Zinc in primary teeth from children in Norway.

Human primary teeth have been used as indicators of exposure to several heavy metals both in Norway and elsewhere. Local dentists in all 19 counties of Norway collected 2747 primary teeth during 1990-1994. Samples of tooth powder from whole, ground teeth were analyzed for zinc concentration by flame atomic absorption spectrophotometry. The overall geometrical mean was 144.5 micrograms of Zn/g of tooth substance (S.D. = 1.6). The result represents a small increase (5.2%) compared with a similar investigation in the 1970s. However, the mean zinc concentrations in the geographically matching parts of the two materials did not differ significantly. The variation in tooth zinc concentrations between the different counties declined from the 1970s to the 1990s. We found no correlation between the tooth zinc concentration and available environmental data on zinc in drinking-water, discharge of zinc from industrial point sources or population density in the same geographical areas. The zinc concentrations varied significantly with caries status, tooth type and root length. Few samples had a zinc concentration below 90 micrograms/g, indicating that most children consume sufficient zinc. Some very high values could not immediately be explained, but may be caused by contamination from zinc-containing dental restorations.

Lead in primary teeth from Norway: changes in lead levels from the 1970s to the 1990s.

Lead is one of the most important and widely distributed pollutants in the environment. In the human population children are particularly at risk. Local dentists in all 19 counties in Norway collected 2746 primary teeth from 1990 to 1994. Tooth substance from whole, ground teeth were analyzed for lead concentration by electrothermal atomic absorption spectrophotometry. The geometrical mean for the entire material was 1.27 micrograms lead/g tooth substance (S.D. 1.87). The mean lead levels in each of the counties were significantly lower than those obtained in a corresponding study in the 1970s. Two counties, Oslo and Vest-Agder, had significantly higher lead levels than the majority of the other counties. Tooth lead concentration and atmospheric deposition of lead in the same areas were significantly and positively correlated, as shown by analysis of naturally growing moss. We conclude that lead concentrations in primary teeth from children in Norway have been reduced by approx. 50% from the 1970s to the 1990s. The reduction probably reflects a decrease in the environmental lead burden in Norway.

Mercury content in rat teeth after administration of organic and inorganic mercury. The effects of interrupted exposure and of selenite.

Rat molars are indicators of exposure concentration and target organ content in chronic mercury vapor exposure. We wished to study the accumulation and persistence of organic and inorganic mercury in rat teeth and the effect of selenium on mercury retention. Male Wistar rats received either inorganic or organic mercury (with or without addition of selenite), selenite only, or no mercury or selenite (controls) in the drinking water for 4 weeks. Group A was killed after exposure. Group B was killed 20 weeks later. The mercury content was measured by cold-vapor atomic absorption spectrophotometry. The mercury content in the molars in group B was 66% and 77% less than in group A after inorganic and organic exposure, respectively. In the incisors the corresponding reductions were 90% and 97%. Selenite had limited effect on mercury retention in group A and none in group B. We suggest that rat molars and, by inference, human deciduous teeth may serve as indicators of organic and inorganic mercury exposure.

Autometallographic demonstration of mercury in rat molars.

Male, adult Wistar rats were exposed to 500 micrograms/m3 mercury vapor 6 h per day, 5 days a week for 4 wk. They were subsequently killed by transcardial perfusion. The molars were extracted, demineralized, and embedded in resin before sectioning. Autometallographic development was performed according to the method of Danscher & Möller-Madsen. Mercury deposits were found in small amounts in several areas of the pulp, but with larger accumulations of grains in relation to odontoblasts. Mercury also could be seen in odontoblastic processes in the dentin and predentin. Our conclusion is therefore that systemic uptake of mercury vapor leads to accumulation of mercury in the odontoblasts and that the mercury may be transported into the dentin tubules in the odontoblastic process.

Mercury contents of indicators and target organs in rats after long-term, low-level, mercury vapor exposure.

Five groups of Wistar rats received graded concentrations of mercury vapor from 10 to 100 micrograms Hg/m3 6 hr, 5 days a week, from 4 to 11 weeks of age. One group breathing ambient air served as controls. The mercury levels of the indicators blood, hair, molars, and incisors as well as the target organs kidney cortex, cerebrum, cerebellum, liver, lung, spleen, tongue, and femur were measured by cold-vapor atomic absorption spectrophotometry. The mercury vapor had no negative influence on the weight gain of the animals. The results showed that the kidney cortex had the highest concentration of mercury. The mercury contents of all the indicators and all the target organs, with the exception of femur, were positively and significantly correlated with the exposure concentration. The rat molars had the highest correlation coefficient with the kidney mercury values, but no indicator had a significant correlation with all target organs. Rat molars are to some degree comparable to human deciduous teeth regarding time of mineralization and eruption. Based on the results presented in this study, we tentatively suggest that human deciduous teeth can be useful indicators of chronic mercury exposure not only at the exposure concentration level, but also as indicators of the mercury uptake in organs such as kidney and cerebrum.

A simple system for generating low-dosage mercury vapor for animal experiments.

A system using unlabeled, metallic mercury for generating low-dosage vapor for animal experiments is described. The system consists of four acrylic plastic chambers: one chamber containing the mercury source, one for mixing the mercury vapor with air, one exposure chamber, and one containing activated coal filters and mechanisms for regulating the airflow. The chambers are connected to each other by means of 80-mm-diameter polyvinyl chloride tubes reinforced with wire. Additional control and supporting equipment is also used. The system is easy to set up and requires minimal attendance during use. A standard deviation of 3-4% in the mercury vapor level during 6 h of exposure is typical. The conditions for the animals during exposure and the safety for the personnel during use are optimal.

The distribution of lead in human hemopoietic tissue and spongy bone after lead poisoning and Ca-EDTA chelation therapy. Observations made by atomic absorption spectroscopy, laser microbeam mass analysis and electron microbeam X-ray analysis.

Two iliac crest needle biopsies were taken from a 43-year-old lead-poisoned woman during and after completion of a Ca-EDTA treatment. By atomic absorption spectroscopy the first and second biopsy were found to contain 56, respectively 41.6 micrograms lead/g wet tissue. In both biopsies 36% of the lead was extractable in 0.1 N HCl. Electron microbeam X-ray analysis proved to have too low sensitivity for quantitation of the lead in these biopsies. Laser microbeam mass analysis (LAMMA), performed only on the second biopsy, revealed a high and fairly constant residual lead concentration in all bone marrow cell nuclei (approximately 55 micrograms/g) and a low lead concentration in the cytoplasm of the same cells (4-12 micrograms/g). The extracellular bone matrix lead was greatly concentrated in the superficial 3-6 microns osteoid zone of the bony trabeculae and totally absent from deeper parts of the mineralized matrix. The LAMMA results are in good agreement with those of subcellular fractionation experiments and atomic absorption spectroscopy, provided that the relative volume fraction of nucleus and cytoplasm is accounted for. The high residual osteoid lead after completed chelation therapy indicates that lead has a stronger affinity for the organic than the mineral components of bone matrix.

Some effects of bone meal supplemented diet on bone and teeth of growing rats.

Bone meal (containing 500 ppm F) was added to the diet of growing rats in an amount corresponding to that recommended ingested by children. Addition of bone meal did not influence body weight increment, or growth and ash content of bone and teeth. Fluoride in bone and teeth increased as compared to control animals, but the increase was 2-4 times less than if fluoride had been given as NaF. Analyses of feces disclosed significantly increased values of Ca and F in animals fed the bone meal supplemented diet, indicating low absorption of these minerals from bone meal.