Lead levels among various deciduous tooth types - National Taiwan ...

Bull. Environ. Contam. Toxicol. (1991) 47:602--608 9 1991 Springer-Verlag New York Inc.

Environmental ~C o n t a m i n a t i o n ~and Toxicology

Lead Levels among Various Deciduous Tooth Types Michael B. Rabinowitz, 1'2 David Bellinger, 1 Alan Leviton, 1 and Jung-Der Wang 2 1Neuroepidemiology Unit, Children's Hospital, Boston, Massachusetts 02115, USA and 2Graduate Institute of Public Health, National Taiwan University, Taipei, Taiwan

The amount of lead in d e c i d u o u s teeth has been u s e d e x t e n s i v e l y as a marker for infant lead e x p o s u r e and body burden (Needleman et al 1972 and F e r g u s s o n et al 1989). However, the p a t t e r n of lead a b u n d a n c e s among the v a r i o u s tooth p o s i t i o n s in a child's m o u t h appears to be non-uniform. Several i n v e s t i g a t o r s have r e p o r t e d that, on average, shed incisors have higher lead concentrations than molars (Mackie et al 1977 and P i n c h i n et al 1978). Shapiro et al (1975) r e p o r t e d that canines have more lead than incisors, while Patterson et al (1988) found that incisors have more than canines. Teeth from the lower jaw have b e e n r e p o r t e d to have more lead than upper teeth (Pinchin et al 1978), and the opposite relationship has also been d e m o n s t r a t e d (Smith et al 1983). Taken together these findings show an apparently inconsistent pattern among the tooth types. These c o m p a r i s o n are c o m p l i c a t e d by d i f f e r e n t r e s e a r c h groups u s i n g d i f f e r e n t p o r t i o n s of the tooth (ie, some use the whole crown, some use s e c o n d a y dentin, and others the c i r c u m p u l p a l dentin), so some of the v a r i a t i o n among tooth types might be an artifact of analytical techniques. A n a t o m i c a l v a r i a b i l i t y among tooth types or p o p u l a t i o n based d i f f e r e n c e s in e x p o s u r e p a t t e r n s might also account for some of these a p p a r e n t d i s c r e p a n c i e s . This issue is of significance to those who w i s h to c o m p a r e the lead b u r d e n of c h i l d r e n but have a v a i l a b l e teeth from different positions from the various children. By e x a m i n i n g a large n u m b e r of teeth from two d i f f e r e n t populations, we hope to explore the more u n i v e r s a l aspects of any v a r i a b i l i t y among tooth types. Send reprint requests Biological Laboratory,

to M. B. Woods Hole,

602

Rabinowitz, M a r i n e MA 02543 USA.

MATERIALS

AND

METHODS

As part of on-going studies of the role of lead in child development, we collected shed teeth from a cohort of unexceptional children who have been followed from birth in Boston. Details of the p o p u l a t i o n ( N e e d l e m a n et al 1984) and c h e m i c a l a n a l y s i s ( R a b i n o w i t z et al 1989) h a v e b e e n p u b l i s h e d . The o t h e r cohort was primary school children in Taiwan, the R e p u b l i c of China (Rabinowitz et al 1991). Two of those s e v e n s c h o o l s w e r e c h o s e n b e c a u s e they w e r e n e a r lead smelters, and five s c h o o l s in u r b a n Taipei. The t e a c h e r s in grades 1 to 3 a s k e d the c h i l d r e n for any shed t e e t h over a 14 w e e k period. The m e a n (SD) ages of s h e d d i n g was 7.2 (.7) y e a r s for incisors, 8.2 (.8) for canines and 8.3 (.9) for molars. There was no d i f f e r e n c e in these ages b e t w e e n the c h i l d r e n n e a r the s m e l t e r s or in the city for any tooth type (t=.7, p=.5). All of these t e e t h w e r e t r e a t e d e x a c t l y the same to i s o l a t e the p o s t - n a t a l d e n t i n and m e a s u r e lead by anodic s t r i p p i n g v o l t a m e t r y . The lead was determined in two p o r t i o n s of d e n t i n t a k e n f r o m the zone p r e s u m a b l y r e p r e s e n t a t i v e of p o s t natal deposition. A f t e r washing, c r o s s - s e c t i o n a l slabs of the shed tooth m a t e r i a l were o b t a i n e d by s a g i t t a l l y s l i c i n g the tooth with a l o w - s p e e d saw. This slab was w r a p p e d w i t h Parafilm, and a h a n d chisel was u s e d to i s o l a t e the d e s i r e d p o r t i o n s . A cut was m a d e f r o m just b e l o w the c e m e n t u m - e n a m e l junction, w h i c h was v i s i b l e in the silhouette of the tooth, to a p o i n t m i d w a y b e t w e e n the top of the p u l p c a v i t y and the crown. For incisors this cut approximates the n e o n a t a l line. A m i d l i n e cut was also made. For deciduous teeth w i t h the n o r m a l a m o u n t of root r e s o r p t i o n , this y i e l d e d two enamel free specimens of 10-15 mg each from the interior. Identical standards and i n s t r u m e n t s w e r e u s e d for b o t h populations. Statistical comparisons use a 2-tailed Student's t-test of the logarithm of the lead concentration. RESULTS AND DISCUSSION In g e n e r a l t e e t h from American and Chinese children have overlapping r a n g e s of lead c o n c e n t r a t i o n s (Table i). In b o t h cohorts, maxillary and mandibular teeth h a v e the same a v e r a g e lead c o n c e n t r a t i o n s , w h e t h e r all teeth or only incisors are considered. Concerning lateral and central incisors, in Boston the u p p e r c e n t r a l i n c i s o r s h a d m o r e lead (pffi.004), but in T a i w a n this difference was absent. In both cohorts the i n c i s o r s h a v e m o r e lead than canines. However, the 603

Table I. Dentin two cohorts T o o t h Type N Incisors All Central Upper Lower Lateral Upper Lower Canines All Upper Lower Molars First Upper Lower Second U p p e r Lower All T e e t h Upper Lower

lead

levels

in d e c i d u o u s

Taiwan Mean SD

N

teeth

from

Boston Mean

SD

567 284 161 123 283 144 139

4.5 4.4 4.4 4.4 4.7 4.6 4.7

3.4 2.8 2.9 2.8 3.9 2.7 4.9

2187 1336 617 719 851 487 364

3.4 3.4 3.5 3.4 3.3 3.1 3.4

2.6 2.4 2.6 2.3 2.6 2.5 2.7

*,# @

111 44 67 75 37 30 4 4

3.8 3.6 3.9 2.9 3.1 2.5 3.5 2.9

2.8 2.0 3.2 2.2 2.7 1.6 1.9 1.5

21 9 12 123 34 86 2 1

2.3 1.9 2.7 3.3 4.2 2.9 3.4 5.4

1.6 .8 1.9 4.3 7.7 1.8 2.9

*

390 363

4.3 4.3

2.7 3.8

1149 1182

3.4 3.4

2.8 2.4

@

#

* Incisors have more lead than canines in each cohort, p=.03 in Taiwan, p=.002 in Boston. # Incisors have more lead than molars, p = . 0 0 0 1 in Taiwan, p=.07 in Boston. @ L a t e r a l incisors have less lead than central incisors in Boston, p=.01, in T a i w a n lateral incisors have more, p=.2.

molars, w h i c h are the last to form, have higher levels than the canines in B o s t o n but not Taiwan.

lead

In c o m p a r i n g the p a t t e r n s of lead c o n c e n t r a t i o n s seen in this study with published accounts of similar examinations, a strikingly disparate pattern is apparent (Table 2). For example, among 7 studies compairing central to lateral incisors, the central i n c i s o r s a v e r a g e d h i g h e r lead levels than the lateral incisors in three and in three other groups the reverse tended to be true. The r e l a t i o n s h i p b e t w e e n lead levels in upper and lower teeth also seems to v a r y among the studies.Differing analytical techniques which make use of d i f f e r e n t p o r t i o n s of the tooth have b e e n used by various workers, and this can be r e s p o n s i b l e for some of the disparity. For example, Grandjean (1986) r e p o r t e d that upper central incisors have more or less lead than other incisors d e p e n d i n g on w h e t h e r the w h o l e 604

tooth or the c i r c u m p u l a l d e n t i n is used. However, we u s e d the same technique, m e a s u r i n g p o s t - n a t a l d e n t i n in two cohorts, and found the central i n c i s o r to have m o r e in B o s t o n but not Taiwan. These d i f f e r e n c e s in lead levels among d e c i d u o u s tooth types among populations are unlikely to reflect p h y s i o l o g i c a l factors (ie. blood supply to teeth or mineralization rates). Rather these population d i f f e r e n c e s are much more lilely to depend on age related, and c o n s e q u e n t l y tooth related, d i f f e r e n c e s in exposure patterns among the populations. D e n t i n in incisors, canines, and m o l a r s c a l c i f y at o v e r l a p p i n g but d i f f e r e n t times (Schour and M a s s l e r 1941). So they could retain varying amounts of lead. Thus, if a child's b l o o d lead level varied widely d u r i n g these years of tooth formation, d i f f e r e n t amounts of lead would be deposited in teeth at different rates (Rabinowitz et al 1984). Calcification of a tooth never c o m p l e t e l y stops as long as there is b l o o d supply, but the shed p o r t i o n s we collected, which are mostly from within the tooth crown, are deposited early in the tooth's h i s t o r y (Levine et al 1979). C a l c i f i c a t i o n of d e c i d u o u s d e n t i n appears first w i t h i n the crown, and then p r o g r e s s i v e l y a d v a n c e s towards the root and inward towards the p u l p along a conical zone of mineralization. For the d i f f e r e n t tooth types these events occur at d i f f e r e n t times. For example, upper central incisors begin calcification near the third fetal month and the coronal d e n t i n is l a r g e l y c o m p l e t e d by the third post natal month. Lower central incisors u s u a l l y lag by one or two months. Canine crowns c a l c i f y d u r i n g the forth through ninth p o s t - n a t a l months, w h i l e m o l a r s b e g i n in utero and c o n t i n u e to c a l c i f y d u r i n g the first year. If lead deposition were simply concurrent with calcification, and if lead exposure varied considerably during these spans of c a l c i f i c a t i o n , then the teeth w o u l d s h o w different lead levels. Even if tooth lead levels r e p r e s e n t b l o o d lead n e a r e r the time of s h e d d i n g (Rabinowitz et al 1989), d i f f e r e n c e s in exposure patterns among populations could at least p a r t i a l l y a c c o u n t for these d i f f e r e n t trends. Taiwan and Boston differ in their patterns of childhood lead expsoure. In Taipei r e s p i r e d lead is the majo~ factor (Hwang and Wang, 1990), w h i l e in Boston ingested lead is the m a j o r d e t e r m i n a n t of the childs lead level (Rabinowitz et al 1985). R e s p i r a t i o n rates (volume of air per unit of b o d y mass) are at their maximum during infancy, but mouthing and ingestion reach their maximum during the toddler period. 605

Table 2. C o m p a r i s o n of studies of tooth lead a c c o r d i n g to tooth type. Reported patterns of lead a b u n d a n c e s among tooth types are shown. Some investigators a n a l y z e d the bulk tooth, other used an inner zone of dentin along the pulp cavity. We o b t a i n e d the postn a t a l d e n t i n from w i t h i n the crown of shed teeth.

Reference

Place Mexico England England England Denmark

Mean Lead ug/g

1975 1977 1978 1983 1986

Fergusson

1989 N Z

3 6

whole dentin

997

Khandekar Patterson

1986 India 1988 S c o t l a n d

4 9

whole whole

103 583

2 3

whole dentin

4

"

Taiwan

inner whole whole whole inner

Number

Shapiro Mackie Pinchin Smith Grandjean

Ewers 1990 G e r m a n y This study Boston

5 12 4 5 I0

Part Used

U = m a x i l l a r y tooth, J = m a n d i b u l a r incisor, L I = l a t e r a l i n c i s o r I=incisor, C=canine, M = m o l a r w h o l e = e n t i r e crown analyzed, i n n e r = d e n t i n near pulp c a v i t y

36 1392 57 2564 714

76 2331 753

tooth,

Reported Trends IC>M UM U>J CI=LI UCIJI UCI>ULI U>J CI

M U>J CI>LI I>C>M U>J CI>LI U=J CI>LI I=>M>C U=j CIM>C

CI=central

Since the C h i n e s e g r o u p i n c l u d e d two schools near s m e l t e r s and other schools in the city, we were able to e x a m i n e w h e t h e r the p a t t e r n s of lead a b u n d a n c e among the tooth types were d i f f e r e n t a c c o r d i n g to this d i f f e r e n c e in lead exposure. The p a t t e r n s were the same; in both s u b - g r o u p s of c h i l d r e n the incisors, canines, and m o l a r s had the same d e s c e n d i n g p a t t e r n of lead c o n c e n t r a t i o n s . For e a c h tooth type the c h i l d r e n n e a r the s m e l t e r s had h i g h e r lead levels. Thus the r e p o r t e d d i f f e r e n c e s among i n v e s t i g a t o r s in the p a t t e r n among these tooth types is likely not a result of only d i f f e r e n t q u a n t i t e s of lead. R a t h e r these d i f f e r e n t p a t t e r n s may r e f l e c t the v a r i e t y across p o p u l a t i o n s of changes in e x p o s u r e w i t h age.

606

A c k n o w l e d g m e n t s . The authors are g r a t e f u l for the advice of Drs. H e r b e r t N e e d l e m a n and H o w a r d N e e d l e m a n and the g e n e r o u s c o o p e r a t i o n of the teachers, parents and children. E x c e l l e n t technical support was p r o v i d e d by W e n - y i n g Chao, C h i n - s i u n g Lu, Dr. K u n - y u Chao, Ann L e w a n d o w s k i and E l i z a b e t h Allred. R e s e a r c h f u n d i n g was s u p p l i e d by the N a t i o n a l I n s t i u t e of C h i l d H e a l t h and H u m a n D e v e l o p m e n t (HD 08945) and the N a t i o n a l Science C o u n c i l of the R e p u b l i c of China (NSC 79-0421-B002-1Z). REFERENCES

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