Lead levels in teeth of an urban Indian population

The Science of the Total Environment, 58 (1986) 231-236 Elsevier Science Publishers B.V., Amsterdam - - Printed in The Netherlands

231

L E A D L E V E L S IN T E E T H O F AN U R B A N I N D I A N P O P U L A T I O N

R.N. KHANDEKAR, RADHA RAGHUNATH and U.C. MISHRA

Air Monitoring Section, Bhabha Atomic Research Centre, Trombay, Bombay 400 085 (India)

ABSTRACT The lead content of teeth of Bombay residents has been determined using differential pulse anodic stripping voltammetry. The median tooth lead concentrations for adults and children in Bombay are estimated to be 8.31 and 3.01 #g/g of tooth, respectively. The data indicate that the lead concentration of a tooth increases with the age of the donor. For children the tooth lead content varies with the type of tooth. Further, children living in industrial areas have a higher tooth lead content than children living in the cleaner suburbs of Greater Bombay.

INTRODUCTION There is considerable concern regarding the environmental lead exposure of urban populations and its harmful effects, especially on growing children. It is well known t h a t small quantities of this element can cause profound biochemical and neurological changes in man. Several sources, such as lead in paint, atmospheric emissions from industries, lead plumbing and automobile exhaust, have been identified as potential contributors to the intake of lead by the population. T h r o u g h ingestion and inhalation, the hum an body acquires small but measurable concentrations of lead which gradually accumulate. Elevated levels of this metal are therefore observed in some tissues and have been used to discriminate between groups of individuals subjected to different degrees of exposure. Generally, blood is a good indicator of current exposure to lead. Since blood lead levels decline once exposure ceases, they cannot be considered as indicative of earlier exposure. Tooth lead levels, on the other hand, have the advantage of reflecting the cumulative lead burden over a finite time. Although the q u an tity of lead stored in t e e t h is only a small fraction of the total lead in the body, toot h lead constitutes a uniquely accessible indicator of cumulative lead exposure. Bombay is one of the largest industrial cities of India, having many industrial users of lead and more t h a n 400 000 motor vehicles. It is estimated t hat nearly 450 tonnes of lead is emitted annually into the atmosphere of G reat er Bombay t h r o u g h automobile exhaust [1]. Environmental monitoring of air, water and food was therefore carried out in Bombay to assess the exposure of the population to this metal [2]. Biological monitoring t hrough blood and teeth was carried out to provide an essential link to health effect monitoring. A

232 preliminary report on the lead levels in the teeth of Bombay residents has been published [3]. This work has now been extended and the present paper gives a detailed report on lead levels in teeth of Bombay residents. EXPERIMENTAL

Sampling All subjects studied are members of the Bhabha Atomic Research Centre's (BARC) Contributory Health Service Scheme and reside in different areas of Bombay. Teeth samples were collected at random from the Dental Unit of BARC Hospital. Information, such as age at the time of extraction, sex and address, was recorded. All teeth were non-carious and non-restored. After collection the teeth were cleaned with double distilled water and kept in 30~o H202 solution for 30min. After air drying and weighing, they were placed in cleaned polythene bags and sealed. The tooth weight varied from 0.06 to 1.8 g.

Decomposition and Dissolution All laboratory ware was first t hor oughl y cleaned, immersed in a mixture of 2 M H N Q and 3 MHC1 for several days and then rinsed t horoughl y with double distilled water. Each tooth sample ( ~ 0.5 g) was dissolved in 3 ml of 70~o nitric acid (Electronic grade) and 1 ml of 70~/o perchloric acid (Analar grade). After slow heating, a clear, colourless solution was obtained which was evaporated to n ear dryness. The residue was t a k e n up in 10 ml of 0.25% nitric acid. The lead in 0.1 ml of this solution was determined.

Analysis The lead concentrations were measured by differential pulse anodic stripping voltammetry (DPASV) using a P r i n c e t o n Applied Research PARC-174-13 polarographic analyzer system. The details of the measurements are given elsewhere [4]. Together with each batch of five samples, one reagent blank was determined t h r o u g h o u t the whole procedure to assess the lead blank value for the chemicals used and also the positive or negative contamination during the decomposition procedure. Reagent blank values were quite low compared with those of teeth samples (the ratio of sample to blank varied between 5 and 60). The accu r acy and precision of the voltammetric method was checked by measurements with thermal ionization isotope dilution mass spectrometry during our precipitation in an i n t e r l a b o r a t o r y t oot h lead analysis experiment [5] arranged by the Chemistry Department, University of Birmingham and the Dental Unit of the Medical Research Council, Bristol, U.K. The mass spectr o metr y measurements were very similar (within 5%) to the voltammetric determinations. The standard deviation, calculated on the basis of 15 indepen-

233 dent determinations on a synthetic solution, was within + 4%. The results of quadruplicate analyses of actual teeth samples agreed within _+6%. RESULTS AND DISCUSSION The distribution of lead in the teeth of a particular population can be represented by a log-normal distribution, as shown in our earlier report [3]. Consequently, all statistical analyses in this report have been carried out using ln[Pb], where [Pb] is the lead c o n c e n t r a t i o n in #g/g of whole tooth. The median tooth lead c o n c e n t r a t i o n s and the geometric standard deviations for adults and children of G r e a t e r Bombay are given in Table 1. The tooth lead c o n c e n t r a t i o n for children ranged from 0.22 to 14.4 pg/g of tooth with a median c o n c e n t r a t i o n of 3.01 pg/g of tooth. This is comparable with the Norwegian value of 2.92 pg/g of to o th [6] and lower t han American values [7, 8]. The lead c o n c e n t r a t i o n in adult teeth in Bombay ranged from 2 to 28.8pg/g of whole tooth with a geometric mean of 8.31#g/g of tooth, which is lower t han our previously reported value (15.5#g/g of tooth). This may partly be due to the use of improved analytical techniques which are free from interference and matrix effects. The previous results are, therefore, not included in this report. The median tooth lead c o n c e n t r a t i o n for a Bombay male adult (8.79 #g/g of tooth) is higher t han t h a t of a female adult (7.98 pg/g of tooth); however, the 't' test shows t hat there is no significant difference between the median values of the lead content of teeth of males and females. Similarly, Bombay male children have a higher lead co n ten t (median c o n c e n t r a t i o n 3.14 pg/g of tooth) t han female children (median c o n c e n t r a t i o n 2.9 #g/g of tooth), but the difference is not statistically significant. The age distribution of tooth lead in Bombay residents (Table 2) indicates t h a t the lead c o n c e n t r a t i o n in teeth increases with age of the donor. Similar results were observed by Fremlin and Edmonds [9] for residents of Birmingham and Sheffield and by Strehlow and Kneip [10] for American subjects. Lead, like calcium, is deposited in the skeleton by mineral formation as well as by long term exchange. Unlike bone, dental hard tissues are not normally involved in TABLE 1 Tooth lead concentration of Bombay residents (pg of lead/g of tooth) Sample

Adult

Number of samples

Geometric mean (~g/g of tooth)

Geometric standard deviation

Range

(total) Male Female

71 30 41

8.31 8.79 7.98

1.20 1.24 1.17

2.0-28.8 2.2-28.8 2.0-24.8

Children (total) Male Female

179 85 94

3.01 3.14 2.91

1.22 1.18 1.26

0.22 14.4 1.1-14.4 0.22-14.3

234 TABLE 2 Age distribution of tooth lead Age of donor (years)

Number of samples

Geometric mean ~ g / g of tooth)

Geometric standard deviation

1-14 1~29 3{~44 45~0

179 15 35 21

2.97 5.69 8.11 11.33

1.22 1.Q8 1.16 1.26

the life-long remodeling process. Once fully formed, the dentine and enamel do not undergo calcification. The dentine is subject only to a deposition of minerals. However, both dentine and enamel are subject to ionic exchange with adjacent fluids whether they be connective tissue fluids or saliva (in the case of enamel). Several t r a c e r studies indicate t hat teeth are permeable to ions in both directions, w he t he r uptake is from internal or external exposure [10]. It may be noted t hat some investigators have observed more lead in the dentine portion of teeth [9, 11, 12] and others have observed more lead in the enamel [10, 13]. It has been observed by Fosse [6] t hat the whole tooth lead levels are comparable with dentine lead levels, since the ratio between dentine and whole tooth lead is 1.13 due to the high volume of dentine per tooth. We did not separate the enamel and dentine of teeth; the lead concentrations given in this paper are for the whole tooth. The lead c ont e nt of the teeth of children was examined in terms of the type of tooth (Table 3). For each type of t oot h studied, the geometric mean lead levels in incisors and canines were higher t han t hat in molars (P < 0.05) (two side 't' test). The difference between canines and incisors was not significant. Similar observations on the variations in lead content with type of tooth have been reported by Lockeretz [7] and Waldram et al. [14], and one should take this point into account when comparing or classifying children as having lower or higher dental lead levels. The data for the lead content of canines and incisors of children living in four different suburbs of G r eat er Bombay are summarized in Table 4. The tooth TABLE 3 Lead c o n c e n t r a t i o n in different types of childrens teeth Type of tooth

N u m b e r of samples

Geometric mean (#g/g of tooth)

Geometric standard deviation

Incisor Canine Molar

38 23 42

4.5 4.1 2.5

2.2 2.0 1.7

235 TABLE 4 Area distribution of tooth lead in children Place of residence

Number of samples

Geometric mean (pg/g of tooth)

Range

Bandra Chembur Anushkti Nagar (Deonar) Ghatkopar

14 21 71

2.27 2.44 2.77

0.27-3.73 0.2~7.27 0.9~.85

21

4.52

1.7 14.4

lead levels a r e low in B a n d r a (2.27pg/g of tooth), C h e m b u r (2.44#g/g) a n d A n u s h a k t i N a g a r (2.77 pg/g), a n d h i g h in G h a t k o p a r (4.52 pg/g). B a n d r a , Chemb u r a n d A n u s h a k t i N a g a r a r e r e l a t i v e l y u n p o l l u t e d s u b u r b a n a r e a s of G r e a t e r B o m b a y , h a v i n g low v e h i c u l a r traffic d e n s i t y a n d p r a c t i c a l l y no i n d u s t r i a l e m i s s i o n s of lead. H i g h e r t o o t h lead levels in t h e G h a t k o p a r a r e a c a n be a t t r i b u t e d to h i g h e r v e h i c u l a r traffic d e n s i t y a n d i n d u s t r i a l emissions. H i g h a t m o s p h e r i c lead c o n c e n t r a t i o n s h a v e also b e e n o b s e r v e d a t G h a t k o p a r comp a r e d w i t h C h e m b u r , B a n d r a a n d A n u s h a k t i N a g a r [15]. I n the city of B o m b a y a u t o m o b i l e e x h a u s t e m i s s i o n is a significant s o u r c e of a t m o s p h e r i c lead. T h e e n v i r o n m e n t a l lead e x p o s u r e of t h e a d u l t p o p u l a t i o n h a s b e e n e s t i m a t e d by m e a s u r i n g lead in air, w a t e r , food a n d c i g a r e t t e s m o k e [16]. It h a s b e e n estim a t e d t h a t t h e a v e r a g e lead i n t a k e of a n a d u l t living in B o m b a y is 33 pg per day. H o w e v e r , t h e lead i n t a k e of B o m b a y c h i l d r e n could n o t be e s t i m a t e d , as the food i n t a k e d a t a for c h i l d r e n is n o t a v a i l a b l e . I t h a s b e e n o b s e r v e d t h a t t h e blood lead levels of c h i l d r e n living in t h e c e n t r a l p a r t s of B o m b a y a r e h i g h e r (14.6#g dl 1) t h a n t h o s e of c h i l d r e n living in s u b u r b a n a r e a s (9.4pgd1-1) [1]. Efforts a r e b e i n g m a d e to o b t a i n t o o t h s a m p l e s of c h i l d r e n f r o m c e n t r a l p a r t s of B o m b a y , as t h e y m a y show m u c h h i g h e r lead levels. T h i s s u r v e y of t o o t h lead levels h a s s h o w n t h a t t h e a b s o r p t i o n of lead f r o m the e n v i r o n m e n t by c h i l d r e n of s u b u r b a n B o m b a y is of m o d e r a t e degree. ACKNOWLEDGEMENTS T h e a u t h o r s wish to express t h e i r t h a n k s to D r S.K. S a h u k a r a n d Dr K.R. M u n i m of t h e D e n t a l U n i t of B A R C H o s p i t a l for s u p p l y i n g the t e e t h samples. H e l p f r o m D r P.V. J o s h i is also a c k n o w l e d g e d . REFERENCES 1 R.N. Khandekar, in Proceedings of All-India Seminar on Vehicular Emissions, The Institute of Engineers (India), 1985, pp. C300-C312. 2 R.N. Khandekar, U.C. Mishra and K.G. Vohra, Sci. Total Environ., 40 (1984) 269-278. 3 R.N. Khandekar, S.C. Ashawa and D.N. Kelkar, Sci. Total Environ., 10 (1976) 129-133.

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