The determination of copper , zinc , and lead in human teeth using inductively coupled plasma atomic emission spectrometry ( ICP-AES )

The concentrations of copper, lead, and zinc were measured in human teeth of varying ages. The levels of these metals in the teeth reflect those of the bone. Teeth have proved to be a considerable source of copper, lead, and zinc, and with the demographical information of each tooth, general trends were also examined. It was determined that lead concentration appears to increase with age; however, no such trend was obvious for copper or zinc. In addition, no significant difference between males and females was observed. Introduction Certain metals are necessary for proper bodily function. For example, the ionic form of copper is utilized in the electron transport chain as an electron donor.1 In addition, Zn2+ functions to displace electrons forming covalent bonds, usually in amino acid chains, so that carboxypeptidases can more easily break the bonds. It should be noted that lead does not appear to have a biological role in the body. It is a heavy metal that is toxic to animals in small amounts.2 Over time, various ingested elements can build up in the body due to environmental exposure, diet, and/or disease.3 While elemental deficiency is more commonly a concern, an excess of trace elements in the body can lead to adverse effects such as high infant mortality rate and shorter life span.4 Of particular interest in the past has been the study of lead accumulation in the body. Not only is overexposure to lead toxic, but buildup of this element can also affect the concentrations of zinc and copper in the body.4 Elements can accumulate in the hard tissues of the body such as bone, teeth, and fingernails. The most practical of these hard tissues to use for elemental measurements is teeth because bone is generally not readily available and fingernails are often impure samples.5 In addition, teeth of different ages can be easily accessed in order to compare the elemental concentrations of multiple generations of people at one time. Inductively coupled plasma atomic emission spectrometry (ICP-AES) appears to be the most commonly used method of determining the concentrations of these trace metals in teeth, but ICP mass spectrometry,6 particle induced X-ray emission analysis,7 and laser ablation8 have also been used to determine the concentrations of trace metals in human and animal teeth, as well as bone. Scientists have determined the ranges of these trace metals in human teeth to be ≤3 μg/g, 320 ± 10 μg/g,7 and 400-480 μg/g9 for lead, zinc, and copper, respectively. In this experiment, teeth from a wide range of ages were analyzed for copper, lead, and zinc concentrations using ICP-AES. Concordia College Journal of Analytical Chemistry 3 (2012), 33-39 34 Experimental The method for analyzing teeth was adapted from a previous study by Chew et al.3 Tooth Sample Preparation Extracted teeth were obtained from people in an age range of 16-83 years. The extractions were performed by an oral surgeon for functional or cosmetic reasons. Of the seventeen samples, eight were extracted from Caucasian males, eight from Caucasian females, and one was from an African American female. Upon receiving the teeth, each was washed with ultrapure water. Subsequently, each tooth was placed in a 25 mL solution of concentrated nitric acid (70%) (Fisher) for five minutes to remove leftover tissues. Then, each tooth was rinsed first with ultrapure water, followed by acetone (analytical grade). In order to dry the teeth, each was placed in a drying oven for five minutes at 90oC. Once the teeth had cooled, each was weighed and transferred to a dry test tube, which was filled with approximately 25 mL of 10% nitric acid (Fisher) solution. The test tubes were then placed in a water bath at about 90°C for an hour. The samples were then left overnight in a fume hood. The following day, the test tubes were again placed in the 90oC water bath until each sample had dissolved. Concentrated nitric acid was added to individual test tubes as needed to aid the dissolving process, especially in the cases in which the tooth mass was greater than 2 grams. Once the samples had dissolved, each solution was filtered into a labeled 50-mL volumetric flask using hardened, ashless filter paper (Whatman 540). Ultrapure water was used to rinse each filtrate several times. The solutions were diluted to volume with ultrapure water. Standard Solution Preparation Varying amounts of 1000 ppm Zn (SCP Science), Cu (Ricca), and Pb (Fisher) stock solutions were diluted to make standard solutions. The ranges used are shown in Table 1. Table 1. Concentrations of standards used in ICP-AES analysis of tooth samples. Element Standard 1 Standard 2 Standard 3 Standard 4 Copper 0.4 ppm 1.0 ppm 1.6 ppm 2.0 ppm Lead 0.4 ppm 1.0 ppm 1.6 ppm 2.0 ppm Zinc 1.0 ppm 2.0 ppm 3.0 ppm 4.0 ppm