, Peddar Road and Borivli is vehicular traffic, with Borivli having the least. The observed mutagenicity due to SPM from these areas is proportionately less.
CONCLUSION The overall pattern of mutagenic air pollution in Bombay, discussed above, seems to suggest the occurrence of c o m m o n sources of pollution such as gases from industries or coal gas plants, or automobile exhausts. These studies need to be carried out more extensively with chemical analysis and perhaps with one more bioassay system so that the data thus obtained would help in the design of future townships and in the more efficient monitoring of air pollution.
REFERENCES
1 T.J.Hughes, E. Pellizzari, L. Little, C.Sparcino and A. Kolber, Ambient airpollutants: collection, chemical characterization and mutagenicity testing, Murat. Res., 76 (1980) 51--83. 2 A.M.Mohan Rao and K.G. Vora, The concentration of benzo(a)pyrene in Bombay, Atmos. Environ. 9 (1975) 403--408. 3 P.S. Kamath, Prospective study of health morbidity in relation to air pollution in Bombay, India, urban and rural comparison, Report of the study by Air Pollution Prevention Cell, Municipal Corporation of Greater Bombay, Bombay, 1978. 4 J.N.B. Bell, Air pollutants act in combination, Nature, 300 (1982) 14--15. 5 R.J. Gordon, R.J. Bryan, J.S. Rhim, C. Demoise, R.G. Wolford, A.E. Freeman and R.J. Huebner, Transformation of rat and mouse embryocells by a new class of carcinogenic compounds isolated from city air, Int. J. Cancer, 12 (1973) 223--232.
281 6 R. Talcott and E. Wei, Airborne mutagens bioassayed in Salmonella typhimurium, J. Natl. Cancer Inst., 58 (1977) 449--451. 7 T. Hiroshi, S. Kitamori, K. Takahashi and Y. Ohnishi, Mutagenic and chemical assay of extracts of airborne particulates, Mutat. Res., 77 (1980) 99--108. 8 C.E. Chrisp and G.L. Fisher, Mutagenicity of airborne particles, Mutat. Res., 76 (1980) 143--164. 9 H.Fukino, S. Mimura, K. Inoue and Y. Yamane, Mutagenicity of airborne particles, Mutat. Res., 102 (1982) 237--247. 10 B.N. Ames, J. McCann and E. Yamasaki, Method for detecting carcinogens and mutagens with a Salmonella]mammalian microsome mutagenicity test, Mutat. Res., 31 (1975) 347--364. 11 W.J. Nocholson and F.L. Pundsack, Asbestos in The Environment, in P. Bagovski, J.C. Gilson, V. Timbrell and J.C. Wagner (Eds.,) Biological Effects of Asbestos IARC Publication No. 8, Lyon, 1973, pp. 126--132.
275
STUDY OF MUTAGENIC POLLUTION IN BOMBAY
C.N. SHENOY and K.A. CHAUBAL Biophysics Division, Cancer Research Institute, Tata Memorial Centre, Parel, Bombay-400 012 (India)
(Received October 18th, 1983; accepted November 30th, 1983)
ABSTRACT Airborne suspended particulate matter (SPM) from seven areas in and around Bombay city were collected over glass fibre filters (0.8 pm porosity). The chemicals from the SPM were extracted in dimethylsulfoxide and distilled water and were further tested for mutagenicity by Ames' test using five mutants of Salmonella typhimurium. Of the seven areas studied, only four exhibited mutagenicity, which was confirmed by dose--response assays using the mutant strain TA 100. The very high mutagenicity observed in central Bombay correlates with the higher incidence of respiratory tract diseases in the resident population.
INTRODUCTION T h e i n c i d e n c e o f lung c a n c e r a n d c a n c e r m o r b i d i t y r a t e s are o n t h e increase all o v e r t h e w o r l d . A n u m b e r o f n e w c h e m i c a l s are b e i n g s y n t h e s i z e d a n d r e a c h h u m a n p o p u l a t i o n t h r o u g h f o o d , w a t e r a n d air. Several o f t h e s e c h e m i c a l s m a y b e c a p a b l e o f p r o d u c i n g c a n c e r o u s c o n d i t i o n s a n d an increase in t h e i r n u m b e r a p p e a r s u n a v o i d a b l e , c o n s i d e r i n g t h e a c c e l e r a t i n g t e c h n o l ogical g r o w t h y e a r a f t e r y e a r . T h e u r b a n air c o n t a i n s a large v a r i e t y o f p o l l u t a n t s [ 1 - - 9 ] , b o t h gaseous a n d p a r t i c u l a t e , o r i g i n a t i n g m a i n l y f r o m industrial c h i m n e y s , a u t o m o b i l e e x h a u s t s a n d d o m e s t i c sources. A s t u d y o f air p o l l u t a n t s a n d h e a l t h m o r b i d i t y in B o m b a y , I n d i a [3] s e e m s to c o n f i r m c o r r e l a t i o n b e t w e e n higher levels o f p o l l u t a n t s ( s u s p e n d e d p a r t i c u l a t e m a t t e r (SPM), s u l p h u r d i o x i d e a n d n i t r o g e n o x i d e ) a n d higher i n c i d e n c e o f r e s p i r a t o r y diseases. In a n o t h e r s t u d y in B o m b a y , e m p l o y i n g c h e m i c a l analysis [ 2 ] , a higher c o n c e n t r a t i o n o f t h e c a r c i n o g e n b e n z o [a] p y r e n e (BaP) was n o t i c e d in t h e area w h i c h i n d i c a t e d higher m o r b i d i t y . P r o m p t e d b y t h e s e o b s e r v a t i o n s , it was d e c i d e d t o c o l l e c t SPM in several areas (industrial a n d residential) in a n d a r o u n d t h e c i t y o f B o m b a y , a n d t o a n a l y s e t h e s e f o r t h e i r m u t a g e n i c p o t e n t i a l . T h e s e studies c o u l d be e x t e n d e d in o r d e r t o v e r i f y w h e t h e r m u t a g e n i c i t y is d u e t o o n e c h e m i c a l or a c o m b i n a t i o n o f c h e m i c a l s . This a s p e c t has t o be e m p h a s i s e d i n
276
13-
3ool
LOCALITY: L A L B A G STRAIN : TA 1OO
®
200 W > 0----0 0---0 .C.. -', A,---.A
100 .,./
tl
~
0,1
0.2 AMOUNT
300
DMSO + DMSOWATER WATER
0,5 OF
O- 4
EXTRACT
LOCALITY
: PAREL
STRA, N
: TA 100
$9 $9 + $9 - $9
IN
ML
@
o.
~ =
~°° F
~oDMSO 4- S9 ~j~______..~ ,,,ATER + S9
I look
~ _ _ . - o OMSO - S9 .~.-::-:::----,
F
,',ATE.-
S.
;2-"'I 0.2
0,1 AMOUNT
u,I
300 ,.I a. n,.
OF
I 0'3
EXTRACT
LOCALITY
:
STRAIN
: TA I 0 0
I 0,4
(ml)
SANTACRUZ
ImJ
a.
200 z I,,t¢
DMSO + $9 OMSO
--
S9
WATER -- $9 . ~ : 2 - ~ 2 2 - - -~-AI
0-1 AMOUNT
0'2 OF
EXTRACT
0'3 (ml)
0-4
277 laJ I--
<
..I Q.
300
LOCALITY
: CHEMBUR
STRAIN
: TA
IOO
a* r,
co 2 0 0 Iz
w
h,
D M S O + S~,) W A T E R -4- S 9
100
OMSO
j-~'.-~
0.1
0.2 AMOUNT
OF
0.3 EXTRACT
--
$9
W A T E R -- $ 9
0.4
(ml)
Fig. 1. Dose--response graphs of SPM extracts from four areas in Bombay: (a) Lalbag, (b) Parel, (c) Santacruz, (d) Chembur. The n u m b e r of revertants per plate with DMSO and water (155 + 20 and 150 + 20, respectively) were subtracted. Each graph is representative of three independent experiments.
air pollution studies as there is more possibility of chemicals occurring in the complex form than as individual ones [ 1 ].
MATERIALS AND METHODS
It is k n o w n t h a t SPM of size < 3 . 5 p m contains a greater a m o u n t of mutagenic activity/unit sample mass [1]. It is also known that SPM of size > 0 . 8 # m is respirable [11]. Hence, SPM of size > 0 . 8 p m was collected for 24 h on glass fibre filter paper (BARC, Bombay, India) with a vacuum pump having a suction rate of about 16 m3/min. The samples were collected from surroundings which were about 10--12 ft from the ground level and about 20 ft from the nearest road. The different areas selected for this study are shown in Fig. 2.
Extraction o f mutagens The filter paper, with its deposit of SPM, was cut into two halves, each half being further cut into smaller bits and ground in a pestle and mortar using d i m e t h y l sulfoxide (DMSO) as solvent for one half and distilled water for the other. It was then sonicated in cold and centrifuged to remove glass fibre residues. The two supernatants, containing chemicals soluble in DMSO and water, respectively, were t h e n filtered through filters of porosity 0.45 pm (Millipore) to remove microbial contamination.
Mutagenicity test The mutagenicity of the extracts was tested following the procedure of Ames et al. [10]. In the initial screening all five strains, namely TA 1535, TA 1537, TA 1538, TA 98 and TA 100, were studied. The criterion of
278 comparing the number of revertant colonies, corrected to background, was e m p l o y e d to check the sensitivity of the five strains. The dose--response relationships were obtained using the strain TA 100, which showed m a x i m u m activity, and were confined to the extracts from the areas Lalbag, Parel, Chembur and Santacruz, which gave high to very high mutagenicity.
Microsomal activation system Wistar rats weighing 150--200g were injected with Aroclor 1254 to elevate the microsomal enzyme activity, which is an essential step in achieving m a x i m u m activation of mutagens to their ultimate electrophilic form. Positive controls 3,4-Benzo[a]pyrene (BaP) and N-methyl-N-nitro-N-nitrosoguanidine (MNNG) were used as positive controls in these experiments. RESULTS Calculations made after considering the rate of pumping air through the filter paper have shown that 0.1 ml of extract, in the present work, is equivalent to 0.5 m 3 of air sample. The DMSO and water extracts of samples from all the areas studied in this work exhibited mutagenicity. It was highest for Lalbag, followed by Parel, Chembur, Santacruz and Peddar Road, Vidyavihar, Borivli. In both DMSO and water extracts the number of revertants increased with the addition of $9 mixture. With 2 pg of MNNG alone, i.e., w i t h o u t the $9 fraction, the number of revertants per. 2 × 10 s bacteria of TA 100 was 550; while the similar number for 4 pg (BaP) with the $9 fraction was 1600. The extracts from Peddar Road, Vidyavihar and Borivli, studied initially with all five strains, showed marginal activity in preliminary tests and hence the dose--response relationship for SPM from these areas was not obtained. The graphs shown in Fig. l a d are representative of three independent experiments. These show that the extracts from Lalbag, Parel, Chembur and Santacruz exhibit high to very high mutagenicity and that it is due to the water/DMSO soluble fraction of SPM. Several other factors such as location of industries, air-port, open areas with trees, flow of air currents, for which no measurements were made, are compared with the mutagenic pollution studied in this work and are shown in Fig. 2. The + signs in Fig. 2 have been chosen arbitrarily to give a rough estimate of the a m o u n t of air pollution in terms of (BaP) activity.
DISCUSSION As mentioned in the Results, 0.1ml of extract from the Lalbag area is from 0.5 m 3 of air and corresponds to 287 revertants. Extrapolation of this
279
SANTACRUZ (+ -t- + )
BORIVLI (+)
/9"'" ~
eeo
~
o°
~
t
...
VIDYAVIHAR (+)
i oo
,A/
~ eo
J/
oeo
i
c~ °
/
-'"
PAREL (+
I
1ODe
,/J
~ ~
ooo
...
CHEMBUR (-t--t--I" )
000
~
LALBAUG (++++-I-)
~'~/
°"
[~
ool
~
•
~'~%.~)'
JJ° '~
* *
0
"-
*
PEDDAR Rd.(+]
~-~j-
TEXTILE
MILLS
¢~_.~-- VEHICULAR
...
TRAFFIC
-- P O P U L A T I O N
JJ
•
,,/,/ . . . '~
(+)
INDICATES MUTAGENS EOUIVALENT TO 1-2/Jgms OF B (o)P/tSm 3 AIR
DENSITY
-- PETROCHEMICALS - - COAL
UTILIZATION
-- A I R I.
TRAFFIC
I -- O P E N
SPACE
,~
-- T R E E S eee
HiGH 1
ee
MEOIUMp
•
LOW #//~v/
-- AIR
CURRENTS
Fig. 2. A map of Bombay showing the location of zones where SPM samples were collected. The other factors in the Figure (see Results), represented for comparison, are from general observation.
n u m b e r o f 15 m 3 o f air, which is a b o u t the q u a n t i t y a man breathes per day, means ar o u n d 2870 revertants. Earlier studies carried out in the same area [2] have shown the mean BaP value is 4 0 p g per 1 0 0 m 3 of air, i.e., 6 p g of BaP per 15 m 3 o f air. The positive c o n t r o l e xpe r i m e nt s described in t he present w o r k have shown th at 4 pg o f BaP produces 1600 revertants. If this n u m b e r is extrap o lated to 6 #g, we obtain ar ound 2400 revertants. The facts that: (a) 2 8 7 0 revertants cor r es pond t o an ext ract from a 15-m 3 air sample, (b) 15 m 3 o f air contain a b o u t 6 pg of BaP, (c) 6/~g o f BaP gives a b o u t 2400 revertants, as shown by these studies, imply t hat the air samples f r o m Lalbag contain mutagens whose c o m b i n e d activity is detectable with the present bioassay. In similar studies, G or da n et al. [5] emphasise t hat BaP alone c a n n o t be considered as the index of air pollution.
280 In another study in the Lalbag area, the presence of gases such as NO2 and SO2 and a higher incidence of respiratory-tract disease were reported [3]. Independent experiments employing fumigation with the two gases, separately and together, have shown that higher toxicity towards the plant Poa pratensis was noted when the two gases were present together [4]. The Lalbag area is located in central Bombay and is known for its high population density, large number of textile mills, closely spaced buildings, a coal gas plant and heavy vehicular traffic through three main traffic arteries. Hence, the observed higher morbidity in this area is self-explanatory and agrees with the higher experimental value of mutagenicity given here due to the SPM from this region. For the Chembur, Santacruz and Parel areas, the number of revertants of TA 100 per 1 5 m 3 of air sample are 1570, 1380 and 1280, respectively, indicating moderately high mutagenicity. There are fewer sources of air pollution in Parel and Chembur than in Lalbag. Santacruz is devoid of textile mills and coal gas plants and has a smaller, diffuse population, but international and domestic airports are located in this region. The only source of air pollution in the other areas Vidyavihar, Peddar Road and Borivli is vehicular traffic, with Borivli having the least. The observed mutagenicity due to SPM from these areas is proportionately less.
CONCLUSION The overall pattern of mutagenic air pollution in Bombay, discussed above, seems to suggest the occurrence of c o m m o n sources of pollution such as gases from industries or coal gas plants, or automobile exhausts. These studies need to be carried out more extensively with chemical analysis and perhaps with one more bioassay system so that the data thus obtained would help in the design of future townships and in the more efficient monitoring of air pollution.
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