Biol Trace Elem Res DOI 10.1007/s12011-011-9102-1
Background Values for Essential and Toxic Elements in Children’s Nails and Correlation with Hair Levels Maria Fernanda Hornos Carneiro & Denise Grotto & Bruno Lemos Batista & Claudia Ramos Rhoden & Fernando Barbosa Jr
Received: 17 May 2011 / Accepted: 25 May 2011 # Springer Science+Business Media, LLC 2011
Abstract Human nails are an attractive matrix for assessing environmental exposures to toxic elements as well as the deficiency of essential elements since it is noninvasively collected and can be stored at room temperature. However, reference or baseline levels in nonexposed and healthy populations are not yet established. Then, the aims of this study were (a) to estimate background values for essential and toxic elements in nails from a healthy young population in southern Brazil and (b) to evaluate possible correlations between essential and toxic elements in nails. Furthermore, this report took part of a recent study of background values in the hair of a young population. Thus, correlations between chemical elements in nails and hair were also evaluated. Nails were collected from healthy children (n=126), and element concentrations were determined by inductively coupled plasma mass spectrometry. This study provides new and reliable reference concentrations for toxic and essential elements in children’s nails. The results can be used as reference values for epidemiological or clinical investigations based on trace elements in nails. Additionally, we also showed weak to strong correlations between Cu, Mg, Mn, Se, and Zn levels in nails and hair. Keywords Chemical elements . Reference values . Nails . School age children . ICP-MS . Hair
M. F. H. Carneiro : D. Grotto : B. L. Batista : F. Barbosa Jr (*) Laboratório de Toxicologia e Essencialidade de Metais, Departamento de Análises Clínicas, Toxicológicas e Bromatológicas, Faculdade de Ciências Farmacêuticas de Ribeirão Preto, Universidade de São Paulo, Avenida do Café s/n, Monte Alegre, 14040-903 Ribeirão Preto, São Paulo, Brazil e-mail:
[email protected] C. R. Rhoden Laboratório de Estresse Oxidativo e Poluição Atmosférica, Universidade Federal de Ciências da Saúde de Porto Alegre, Avenida Sarmento Leite, 245, Centro, CEP 90050-170 Porto Alegre, Rio Grande do Sul, Brazil
Carneiro et al.
Introduction Human nails are an attractive matrix for large population assessment of environmental exposures to toxic elements as well as the deficiency of essential elements since it is noninvasively collected and can be stored at room temperature [1, 2]. Due to these inherent beneficial characteristics, several epidemiological studies have estimated individual’s body burden of trace elements by using nails as the biological matrix [3–7]. However, background values for toxic and essential elements in nails, especially children, are still scarce [8]. Thus, the aims of this study were (a) to estimate background values for essential and toxic elements in nails from Brazilian healthy schoolchildren, (b) to evaluate possible correlations between essential and toxic elements in nails, and (c) to assess possible correlations between trace elements in nails and hair collected from these children.
Materials and Methods Studied Population and Sampling In July and August, 2009, nails were collected from 126 healthy students from nine public schools in Porto Alegre, the capital of Brazil’s southernmost state, Rio Grande do Sul. The city is situated at latitude 30°01′59″ S and longitude 51°13′48″ W and is approximately 100 km far from the Atlantic Ocean. The total population is 1,446,777 inhabitants in an area of 497 km2, with a population density of 2.91 inhabitants/km2. Services are the principal economic activity, followed by industry and agriculture [9]. The study population was considered to be a typical group of students, ranging in age from 12 to 18 years old, living in an urban area in Brazil, not exposed to toxic substances and not living in unusual conditions. Before sample collection, the participants filled out a questionnaire with questions about individual and socioeconomic characteristics and medical history. None of the students reported having a chronic disease. Nails were clipped with a stainless steel cutting instrument and placed inside metal-free plastic tubes. Informed consent was obtained from each survey participant as well as from their parents/guardians and school supervisors following guidelines approved by the Ethics Committee of the Federal University of Health Sciences in Porto Alegre. Reagents and Instrumentation All reagents used were of analytical reagent grade except nitric acid (HNO3), which was previously purified in quartz sub-boiling stills (Kürner). A clean laboratory and laminar flow hood capable of producing class 100 were used for preparing solutions. High-purity deionized water (resistivity 18.2 MΩ cm) obtained from a Milli-Q water purification system (Millipore, Milli-Q RiOs®, Bedford, MA, USA) was used throughout. Plastic bottles and glassware were cleaned by soaking in 10% (v/v) HNO3 for 24 h, rinsed five times with Milli-Q water, and dried in a class 100 laminar flow hood before use. All operations were performed on a clean bench. All solutions were stored in high-density polyethylene bottles. Tetramethylammonium hydroxide (TMAH) and L-cysteine were purchased from Sigma (Sigma, St. Louis, MO, USA), and multi-element stock solutions containing 1,000 mg L−1 of each element were obtained from Perkin-Elmer (Norwalk, CT, USA). All measurements were made with an inductively coupled plasma mass spectrometry (ICPMS; Elan DRC II PerkinElmer, Norwalk, CT, USA) with high-purity argon (99.999%, White
Background Values for Essential and Toxic Elements
Martins, Brazil). A Meinhard concentric nebulizer (Spectron/Glass Expansion, Ventura, CA, USA) connected to a cyclonic spray chamber was used. A radiofrequency with 1,100 W of power was selected in pulse mode with autolens one. Sample data were acquired by using 20 sweeps/reading, 1 reading/replicate, and a dwell time of 50 ms. The argon nebulizer gas flow rate was optimized daily from 0.5 to 0.9 Lmin−1. Data were acquired in counts per second. Determination of Trace Elements in Nails by ICP-MS After washing (acetone/water/acetone), samples were dried in a class −100 laminar flow hood. Prior to analysis, nails were cleaned and weighed (10–20 mg) into 15 mL conical tubes. After that, 1 mL of 25% (w/v) TMAH solution was added and the tubes were incubated at room temperature for 12 h. Then, the volume was made up to 10 mL with 1% (v/v) HNO3 and directly analyzed by ICP-MS following the method reported by Batista et al. [10]. In all analysis, rhodium was added as an internal standard to get a final concentration of 10 μg L−1. Quality Control of the Results Quality control of trace metal determination in nails was ensured by analyzing a hair reference material provided by the Institut National de Santé Publique du Québec, Canada (INSP-external quality assessment scheme—EQAS ICP03H-09). Obtained values were in good agreement with the target values. Reference samples were analyzed before and after ten ordinary samples. Statistical Analysis Since the data are non-parametric, Spearman’s correlation test was used to evaluate the correlation among the different elements in nails. Additionally, as this report took part of a study of background values in hair of the same young population [11], the Mann–Whitney U test was used to evaluate differences between element concentrations in nails and hair. Spearman’s correlation test was also used to evaluate correlations between trace element level in nails and hair. The SPSS statistical package version 13.0 was used for calculations and for plotting figures (SPSS, version 13.0, Inc., Chicago, IL, USA). Statistical significance was set at 5%.
Results The concentration range as well as the mean, standard deviation, and percentiles (10, 25, 50, 75, and 90) of the elements As, Ba, Cd, Co, Cu, Mg, Mn, Pb, Rb, Se, Sb, U, and Zn obtained in scalp hair and nails of the participants are described in Table 1. Except for U, all elements had statistically higher concentrations in nails than in hair. In some cases, the accumulation rate was up to eight times higher in nails. Among toxic elements, Ba had the highest median concentration in the children’s hair and nails while the essential element most prevalent in the biological samples was Zn. Table 2 shows a comparison between trace elements concentration obtained in nails in the present report as well as in other studies carried out worldwide. Except for Ba, the levels of toxic elements in nails in the present population were lower than those observed in other studies (Table 2). The interrelationships between the elements detected in nails are presented in Table 3. Although weaker than those found in a previous study with hair samples [11],
Carneiro et al. Table 1 Comparison between the element concentrations accumulated in hair and nails of the studied population Element
Sample
Concentration (μg g−1) Minimum
Maximum
Mean
SD
P10
P25
Median
P75
P90
Hair
0.001
0.02
0.007
0.005
0.001
0.003
0.006
0.01
0.02
Nail
0.002
1.0
0.06
0.11
0.01
0.02
0.04*
0.06
0.1
Hair
0.02
7.6
1.0
1.1
0.09
0.2
0.8
1.5
2.1
Nail
0.4
83
5.6
10
1.6
2.2
3.3*
4.5
8.3
Hair
0.001
0.04
0.006
0.007
0.000
0.001
0.003
0.007
0.02
Nail
0.01
1.0
0.08
0.1
0.02
0.03
0.05*
0.1
0.2
Co
Hair
0.0001
0.04
0.008
0.007
0.001
0.002
0.006
0.01
0.02
Nail
0.01
1.0
0.08
0.1
0.03
0.04
0.06*
0.08
0.1
Cu
Hair
0.4
17
4.1
2.8
0.9
1.9
3.7
5.4
8.2
Nail
0.05
107
13
14.2
4.4
6.4
10*
15
22
Hair
0.04
184
14
18
2
5
10
17
26
Nail
0.2
426
92
54
45
64
82*
102
134
Hair
0.0009
4.6
0.4
0.6
0.03
0.1
0.3
0.5
0.9
Nail
0.1
15
1.6
1.5
0.8
1.0
1.4*
1.9
2.7
Hair
0.0004
0.8
0.2
0.2
0.009
0.03
0.1
0.2
0.4
Nail
0.03
32
1.0
2.9
0.3
0.4
0.5*
0.8
1.6
Hair
0.05
1.1
0.1
0.1
0.008
0.02
0.04
0.1
0.2
Nail
0.003
5.9
1.7
1.0
0.7
1.0
1.5*
2.2
3.2
Hair
0.004
0.5
0.1
0.1
0.04
0.07
0.1
0.2
0.3
Nail
0.04
6.5
0.3
0.6
0.2
0.2
0.3*
0.4
0.6
Hair
0.0001
0.02
0.004
0.006
0.000
0.000
0.002
0.006
0.02
Nail
0.01
0.3
0.05
0.06
0.02
0.02
0.03*
0.05
0.1
Hair
0.001
0.03
0.003
0.004
0.000
0.000
0.002*
0.004
0.007
Nail
0.001
0.03
0.003
0.003
0.0000
0.001
0.002
0.003
0.006
Hair
7
197
60
34
20
33
59
77
96
Nail
33
1,797
150
190
76
91
113*
144
183
As Ba Cd
Mg Mn Pb Rb Se Sb U Zn
Hair values were extracted from a previous study [13]. Data about the elements are expressed in micrograms per gram. Rank sum test. P10, P25, P75, and P90 correspond to respective percentiles SD standard deviation *P
