Abstract
Studies have shown that hair and nail samples can be used as a marker to assess occupational exposure to heavy metals. The objective of this study was to estimate the levels of heavy metals: Lead (Pb), Nickel (Ni), Cadmium (Cd), and Manganese (Mn) in hair and nail samples of welders working in United Arab Emirates and to find an association between the heavy metal concentration with the parameters like smoking habits, exposure/day, years of experience and use of protective personal equipment (PPE). Hair and toes nail samples were collected from exposed and non-exposed subjects with respect to, social habits, exposure/day and years of welding experience. The levels of Pb, Cd, Mn, and Ni, in hair and toenails, assayed by atomic absorption spectrophotometer. We observed that the metal concentration was higher in toenail as compared to hair samples in both the groups. Cd was significantly high in both the groups whereas, Mn in the hair was high in the exposed group. The Mn in hair was notably higher among smokers and the Cd in hair and Ni in the nail samples was significantly higher in the subjects with > 8 h/day exposure. The concentration of Cd and Ni in hair increased with increasing years of experience and was maximum in the subjects with welding experience of > 20 years. Our results signify that hair and nail samples can be used as an indicator to heavy metal exposure. Given that the present study shows high level of some metals in the hair and nail of welders, awareness of occupational hazards and annual assessment of welder’s health is necessary.
Keywords: Heavy metals, Occupational hazards, Welding, Atomic absorption spectrophotometer
Introduction
Exposure to heavy metals resulting from different sources and activities may have deleterious effects on human health. The process of welding is one of them which exposes the workers continuously to the fumes of different agents which could be hazardous. Approximately 110 million of workers are exposed to the welding fumes globally [1]. The agents produced during welding are gases (acetylene, carbon monoxide, oxides of nitrogen etc.), metals (arsenic, silver, beryllium, cadmium, chromium, tin, cobalt, copper, iron, lead, manganese, nickel, and zinc) and various physical agents [2, 3].
Heavy metal poisoning is known to affect vital organs such as the central nervous system, circulatory system, respiratory system, kidneys, liver etc. Chronic exposure to heavy metals can lead to degenerative neurologic diseases, allergies, lung diseases, eye irritation, reduced sperm count, non-melanocytic skin cancer and malignant melanoma [2, 4]. Therefore, it is imperative to estimate the metal concentrations especially in the subjects who are highly exposed to monitor and evaluate the influence of exposure on their health.
The assessment of exposure is usually done by measuring the levels of heavy metals in blood, serum, urine, hair, fingernails, saliva etc. of the exposed group [5]. In comparison to blood and other body fluids, nails give a constant record of metal levels in the body. Their growth rate is 0.05–1.2 mm/week, while toenails grow 30–50% slower in contrast to other nails providing a longer incorporation time for the metals. They are easy to sample, transport and store, and the analysis is feasible, making them an idea tool for screening and diagnosing [6]. There are several studies available that have reported that nails can be used as bio-indicators of metal toxicity [7–10].
The other body sample useful in screening for metal exposure are hairs. Hair closest to the nape of the scalp by one- and one-half inches gives an idea on the exposure in the previous three months. Keratin, being rich in sulfur-containing cysteine residues, is known to be an important part of hair. When metals in blood reach the hair follicle, they bind with the keratin, and gets trapped in the hair shaft. Hair stores metals tenfold more the levels seen in blood. Hence, the hairs and nails are considered as an important biological matrix because the concentration of heavy metals in them reflect their mean level in the body during a longer period as compared to body fluids [4].
Keeping in mind the continuous exposure that the workers experience in the field of welding, the present study was undertaken to estimate the levels of lead (Pb), cadmium (Cd), manganese (Mn) and nickel (Ni) in their hair and nails samples. As limited data is available in this regard in United Arab Emirates (UAE), hence the results can contribute to the new measures and regulatory guidelines regarding metal exposure and occupational health hazards.
Materials and methods
The study took place in Centre for Advanced Biomedical Research and Innovation (CABRI), Gulf Medical University, Ajman, UAE. The samples were collected from 50 welders working in welding factory (Exposed group) and 25 office workers (Non-exposed group). Males above the age of 30 years with minimum 5 years of exposure in welding activities were included in the exposed group. Age below 30 years, job exposure less than 5 years, presence of orthodontic appliances/intraoral metal restoration and usage of hair dye/bleaching in the past 1 week was the exclusion criteria.
Sample collection
Hair samples were cut 2 mm away from the nape of the scalp using a sterilized scissors washed with ethanol. For nail samples collection, the subjects were asked to wash their toes carefully with a medicated soap and then dry. All the samples were placed in plastic bags prior to analysis. Hair and nail samples were collected from all individuals giving a total of 150 samples for the analysis.
A questionnaire was filled to obtain personal, medical and occupational history of the subjects and an informed consent was obtained. The necessary approval has been obtained from the Institutional Ethics committee.
Sample preparation
The sample washing and digestion was done as per the method described by Mehra and Juneja [10].
Instrumentation
Heavy metal estimation in all the samples was done using atomic absorption spectrophotometer (AA500FG,PG Instruments Ltd, Leicestershire, UK). Standard operating parameters were set (using an air-acetylene flame) and given in Table 1. The standards and the samples were analyzed using the analytical cookbook and data entered using AAWin software (Version 1.0; PG Instruments, UK).
Table 1.
Absorbance measurements of standard solutions and working parameters for Pb, Cd, Ni, and Mn using atomic absorption spectrophotometer
| Absorbance (Au) | ||||
|---|---|---|---|---|
| Lead (Pb) | Cadmium (Cd) | Nickel (Ni) | Manganese (Mn) | |
| Standard solution (µg/ml) | ||||
| 0.1 | 0.0100 | 0.0147 | 0.0050 | 0.0073 |
| 0.2 | 0.0125 | 0.0310 | 0.0112 | 0.0123 |
| 0.4 | 0.0225 | 0.0473 | 0.0225 | 0.0386 |
| 0.8 | 0.0337 | 0.0786 | 0.0475 | 0.0775 |
| Relative factor | 0.098765 | 0.98898 | 0.99852 | 0.99537 |
| Working parameters | ||||
| Wave length (nm) | 217.0 | 228.8 | 232.0 | 279.8 |
| Bandwidth | 0.4 | 0.4 | 0.2 | 0.4 |
The calibration curve for each metal was achieved by measuring the absorbance for working standards (0.1, 0.2, 0.4, 0.8 µg/ml) with linearity and coefficient of determination. Heavy metal concentration in all the samples were calculated using their respective linear calibration curves (Table 1).
Statistical analysis
Results are expressed as mean ± SD. Statistical analysis of the data was performed using Student’s “t” test. The p values equal to or less than 0.05 were adjudged statistically significant.
Results
Demographic details
In the exposed group, 70.7% were non-smokers, 12% has respiratory complaints, 8% had cardiovascular issues, 5% had musculoskeletal and 4% had diabetic complaints. In the non-exposed group, 8% subjects were having gastrointestinal (GI) complaints and 4% has the complaint of regular headaches. Forty percent of the welders were working for 8 h shift daily and the rest for 10–12 h/day. The majority (52%) had welding experience from 10 to 20 years, followed by 28% from 5 to 10 years, the minority was > 20 years 20%.
Table 2 shows the concentration of Pb, Cd, Mn and Ni in hair and nail samples. The levels of the metals in hair samples were in the following order Pb > Mn > Ni > Cd in the exposed group. Cd and Mn in hairs were found to be significantly higher than the non-exposed group (p < 0.01). The levels of the metals in nail samples were in the following order Cd > Ni > Mn > Pb in the exposed group. Cd in nail samples was found to be significantly higher in the exposed than the non-exposed group (p < 0.01).
Table 2.
Concentration of heavy metals in hair and nail samples of non-exposed (n = 25) and exposed group (n = 50)
| Non-exposed conc. (µg/g) | Exposed conc. (µg/g) | p Value | |||||
|---|---|---|---|---|---|---|---|
| Mean ± SD | Min | Max | Mean | Min | Max | ||
| Hair | |||||||
| Pb | 0.438 ± 0.49 | 0.005 | 1.445 | 0.741 ± 0.54 | 0.005 | 2.970 | NS |
| Mn | 0.463 ± 0.16 | 0.142 | 0.660 | 0.673 ± 0.32 | 0.235 | 1.790 | ≤ 0.01 |
| Ni | 0.57 ± 0.16 | 0.252 | 0.840 | 0.535 ± 0.19 | 0.265 | 0.940 | NS |
| Cd | 0.205 ± 0.17 | 0.020 | 0.540 | 0.527 ± 0.33 | 0.030 | 1.115 | ≤ 0.01 |
| Nail | |||||||
| Pb | 1.187 ± 0.95 | 0.130 | 3.903 | 0.978 ± 0.71 | 0.010 | 2.840 | NS |
| Mn | 0.884 ± 0.36 | 0.295 | 1.490 | 1.07 ± 1.08 | 0.260 | 8.000 | NS |
| Ni | 1.060 ± 0.58 | 0.313 | 2.940 | 1.108 ± 0.43 | 0.350 | 2.390 | NS |
| Cd | 0.738 ± 0.44 | 0.130 | 1.550 | 1.141 ± 0.55 | 0.130 | 2.600 | ≤ 0.01 |
Mean concentration of metals in hair and nail of welders were compared based on smoking habits (Table 3). Only Mn in hair was found to be significantly higher among smokers (0.806 ± 0.417 µg/g) as compared to non-smokers 0.610 ± 0.253 µg/g) (p ≤ 0.05).
Table 3.
Concentration of heavy metals in hair and nail samples of smokers (n = 16) and non-smoker (n = 34) among welders
| Smokers | Non-smokers | p Value | |||||
|---|---|---|---|---|---|---|---|
| Mean ± SD (µg/g) | Min | Max | Mean ± SD (µg/g) | Min | Max | ||
| Hair | |||||||
| Pb | 0.663 ± 0.36 | 0.005 | 1.395 | 0.680 ± 0.61 | 0.005 | 2.970 | NS |
| Cd | 0.509 ± 0.34 | 0.030 | 1.115 | 0.535 ± 0.33 | 0.030 | 0.970 | NS |
| Ni | 0.557 ± 0.15 | 0.350 | 0.940 | 0.524 ± 0.20 | 0.265 | 0.940 | NS |
| Mn | 0.806 ± 0.42 | 0.385 | 1.790 | 0.610 ± 0.25 | 0.235 | 1.345 | < 0.05 |
| Nail | |||||||
| Pb | 0.911 ± 0.54 | 0.180 | 2.040 | 1.001 ± 0.77 | 0.010 | 2.840 | NS |
| Cd | 1.226 ± 0.66 | 0.190 | 2.600 | 1.099 ± 0.49 | 0.130 | 1.900 | NS |
| Ni | 1.168 ± 0.52 | 0.480 | 2.390 | 1.080 ± 0.39 | 0.350 | 1.780 | NS |
| Mn | 0.946 ± 0.37 | 0.400 | 1.630 | 1.129 ± 1.29 | 0.260 | 8.00 | NS |
Comparison based on their exposure time/day shows Cd in hair and Ni in nail were significantly higher (p < 0.05) in welders exposed more than 8 h/day (Table 4).
Table 4.
Concentration of heavy metals in hair and nail samples of welders based on exposure time/day
| 8 h (n = 20) Conc. (µg/g) |
> 8 h (10–12) (n = 30) Conc. (µg/g) |
p Value | |||||
|---|---|---|---|---|---|---|---|
| Mean ± SD | Min | Max | Mean ± SD | Min | Max | ||
| Hair | |||||||
| Pb | 0.643 ± 0.43 | 0.005 | 1.270 | 0.813 ± 0.61 | 0.050 | 2.970 | NS |
| Cd | 0.440 ± 0.33 | 0.055 | 0.960 | 0.635 ± 0.27 | 0.030 | 1.115 | < 0.05 |
| Ni | 0.520 ± 0.19 | 0.265 | 0.940 | 0.544 ± 0.18 | 0.275 | 0.940 | NS |
| Mn | 0.691 ± 0.31 | 0.235 | 1.345 | 0.661 ± 0.34 | 0.350 | 1.790 | NS |
| Nail | |||||||
| Pb | 1.099 ± 0.84 | 0.010 | 2.840 | 0.864 ± 0.56 | 0.030 | 1.990 | NS |
| Cd | 1.168 ± 0.43 | 0.350 | 1.720 | 1.121 ± 0.62 | 0.130 | 2.600 | NS |
| Ni | 0.962 ± 0.47 | 0.350 | 2.390 | 1.206 ± 0.39 | 0.480 | 1.780 | < 0.05 |
| Mn | 1.345 ± 1.65 | 0.340 | 8 | 0.887 ± 0.32 | 0.260 | 1.700 | NS |
The distribution of Pb, Cd, Mn and Ni in hair and nail samples of welders based on their years of experience is represented in Table 5. Cd and Ni in hair was found to be significantly high (p < 0.05) in the subjects working for more than 20 years as compared to the other groups.
Table 5.
Concentration of heavy metals in hair and nail samples based on the years of experience in welding
| 5–10 years (n-14) Conc. (µg/g) | 10–20 years (n-26) Conc. (µg/g) | > 20 years (n-10) Conc. (µg/g) | p Value | |||||||
|---|---|---|---|---|---|---|---|---|---|---|
| Mean ± SD | Min | Max | Mean ± SD | Min | Max | Mean ± SD | Min | Max | ||
| Hair | ||||||||||
| Pb | 0.963 ± 0.77 | 0.3 | 2.97 | 0.715 ± 0.44 | 0.005 | 1.455 | 0.544 ± 0.43 | 0.005 | 1.16 | NS |
| Cd | 0.345 ± 0.25 | 0.03 | 0.785 | 0.595 ± 0.31 | 0.03 | 1.115 | 0.613 ± 0.39 | 0.05 | 0.97 | < 0.05 |
| Ni | 0.494 ± 0.16 | 0.275 | 0.79 | 0.506 ± 0.16 | 0.265 | 0.915 | 0.666 ± 0.25 | 0.365 | 0.94 | < 0.05 |
| Mn | 0.646 ± 0.35 | 0.385 | 1.79 | 0.719 ± 0.33 | 0.37 | 1.7 | 0.591 ± 0.28 | 0.235 | 1.055 | NS |
| Nail | ||||||||||
| Pb | 0.713 ± 0.45 | 0.03 | 1.42 | 0.996 ± 0.73 | 0.01 | 2.69 | 1.171 ± 0.85 | 0.25 | 2.84 | NS |
| Cd | 1.041 ± 0.53 | 0.37 | 2.6 | 1.038 ± 0.49 | 0.13 | 1.72 | 1.464 ± 0.62 | 0.35 | 1.74 | NS |
| Ni | 0.977 ± 0.23 | 0.48 | 1.78 | 1.104 ± 0.47 | 0.35 | 2.39 | 1.21 ± 0.46 | 0.5 | 1.25 | NS |
| Mn | 0.751 ± 0.21 | 0.34 | 1.21 | 0.731 ± 0.17 | 0.26 | 8 | 1.373 ± 1.43 | 0.501 | 1.05 | NS |
Based on the questionnaire results, 12% of welders admitted they were irregular with using the PPE. The groups were not compared for statistical differences as the numbers in irregular use of PPE group was very small (Table 6).
Table 6.
Concentration of Heavy Metals in Hair and Nail Samples Based on the Usage of Protective Personal Equipment
| Regular use (n = 44) Conc.(µg/g) | Irregular use (n = 6) Conc.(µg/g) | |||||
|---|---|---|---|---|---|---|
| Mean ± SD | Min | Max | Mean ± SD | Min | Max | |
| Hair | ||||||
| Pb | 0.784 ± 0.55 | 0.005 | 2.970 | 0.466 ± 0.38 | 0.050 | 1.085 |
| Cd | 0.553 ± 0.33 | 0.030 | 1.115 | 0.259 ± 0.18 | 0.060 | 0.495 |
| Ni | 0.541 ± 0.19 | 0.265 | 0.940 | 0.485 ± 0.11 | 0.350 | 0.640 |
| Mn | 0.649 ± 0.30 | 0.235 | 1.700 | 0.848 ± 0.48 | 0.455 | 1.790 |
| Nail | ||||||
| Pb | 1.046 ± 0.74 | 0.010 | 2.840 | 0.522 ± 0.22 | 0.180 | 0.800 |
| Cd | 1.154 ± 0.55 | 0.130 | 2.600 | 1.052 ± 0.56 | 0.260 | 1.590 |
| Ni | 1.142 ± 0.42 | 0.350 | 2.390 | 0.860 ± 0.46 | 0.480 | 1.570 |
| Mn | 1.105 ± 1.14 | 0.340 | 8 | 0.812 ± 0.41 | 0.260 | 1.310 |
Discussion
The present study focused on the importance of using non-invasive human samples, such as toenail and hair samples to assess occupational hazard among the welders working in UAE. The exposed group consisted of 50 welders from 3 different welding company, mainly working on mild steel and galvanized iron. It was observed that hair samples contain lower concentrations of metals than nails, which could be due to the usage of shampoos causing leaching of metals from the hair shaft. Several other studies also reported more concentration of heavy metal in nails in comparison to hair samples [6, 9].
Different types of industrial work like lead battery, painting, black smith, welding etc. workers have been found to have high levels of elements based on their type of work [9, 10]. Significantly higher level of Cd, Pb and Ni in the hair samples of subjects involved in electroplating work have been reported suggestive of increased risk of metal toxicity [11]. In our study, all metals (Pb, Cd, Mn and Ni) showed lower concentration in hair and nail samples as compared to earlier reports probably due to the regular use of personal protective equipment (PPE) during working hours [6]. The accepted level of Pb in hair and nail is < 4.0 µg/g and a concentration more than 10 µg/g in hair indicates significant lead exposure [12]. Based on the given reference, we observed that all the participants had Pb concentration within the normal range.
The accepted level of Cd and Ni in hair is < 0.50 μg/g and < 1 µg/g, respectively. In exposed group, 42% of welders had Cd levels above 0.5 µg/g, the highest being 1.115 µg/g. All participants had Ni level below the levels of acceptable range. Literature shows a mean concentration of Ni in hair samples from 55 subjects was 1.01 ppm; populations from cities in Japan, India, Canada, and Poland had mean Ni levels between 0.26 and 2.70 ppm [13].
In the present study, only 3 participants from the exposed group had Mn level in hair above the current reference value (1.2 µg/g), maximum being 1.79. The highest concentration of Mn demonstrated in the hair samples was 1.8–2.5 ppm which was within the permissible range (0–13 ppm) reported earlier [14, 15].
The concentration of metals in the biological samples is not constant and is affected by many factors. It has been reported that Cd in hair is a reliable indicator of high environmental contamination and tobacco smoking. Smokers absorb 1–2 μg of Cd per pack of cigarettes, approximately doubling the average exposure as compared to a non-smoker [16]. Other studies have reported high levels of Cd, Pb, Cr, Fe, Ni, Cu and Zn in smokers as compared to nonsmokers [10, 17]. Besides tobacco, the other sources of metal in cigarettes are wrapping paper and the filter. We also observed no significant difference in alcohol consumption and non-alcoholic group (data not shown).
Exposure time/day and years of welding exposure are other factors that contribute to the metal accumulation in the body. We found that Cd in hair and Ni in nail was significantly higher based on exposure time. Other studies also reported that from three periods of exposure, 1–10 years, 11–20 years and 21–30 years, the mean concentration of metals was found to be significantly higher in workers with 21–30 years of experience [18].
Various studies have published an association of metal concentrations with health problems [9, 19–21]. The pathological symptoms reveal that there is a significant correlation between metal load and certain diseases, such as hypertension and Cd/Mn concentration; Mental stress and Cd/Pb/Mn/ Ni; diabetes and Mn/Ni; chest pain and Pb; Respiratory trouble and Mn/Ni/ Zn/Cd; ophthalmic trouble and Mn/Fe/Ni etc. [9]. It is a well-known fact that regular use of PPE reduces the possibility of health complaints. We observed in our study that majority of welders took precautions towards exposure to metal fumes during their course of work.
The present study reveals significant difference in the metal concentration in hair and nail sample among welders and is also related to duration of exposure. Necessary measures regarding awareness of occupational hazard and emphasis on using PPE, and regular checkup leading to healthy lifestyle is recommended.
Compliance with ethical standards
Conflict of interest
The authors have no conflict of interest to disclose.
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