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ICP-OES determination of metals present in textile materials
Microchemical Journal 85 (2007) 46 – 51 www.elsevier.com/locate/microc
ICP-OES determination of metals present in textile materials Iva Rezić a,⁎, Ilse Steffan b a
Laboratory of Analytical Chemistry, Department of Applied Chemistry, Faculty of Textile Technology, University of Zagreb, Prilaz Baruna Filipoviæa 30 10000 Zagreb, Croatia b Department of Analytical Chemistry and Food Chemistry, University of Vienna, Austria Received 13 January 2006; received in revised form 14 June 2006; accepted 14 June 2006 Available online 24 July 2006
Abstract The aim of this work was to quantify the content of elements present in textile materials since it is known that textiles containing metals may represent a health hazard to consumers. Determination of metal content can be also useful to the textile industry since some metals present in textiles may contribute to problems during textile production. Extraction of metals from different textile materials was performed in an artificial acidic sweat solution according to the Öko Tex standard for materials coming into direct contact with the skin. After extraction from textile products made of cotton, flax, wool, silk, viscose, and polyester materials, all elements were determined by means of inductively coupled plasmaoptical emission spectrometry (ICP-OES). Results in the sweat extracts (minimum–maximum in μg/mL) were: Al 0.11–1.58, Cd 0.02–0.05, Cr 0.01–0.32, Cu 0.05–1.95, Mn 0.01–2.17, and Ni 0.05–0.10. Concentrations of other elements were bellow detection limits. The total amount of metals present was determined after microwave assisted acidic digestion of textile materials with 7 M nitric acid. According to the results, the majority of the detected elements were below the concentration limits given by the Öko Tex, and for this reason the textile materials investigated do not represent a health hazard to consumers. © 2006 Elsevier B.V. All rights reserved. Keywords: Textiles; ICP-OES; Öko Tex Standard
1. Introduction People are often exposed to different allergenic and toxic chemicals coming from textiles due to daily contact with clothes, bed linen and similar products. Many textiles contain chemicals that may represent a health hazard to consumers. The major chemical pollutants on textiles are dyes containing carcinogenic amines, toxic heavy metals, pentachlorophenol, chlorine bleaching, halogen carriers, free formaldehyde, biocides, fire retardants, and softeners [1]. Heavy metals are often present in different textile processes [2]. The reagents mostly used are: metal complex dyes, dye stripping agents, fastness improvers, oxidizing compounds, and finishers like water repellants, flame retardants, antifungal and odor-preventive agents [3]. Raw textile materials may also contain heavy metals [4]. Cotton, flax and hemp sometimes adsorb very large amounts of metals from the environment [5,6], and can be used as bio-absorbers [7].
⁎ Corresponding author. Tel.: +385 1 4597209; fax: +385 1 3712 599. E-mail addresses: [email protected], [email protected] (I. Rezić). 0026-265X/$ - see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.microc.2006.06.010
Determination of metal content of different textile materials is very important not only for the safety of consumers, but also for the textile industry. It is known that some metals present in cotton may contribute to problems in yarn manufacturing, bleaching and dyeing, and processing quality [8]. Problems reported from dyeing processes are related with metal contribution to the light-induced yellowing of whitewashed denim. Manganese and ferrous ions are readily air-oxidized to compounds that cause yellowing. In addition, transition metals catalyze organic reactions and function as mordant that strongly bind many organic compounds to cotton [9]. For this reason the textiles treated in those processes should be monitored for the presence of different metals (aluminum, calcium, copper, iron, magnesium, manganese, and titanium) and their presence has to be reduced by applying different production methods [10]. Metals are most frequently used in textile wet processing, although some of them are extremely toxic to many organisms. The use of chromium based dyes is essential for the fast black dyeing on wool and nylon, but in the future it will probably be replaced by newly developed dyes containing less toxic metals like iron [11]. Cobalt, chromium and occasionally copper and
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nickel form part of the most commonly used dyes, especially dyes for leather materials, nylon and wool. While chromium is generally used, cobalt has found selected applications. As a group, metal complex dyes offer good overall fastness properties [12]. Because of their wide application, metals are frequently present in textile dyeing wastewaters as free ionic metals or complex metals, which contributes to the environmental concerns [13]. Cobalt and chromium dyes are applied particularly in dyes for wool: there is no wool mordant dye that does not use chromium compounds. The chromium dye C.I. Mordant Black 11 is one of the most widely used dyes in the world [14]. Copper salts are used to fix direct dyes and to enhance the light fastness on the nylon. Antimony improves wash fastness properties on nylon fibers [15]. Cationic dyes contain zinc as well as trace concentrations of mercury, cadmium and arsenic as impurities from intermediates. Zirconium, aluminum and other salts are also used extensively in textile processing [16]. Usual concentrations of heavy metals in dyes are (in μg/g): 1.0 to 1.4 (As), up to 1.0 (Cd), 3.0–83.0 (Cr), 1.0–3.2 (Co), 33.0–110.0 (Cu), 6.0–52.0 (Pb), 0.5–1.0 (Hg), and 3.0–32.0 (Zn) [17].
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Table 2 Instrument parameters for ICP-OES Optima 3000 XL View Optical system Detector RF frequency/MHz Power/W Plasma gas flow/L min− 1 Auxiliary gas flow/L min− 1 Nebulizing chamber Nebulizer Sample flow rate/mL min− 1
Axial view Echelle Solid state detector 40.68 1 300 15.0 0.5 Cyclone Excentric ⁎ 0.8
⁎ Nebulizer (excentric) was produced by CPI, International, P/N 4060-010588.
Toxic effects of heavy metals on human health are very well known: damages of organs, disorders in the respiratory tract and lung diseases, dysfunction of heart, blood and blood producing organs, disorders in nervous system, skin diseases, abnormalities in fertility and pregnancy. Accumulation of heavy metals in body tissues and binding to enzymes may disrupt the functioning of cells, which may also lead to development of tumors or cancers
Table 1 Textile samples Number
Sample description
1
Red cotton
2
Sample picture
Number
Sample description
9
Green silk
Green cotton
10
Blue silk
3
White cotton
11
Red wool
4
Red/blue cotton
12
Brown wool
5
Black/coloured cotton
13
Pink viscose/ polyester
6
Yellow flax
14
Yellow viscose/ polyester
7
Black flax
15
Blue polyester
8
Green flax
16
Orange polyester
Sample picture
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[18]. To prevent those effects, different standards are now in use: MST (Markenzeichen schadstoffgeprüfter Textilien), Öko Tex Standard (Internationale Gemeinschaft für Forschung und Prüfung auf dem Gebiet der Textilökologie), Clean fashion, Steilman, Commitextile, EC Approach, EPG (The European Product Guarantee) and Ecomarc Scheme [19]. According to the requirements of Öko Tex the goods are controlled for pH, fastness properties, formaldehyde, carcinogenic dyes, dyes that can break down into carcinogenic aryl amines or can cause allergic reactions to the skin, extractable harmful heavy metals, halogenated carriers or contaminations with pentachlorophenol and pesticides [20]. Textile is categorized according to its utilization into products for babies, products with direct contact to skin, products without direct contact to skin, and decorative materials [21]. The limits for heavy metals vary depending upon the degree of the contact of a fabric to consumer's skin as well as on the toxicity of the heavy metal [22]. The limits do not involve the total amount of metals present in the fabric, but the part which can be extracted [23]. According to current standards, the use of metals and metal complex dyes is not prohibited in textile industry because their abandoning would result in a loss of some important shades like turquoise, brilliant green, violet, blue or navy shades [11]. The majority of problems arise when metals are extracted from the fabrics by perspiration. Because metals may represent a health hazard to consumers by causing allergenic skin reactions, and due to the fact that metals present in textiles may contribute to problems during processing, the aim of our study was to quantify the content of metals present in different textile materials. 2. Experimental
Table 4 Detection limits calculated for 7 M nitric acid ⁎ Element
Limits of detection / μg/L in 7 M nitric acid (λ/nm)
Al As Be Bi Co Cr Cu Fe K Mg
28.3 (308.215), 171.3 (394.401), 37.9 (396.152) 5.4 (188.979), 8.9 (193.696), 10.8 (197.197), 1.3 (228.812) 0.3 (234.861), 9.2 (265.045), 0.4 (313.042), 0.2 (313.107) 7.3 (190.178), 8.6 (222.825), 3.2 (223.061), 42. 9 (406.772) 3.0 (228.616), 0.2 (230.786), 1.5 (231.160), 0.5 (238.892) 0.7 (205.560), 1.7 (206.149), 0.1 (267.716), 0.4 (357.896) 8.2 (213.598), 86.6 (224.700), 121.8 (324.754), 110.5 (327.396) 1.0 (234.349), 0.3 (238.204), 0.5 (239.562), 0.1 (259.940) 32.0 (310.179), 116.7 (310.205), 0.4 (766.491) 11.6(202.582),0.5(279.079),0.3(279.553),0.3(280.270), 0.3(285.213) 0.1 (257.610), 0.1 (260.569), 0.6 (279.482), 0.9 (294.920) 0.8 (203.844), 2.4 (204.598), 1.6 (281.615) 2.2 (221.647), 2.0 (231.604), 2.6 (232.003), 1.1 (341.476) 0.6 (212.412), 0.5 (251.611), 4.1 (252.851), 0.8 (288.158) 12.3 (189.933), 31.7 (235.484), 33.7 (242.170), 33.2 (283.999) 3.5 (190.800), 2.7 (276.787), 10.6 (351.924) 0.5 (202.548), 2.8 (206.191), 0.6 (213.856)
Mn Mo Ni Si Sn Tl Zn
⁎ Bold values refer to selected lines.
and 1000 μg/mL standards (Al, As, Be, Bi, Co, Cr, Fe, K, Mg, Mn, Mo, Ni, Si, Sn, Tl) used for this research work were of p.a. grade, supplied by Merck, Darmstadt, Germany and by Perkin Elemer (Cd, Cu, and Zn). The liquid reference materials NIST 1640 (trace elements in water) and NIST 1643 (trace elements in natural water) were used for checking the accuracy of the measurements by ICP-OES. A certified comparative reference material for cotton trace element analysis IAEA-V-9 was used for checking the accuracy of the digestion procedure as well as the confirmation of the results.
2.1. Samples 2.3. Instrumentation The tests covered 16 textile samples of different origin (Table 1). All the samples taken for the purpose of this investigation were processed in the Croatian textile industry. The origin of the materials was known before analysis, but not the dye composition of the painted layer.
The inductively coupled plasma-optical emission spectrometer used was a Perkin Elmer Optima 3000 XL. The instrument was equipped with a standard one piece extended torch with a quartz injector tube, a cyclone spray chamber and an excentric1 nebulizer (Table 2).
2.2. Chemicals and standard solutions 2.4. Sample preparation All the chemicals (nitric acid, sodium chloride, ammonium chloride, sodium hydroxide, acetic acid, lactic acid and urea) Table 3 Detection limits in the artificial acidic sweat solution ⁎ Element
Limits of detection/μg/L in acidic sweat solution (λ/nm)
Al As Cd Co Cr Cu Fe Mn Mo Ni
0.8 (308.215), 9.7 (309.271), 3.1 (396.152) 14.0 (193.696), 14.1 (197.197), 3.9 (228.812) 1.4 (214.438), 0.2 (226.502), 3.2 (228.802) 2.0 (228.616), 3.0 (231.160), 2.4 (238.892) 0.3 (357.896), 2.0 (267.716), 1.6 (205.560) 1.7 (324.754), 0.1 (327.396), 0.1 (224.700) 19.7 (259.940), 1.7 (238.204), 1.9 (239.562) 1.8 (257.610), 1.7 (260.569), 3.3 (279.482) 1.6 (202.030), 1.4 (204.598), 3.9 (281.615) 6.4 (221.647), 3. 8 (232.003), 2.8 (341.476)
⁎ Bold values refer to selected lines.
2.4.1. Extraction in the artificial sweat solution Textile samples were dried for 48 h at 60 °C before analysis, and afterwards cut and weighed. 1.5 g of a sample was mixed for 2 h at 40 °C with 25 mL of artificial sweat solution, which was prepared according to the ISO 3160/2 standard. After filtration, the solutions were analyzed for all the elements by inductively coupled plasma-optical emission spectrometry (ICP-OES). 2.4.2. Microwave digestion For the determination of the total metal content of textile materials, the samples were dried for 48 h at 60 °C, cut and weighed. 0.5 g of dried samples were put into the digestion vessels of the microwave oven and digested with 8 mL of 7 M 1
Excentric nebulizer — page 23 attached to the Covering Letter.
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nitric acid. A closed-vessel microwave digestion system MLS 1200 Mega (produced by Milestone) equipped with a temperature control was used for the sample digestion. The temperature program was as follows: 5 min at 150 °C (power 250 W), 15 min 180 °C (300 W) and 20 min at the maximum temperature of 200 °C (350 W). The resulting solutions were cooled, filled up to 10 mL with 7 M nitric acid and analyzed by ICP-OES. The reference material for cotton trace element analysis IAEA-V-9 was digested in the same way. 2.4.3. Line selection After sample preparation, line selection was performed in order to select the optimal spectral lines for measurement. Multielement standard solutions in different matrix systems (acidic artificial sweat solution and 7 M nitric acid) were scanned by ICPOES over the selected wavelength range of interest to monitor line interferences. The chosen lines are presented in Tables 3 and 4. 2.5. Calibration and statistics For calibration, mixed standard solutions were prepared from the stock standard solution of 1000 μg/mL by dilution with the artificial sweat solution and with 7 M nitric acid. The ranges of the calibration curves (7 points) were selected to match the expected concentrations (0–5 μg/mL) for all the elements of the samples investigated. Linearity was checked in the range of 0–40 μg/mL. Detection limits were calculated as the concentrations of an element that gave a signal equal to three times the standard deviation of a series of eleven successive measurements of the blank solution at the element peak. 3. Results and discussion 3.1. General Since the threats to human health may be linked to the presence of metals on textile products, the aim of the study was to quantify the content of metals present in different textile materials by extraction and digestion experiments. ICP-OES Table 5 Accuracy data for the ICP-OES measurements NIST
1640
NIST
1643
Element
Certified/μg/mL
Found/μg/mL
Certified/μg/mL
Found/μg/mL
Al As Bi Cd Co Cr Cu K Mn Mo Ni Si Sn
0.052 0.027 – 0.022 0.020 0.038 0.085 0.994 0.121 0.047 0.027 4.73 0.013
0.051 0.020 0.003 0.023 0.017 0.033 0.088 1.650 0.124 0.057 0.038 4.37 0.018
0.141 0.060 0.014 0.006 0.027 0.020 0.022 2.034 0.038 0.121 0.062 – 0.058
0.131 0.046 0.016 0.029 0.021 0.025 0.014 1.91 0.032 0.118 0.067 0.027 0.070
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Table 6 Accuracy data of IAEA V-9 reference material for microwave digestion, n = 9 Element
Certified/μg/g
95% confidence interval
Found/μg/g
SD
Al As Be Bi Co Cr Cu Fe Mg Mn Mo Ni Si Zn
44 – – – – 0.11 0.59 11 53 0.15 0.034 0.09 – –
13–53 – – – – 0.08–0.14 0.47–0.94 7–15 46–67 0.12–0.21 0.030–0.049 0.07–0.18 – –
43.19 3.84 3.97 0.22 2.02 0.12 0.67 12.51 64.57 0.52 0.029 0.06 69.25 3.41
2.55 0.39 0.15 0.06 0.59 0.04 1.20 3.06 6.51 0.20 0.01 0.01 5.36 0.45
measurements were performed using an excentric nebulizer and an axial viewed torch system. This configuration was chosen due to many advantages, such are reducing interferences, improving the detection limits and achievable linear dynamic range [24]. Excentric nebulizers are great replacements for the concentric nebulizers, because they increase sensitivity and are ideal for the analysis with the limited sample amounts. 3.2. Line selection Line selection was performed with regard to the complex matrix. This was a very important step because different interferences occurred in monitored complex systems, in sweat solution and nitric acid. To define the interferences, single and multi element standards were measured, and afterwards compared to the literature data [25]. For example, OH molecular interference with Al in very low concentration levels at 308.215 nm was defined by measuring a single element standard, and also the spectral interference of the As (228.812 nm) and Cd (228.802 nm) were detected in multi element standards, as well as many others [26,27]. Lines selection was performed for the analysis of elements in the artificial sweat extracts and the nitric acid: 10 different elements were chosen for the preparation of the multi element standard used for the extraction experiments. These elements are expected to be present on textile materials. For their determination 29 different lines were tested for their applicability (Table 3). Another multi element standard consisting of 17 elements was prepared for measurements of the digestion samples. In this case 64 lines were tested for their applicability (Table 4). For the digestion experiments other additional elements were expected because of the composition of the natural fibers, cotton and flax. 3.3. Reference materials Calculated detection limits and selected spectral lines (bold values) are presented in Tables 3 and 4. The data obtained for the reference materials NIST-1640 and 1643 are reported in Table 5. They are in agreement with the available certified values. In all experiments the precision of the measurements was specified
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Table 7 Heavy metals extracted from textile materials after 2 h of mixing in an artificial sweat solution at 400 °C (concentrations are expressed in μg/mL) Samples
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
0.13 <0.014 0.04 <0.003 0.12 0.05 0.05
0.14 <0.014 0.04 <0.003 0.15 0.05 0.10
0.11 <0.014 <0.002 <0.003 0.05 0.03 0.10
0.13 <0.014 0.03 <0.003 0.213 0.05 0.06
0.17 <0.014 0.07 <0.003 0.07 0.04 <0.004
0.18 <0.014 0.02 0.32 0.05 0.14 0.08
1.58 <0.014 0.03 0.02 0.10 <0.002 0.08
0.16 <0.014 0.03 0.02 0.06 0.01 0.09
0.18 0.09 0.04 0.02 1.95 0.32 0.08
0.17 <0.014 0.04 <0.003 0.06 0.05 0.09
0.19 <0.014 0.04 <0.003 0.07 0.24 0.08
0.20 <0.014 0.04 <0.003 0.05 <0.002 0.09
0.21 0.02 0.05 <0.003 0.06 0.36 0.09
0.21 <0.014 0.05 0.01 0.05 0.31 0.10
0.29 <0.014 0.03 <0.003 0.05 2.17 0.08
0.27 <0.014 0.03 <0.003 0.05 1.17 0.08
Element Al As⁎ Cd⁎ Cr⁎ Cu⁎ Mn Ni⁎
⁎ Restricted metals according to the Öko-tex, ⁎ Values higher then allowed, ⁎⁎ Mo, Fe and Co were
with a relative standard deviation within 0.2–2.2%, and the relative standard deviations for three digestion replicates of each sample were in the range from 2% to 17%. In order to compare the extractable part with the total amount of metals present, a microwave acid digestion of the reference cotton material IAEA V-9 was performed. The results reported in Table 6 are in a good agreement for the majority elements investigated. 3.4. Acidic artificial sweat extraction The extraction experiment was performed according to standards for textiles used in direct contact with the human body. The results obtained for the textile materials extraction after 2 h of mixing in the artificial sweat solution at 400 °C are presented in Table 7. For some materials the concentration values found were above the limit values prescribed by different ecological standards (Table 9). Those values are marked as bold. 3.5. Microwave digestion Results obtained digestion of the textile materials in 7 M nitric acid are presented in Table 8. According to the results obtained after microwave digestion and the literature data for elementary composition of cotton and flax [3,28], the majority of the present unwanted metals are resulting from textile processing, and may be extracted from textiles during use.
4. Conclusion People are exposed to different chemical substances coming from textile materials due to daily contact with textiles like clothes, bed linen and similar products. Many of the chemicals applied on textiles may represent a health hazard for consumers, so it is crucial that the quantity of those substances is as low as possible. The metal content of natural fibers is also important for textile industry, because many elements contribute to problems during processing of textiles. A fast and simple method for quantification of the metal content in textile materials is described in this paper. An extraction procedure in artificial acidic sweat solution followed by microwave digestion using 7 M nitric acid and quantification with ICP-OES is reported. The most important advantage of the ICP-OES method is its ability to analyze a larger number of elements simultaneously, with low detection limits of the investigated trace elements. The described extraction method was applied for the determination of many elements present on 16 different textile materials. Their concentrations did not exceed the permissible values according to different standards (Table 9) and for this reason the investigated textile materials are no health hazard for consumers. The concentrations of particular elements were above the prescribed limits: zinc and cadmium were found in cotton (samples 4, 5) and polyester samples (samples 13, 14, 15, 16); Chromium was detected in flax, silk and polyester samples (6, 7,
Table 8 Microwave digestion in 7 M nitric acid (concentrations expressed as μg of metal/g of textiles) Samples⁎ Al As Be Bi Co Cr Cu Fe K Mg Mo Ni Si Zn
1
2
25.75 31.00 2.03 0.97 0.10 0.30 5.29 5.65 1.81 0.19 0.26 0.36 0.36 193.9 12.52 14.85 – – 219.3 232.6 0.64 0.64 2.35 1.53 1086.52 1810.77 8.37 9.56
3
4
13.09 26.36 3.55 0.04 0.38 <0.0004 4.96 4.02 0.16 0.16 0.18 0.62 <0.0082 22.74 7.38 325.9 – – 450.6 207.2 1.19 0.80 1.15 1.63 797.9 1358.2 2.96 8.55
5 29.57 0.36 0.20 5.11 0.18 0.32 28.36 33.2 – 163.7 0.58 2.55 86.48 4.73
6
7
8
9
10
11
12
30.44 2.64 0.08 2.76 0.08 10.71 4.37 25.15 47.08 79.54 0.10 1.29 527.5 4.40
24.52 1.41 0.06 6.22 0.02 0.09 98.91 15.12 69.89 61.92 0.12 23.03 302.5 4.17
15.86 2.39 0.08 7.29 0.02 0.06 89.5 6.98 33.00 58.19 0.04 1.49 39.36 2.44
19.34 8.39 6.37 <0.0429 4.79 8.04 6.25 8.36 54.04 40.65 6.81 6.77 210.3 5.40
8.59 6.47 4.93 <0.0429 4.09 4.55 5.04 5.69 41.67 10.54 4.51 5.22 157.6 4.42
8.66 6.99 5.43 <0.0429 5.07 5.07 5.55 5.17 45.94 47.33 9.93 5.62 519.3 5.01
9.38 7.12 5.48 <0.0429 5.23 4.93 5.58 5.26 0.72 4.22 2.63 5.62 204.2 2.77
I. Rezić, I. Steffan / Microchemical Journal 85 (2007) 46–51 Table 9 [21–23]Limits for heavy metals suggested by different ecological standards Heavy metals/μg mL− 1 Öko Tex
EPG
Eco-tex TOX PROOF M.U.T.
Antimony (Sb) Arsenic (As) Cadmium (Cd) Chromium III (Cr) Chromium VI (Cr) Cobalt (Co) Copper (Cu) Lead (Pb) Mercury (Hg) Nickel (Ni) Zinc (Zn)
– 0.01 0.005 0.1 – 0.2 3.0 0.04 0.001 0.2 5.0
– 0.01 0.005 0.1 0.0 0.2 3.0 0.04 0.001 0.2 3.0
0.2 – 1.0 0.1 1.0 – 2.0 0.0 1.0 – 4.0 25 – 50 0.2 – 1.0 0.02 1.0 – 4.0 –
0.2 0.2 0.1 1.0 0.0 1.0 20.0 0.8 0.02 1.0 20.0
– – – 0.5 0.1 – 0.5 – – 0.5 2.0
8, 9, 14), while copper in silk (9), and arsenic in silk and polyester samples (9 and 13). For this reason it is important to monitor the presence of these elements on other textile materials processed in the same textile industry as well. Acknowledgements This research work was supported by the Austrian Academic Exchange Service (ÖAD) Scholarship Nr. 467-7/2004. The authors would like to express special thanks to Dr. András Törvényi for his advice and help. References [1] A.A. Ansari, B.D. Thakur, Colourage 11 (1999) 21. [2] E. Rybicki, T. Swiech, E. Lesniewska, J. Albinska, M.I. Szynkowska, T. Paryjczak, S. Sypniewski, Fibres Text. East. Eur. 12 (2004) 67.
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ICP-OES determination of metals present in textile materials Iva Rezić a,⁎, Ilse Steffan b a
Laboratory of Analytical Chemistry, Department of Applied Chemistry, Faculty of Textile Technology, University of Zagreb, Prilaz Baruna Filipoviæa 30 10000 Zagreb, Croatia b Department of Analytical Chemistry and Food Chemistry, University of Vienna, Austria Received 13 January 2006; received in revised form 14 June 2006; accepted 14 June 2006 Available online 24 July 2006
Abstract The aim of this work was to quantify the content of elements present in textile materials since it is known that textiles containing metals may represent a health hazard to consumers. Determination of metal content can be also useful to the textile industry since some metals present in textiles may contribute to problems during textile production. Extraction of metals from different textile materials was performed in an artificial acidic sweat solution according to the Öko Tex standard for materials coming into direct contact with the skin. After extraction from textile products made of cotton, flax, wool, silk, viscose, and polyester materials, all elements were determined by means of inductively coupled plasmaoptical emission spectrometry (ICP-OES). Results in the sweat extracts (minimum–maximum in μg/mL) were: Al 0.11–1.58, Cd 0.02–0.05, Cr 0.01–0.32, Cu 0.05–1.95, Mn 0.01–2.17, and Ni 0.05–0.10. Concentrations of other elements were bellow detection limits. The total amount of metals present was determined after microwave assisted acidic digestion of textile materials with 7 M nitric acid. According to the results, the majority of the detected elements were below the concentration limits given by the Öko Tex, and for this reason the textile materials investigated do not represent a health hazard to consumers. © 2006 Elsevier B.V. All rights reserved. Keywords: Textiles; ICP-OES; Öko Tex Standard
1. Introduction People are often exposed to different allergenic and toxic chemicals coming from textiles due to daily contact with clothes, bed linen and similar products. Many textiles contain chemicals that may represent a health hazard to consumers. The major chemical pollutants on textiles are dyes containing carcinogenic amines, toxic heavy metals, pentachlorophenol, chlorine bleaching, halogen carriers, free formaldehyde, biocides, fire retardants, and softeners [1]. Heavy metals are often present in different textile processes [2]. The reagents mostly used are: metal complex dyes, dye stripping agents, fastness improvers, oxidizing compounds, and finishers like water repellants, flame retardants, antifungal and odor-preventive agents [3]. Raw textile materials may also contain heavy metals [4]. Cotton, flax and hemp sometimes adsorb very large amounts of metals from the environment [5,6], and can be used as bio-absorbers [7].
⁎ Corresponding author. Tel.: +385 1 4597209; fax: +385 1 3712 599. E-mail addresses: [email protected], [email protected] (I. Rezić). 0026-265X/$ - see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.microc.2006.06.010
Determination of metal content of different textile materials is very important not only for the safety of consumers, but also for the textile industry. It is known that some metals present in cotton may contribute to problems in yarn manufacturing, bleaching and dyeing, and processing quality [8]. Problems reported from dyeing processes are related with metal contribution to the light-induced yellowing of whitewashed denim. Manganese and ferrous ions are readily air-oxidized to compounds that cause yellowing. In addition, transition metals catalyze organic reactions and function as mordant that strongly bind many organic compounds to cotton [9]. For this reason the textiles treated in those processes should be monitored for the presence of different metals (aluminum, calcium, copper, iron, magnesium, manganese, and titanium) and their presence has to be reduced by applying different production methods [10]. Metals are most frequently used in textile wet processing, although some of them are extremely toxic to many organisms. The use of chromium based dyes is essential for the fast black dyeing on wool and nylon, but in the future it will probably be replaced by newly developed dyes containing less toxic metals like iron [11]. Cobalt, chromium and occasionally copper and
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nickel form part of the most commonly used dyes, especially dyes for leather materials, nylon and wool. While chromium is generally used, cobalt has found selected applications. As a group, metal complex dyes offer good overall fastness properties [12]. Because of their wide application, metals are frequently present in textile dyeing wastewaters as free ionic metals or complex metals, which contributes to the environmental concerns [13]. Cobalt and chromium dyes are applied particularly in dyes for wool: there is no wool mordant dye that does not use chromium compounds. The chromium dye C.I. Mordant Black 11 is one of the most widely used dyes in the world [14]. Copper salts are used to fix direct dyes and to enhance the light fastness on the nylon. Antimony improves wash fastness properties on nylon fibers [15]. Cationic dyes contain zinc as well as trace concentrations of mercury, cadmium and arsenic as impurities from intermediates. Zirconium, aluminum and other salts are also used extensively in textile processing [16]. Usual concentrations of heavy metals in dyes are (in μg/g): 1.0 to 1.4 (As), up to 1.0 (Cd), 3.0–83.0 (Cr), 1.0–3.2 (Co), 33.0–110.0 (Cu), 6.0–52.0 (Pb), 0.5–1.0 (Hg), and 3.0–32.0 (Zn) [17].
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Table 2 Instrument parameters for ICP-OES Optima 3000 XL View Optical system Detector RF frequency/MHz Power/W Plasma gas flow/L min− 1 Auxiliary gas flow/L min− 1 Nebulizing chamber Nebulizer Sample flow rate/mL min− 1
Axial view Echelle Solid state detector 40.68 1 300 15.0 0.5 Cyclone Excentric ⁎ 0.8
⁎ Nebulizer (excentric) was produced by CPI, International, P/N 4060-010588.
Toxic effects of heavy metals on human health are very well known: damages of organs, disorders in the respiratory tract and lung diseases, dysfunction of heart, blood and blood producing organs, disorders in nervous system, skin diseases, abnormalities in fertility and pregnancy. Accumulation of heavy metals in body tissues and binding to enzymes may disrupt the functioning of cells, which may also lead to development of tumors or cancers
Table 1 Textile samples Number
Sample description
1
Red cotton
2
Sample picture
Number
Sample description
9
Green silk
Green cotton
10
Blue silk
3
White cotton
11
Red wool
4
Red/blue cotton
12
Brown wool
5
Black/coloured cotton
13
Pink viscose/ polyester
6
Yellow flax
14
Yellow viscose/ polyester
7
Black flax
15
Blue polyester
8
Green flax
16
Orange polyester
Sample picture
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[18]. To prevent those effects, different standards are now in use: MST (Markenzeichen schadstoffgeprüfter Textilien), Öko Tex Standard (Internationale Gemeinschaft für Forschung und Prüfung auf dem Gebiet der Textilökologie), Clean fashion, Steilman, Commitextile, EC Approach, EPG (The European Product Guarantee) and Ecomarc Scheme [19]. According to the requirements of Öko Tex the goods are controlled for pH, fastness properties, formaldehyde, carcinogenic dyes, dyes that can break down into carcinogenic aryl amines or can cause allergic reactions to the skin, extractable harmful heavy metals, halogenated carriers or contaminations with pentachlorophenol and pesticides [20]. Textile is categorized according to its utilization into products for babies, products with direct contact to skin, products without direct contact to skin, and decorative materials [21]. The limits for heavy metals vary depending upon the degree of the contact of a fabric to consumer's skin as well as on the toxicity of the heavy metal [22]. The limits do not involve the total amount of metals present in the fabric, but the part which can be extracted [23]. According to current standards, the use of metals and metal complex dyes is not prohibited in textile industry because their abandoning would result in a loss of some important shades like turquoise, brilliant green, violet, blue or navy shades [11]. The majority of problems arise when metals are extracted from the fabrics by perspiration. Because metals may represent a health hazard to consumers by causing allergenic skin reactions, and due to the fact that metals present in textiles may contribute to problems during processing, the aim of our study was to quantify the content of metals present in different textile materials. 2. Experimental
Table 4 Detection limits calculated for 7 M nitric acid ⁎ Element
Limits of detection / μg/L in 7 M nitric acid (λ/nm)
Al As Be Bi Co Cr Cu Fe K Mg
28.3 (308.215), 171.3 (394.401), 37.9 (396.152) 5.4 (188.979), 8.9 (193.696), 10.8 (197.197), 1.3 (228.812) 0.3 (234.861), 9.2 (265.045), 0.4 (313.042), 0.2 (313.107) 7.3 (190.178), 8.6 (222.825), 3.2 (223.061), 42. 9 (406.772) 3.0 (228.616), 0.2 (230.786), 1.5 (231.160), 0.5 (238.892) 0.7 (205.560), 1.7 (206.149), 0.1 (267.716), 0.4 (357.896) 8.2 (213.598), 86.6 (224.700), 121.8 (324.754), 110.5 (327.396) 1.0 (234.349), 0.3 (238.204), 0.5 (239.562), 0.1 (259.940) 32.0 (310.179), 116.7 (310.205), 0.4 (766.491) 11.6(202.582),0.5(279.079),0.3(279.553),0.3(280.270), 0.3(285.213) 0.1 (257.610), 0.1 (260.569), 0.6 (279.482), 0.9 (294.920) 0.8 (203.844), 2.4 (204.598), 1.6 (281.615) 2.2 (221.647), 2.0 (231.604), 2.6 (232.003), 1.1 (341.476) 0.6 (212.412), 0.5 (251.611), 4.1 (252.851), 0.8 (288.158) 12.3 (189.933), 31.7 (235.484), 33.7 (242.170), 33.2 (283.999) 3.5 (190.800), 2.7 (276.787), 10.6 (351.924) 0.5 (202.548), 2.8 (206.191), 0.6 (213.856)
Mn Mo Ni Si Sn Tl Zn
⁎ Bold values refer to selected lines.
and 1000 μg/mL standards (Al, As, Be, Bi, Co, Cr, Fe, K, Mg, Mn, Mo, Ni, Si, Sn, Tl) used for this research work were of p.a. grade, supplied by Merck, Darmstadt, Germany and by Perkin Elemer (Cd, Cu, and Zn). The liquid reference materials NIST 1640 (trace elements in water) and NIST 1643 (trace elements in natural water) were used for checking the accuracy of the measurements by ICP-OES. A certified comparative reference material for cotton trace element analysis IAEA-V-9 was used for checking the accuracy of the digestion procedure as well as the confirmation of the results.
2.1. Samples 2.3. Instrumentation The tests covered 16 textile samples of different origin (Table 1). All the samples taken for the purpose of this investigation were processed in the Croatian textile industry. The origin of the materials was known before analysis, but not the dye composition of the painted layer.
The inductively coupled plasma-optical emission spectrometer used was a Perkin Elmer Optima 3000 XL. The instrument was equipped with a standard one piece extended torch with a quartz injector tube, a cyclone spray chamber and an excentric1 nebulizer (Table 2).
2.2. Chemicals and standard solutions 2.4. Sample preparation All the chemicals (nitric acid, sodium chloride, ammonium chloride, sodium hydroxide, acetic acid, lactic acid and urea) Table 3 Detection limits in the artificial acidic sweat solution ⁎ Element
Limits of detection/μg/L in acidic sweat solution (λ/nm)
Al As Cd Co Cr Cu Fe Mn Mo Ni
0.8 (308.215), 9.7 (309.271), 3.1 (396.152) 14.0 (193.696), 14.1 (197.197), 3.9 (228.812) 1.4 (214.438), 0.2 (226.502), 3.2 (228.802) 2.0 (228.616), 3.0 (231.160), 2.4 (238.892) 0.3 (357.896), 2.0 (267.716), 1.6 (205.560) 1.7 (324.754), 0.1 (327.396), 0.1 (224.700) 19.7 (259.940), 1.7 (238.204), 1.9 (239.562) 1.8 (257.610), 1.7 (260.569), 3.3 (279.482) 1.6 (202.030), 1.4 (204.598), 3.9 (281.615) 6.4 (221.647), 3. 8 (232.003), 2.8 (341.476)
⁎ Bold values refer to selected lines.
2.4.1. Extraction in the artificial sweat solution Textile samples were dried for 48 h at 60 °C before analysis, and afterwards cut and weighed. 1.5 g of a sample was mixed for 2 h at 40 °C with 25 mL of artificial sweat solution, which was prepared according to the ISO 3160/2 standard. After filtration, the solutions were analyzed for all the elements by inductively coupled plasma-optical emission spectrometry (ICP-OES). 2.4.2. Microwave digestion For the determination of the total metal content of textile materials, the samples were dried for 48 h at 60 °C, cut and weighed. 0.5 g of dried samples were put into the digestion vessels of the microwave oven and digested with 8 mL of 7 M 1
Excentric nebulizer — page 23 attached to the Covering Letter.
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nitric acid. A closed-vessel microwave digestion system MLS 1200 Mega (produced by Milestone) equipped with a temperature control was used for the sample digestion. The temperature program was as follows: 5 min at 150 °C (power 250 W), 15 min 180 °C (300 W) and 20 min at the maximum temperature of 200 °C (350 W). The resulting solutions were cooled, filled up to 10 mL with 7 M nitric acid and analyzed by ICP-OES. The reference material for cotton trace element analysis IAEA-V-9 was digested in the same way. 2.4.3. Line selection After sample preparation, line selection was performed in order to select the optimal spectral lines for measurement. Multielement standard solutions in different matrix systems (acidic artificial sweat solution and 7 M nitric acid) were scanned by ICPOES over the selected wavelength range of interest to monitor line interferences. The chosen lines are presented in Tables 3 and 4. 2.5. Calibration and statistics For calibration, mixed standard solutions were prepared from the stock standard solution of 1000 μg/mL by dilution with the artificial sweat solution and with 7 M nitric acid. The ranges of the calibration curves (7 points) were selected to match the expected concentrations (0–5 μg/mL) for all the elements of the samples investigated. Linearity was checked in the range of 0–40 μg/mL. Detection limits were calculated as the concentrations of an element that gave a signal equal to three times the standard deviation of a series of eleven successive measurements of the blank solution at the element peak. 3. Results and discussion 3.1. General Since the threats to human health may be linked to the presence of metals on textile products, the aim of the study was to quantify the content of metals present in different textile materials by extraction and digestion experiments. ICP-OES Table 5 Accuracy data for the ICP-OES measurements NIST
1640
NIST
1643
Element
Certified/μg/mL
Found/μg/mL
Certified/μg/mL
Found/μg/mL
Al As Bi Cd Co Cr Cu K Mn Mo Ni Si Sn
0.052 0.027 – 0.022 0.020 0.038 0.085 0.994 0.121 0.047 0.027 4.73 0.013
0.051 0.020 0.003 0.023 0.017 0.033 0.088 1.650 0.124 0.057 0.038 4.37 0.018
0.141 0.060 0.014 0.006 0.027 0.020 0.022 2.034 0.038 0.121 0.062 – 0.058
0.131 0.046 0.016 0.029 0.021 0.025 0.014 1.91 0.032 0.118 0.067 0.027 0.070
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Table 6 Accuracy data of IAEA V-9 reference material for microwave digestion, n = 9 Element
Certified/μg/g
95% confidence interval
Found/μg/g
SD
Al As Be Bi Co Cr Cu Fe Mg Mn Mo Ni Si Zn
44 – – – – 0.11 0.59 11 53 0.15 0.034 0.09 – –
13–53 – – – – 0.08–0.14 0.47–0.94 7–15 46–67 0.12–0.21 0.030–0.049 0.07–0.18 – –
43.19 3.84 3.97 0.22 2.02 0.12 0.67 12.51 64.57 0.52 0.029 0.06 69.25 3.41
2.55 0.39 0.15 0.06 0.59 0.04 1.20 3.06 6.51 0.20 0.01 0.01 5.36 0.45
measurements were performed using an excentric nebulizer and an axial viewed torch system. This configuration was chosen due to many advantages, such are reducing interferences, improving the detection limits and achievable linear dynamic range [24]. Excentric nebulizers are great replacements for the concentric nebulizers, because they increase sensitivity and are ideal for the analysis with the limited sample amounts. 3.2. Line selection Line selection was performed with regard to the complex matrix. This was a very important step because different interferences occurred in monitored complex systems, in sweat solution and nitric acid. To define the interferences, single and multi element standards were measured, and afterwards compared to the literature data [25]. For example, OH molecular interference with Al in very low concentration levels at 308.215 nm was defined by measuring a single element standard, and also the spectral interference of the As (228.812 nm) and Cd (228.802 nm) were detected in multi element standards, as well as many others [26,27]. Lines selection was performed for the analysis of elements in the artificial sweat extracts and the nitric acid: 10 different elements were chosen for the preparation of the multi element standard used for the extraction experiments. These elements are expected to be present on textile materials. For their determination 29 different lines were tested for their applicability (Table 3). Another multi element standard consisting of 17 elements was prepared for measurements of the digestion samples. In this case 64 lines were tested for their applicability (Table 4). For the digestion experiments other additional elements were expected because of the composition of the natural fibers, cotton and flax. 3.3. Reference materials Calculated detection limits and selected spectral lines (bold values) are presented in Tables 3 and 4. The data obtained for the reference materials NIST-1640 and 1643 are reported in Table 5. They are in agreement with the available certified values. In all experiments the precision of the measurements was specified
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Table 7 Heavy metals extracted from textile materials after 2 h of mixing in an artificial sweat solution at 400 °C (concentrations are expressed in μg/mL) Samples
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
0.13 <0.014 0.04 <0.003 0.12 0.05 0.05
0.14 <0.014 0.04 <0.003 0.15 0.05 0.10
0.11 <0.014 <0.002 <0.003 0.05 0.03 0.10
0.13 <0.014 0.03 <0.003 0.213 0.05 0.06
0.17 <0.014 0.07 <0.003 0.07 0.04 <0.004
0.18 <0.014 0.02 0.32 0.05 0.14 0.08
1.58 <0.014 0.03 0.02 0.10 <0.002 0.08
0.16 <0.014 0.03 0.02 0.06 0.01 0.09
0.18 0.09 0.04 0.02 1.95 0.32 0.08
0.17 <0.014 0.04 <0.003 0.06 0.05 0.09
0.19 <0.014 0.04 <0.003 0.07 0.24 0.08
0.20 <0.014 0.04 <0.003 0.05 <0.002 0.09
0.21 0.02 0.05 <0.003 0.06 0.36 0.09
0.21 <0.014 0.05 0.01 0.05 0.31 0.10
0.29 <0.014 0.03 <0.003 0.05 2.17 0.08
0.27 <0.014 0.03 <0.003 0.05 1.17 0.08
Element Al As⁎ Cd⁎ Cr⁎ Cu⁎ Mn Ni⁎
⁎ Restricted metals according to the Öko-tex, ⁎ Values higher then allowed, ⁎⁎ Mo, Fe and Co were
with a relative standard deviation within 0.2–2.2%, and the relative standard deviations for three digestion replicates of each sample were in the range from 2% to 17%. In order to compare the extractable part with the total amount of metals present, a microwave acid digestion of the reference cotton material IAEA V-9 was performed. The results reported in Table 6 are in a good agreement for the majority elements investigated. 3.4. Acidic artificial sweat extraction The extraction experiment was performed according to standards for textiles used in direct contact with the human body. The results obtained for the textile materials extraction after 2 h of mixing in the artificial sweat solution at 400 °C are presented in Table 7. For some materials the concentration values found were above the limit values prescribed by different ecological standards (Table 9). Those values are marked as bold. 3.5. Microwave digestion Results obtained digestion of the textile materials in 7 M nitric acid are presented in Table 8. According to the results obtained after microwave digestion and the literature data for elementary composition of cotton and flax [3,28], the majority of the present unwanted metals are resulting from textile processing, and may be extracted from textiles during use.
4. Conclusion People are exposed to different chemical substances coming from textile materials due to daily contact with textiles like clothes, bed linen and similar products. Many of the chemicals applied on textiles may represent a health hazard for consumers, so it is crucial that the quantity of those substances is as low as possible. The metal content of natural fibers is also important for textile industry, because many elements contribute to problems during processing of textiles. A fast and simple method for quantification of the metal content in textile materials is described in this paper. An extraction procedure in artificial acidic sweat solution followed by microwave digestion using 7 M nitric acid and quantification with ICP-OES is reported. The most important advantage of the ICP-OES method is its ability to analyze a larger number of elements simultaneously, with low detection limits of the investigated trace elements. The described extraction method was applied for the determination of many elements present on 16 different textile materials. Their concentrations did not exceed the permissible values according to different standards (Table 9) and for this reason the investigated textile materials are no health hazard for consumers. The concentrations of particular elements were above the prescribed limits: zinc and cadmium were found in cotton (samples 4, 5) and polyester samples (samples 13, 14, 15, 16); Chromium was detected in flax, silk and polyester samples (6, 7,
Table 8 Microwave digestion in 7 M nitric acid (concentrations expressed as μg of metal/g of textiles) Samples⁎ Al As Be Bi Co Cr Cu Fe K Mg Mo Ni Si Zn
1
2
25.75 31.00 2.03 0.97 0.10 0.30 5.29 5.65 1.81 0.19 0.26 0.36 0.36 193.9 12.52 14.85 – – 219.3 232.6 0.64 0.64 2.35 1.53 1086.52 1810.77 8.37 9.56
3
4
13.09 26.36 3.55 0.04 0.38 <0.0004 4.96 4.02 0.16 0.16 0.18 0.62 <0.0082 22.74 7.38 325.9 – – 450.6 207.2 1.19 0.80 1.15 1.63 797.9 1358.2 2.96 8.55
5 29.57 0.36 0.20 5.11 0.18 0.32 28.36 33.2 – 163.7 0.58 2.55 86.48 4.73
6
7
8
9
10
11
12
30.44 2.64 0.08 2.76 0.08 10.71 4.37 25.15 47.08 79.54 0.10 1.29 527.5 4.40
24.52 1.41 0.06 6.22 0.02 0.09 98.91 15.12 69.89 61.92 0.12 23.03 302.5 4.17
15.86 2.39 0.08 7.29 0.02 0.06 89.5 6.98 33.00 58.19 0.04 1.49 39.36 2.44
19.34 8.39 6.37 <0.0429 4.79 8.04 6.25 8.36 54.04 40.65 6.81 6.77 210.3 5.40
8.59 6.47 4.93 <0.0429 4.09 4.55 5.04 5.69 41.67 10.54 4.51 5.22 157.6 4.42
8.66 6.99 5.43 <0.0429 5.07 5.07 5.55 5.17 45.94 47.33 9.93 5.62 519.3 5.01
9.38 7.12 5.48 <0.0429 5.23 4.93 5.58 5.26 0.72 4.22 2.63 5.62 204.2 2.77
I. Rezić, I. Steffan / Microchemical Journal 85 (2007) 46–51 Table 9 [21–23]Limits for heavy metals suggested by different ecological standards Heavy metals/μg mL− 1 Öko Tex
EPG
Eco-tex TOX PROOF M.U.T.
Antimony (Sb) Arsenic (As) Cadmium (Cd) Chromium III (Cr) Chromium VI (Cr) Cobalt (Co) Copper (Cu) Lead (Pb) Mercury (Hg) Nickel (Ni) Zinc (Zn)
– 0.01 0.005 0.1 – 0.2 3.0 0.04 0.001 0.2 5.0
– 0.01 0.005 0.1 0.0 0.2 3.0 0.04 0.001 0.2 3.0
0.2 – 1.0 0.1 1.0 – 2.0 0.0 1.0 – 4.0 25 – 50 0.2 – 1.0 0.02 1.0 – 4.0 –
0.2 0.2 0.1 1.0 0.0 1.0 20.0 0.8 0.02 1.0 20.0
– – – 0.5 0.1 – 0.5 – – 0.5 2.0
8, 9, 14), while copper in silk (9), and arsenic in silk and polyester samples (9 and 13). For this reason it is important to monitor the presence of these elements on other textile materials processed in the same textile industry as well. Acknowledgements This research work was supported by the Austrian Academic Exchange Service (ÖAD) Scholarship Nr. 467-7/2004. The authors would like to express special thanks to Dr. András Törvényi for his advice and help. References [1] A.A. Ansari, B.D. Thakur, Colourage 11 (1999) 21. [2] E. Rybicki, T. Swiech, E. Lesniewska, J. Albinska, M.I. Szynkowska, T. Paryjczak, S. Sypniewski, Fibres Text. East. Eur. 12 (2004) 67.
51
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