The distribution of lead within ancient and modern human teeth: implications for long-term and historical exposure monitoring

Application of Trace Elemental Profile of Known Teeth for Sex and Age Estimation of Ajnala Skeletal Remains: a Forensic Anthropological Cross-Validation Study

Teeth store crucial information needed for medical, environmental, genomics, public health, and forensic anthropological research work. The prolonged forensic utility of teeth is ensured by their extended postmortem longevity as they can resist almost all sorts of chemical, biological, and physical degradations or destructions. The main aim of the present investigation was to utilize the discriminant functions and regression equations generated from the elemental profile of known teeth for estimating sex and age of unknown human skeletal remains excavated from an abandoned well at Ajnala (Amritsar, India). The written records mentioned that 282 Indian mutineer soldiers were killed in July 1857, their cadavers were dumped in the disused well, and then a religious structure was built over the periphery of the said well. These human remains, along with some contextual items, were excavated non-scientifically in April 2014. Preliminary results obtained from application of different forensic anthropological techniques like stable isotope, pulp-tooth area ratio, and mtDNA analyses have indicated that these remains belonged to adult males. In present study, the elemental concentrations of 100 mandibular molars of known age and sex were estimated from wavelength-dispersive X-ray fluorescence spectrophotometer (WD-XRF) analyzer. The statistical equations so generated from elemental concentrations of known teeth were applied to estimate the probable age and the sex of unknown mandibular teeth (N = 100) collected from Ajnala skeletal assemblage. The elements Pb and As were detected in ancient teeth only whereas the detection of elements like Ba, Se, and Te was limited to modern teeth samples only. When the statistical equations so generated were applied to elemental concentrations of Ajnala teeth, it was found that 96% teeth belonged to adult males and the remaining ones were classified to be that of females. Though sexual differences were observed in concentrations of majority of elements, statistically significant differences were found in elemental concentrations of very few teeth. Age estimates of unknown teeth were found in the age ranges of 19 to 48 years. Thus, the trace elemental analysis results supported the written records that the victims were adult males. The cross-validated application of elemental profiles of known teeth for establishing the identity of unknown teeth is the first forensic anthropological study reported from India. Though the obtained accuracy levels were not found within acceptable forensic threshold limits, the present study results may guide future researches involving human hard tissues. It may be concluded that trace elemental concentrations of teeth may be influenced by the factors like age and sex of an individual and thus cannot be used for accurate and reliable forensic sex or age estimations. Dental trace elemental composition can be used as a forensic tool only if used in conjunction with other morphological or molecular analysis of the unknown dental remains.

Can in vivo surface dental enamelmicrobiopsies be used to measure remote lead exposure?

Measuring lead in the surface dental enamel (SDE) using biopsies is a rapid, safe, and painless procedure. The dental enamel lead levels (DELLs) decrease from the outermost superficial layer to the inner layer of dental enamel, which becomes crucial for the biopsy depth (BD) measurement. However, whether the origin of lead found in SDE is fully endogenous is not yet established. There is also controversy about the biopsy protocol. The aims of this study were to investigate if DELLs are altered by extrinsic contamination (A) and to evaluate the real geometric figure formed by the erosion provoked by biopsy procedure and the respective BD in SDE (B). To accomplish the aim A, lead from 90 bovine incisor crowns lead was determined by graphite furnace atomic absorption spectrometer as a function of exposure time and lead concentration. Two biopsies were performed in each tooth, before and after lead exposure. Six 15-tooth groups differed by exposure time (1 or 30 min) and lead concentrations (A. 0 mg/L-placebo, B. 0.01 mg/L-standard for drinking water, or C. 0.06 mg/L-concentration found in contaminated groundwater). Phosphorus was determined by an inductively coupled plasm optical emission spectrometer to quantify the enamel removed. To compare intakes/losses of lead in SDE among the groups, values of DELL differences between before and after lead exposure were compared by ANOVA (p < 0.05). To attain the objective B, one extracted human permanent tooth was studied by confocal Raman microscopy. Lead measurements and the surface profile were determined. There was no difference in DELL among the groups (p = 0.964). The biopsy bottom surface area, analyzed by microscopy, showed an irregular area, with regions of peaks and valleys, where areas with depth ranging from 0.2 (peaks) to 1.8 μm (valleys) (± 0.1 μm) could be found. BD carried out in vivo is commonly calculated using the cylinder height formula. The real BD was shown to be very similar to already published data. In conclusion, the SDE of erupted teeth does not seem to be susceptible to environmental lead intake, being thus reliable to measure remote exposures to lead.

Tooth manganese as a biomarker of exposure and body burden in rats

BACKGROUND

Neonates and children are particularly vulnerable to the toxic effects of excess manganese (Mn), but studies of Mn exposure during these developmental periods are hampered by a lack of validated biomarkers. Deciduous teeth may be used to assess Mn exposure during these developmental periods but require further validation to determine the relationship between tooth Mn, Mn in target tissues, and exposure.

OBJECTIVES

To determine the relationship of tooth Mn concentrations with: (i) exposure dose, (ii) the timing/duration of exposure, and (iii) with Mn concentrations in blood, brain and bone.

METHODS

Rats in different treatment groups were orally exposed to 0, 25 or 50µg/g/day Mn either from postnatal day (PND) 1 - 21 and culled at PND 24, from PND 1 - 21 and culled as adults (>PND 290), or from PND 1 - throughout life and culled at >290 PND. Mn was measured in second molars, femurs, brain and blood by ICP-MS.

RESULTS

Tooth Mn increased significantly with dose in rats exposed for 21 PND and culled at 24 PND (p<0.001). In rats culled at >290 PND, tooth Mn increased with exposure duration (p<0.001) and reflected exposure duration. A significant, positive association between tooth Mn and Mn levels in blood (Spearman's rho 0.69, p<0.01) brain (rho 0.59, p<0.05) and bone (rho 0.69, p<0.01) was observed in animals with lifelong exposure. Tooth Mn and Mn levels in bone were also significantly positively associated in animals exposed only early in life (rho 0.76, p<0.001).

CONCLUSIONS

Teeth are a sensitive biomarker of active and past Mn exposure and Mn burden in tissues. Unlike blood, teeth retain information on exposure history over the short and long-term.

Lead (Pb) Isotope Baselines for Studies of Ancient Human Migration and Trade in the Maya Region

We examined the potential use of lead (Pb) isotopes to source archaeological materials from the Maya region of Mesoamerica. The main objectives were to determine if: 1) geologic terrains throughout the Maya area exhibit distinct lead isotope ratios (²⁰⁶Pb/²⁰⁴Pb, ²⁰⁷Pb/²⁰⁴Pb, and ²⁰⁸Pb/²⁰⁴Pb), and 2) a combination of lead and strontium ratios can enhance sourcing procedures in the Mesoamerica region. We analyzed 60 rock samples for lead isotope ratios and a representative subset of samples for lead, uranium, and thorium concentrations across the Maya region, including the Northern Lowlands of the Mexican Yucatan Peninsula, the Southern Lowlands of Guatemala and Belize, the Volcanic Highlands, the Belizean Maya Mountains, and the Metamorphic Province/Motagua Valley. Although there is some overlap within certain sub-regions, particularly the geologically diverse Metamorphic Province, lead isotopes can be used to distinguish between the Northern Lowlands, the Southern Lowlands, and the Volcanic Highlands. The distinct lead isotope ratios in the sub-regions are related to the geology of the Maya area, exhibiting a general trend in the lowlands of geologically younger rocks in the north to older rocks in the south, and Cenozoic volcanic rocks in the southern highlands. Combined with other sourcing techniques such as strontium (⁸⁷Sr/⁸⁶Sr) and oxygen (δ¹⁸O), a regional baseline for lead isotope ratios can contribute to the development of lead isoscapes in the Maya area, and may help to distinguish among geographic sub-regions at a finer scale than has been previously possible. These isotope baselines will provide archaeologists with an additional tool to track the origin and movement of ancient humans and artifacts across this important region.

Anatomical variations in primary teeth microelements with known differences in lead content by micro-Synchrotron Radiation X-Ray Fluorescence (μ-SRXRF) - A preliminary study

Shed teeth have been proposed as trace element biomarkers. This study determined variations in the spatial distribution of Ca, K, Zn, Pb, Mn, Cu, and Sr in four anatomical locations: superficial enamel (SE, 0-10μm), subsuperficial enamel (SSE, 10-30μm), primary dentin (PD), and secondary dentin (SD). Five primary incisors were analyzed by micro Synchrotron Radiation X-Ray Fluorescence (μ-SRXRF). Two teeth had low concentrations of lead in the SE (<250μg/g), while three contained very high lead concentrations in the SE (>2000μg/g). Teeth were sliced, and five spot measurements (20μm beam diameter) were accomplished in each location. The data are shown as absolute values and as the ratio between the different elements and Ca. The distribution of K was close to that of Ca. Zn was the third most abundant element, with the highest levels being found in the SE and SD and low levels detected in the PD. Increasing Sr levels were found progressing from the enamel to the dentin, with the highest levels being found in the SD, a distribution that was unique. Pb, Mn, and Cu exhibited a similar trend, with higher signals for these elements detected in the SE. This study provides preliminary data on the heterogeneous distribution of different elements in the tooth, highlighting the importance of the first 10μm of the SE for determination of some elements, such as Zn, Pb, Mn, and Cu.

Radiobiological long-term accumulation of environmental alpha radioactivity in extracted human teeth and animal bones in Malaysia

In this study, the radiobiological analysis of natural alpha emitters in extracted human teeth and animal bones from Malaysia was estimated. The microdistributions of alpha particles in tooth and bone samples were measured using CR-39 alpha-particle track detectors. The lowest and highest alpha emission rates in teeth in the Kedah and Perak states were 0.0080 ± 0.0005 mBq cm(-2) and 0.061 ± 0.008 mBq cm(-2), whereas those of bones in the Perlis and Kedah states were 0.0140 ± 0.0001 mBq cm(-2) and 0.7700 ± 0.0282 mBq cm(-2), respectively. The average alpha emission rate in male teeth was 0.0209 ± 0.0008 mBq cm(-2), whereas that of female teeth was 0.0199 ± 0.0010 mBq cm(-2). The alpha emission rate in teeth is higher in smokers (0.0228 ± 0.0008 mBq cm(-2)) than in non-smokers (0.0179 ± 0.0008 mBq cm(-2)). Such difference was found statistically significant (p < 0.01).

Importance of laser-induced breakdown spectroscopy for hard tissues (bone, teeth) and other calcified tissue materials

Laser-induced breakdown spectroscopy (LIBS) as a sensitive optical technique capable of fast multielemental analysis proved to be a versatile tool in different applications. It became visible in the analytical atomic spectroscopy scene in the late 1980s and since then, its applications having been developed continuously in different field of science and technology including biomedical science. Here, we review the use and importance of LIBS for trace element determination in different calcified tissue materials. In this article, we have also reported a comprehensive review of the recent progress of biomedical applications of LIBS.

LIBS analysis of artificial calcified tissues matrices

In most laser-based analytical methods, the reproducibility of quantitative measurements strongly depends on maintaining uniform and stable experimental conditions. For LIBS analysis this means that for accurate estimation of elemental concentration, using the calibration curves obtained from reference samples, the plasma parameters have to be kept as constant as possible. In addition, calcified tissues such as bone are normally less "tough" in their texture than many samples, especially metals. Thus, the ablation process could change the sample morphological features rapidly, and result in poor reproducibility statistics. In the present work, three artificial reference sample sets have been fabricated. These samples represent three different calcium based matrices, CaCO3 matrix, bone ash matrix and Ca hydroxyapatite matrix. A comparative study of UV (266 nm) and IR (1064 nm) LIBS for these three sets of samples has been performed under similar experimental conditions for the two systems (laser energy, spot size, repetition rate, irradiance, etc.) to examine the wavelength effect. The analytical results demonstrated that UV-LIBS has improved reproducibility, precision, stable plasma conditions, better linear fitting, and the reduction of matrix effects. Bone ash could be used as a suitable standard reference material for calcified tissue calibration using LIBS with a 266 nm excitation wavelength.

Teeth as a biomarker of past chemical exposure

PURPOSE OF REVIEW

Accurate prenatal exposure assessment is one of the major challenges in environmental epidemiologic studies. Variations in placental transport make maternal biospecimens unreliable for many chemicals and fetal specimens collected at birth do not provide information on exposure timing over the prenatal period.

RECENT FINDINGS

The skeletal compartment is an important chemical repository, making calcified tissues important for measuring exposure. For decades teeth have been used to estimate long-term cumulative exposure to metals and some organic chemicals. Recently developed methodologies that combine sophisticated histological and chemical analysis to precisely sample tooth layers that correspond to specific life stages have the potential to reconstruct exposure in the second and third trimesters of prenatal development and during early childhood.

SUMMARY

Such a retrospective biomarker that precisely measures exposure intensity and timing during prenatal development would substantially aid epidemiologic investigations, particularly case-control studies of rare health outcomes.

Lead contents in the surface enamel of primary and permanent teeth, whole blood, serum, and saliva of 6- to 8-year-old children

This study aimed to evaluate associations of Pb-enamel values determined in two successive enamel microbiopsies taken from a primary and a permanent tooth, and to assess how Pb-enamel correlates with Pb-blood and Pb-serum as well as whole (Pb-whole-saliva), submandibular/sublingual (Pb-sub-saliva) and parotid saliva (Pb-parotid-saliva). The study population included 444 children aged 6 to 8years attending 4 government schools in the district of Campos Eliseos, in Ribeirao Preto, Sao Paulo State, Brazil. Whole blood, serum, parotid, submandibular/sublingual ("sub-saliva"), and whole saliva were collected in trace element-free tubes. Two successive microbiopsies were taken from the surface of a primary and a permanent tooth of each child. Lead concentrations were determined by inductively coupled plasma mass spectrometry (ICP-MS). There was a significant correlation between primary and permanent teeth in terms of Pb-enamel, for both the first and the second microbiopsies. When the median Pb-enamel values were compared between the two genders using only the highest 10th percentile Pb-enamel, there was a significant difference between girls and boys for both primary (474.2 vs 910.0μg/g, respectively; p=0.02) and permanent teeth (739.5 vs 1325μg/g, respectively; p=0.04). There were no significant correlations between Pb-enamel and Pb-blood or between Pb-enamel and lead in the 3 different salivas. However, there was a statistically significant correlation between Pb-enamel and Pb-serum when only the highest 10th percentile Pb-enamel was analyzed (r=0.57 and p=0.0002 for primary teeth; r=0.56 and p<0.0001, for permanent teeth). In conclusion, our findings have demonstrated a significant correlation between Pb-enamel found in primary and permanent teeth, as well as a significant correlation between Pb-serum and lead in primary and permanent tooth enamel. Boys presented higher Pb-enamel than girls. Our study also suggests that Pb-enamel has no correlation with Pb-blood or with lead in the 3 different salivas.

Spatial distribution of manganese in enamel and coronal dentine of human primary teeth

Emerging evidence indicates that excessive exposure to manganese (Mn) during the prenatal period and early childhood may result in neurodevelopmental deficits. However, accurate exposure biomarkers are not well established, limiting our understanding of exposure-response relationships over these susceptible periods of development. Naturally shed deciduous teeth are potentially a useful biomarker of environmental exposure to Mn. However, the uptake and distribution of Mn in human teeth has not been studied in detail. Mn distribution was measured at high resolution (~20 μm) in eight human primary teeth using laser ablation-inductively coupled plasma-mass spectrometry. A bio-imaging methodology was applied to construct detailed elemental maps of three incisors, and bone meal (NIST SRM 1486) was used to validate the analyses. The distribution of Mn in enamel and coronal dentine showed a distinct and reproducible pattern. In enamel, the ⁵⁵Mn:⁴³Ca ratio was highest at the outer edge of enamel (range=0.57 to 4.74) for approximately 20-40 μm but was substantially lower in deeper layers (range=0.005 to 0.013). The highest levels of Mn were observed in dentine immediately adjacent the pulpal margin (⁵⁵Mn:⁴³Ca range=2.27 to 6.95). Importantly, a clearly demarcated high Mn zone was observed in dentine at the incisal end of the teeth. Using confocal laser scanning microscopy to visualize the neonatal line, this region was identified as being in the prenatally formed dentine. The high-resolution map of the spatial distribution of Mn in human primary teeth highlighted specific reproducible patterns of Mn distribution in enamel and coronal dentine.

Microbiopsies of surface dental enamel as a tool to measure body lead burden

Lead (Pb) poisoning is preventable but continues to be a public health problem in several countries. Measuring Pb in the surface dental enamel (SDE) using microbiopsies is a rapid, safe, and painless procedure. There are different protocols to perform these microbiopsies, but the reliability of dental enamel lead levels (DELL) determination is dependent upon biopsy depth (BD). It is established that DELL decrease from the outermost superficial layer to the inner layer of dental enamel. The aim of this study was to determine DELL obtained by two different microbiopsy techniques on SDE termed protocol I and protocol II. Two consecutive enamel layers were removed from the same subject group (n=138) for both protocols. Protocol I consisted of a biopsied site with a diameter of 4 mm after the application of 10 microl HCl for 35 s. Protocol II involved a biopsied site of 1.6 mm diameter after application of 5 microl HCl for 20 s. The results demonstrated that there were no significant differences for BD and DELL between homologous teeth using protocol I. However, there was a significant difference between DELL in the first and second layers using both protocols. Further, the BD in protocol II overestimated DELL values. In conclusion, SDE analyzed by microbiopsy is a reliable biomarker in protocol I, but the chemical method to calculate BD in protocol II appeared to be inadequate for measurement of DELL. Thus, DELL could not be compared among studies that used different methodologies for SDE microbiopsies.

Evaluation of Laser Ablation Inductively Coupled Plasma Mass Spectrometry for the Quantitative Determination of Lead in Different Parts of Archeological Human Teeth

The lead content of teeth or tooth-parts has been used as a biomarker of cumulative lead exposure in clinical, epidemiological, environmental, and archaeological studies. Through the application of laser ablation inductively coupled plasma mass spectrometry, a pilot study of the micrometer-scale distribution and quantification of lead was conducted for two human teeth obtained from an archeological burial site in Manhattan, New York, USA. Lead was highly localized within each tooth, with accumulation in circumpulpal dentine and cementum. The maximum localized lead content in circumpulpal dentine was remarkably high, almost 2000 μg g(-1), compared to the mean enamel and dentine content of about 5 μg g(-1). The maximum lead content in cementum was approximately 700 μg g(-1). The large quantity of cementum found in the teeth suggested that the subjects had hypercementosis (excess cementum formation) of the root, a condition reported to have been prevalent among African-American slave populations. The distribution of lead in these human teeth was remarkably similar to the distribution that we previously reported in the teeth of present-day lead-dosed goats. The data shown demonstrate the feasibility of using laser ablation inductively coupled plasma mass spectrometry to examine lead exposure in archaeological studies.

Stable lead isotopes in environmental health with emphasis on human investigations

There has been widespread use of stable lead isotopes in the earth sciences for more than 40 years focussed on the origin and age of rocks and minerals with lesser application in environmental investigations where the emphasis has been directed typically to the source of lead in environmental media such as air, water and soils. In contrast, the number of environmental health investigations focussed on humans (and primates) is limited in spite of the demonstrated utility of the approach in pioneering studies in the early 1970's. This paper reviews the status of lead isotopes in human investigations especially over the past 2 decades, the period over which most activity has taken place. Following a brief introduction to the method, examples are provided illustrating the use of lead isotopes in a wide spectrum of activities including sources and pathways of lead in diverse environments from urban to mining communities, various applications associated with pregnancy, the contribution of bone lead to blood lead including in the elderly, the half-life of lead in blood, and lead in bones and other media. A brief outline of critical research on non-human primates is also given. The lead isotope method is a powerful technique for tracing lead and could be employed more widely in human investigations.

Chemical composition of enamel and dentine in primary teeth in children from Thailand exposed to lead

Enamel and dentine in teeth of children with high blood levels of lead were analyzed by means of secondary ion mass spectrometry (SIMS) and X-ray micro-analyses (XRMA) and compare with teeth from children with low blood levels of lead. The SIMS analysis revealed detectable levels of Pb in dentine close to the pulp. The XRMA analyses could not detect any lead. There were no differences found in lead level in enamel of high lead level exposed teeth from low level exposed. The results confirm that children with high blood levels of lead have an uptake of lead in dentine close to the pulp.

Lead in teeth from lead-dosed goats: microdistribution and relationship to the cumulative lead dose

Teeth are commonly used as a biomarker of long-term lead exposure. There appear to be few data, however, on the content or distribution of lead in teeth where data on specific lead intake (dose) are also available. This study describes the analysis of a convenience sample of teeth from animals that were dosed with lead for other purposes, i.e., a proficiency testing program for blood lead. Lead concentration of whole teeth obtained from 23 animals, as determined by atomic absorption spectrometry, varied from 0.6 to 80microg g(-1). Linear regression of whole tooth lead (microg g(-1)) on the cumulative lead dose received by the animal (g) yielded a slope of 1.2, with r2=0.647 (p<0.0001). Laser ablation inductively coupled plasma mass spectrometry was employed to determine lead content at micrometer scale spatial resolution in the teeth of seven goats representing the dosing range. Highly localized concentrations of lead, ranging from about 10 to 2000microg g(-1), were found in circumpulpal dentine. Linear regression of circumpulpal lead (microg g(-1)) on cumulative lead dose (g) yielded a slope of 23 with r2=0.961 (p=0.0001). The data indicated that whole tooth lead, and especially circumpulpal lead, of dosed goats increased linearly with cumulative lead exposure. These data suggest that circumpulpal dentine is a better biomarker of cumulative lead exposure than is whole tooth lead, at least for lead-dosed goats.

Comparison of the distributions of bromine, lead, and zinc in tooth and bone from an ancient Peruvian burial site by X-ray fluorescence

Synchrotron micro X-ray fluorescence was used to study the distribution of selected trace elements (Zn, Pb, and Br) in tooth and bone samples obtained from an individual from a pre-Columbian archaeological site (Cabur) located on the north coast of Peru. The results show that Zn, Pb, and Br are present in both the teeth and bone samples and that the Zn and Pb seem to be confined to similar regions (cementum and periostium), while Br shows a novel distribution with enrichment close to the Haversian canals and (or) in regions that appear to be Ca deficient.Key words: teeth, bone, metals, XRF, Br, Zn, and Pb.

Lead contents in the surface enamel of deciduous teeth sampled in vivo from children in uncontaminated and in lead-contaminated areas

This study aimed to: (1) measure lead contents in the surface enamel of two populations consisting of 4-6-year-old children, one from an apparently uncontaminated area (Ribeirão Preto, São Paulo State, SP, Brazil, n=247) and the other from an area notoriously contaminated with lead (Bauru, São Paulo State, Brazil, n=26); (2) compare biopsy depths between the two populations; (3) correlate biopsy depth with lead content; (4) stratify samples according to biopsy depth to compare lead contents in samples from similar biopsy depths. A surface enamel acid-etch microbiopsy was performed in vivo on a single upper deciduous incisor for each sample. Lead was measured by graphite furnace atomic absorption spectrometry (GFAAS) while phosphorus was measured colorimetrically to establish biopsy depth. Samples from both populations were classified into categories of similar biopsy depths based on biopsy depth quartiles. Median lead contents were statistically different between the Ribeirão Preto population (206 microg/g, range: 5-1399 microg/g) and the Bauru population (786 microg/g, range: 320-4711 microg/g) (p<0.001); however, biopsy depth did not differ between the Ribeirão Preto (3.9 microm, Standard Deviation, SD=0.9) and Bauru (3.8 microm, SD=0.9) populations (p=0.7940). Pearson's correlation coefficient for biopsy depths versus log10 lead values was -0.29 for Ribeirão Preto and -0.18 for Bauru. Lead contents were statistically different between the two populations for all quartiles of biopsy depth. These findings suggest that lead accumulated in the surface enamel of deciduous teeth is linked to the environment in which people reside, indicating that this tissue should be further explored as an accessible biomarker of lead exposure.

The application of synchrotron radiation induced X-ray emission in the measurement of zinc and lead in Wistar rat ameloblasts

The development of analytical techniques for the measurement of trace elements in cellular compartments of developing teeth remains an important methodological issue in dental research. Recent advances in third generation synchrotron facilities have provided high brilliance X-ray sources that can be effectively used to study trace element distributions in small spatial regions with low detection limits. The present study describes for the first time the application of synchrotron radiation induced X-ray emission (SRIXE) in measuring the distribution of zinc and lead in the ameloblasts of developing Wistar rat teeth. Wistar rats were fed a standard rat diet, containing the normal dietary requirements of zinc, ad libitum and exposed to 100 ppm of lead in drinking water. Resin embedded sections of first mandibular molars were analysed using a 13.3 keV incident monochromatic X-ray beam focussed to a 0.2 microm spot. Characteristic X-rays arising from the entire thickness of the sample were measured using an energy dispersive detector for quantitative analysis of elemental concentrations. The results showed that intranuclear concentrations of zinc were greater than levels in the cytoplasm. Furthermore, nuclear and cytoplasmic concentrations of zinc in the maturation stage (742+/-27 and 424+/-25 ppm, respectively) were significantly higher than the zinc levels observed in the nucleus and cytoplasm of presecretory stage ameloblasts (132+/-10 and 109+/-10 ppm, respectively) (p<0.05). A clear lead signal above the background was not detected in the ameloblasts and lead concentrations could only be reliably measured in the developing enamel. Overall, SRIXE was an effective method of studying the spatial distribution of zinc in the cells of developing teeth and offered a unique combination of sub-micron spatial resolution and parts-per-million detection limits (0.8-1 and 0.6-1 ppm for zinc and lead, respectively).

Matrix-matched quantitative analysis of trace-elements in calcium carbonate shells by laser-ablation ICP-MS: application to the determination of daily scale profiles in scallop shell (Pecten maximus)

A micro-scale method has been developed for analysis of trace-element concentration profiles in the calcium carbonate shell of the Great Scallop (Pecten maximus). UV laser ablation at 266-nm coupled with ICP-MS detection was used to analyse daily calcite striae of shell samples to obtain high temporal resolution of trace element incorporation. Analysis of scallop shells was carefully examined to determine the quality of calcium carbonate ablation and calibration. An accurate external calibration method based on matrix matching was developed. Twelve sodium-free enriched calcium carbonate standards containing up to twenty-four elements were prepared, by co-precipitation with aqueous ammonia and NH(4)HCO(3), and subsequently back-calibrated in the laboratory. These CaCO(3) standards were found to be homogenous and their use enabled sensitive quantitative analysis (detection limits of a few ng g(-1)) over a wide range of concentrations (0.1 to 500 microg g(-1)). Use of these CaCO(3) standards was also evaluated by analysis of three calcium-rich certified reference materials. Because calibration was consistent with the certified results, this analytical method is a sensitive tool for analysis of environmental calcium carbonate matrices. Repeated analysis of scallop shell samples collected simultaneously at the same location showed that the trace elements are homogeneously distributed along a stria. The reliability of such in-situ records of biogenic calcium carbonate (scallop shells) is apparent from the inter-individual and inter-annual reproducibility of the trace element profiles.

Lead and cadmium in human teeth from Jordan by atomic absorption spectrometry: Some factors influencing their concentrations

The aim of this study was to measure the concentrations of lead (Pb) and cadmium (Cd) in human teeth and to investigate the affecting factors. Teeth samples (n = 268) were collected from people living in different cities in Jordan including Amman, Zarqa, Al-Mafraq and Irbid and analyzed for Pb and Cd using atomic absorption spectrometry (AAS). A questionnaire was used to gather information on each person, such as age, sex, place where the patient lives, smoking, presence of amalgam fillings inside the mouth, and whether the patient uses toothpaste or not. The mean concentrations of Pb and Cd were 28.91 microg/g and 0.44 microg/g, respectively. The results indicate that there is a clear relation between Pb and Cd concentrations and the presence of amalgam fillings, smoking, and place of living. Pb was sex-dependent, whereas Cd was not. Our results show that Pb and Cd concentrations in samples obtained from Al-Mafraq and Irbid are higher than those obtained from Amman and Zarqa. Pb was highest in Mafraq, whereas Cd was highest in Irbid. The Pb and Cd concentrations in teeth from smokers (means: Pb = 31.89 microg/g, Cd = 0.49 microg/g) were significantly higher than those from nonsmokers (means: Pb = 24.07 microg/g, Cd = 0.37 microg/g). Pb and Cd concentrations in teeth of patients with amalgam fillings (means: Pb = 31.02 microg/g and Cd = 0.52 microg/g) were significantly higher than those from patients without amalgam fillings (means: Pb = 26.87 microg/g and Cd = 0.41 microg/g). Our results show that brushing the teeth daily with toothpaste does not significantly decrease the concentration of both Pb and Cd. The mean concentrations of Pb and Cd do not vary significantly between the ages 20-30, 31-40, and 41-50, but both increased rapidly at age 51-60.

Human teeth as historical biomonitors of environmental and dietary lead: some lessons from isotopic studies of 19th and 20th century archival material

The lead isotopic composition of various sections (crown, crown base, root) of teeth was determined in specimens collected from 19th century skulls preserved in museum collections and, upon extraction or exfoliation, from humans of known ages residing in Scotland in the 1990s. For most 20th century samples, calculation of accurate crown-complete or root-complete dates of tooth formation ranging from the 1920s to the 1990s enabled comparison of (206)Pb/(207)Pb ratios for teeth sections (crown base root) with corresponding decadally averaged data for archival herbarium Sphagnum moss samples. This showed that the teeth sections had been significantly influenced by incorporation of non-contemporaneous (more recent) lead subsequent to the time of tooth formation, most probably via continuous uptake by dentine. This finding confirmed that separation of enamel from dentine is necessary for the potential of teeth sections as historical biomonitors of environmental (and dietary) lead exposure at the time of tooth formation to be realised. Nevertheless, the mean 19th century value of 1.172+/-0.007 for the (206)Pb/(207)Pb ratio in teeth was very similar to the corresponding mean value of 1.173+/-0.004 for 19th century archival moss, although relative contributions from environmental sources - whether direct, by inhalation/ingestion of dust contaminated by local lead smelting ((206)Pb/(207)Pb~1.17) and coal combustion ((206)Pb/(207)Pb~1.18) emissions, or indirect, through ingestion of similarly contaminated food - and drinking/cooking water contaminated by lead pipes of local origin, cannot readily be determined. In the 20th century, however, the much lower values of the (206)Pb/(207)Pb ratio (range 1.100-1.166, mean 1.126+/-0.013, median 1.124) for the teeth collected from various age groups in the 1990s reflect the significant influence of imported Australian lead of lower (206)Pb/(207)Pb ratio (~1.04) and released to the environment most notably through car-exhaust emissions arising from the use of alkyl lead additives ((206)Pb/(207)Pb~1.06-1.09) in petrol in the U.K. from ca. 1930 until the end of the 20th century.

Calibration of laser ablation inductively coupled plasma mass spectrometry for quantitative measurements of lead in bone

Lead accumulates in bone over many years or decades. Accordingly, the study of lead in bone is important in determining the fate of ingested lead, the potential for remobilization, and for the application of bone lead measurements as a biomarker of lead exposure. Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) was used to measure the spatial distribution of lead in bone on the micrometer scale. In general, LA-ICP-MS studies are somewhat limited by the lack of matrix-matched standards and/or reference materials for calibration and validation purposes. Here we describe the application of pressed pellets prepared from New York State Department of Health candidate Reference Materials for Lead in Bone (levels 1 through 4), to provide a linear calibration for (208)Pb/(43)Ca in the concentration range <1 to 30 μg g(-1). The limit of detection was estimated as 0.2 μg g(-1). The measured lead values for pelletized NIST SRM 1486 Bone Meal and SRM 1400 Bone Ash were in good agreement with certified reference values. Using this approach, we quantitatively measured the spatial distribution of lead in a cross-section of goat metacarpal from a lead-dosed animal. The lead content was spatially variable in the range of 2 to 30 μg g(-1) with a complex distribution. In some sections, lead appeared to be enriched in the center of the bone relative to peripheral areas, indicating preferential accumulation in trabecular (spongy) rather than cortical bone. In addition, there were discrete areas of lead enrichment, or hot spots, of 100 to 200 μm in width.

Pb enamel biomarker: deposition of pre- and postnatal Pb isotope injection in reconstructed time points along rat enamel transect

Exposure to lead (Pb) as well as other heavy metals in the environment is still a matter of public health concern. The development of the enamel biomarker for heavy metal exposure assessment is designed to improve studies of dose-effect relationships to developmental anomalies, particularly embryonic dysfunctions, and to provide a time-specific recount of past exposures. The work presented in this paper demonstrates maternal transfer across the placental barrier of the enriched isotope (206)Pb tracer to the enamel of the rat pup. Likewise, injections of (204)Pb-enriched tracer in the neonate rat resulted in deposition of the tracer in the enamel histology as measured by secondary ion microprobe spectrometry. Through enamel, we were able to observe biological removal and assimilation of prenatal and postnatal tracers, respectively. This research demonstrates that enamel can be used as a biomarker of exposure to Pb and may illustrate the toxicokinetics of incorporating Pb into fetal and neonatal steady-state system processes. The biomarker technique, when completely developed, may be applied to cross-sectional and longitudinal epidemiological research.

Variation in elemental intensities among teeth and between pre- and postnatal regions of enamel

Microspatial analyses of the trace element composition of dental enamel are made possible using laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS). Fine spatial resolution, multielement capabilities, and minimal sample destruction make this technique particularly well-suited for documenting the distribution of elements in sequentially calcifying layers of enamel. Because deciduous enamel forms from week 13 in utero up to 9 months postnatally (thereafter essentially becoming inert), the application of LA-ICP-MS allows for the retrospective measurement of prenatal and early postnatal trace-element uptake during a critical period of child development. In this study, we compared intra- and intertooth intensities of 25Mg, 57Fe, 66Zn, 68Zn, 88Sr, 138Ba, and 208Pb via LA-ICP-MS of 38 exfoliated deciduous incisors and canines donated by 36 participants in the Solís Valley Mexico Nutrition Collaborative Research Support Program (NCRSP). Pre- and postnatal comparisons within teeth showed significant increases (P < 0.001) and greater variation in the abundance of all isotopes in postnatal enamel, with the exception of a decrease in 25Mg (P < 0.001) and constant values for 88Sr (P = 0.681). Conversely, comparisons by tooth type and mouth quadrant revealed few significant differences between teeth of the same individual. We argue that more variation in the trace element composition of teeth occurs across developmental areas within a tooth than among different teeth of the same person. This study further demonstrates that sequentially calcifying areas of enamel have different chemical concentrations. The results support the use of microspatial analyses of enamel for understanding changes in nutrition, pollution, and residence.

Environmental influences on the trace element content of teeth--implications for disease and nutritional status

The aim of this study was to compare the trace element content of children's primary teeth from Uganda and the UK. The Ugandan teeth were from children living in an area where endomyocardial fibrosis (EMF), a cardiac disease, is prevalent. The latter has been putatively linked to insufficient magnesium intake and excess cerium exposure. Primary teeth were collected from 21 Ugandan and 27 UK children. The crowns and roots of the teeth were separated and the former digested and analysed for several major and trace elements by inductively coupled plasma mass spectrometry (ICP-MS) and atomic emission spectrometry (ICP-AES). In addition, the enamel and dentine of eight UK and seven Ugandan primary teeth were isolated via density separation and analysed as above. The data were assessed using non-parametric statistical tests. The Ugandan teeth contained significantly (P < 0.05) greater concentrations of strontium, barium, cerium, lanthanum, praseodymium and significantly less zinc than the UK teeth. No significant difference in the concentrations of aluminium, calcium, copper, magnesium, lead and uranium were found. Analysis of enamel and dentine demonstrated that the former was enriched with several elements including cerium. It is concluded, that the environment, influences the trace element content of primary teeth and this may be useful for monitoring nutritional status. With respect to a geochemical cause for EMF, there is no positive evidence that EMF in Uganda is associated with reduced magnesium and increased cerium uptake in primary teeth. This does not, however, exclude cerium from playing a role in the aetiology of EMF.

Further investigation of the heavy metal content of the teeth of the bank vole as an exposure indicator of environmental pollution in Poland

The content of heavy metals in mineralised dental tissues is an indicator of the exposure of their mineral phase to heavy metals during the time of tooth development and dental tissue formation. Therefore, teeth have been used as bio-indicators which accurately reflect the environmental or dietary exposure of animals and humans to heavy metals. This study follows from the earlier work in which it was demonstrated that the teeth from bank voles inhabiting various environmentally polluted and non-polluted forests in Southern Poland were reliable indicators of exposure to heavy metals. Using analytical techniques employed in the earlier study heavy metal concentrations were obtained in the teeth of bank voles trapped in 1998-2000 to determine if efforts to clean up the environment could be detected in changes in heavy metal concentrations in the teeth. The results show that these efforts are reflected in lower concentrations of heavy metals in the teeth but that cross border contamination remains a problem.

In vivo studies on lead content of deciduous teeth superficial enamel of preschool children

The amount of lead in the superficial enamel of deciduous teeth from 4- and 5-year-old children was determined by means of an enamel biopsy followed by lead analysis by graphite furnace atomic absorption spectrometry. Children examined in this study (n=329) attended public preschools in the city of Piracicaba, SP, Brazil. The selection of preschools was based on geographical location: some were located in an industrial area of the city, whereas others were located in an area devoid of industries. The objectives of this study were (1) to test whether enamel biopsies were an appropriate method for lead content population screening in young children; (2) to verify the lead content of superficial enamel of preschool children's deciduous teeth and to compare the results obtained from children exposed to different environments; (3) to analyze how biopsy depth correlated with lead content and affected comparisons between groups. An adhesive tape with a central hole (diameter=1.6 mm) was placed on one of the upper central incisors. Five microliters of 1.6 M l(-1) HCl in 70% glycerol (v/v) were applied to this area for 20 s, followed by a rinse with 5-microl ultrapurified water for 10 s. It was shown that the technique was feasible for population studies on young children. The lead concentration in enamel biopsies from the industrial area children (median: 169 ppm Pb) was significantly higher than that from the children living far from industries (118.1 ppm Pb) (P<0.0001). Analysis of the data showed that biopsies deeper than 3.9 microm gave more reliable results for comparisons between groups. To our knowledge, this study is the first to use an enamel microbiopsy to characterize a large sample of young children in vivo for lead monitoring in teeth.

Human lead exposure in England from approximately 5500 BP to the 16th century AD

Lead concentration and isotope ratio data are presented for the tooth enamel of 77 individuals buried in England and spanning approximately 5000 years from the Neolithic until the 16th century AD. Whereas other tissues may be affected by diagenesis in the burial environment, the Pb concentration of tooth enamel is directly related to childhood exposure. This record is preserved post-mortem and over archaeological time. Tooth enamel Pb concentrations in the prehistoric period appear to be variable within the range 0.04 to approximately 0.4 ppm, with occasional higher levels. The Romano-British and medieval periods show a marked increase in Pb exposures with enamel concentrations reaching up to approximately 40 ppm. These exposures would today be associated with industrial pollution. Exposures appear to be highly variable compared with modern people, however, with many medieval individuals having very low enamel Pb concentrations comparable with prehistoric people. Lead isotope data refine this picture. We distinguish between the diverse isotopic ratios we believe to be characteristic of 'natural' exposure to Pb-from geological sources via the diet-and the much narrower isotopic range characteristic of exposure to technological Pb from ore sources. Taken together the data suggest that the maximum concentrations associated with 'non-technological' exposure at any period are approximately 0.5-1.0 ppm, similar to that reported for modern people in England.

Isotope and trace element analysis of human teeth and bones for forensic purposes

Isotopic and elemental concentration data can be extremely useful in the identification of human remains. Archaeological, ecological and forensic investigations to date have primarily made use of 87Sr/86Sr, 143Nd/144Nd, 18O/16O and trace element data obtained from analysis of carbonate-hydroxyapatite in bones and teeth, and/or 12C/13C, 14N/15N, 18O/16O and 35S/37S ratios in bone collagen. However, a wide range of other chemical parameters are potentially useful for intersample comparison and environmental characterization, and increasing attention is being given to hair, nail and skin tissues, which provide dietary and environmental information over shorter time periods than bones and teeth. This paper reviews some of the principles which underlie such work and the current position with regard to modern forensic applications.

Analysis of Lead in Tooth Enamel by Laser Ablation-Inductively Coupled Plasma-Mass Spectrometry

Laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) was used to determine the Pb/Ca ratios in the enamel of deciduous incisors, a biomarker of in utero Pb exposure, using pelletized bone certified reference materials (CRMs) as calibrants. The detection limit for Pb by LA-ICP-MS was 11 microg kg(-1) demonstrating an adequate sensitivity for Pb in the teeth of unexposed individuals (0.1-10 mg kg(-1)). The precision for the Pb/Ca ratios in NIST SRM 1486 Bone Meal was 3.4%. The correlation between Pb/Ca ratios obtained by LA-ICP-MS and those obtained by a digestion method was highly significant. We found one point calibration by a CRM was applicable for the quantification of Pb in tooth enamel. This method will be valuable for the assessment of in utero Pb exposure levels.

Human tooth enamel as a record of the comparative lead exposure of prehistoric and modern people

There is a considerable body of evidence to support the contention that the atmospheric Pb burden is now considerably greater than it was in the remote past. However, as there are a diversity of potential environmental pathways leading to Pb ingestion, it is not clear how atmospheric Pb levels relate to human exposure. It is necessary to establish a baseline for human exposure to Pb from natural sources in the pre-metallurgical past, with which contemporary exposure can be compared. This paper addresses this issue by comparing the Pb content of human dental enamel--an established proxy for Pb exposure--from modern and archaeological, pre-metallurgical individuals using thermal and plasma ionisation mass spectrometry. It is shown that mean Neolithic enamel Pb contents are approximately 0.31 +/- 0.04 ppm. These values are only one order of magnitude lower than previously reported data for the same tissues for modern juveniles, despite an established 400-fold increase in the atmospheric Pb burden. The results suggest that 'natural' exposure to Pb in food and water may have been higher than previously thought, and that the link between atmospheric Pb and human exposure warrants further investigation.

The heavy metal content of the teeth of the bank vole (Clethrionomys glareolus) as an exposure marker of environmental pollution in Poland

This investigation is based on the premise that heavy metals are sequestered by the mineral phase of teeth, hydroxyapatite, during their formation. Once formed these tissues are not subject to significant turnover and it is suggested, therefore, that they provide a permanent and cumulative record of heavy metal exposure during the development of the teeth. The teeth of the bank vole (Clethrionomys glareolus) were analysed by inductively coupled plasma mass spectrometry to monitor the animals' exposure to lead, cadmium, zinc, copper and strontium. Animals were trapped in clean and polluted areas in Poland in and around Krakow in 1996 and in Olkusz and Legnica in 1996 and 1997. The control area in 1996 was Bieszcady National Park and in 1997 Borecka Forest. The results showed that there were statistically different concentrations of heavy metals in the teeth of animals from different sites. The high levels of pollution from industrial emissions were related to higher concentrations of heavy metals in the teeth. Unexpectedly high levels of heavy metals in the teeth of animals from Bieszczady National Park, thought to be environmentally clean, suggested cross-border pollution from Slovakia and the Ukraine. It was concluded that the teeth of small mammals, such as the bank vole, are a sensitive and reliable marker of environmental pollution by heavy metals.