Trace elements in skin-contact clothes and migration to artificial sweat: Risk assessment of human dermal exposure

Abstract

The concentrations of a considerable number of trace elements (Ag, Al, As, B, Ba, Be, Bi, Cd, Co, Cr, Cu, Fe, Hg, Mg, Mn, Mo, Ni, Pb, Sb, Sc, Se, Sm, Sn, Sr, Ti, Tl, V and Zn) were determined in various skin-contact clothes (T-shirts, blouses, socks, baby pajamas and bodies) from the Catalan (Spain) market. In addition, migration experiments with artificial acidic sweat were conducted in order to establish the migration rates of these elements. High levels of Zn (186–5749 mg/kg) were found in zinc pyrithione labeled T-shirts, while high concentrations of Sb and Cr were found in polyester and black polyamide fabrics, respectively. An environmental scanning electron microscope (ESEM) confirmed the presence of Ag and Ti particles and aggregates in several clothing items. The use of the ESEM complemented the results of the elemental analysis and migration experiments. Dermal exposure to trace elements was subsequently calculated, and the human health risks were assessed. Antimony showed the highest mean hazard quotient (HQ = 0.4) for male and female adults wearing polyester clothes; for one of the examined items (polyester T-shirt) the HQ was even above the safety limit (HQ > 1). Exposure to Sb from polyester textile could mean potential health risks in subpopulation groups who frequently wear these clothes, and for long time periods. The migration experiments with artificial sweat showed to be essential for establishing the exposure to trace elements through cloth with direct contact with skin.

Keywords

materials incorporation environmental sustainability

In the market, there is a huge variety of clothes made with various materials (i.e. cotton, silk, wool polyester, viscose, spandex or polyamide). Moreover, chemical additives are also incorporated into textiles, mainly in the finishing process, to provide them with several properties.¹ Some of the chemicals present in clothes, such as formaldehyde, brominated and chlorinated flame retardants, nonylphenols, phthalates, perfluoroalkyl substances, nanoparticles, organotins and toxic elements, are of concern to the environment and human health.^2–9 In textile products, metals are used as metal complex dyes (cobalt, copper, chromium, lead), pigments, mordant (chromium), catalyzers in synthetic fabrics manufacture (Sb₂O₃), synergists of flame retardants (Sb₂O₃) and antimicrobials (silver and titanium nanoparticles and zinc pyrithione (ZnPT)), among other uses.^10–16

The high amount and variety of chemicals contained and added to the fabrics can mean a potential health risk, including skin alterations^17–21 (i.e. dermatitis, irritation, allergy and skin micro-flora reduction, among others). It is well known that some metals, such as cobalt, chromium, copper and nickel, are skin sensitizers,^22–24 while other trace elements (e.g. arsenic, cadmium, mercury, lead and antimony) are highly toxic, some of them being carcinogenic.²⁵ Moreover, others elements, either individually or as part of chemical compounds, have biocide properties, therefore affecting the skin’s micro flora population.¹⁸

Some chemicals are not bound or integrated to fabrics, being potentially released during their use or perspiration. In turn, chemicals bound to fabrics may be also detached during frictions or under physical stress with the skin. Consequently, and depending on their specific properties, these elements may penetrate into the body.^25,26 Based on the above, for human exposure to elements due to direct contact with clothes is of high importance to determine not only the levels of trace elements in clothes, but also the migration rates of these chemicals from clothes to the skin.

In the past, several studies have been performed to determine the content of elements in fibers and textiles.^27–31 Other studies have been focused only on analyzing the extractable fraction with artificial sweat,^32–38 being migration studies conducted for single elements (e.g. chromium³² or silver nanoparticles³³) or metal mixtures.³⁴ Most of these investigations have been carried out in specific clothing materials, such as cotton³⁵ or polyamide.³⁶ Unfortunately, information regarding the content of elements in fabrics and their migration from textiles is still scarce. Moreover, studies of risk assessment of dermal exposure to chemicals through skin-contact clothes are extremely limited.^39–42 In the present investigation, the dermal contact exposure to elements and human health risks was assessed by analyzing the levels of 28 elements in 37 skin-contact clothes (T-shirts, blouses, socks, baby pajamas and bodies). In order to establish a more realistic exposure assessment, migration experiments were also carried out by determining the concentration of the same 28 elements in artificial sweat. Dermal exposure to trace elements for adult males and females, as well as for <1-year-old children, were calculated and the associated health risks were assessed.

Materials and methods

Sampling

A number of clothing items (n = 37) were randomly purchased in several stores and supermarkets from two cities (Reus and Tarragona) in Catalonia, Spain. The items purchased were the following: T-shirts (n = 9); blouses (n = 5); underpants (n = 6); socks (n = 6); baby bodysuits (n = 6); and baby pajamas (n = 5). They included colored (n = 24) and white pieces (n = 13), as well as branded (n = 10) and unbranded (n = 27) items. Six of them (among the 37 pieces) were eco-labeled. Once at the laboratory, information such as material, color, place of production, etc., was recorded (Table 1). Fabric density was obtained by cutting and weighing a specified dimension of the clothes (Table 1).

Table 1.

Main characteristics of the skin-contact clothes

No.	Cloth	Materials	Made in	Color	Density^a	Comments
1	T shirt	100% PE	Bangladesh	White	129
2	T shirt	100% PE	China	White	163	Biocide (Zn-pyrithione)
3	T shirt	100% PE (50% recycled PE)	Vietnam	Yellow	172	UV filter. Branded
4	T shirt	100% PE	China	Black	161	Biocide (Zn-pyrithione)
5	T shirt	100% Cot	Turkey	White	159	Branded
6	T shirt	100% Cot	N.S.	White	178
7	T shirt	100% Cot	Bangladesh	Red	146
8	T shirt	100% Cot	Bangladesh	Black	162
9	T shirt	100% Cot	N.S.	Black	149
10	Blouse	100% PE	China	Dark blue	89
11	Blouse	100% Mo	Tunisia	Dark blue	70	Branded
12	Blouse	80% Vis; 20%W	Morocco	Black	76
13	Blouse	100% Cot	Bangladesh	White	164
14	Blouse	100% Cot	Bangladesh	Yellow	132
15	Socks	100% PA	Spain	Dark blue	94
16	Socks	87% PE; 10% Cot; 3% Sp	China	Black and red	334	Branded
17	Socks	52% Cot; 41% PA; 7% Sp	Romania	White	351	Biocide (Zn-pyrithione)
18	Socks	68% Cot; 26% PE; 4% PA; 2% Sp	Pakistan	White	305	Branded
19	Socks	77% Cot; 16% PE; 5% PA; 2% Sp	Turkey	Light grey	223	Branded
20	Socks	80% Cot; 17% PE; 3% Sp	China	Brown	360
21	Underwear	92% PA; 8 % Sp	Portugal	White	253
22	Underwear	92% PA; 8 % Sp	Spain	Black	238	Branded
23	Underwear	93% Cot; 7% Sp	China	Multicolor	149	Branded
24	Underwear	95% Cot; 5% Sp	Cambodia	Red	151
25	Underwear	100% Cot	China	Blue	167
26	Underwear	100% Cot	China	Striped black/grey	128
27	Bodysuits	100% Cot (organic)	N.S.	White	188	Oeko Standard 100
28	Bodysuits	100% Cot (organic)	Bulgaria	White	192	EU Ecolabel DK/16/034;
29	Bodysuits	100% Cot	China	White	191
30	Bodysuits	100% Cot	China	White	166	EcoSafe labeled. Branded
31	Bodysuits	100% Cot	N.S.	Striped yellow/white	178	Oeko Standard 100
32	Bodysuits	100% Cot	India	Light blue	162
33	Pajama	80% Cot (organic); 20% PE	China	Dark blue	237
34	Pajama	100% Cot	Portugal	White	181
35	Pajama	100% Cot	N.S.	Striped blue/white	227	Oeko Standard 100
36	Pajama	100% Cot	N.S.	Light grey	180
37	Pajama	100% Cot	Egypt	Pink	200	EcoSafe labeled. Branded

PE: polyester; Sp: spandex; Vis: viscose; Cot: cotton; PA: polyamide; W: wool; Mo: modal; N.S.: not specified; UV: ultraviolet.^a Density in g/m²

Microwave digestion and artificial sweat extraction test

In order to analyze the total amount of element contained in fabrics, a piece of each sample was completely digested with a microwave-assisted digestion system.³¹ Briefly, cloth samples were dried, and 0.5 g of each sample was digested with 5 mL of HNO₃ (65% Suprapur, Merck, Germany) in a Milestone Start D Microwave Digestion System for 5 min at 105℃, then 15 min at 180℃ and, finally, 20 minutes at 200℃. After cooling, extracts were filtered and brought to a volume of 25 mL with ultrapure water. Quality control/quality assurance (QC/QA) was based on the analysis of blank and replicate samples. Blanks were obtained by following the same procedure without the addition of fabrics, while replicates were used as control samples. Spinach leaves (1570a – National Institute of Standards and Technology, USA) were used as reference material. On the other hand, migration experiments with acidic artificial sweat were conducted in order to simulate element extraction due to body perspiration. Approximately 1 g of dried fabric was cut in small pieces (of approximately 2 cm × 2 cm) in a plastic vessel. Then, 25 mL of acidic artificial sweat were added to each sample and each vessel was closed. According to the EN ISO 105-E04 standard,⁴³ acidic artificial sweat was prepared as follows: 0.5 g of L-histidine monohydrochloride monohydrate, 5 g of NaCl and 2.2 g of NaH₂PO₄·2H₂O, in 1 L of ultrapure water, being adjusted to pH = 5.5 with NaOH 0.1 M. All of the above reagents were purchased from Sigma-Aldrich (USA). After 24 h of incubation at 37 ± 1℃ in a water bath, acidic artificial sweat extracts were cooled and filtered. Blank and replicate samples were also analyzed. The samples of artificial sweat and digestion extracts were kept frozen at –20℃ until the analysis of trace elements. All glass and plastic material in contact with samples and extracts were previously cleaned with a diluted (10%) HNO₃ solution.

Elemental analysis via inductively coupled plasma mass spectrometry

The concentrations of aluminum (Al), arsenic (As), boron (B), barium (Ba), beryllium (Be), bismuth (Bi), cadmium (Cd), cobalt (Co), chromium (Cr), cooper (Cu), iron (Fe), mercury (Hg), magnesium (Mg), manganese (Mn), molybdenum (Mo), nickel (Ni), lead (Pb), antimony (Sb), samarium (Sm), scandium (Sc), selenium (Se), silver (Ag), tin (Sn), strontium (Sr), titanium (Ti), thallium (Tl), vanadium (V) and zinc (Zn) were determined by means of inductively coupled plasma mass spectrometry (ICP-MS, Perkin Elmer Elan 6000). Blank and control samples, as well as a reference material (Spinach leaves, National Institute of Standards and Technology, USA), were used to check the accuracy of the instrumental methods. The recovery percentages of the reference material ranged between 83% and 112%, for Al and B, respectively. Detection limits were as follows: 0.03 mg/kg for Bi, Cd, Fe, Pb, Tl and Zn; 0.05 mg/kg for Ag, Be, Co, Cu, Mn, Mo, Sm, Sn and Sr; 0.10 mg/kg for As, Hg, Mg, Ni, Sb and Sc; 0.25 mg/kg for Ba, Cr, Se and V; 0.50 mg/kg for Al and B; and 1.00 mg/kg for Ti.

Environmental scanning electron microscope

For samples with levels of Ag and Ti above the detection limit, a complementary analysis with an environmental scanning electron microscope (ESEM) was conducted. Around 2 cm² of fabric were cut and hanged to aluminum supports. ESEMs (FEI Quanta 600) attached to an energy dispersive X-ray (EDX) (Oxford Instruments INCA X-Sight, Abingdon, UK) with a large field detector (LFD) and a backscattering detector (BSD) contrast by atomic number (Z) were used to evaluate the presence and composition of nanoparticles in clothing samples. ESEM working parameters were as follows: low vacuum; 20 kV accelerating voltage; and 10 mm working distance.

Human exposure and health risks

The concentrations and migration fractions of trace elements in the clothing items were used to calculate human exposure and health risks. Dermal contact was the only route here considered for exposure to trace elements through skin contact from clothes. Equation (1) was based on the European Chemical Agency (ECHA) guidance on information requirements and chemical safety assessment.⁴⁴ Both the equation and parameters have been recently described:³¹

{Exp}_{derm} = F_{cloth} \times d_{cloth} \times A_{skin} \times F_{mig} \times F_{contact} \times F_{pen} \times T_{contact} \times n / BW

(1)

where Exp_derm is the dermal exposure (in mg/(kg·day)), F_cloth is the fraction of element in clothes (dimensionless), d_cloth is the cloth surface density (in mg/cm²), A_skin is the area of contact between cloth and skin (in cm²), F_mig is the fraction of substance migrating to skin per day (1/day), F_contact is the fraction of contact area for skin (dimensionless), F_pen is the penetration rate (dimensionless), T_contact is the duration of the cloth-skin contact (d), n is the number of events per day (1/day) and BW is the body weight (kg). F_mig is considered equal to the quotient between levels of the element in artificial sweat extract and total element levels in cloth. For elements whose levels in artificial sweat and/or level in cloth were below the detection limit, a F_mig of 0.5% was assumed to calculate the exposure. Dermal exposure parameters are summarized in Table 2.

Table 2.

Dermal exposure parameters

Variable	Description	Value	Reference
d _cloth	Cloth density	Table 1 (mg/cm²)	Present study
F _cloth	Weight fraction of metal in cloth	Table 3	Present study
F _mig	Fraction of substance migrating to skin	Table 3 and 4	Present study
		0.005	¹⁴
F _pen	Fraction of penetration inside body	0.01 (0.03 for As)	⁴⁸
F _contact	Fraction of contact area for skin	1	¹⁴
T _contact	Contact duration between skin-textile	1 d	Assumed
BW	Body weight Adult male	70 kg	¹⁴
	Adult female	60 kg	⁶⁰
	Child <1 year	6.98 kg
A _skin	Skin area Adult male: T-shirt	7120 cm²	⁶⁰
	Underwear	1980 cm²
	Socks	1370 cm²
	Skin area adult female: Blouse	6941 cm²	⁶⁰
	Underwear	1723 cm²
	Socks	1220 cm²
	Skin area child <1 year: Pajama	2754 cm²	⁶⁰
	Body	1285 cm²
n	Mean number of events per day	1 1/d	Assumed

Mean exposure values were calculated using only detected elements. The exposure for adult males was estimated considering a T-shirt, underwear and socks. In turn, adult female exposure was calculated considering that women wear blouses and T-shirts equally, as well as underwear and socks. For children aged < 1 year, exposure was considered as an average between baby bodysuits and pajamas.

The non-carcinogenic risks were assessed using the hazard quotient (HQ), which is defined as the quotient between the predicted exposure and the respective dermal reference dose (RfD). In turn, the cancer risk was evaluated by multiplying the predicted exposure by the respective dermal slope factor (SF). The dermal RfD was calculated multiplying the respective oral RfD by the gastrointestinal (GI) absorption factor, whereas dermal SFs were calculated dividing the respective oral SF by the GI absorption factor.⁴⁵ RfDs and SFs were taken from the Risk Assessment Information System (RAIS),⁴⁶ with the only exception of oral RfD for Pb, not defined in the RAIS and here taken from Seiler and Sigel.⁴⁷ GI absorption factors were gathered from U.S. EPA Preliminary Remediation Goals.⁴⁸

Statistics

For those trace elements whose levels were below their respective limit of detection (LOD), we assumed that their concentrations would be equal to one-half of those LODs (ND = ½LOD). Data analysis was carried out by means of the statistical software package SPSS 20.0. To evaluate significant differences between groups, the Levene test was applied to verify the equality of variances. Analysis of variance (ANOVA) or Kruskal Wallis tests were subsequently applied depending on whether the data followed a normal distribution, or not, respectively. The level of significance was set at a probability lower than 0.05 (p < 0.05).

Results and discussion

Elements levels in clothes and in artificial sweat

Table 3 summarizes the levels of a number of trace elements in the analyzed clothes, while Table 4 shows the concentrations of these elements migrated to acidic artificial sweat. Elements such As, Be, Hg, Se, Sm and V were below their respective detection limits in all the analyzed samples of clothes. Silver, B, Bi, Cd, Mo and Tl were detected only in a reduced number of the 37 analyzed items. In contrast, Mg showed the highest mean value (114 mg/kg), followed by Cr (45.7 mg/kg), Zn (36.4 mg/kg), Al (28.5 mg/kg) and Sb (26.0 mg/kg). The highest individual concentration corresponded to Zn (1185 mg/kg), which was found in a sample (No. 17) of white socks made of cotton (52%), polyamide (41%) and spandex (7%), and labeled containing zinc pyrithione (ZnPT) as biocide. Three articles with ZnPT biocide labeled were analyzed: socks (No. 17) and two polyester T-shirts samples (No. 2 and No. 4). These three items showed the highest Zn levels (1185, 38 and 55 mg/kg, respectively). Other items that did not contain ZnPT, or at least it was not indicated in the labels, showed Zn concentrations ranging from < 0.03 to 9.32 mg/kg. In the three items with labeled ZnPT, Zn migrated to acidic artificial sweat extracts in percentages ranging from 11% to 55%. These values are similar to migration rates reported by other authors³⁸ (range: 0–44%). Assuming that all elemental Zn came from ZnPT, the levels in clothes were 5749, 186 and 267 mg/kg for items No. 17, No. 2 and No. 4, respectively. Zinc pyrithione, an antimicrobial agent of broad spectrum, is also used in shampoos and cosmetics, paints, floor coverings and wire insulations.⁴⁹

Table 3.

Concentrations (mg/kg) of trace elements in skin-contact clothing samples

n = 37	% detected	Mean	Stand. dev	Median	Minimum	Maximum
Ag	11	0.05	0.10	0.03	<0.05	0.57
Al	100	28.5	63.0	8.96	1.68	351
As	0	<0.10
B	8	0.30	0.19	0.25	<0.50	1.27
Ba	86	2.13	3.93	0.73	<0.25	19.1
Be	0	<0.05
Bi	8	0.02	0.02	0.01	<0.03	0.10
Cd	5	0.01	0.01	0.01	<0.03	0.07
Co	14	0.79	3.43	0.03	<0.05	20.4
Cr	32	45.7	161	0.13	<0.25	754
Cu	86	14.8	72.8	0.21	<0.05	439
Fe	100	18.0	34.4	9.54	1.09	194
Hg	0	<0.10
Mg	95	114	160	59.9	<1.00	832
Mn	100	1.05	1.14	0.72	0.07	5.77
Mo	5	0.03	0.03	0.03	<0.05	0.16
Ni	19	0.16	0.34	0.05	<0.10	1.79
Pb	43	0.16	0.37	0.01	<0.03	1.90
Sb	35	26.0	45.3	0.05	<0.10	152
Sc	43	0.19	0.22	0.05	<0.10	0.93
Se	0	<0.50
Sm	0	<0.05
Sn	24	0.05	0.06	0.03	<0.05	0.29
Sr	95	2.21	2.55	1.42	<0.05	10.1
Ti	57	8.34	11.0	2.02	<1.00	37.8
Tl	3	0.01	0.00	0.01	<0.03	0.03
V	0	<0.25
Zn	62	36.4	194	1.44	<0.03	1185

Results are expressed as mg of element per kilogram of textile.

% detected: percentage of samples with concentrations above the detection limit with respect to the total number of analyzed samples (n = 37).

Table 4.

Concentrations (mg/kg) of trace elements migrated to acidic artificial sweat from clothing samples

n = 37	% detected	Mean	Stand. dev	Median	Minimum	Maximum
Ag	8	0.06	0.10	0.03	<0.05	0.33
Al	32	2.52	5.88	0.25	<0.50	30.6
As	0	<0.10
B	11	0.33	0.26	0.25	<0.50	1.43
Ba	59	0.46	0.56	0.32	<0.25	2.78
Be	3	0.03	0.01	0.03	<0.05	0.06
Bi	0	<0.03
Cd	0	<0.03
Co	0	<0.05
Cr	11	0.17	0.17	0.13	<0.25	0.97
Cu	41	0.10	0.17	0.03	<0.05	0.99
Fe	70	1.23	1.72	0.79	<0.01	7.57
Hg	0	<0.10
Mg	100	63.6	62.4	49.5	2.97	261
Mn	95	0.60	0.48	0.44	<0.05	1.50
Mo	0	<0.05
Ni	22	0.07	0.05	0.05	<0.10	0.24
Pb	92	0.02	0.04	0.01	<0.03	0.22
Sb	22	0.37	1.00	0.05	<0.10	5.67
Sc	0	<0.10
Se	0	<0.25
Sm	0	<0.05
Sn	3	0.03	0.02	0.03	<0.05	0.14
Sr	87	1.18	1.32	0.84	<0.05	5.87
Ti	3	0.52	0.13	0.50	<1.00	1.28
Tl	0	<0.03
V	0	<0.25
Zn	62	16.8	88.1	1.17	<0.03	537

Results are expressed as mg of migrated element per kilogram of textile.

% detected: percentage of samples with concentrations above the detection limit with respect to the total number of analyzed samples (n = 37).

Chromium is generally used as a metal complex dye in polyamide black fabrics.⁵⁰ Chromium showed comparatively high levels in dark colored polyamide or viscose items (samples No. 12, 15 and 22). These three items (blouses, socks and underwear) had Cr levels of 377, 552 and 754 mg/kg, respectively, while other items made of other materials, or light colored polyamide (such as samples No. 18, No. 17 and No. 21) showed concentrations between < 0.25 and 1.17 mg/kg. The percentages of migration of Cr in the dark colored polyamide or viscose clothes were between 0.1% and 0.2%. Both high Cr levels in black polyamide fabrics and migration rates were in accordance with the results previously reported by Matoso and Cadore.³⁶ However, these values are somehow lower than those found elsewhere.³²

A sample of a yellow polyester T-shirt (No. 1) showed higher levels of Co (20.4 mg/kg) when compared with the remaining items (range: < 0.05–4.21 mg/kg). However, Co was not detected in any artificial sweat sample. Regarding Cu, high levels of this element (439 mg/kg) were found in cotton:spandex (93:7) and in multicolor (pink, blue, purple, green, orange and red) underwear (sample No. 23). Copper-ferrocyanide and copper-acetates are used as green, blue, red-brown dyes and pigments in the textile industry.^9,10

All fabrics either exclusively (samples No. 1, 2, 3, 4 and 10) or partially (No. 16, 18, 19, 20 and 33) made of polyester showed high levels of Sb. Antimony concentrations in 100% polyester clothes ranged from 57.7 to 152 mg/kg, while clothes with some percentage of polyester in their compositions presented Sb levels ranging from 45.2 to 87.0 mg/kg. High levels of Sb in polyester clothes have been previously given by Brigden et al.⁶ and Rovira et al.,³¹ who reported ranges of 14–293 and 52.4–204 mg/kg, respectively. Migration rates from fabrics to artificial sweat were between 0.3% and 3.7%. Antimony levels in clothes made from other different materials ranged between < 0.10 and 4.10 mg/kg, with only one exception: sample No.35 (100% cotton pajama), whose Sb levels were 47.3 mg/kg. Polymerization reactions for the production of polyester are catalyzed by Sb, which could be present in the final fabric.^11,14 In turn, Sb₂O₃ is also used either as a flame retardant or as a synergist of polybrominated diphenyl ethers (PBDEs) by the textile industry.^13,14,51

With respect to Ti, various clothes, mainly polyester and polyamide, contained high levels of this element. Sample No. 3, a polyester T-shirt labeled containing “UV filter”, showed the highest Ti levels (37.8 mg/kg). Titanium concentrations in artificial sweat extracts were below the LOD, except for sample No. 10 (a dark blue polyester blouse), which presented a value of 1.28 mg/kg and a migration rate of 7.1%. Titanium in oxide form (TiO₂) is used as a pigment in the textile industry. In turn, TiO₂ nanoparticles can also provide antimicrobial, antistatic properties as well as wrinkle resistance and increase the ultraviolet (UV)-protection.^51–53 Due to TiO₂, clothing samples with detected Ti were analyzed by ESEM (Figure 1). Several Ti particles, with sizes ranging from < 100 to 600 nm, were observed in clothing fibers with the BSD (Figures 1(b) and (c)). However, they do not look to be in the own surface of the fibers, as this is smooth when using the LFD (Figure 1(a)). Titanium particles are likely embedded in the fiber, which would explain the lack (or low) migration of Ti to the artificial sweat solution. This result is in agreement with the findings of Windler et al.,⁵² who reported that TiO₂ nanoparticles were contained inside the fiber matrix, making their release during washing relatively low.

Figure 1.

(a) Sample 3 (polyester T-shirt) environmental scanning electron microscope (ESEM) image with Ti particles. (b) ESEM image with backscattering detector in contrast by Z-imaging. (c) Microanalysis of the point marked as “X” in (b) ESEM image and element composition table.

In relation to Ag, only four samples (No. 3, 5, 8 and 18) presented levels higher than its analytical LOD (0.05 mg/kg). Silver concentrations ranged from 0.13 mg/kg, in a cotton black T-shirt (sample No. 8), to 0.57 mg/kg, in cotton/polyester socks (sample No. 18). Migration rates from fabric to artificial sweat were between 19% and 25%, much higher than others studies.^34,54 Silver nanoparticles are used in the textile industry to impart antimicrobial properties to the fabric.^49,55 Samples with detected Ag were also analyzed by ESEM. In those four samples, Ag particles were detected with sizes between <0.080 and 2.7 µm (Figure 2). Particles with sizes between 0.6 and 2.7 µm showed irregular shapes and surfaces, and formed nanoparticle aggregates (Figure 2(b)). In turn, smaller particles, ranging from 0.080 to 0.150 µm, presented a spherical shape (Figure 2(c)). In contrast to Ti particles, Ag particles were deposited on the surface of the fiber, which would explain the higher Ag migration rates. The release of Ag from the fabrics is also likely to be affected by the pH and formulations of artificial sweat,³³ as well as by the process (e.g. masterbatch, finishing) used to treat textile fibers.⁵⁶

Figure 2.

Sample 18 (cotton-polyester-polyamide socks) environmental scanning electron microscope (ESEM) image with Ag nanoparticles and Ag aggregates in clothing samples (a), (b), (c); microanalysis of the point marked as “X” in (c) ESEM image and element composition table (d).

The current results showed that the levels of Cr, Sb and Ti were significantly higher (p < 0.05) in synthetic fabrics than in cotton items. As mentioned above, high concentrations of Cr and Sb were found in black polyamide items and in polyester fabrics, respectively. Titanium levels were under its LOD in most (15 out of 18) cotton items. However, no significant (p < 0.05) differences regarding color (white and colored), manufacture origin (from inside or outside the European Union), eco labeled, branded or not and cotton (organic or not) were found.

Table 5 summarizes trace element limits according to Oeko-Tex and Tox-Proof certificates. All clothes analyzed in the current study fulfill the parameters of the Oeko-Tex standard. Notwithstanding, several polyester clothes (samples No. 1, 10, 16 and 20) exceeded the extractable Sb limit of TOX-Proof standard set at 1.0 mg/kg.

Table 5.

Elements limits (mg/kg) to accomplish with different standards certifications in the European Union (EU).^61,62

	Oeko-tex Standard 100		Tox-Proof (TÜV Rheinland)	EU Ecolabel
	Class I: Baby	Class II: in direct contact with skin	Tox-Proof (TÜV Rheinland)	EU Ecolabel
Extractable heavy metals
As	0.2	1.0	0.2
Cd	0.1	0.1	0.1
Co	1.0	4	1.0
Cr	1.0	2	1.0
Cr(VI)	<0.5	<0.5	<LOD
Cu	25	50	20
Hg	0.02	0.02	0.02
Ni	1	4	1.0
Pb	0.2	1.0	0.8
Sb	30	30	1.0
Heavy metals in digested sample
Cd	40	40
Pb	90	90
Sb				260^a

LOD: Limit of detection. ^a In polyester fibers.

Data from a number of studies regarding total concentrations of elements in textiles and migration experiments are summarized in Table 6. In general terms, the values found in the present study were similar to those found in the scientific literature. However, data comparability is sometimes difficult, since information about the characteristics of the analyzed clothes (i.e. material, color or biocide content, among others) can be incomplete. Furthermore, the methodological procedures for the migration tests, including time and artificial sweat composition, may differ, therefore leading to different results.

Table 6.

Total concentrations and levels of elements migrated to artificial sweat in textiles from other studies

Ref.	36		37		29		38		34		2		31	Present study
	Content	Migrated	Content	Migrated	Content	Migrated	Content	Migrated	Content	Migrated	Content	Migrated	Content	Content	Migrated
	Range (mg/kg)	Range (mg/kg)	Range (mg/kg)	Range (µg/mL)	Range (mg/kg)		Range (mg/kg)	Range (mg/kg)	Range (mg/kg)	Range (mg/kg)	Range (mg/kg)	Range (mg/L)	Range (mg/kg)	Range (mg/kg)	Range (mg/kg)
Ag									ND–149	ND–1.65	ND–183	ND–0.36		ND–0.57	ND–0.33
Al			8.59–31	0.13–1.58			17.6–117.5	ND–36.0					1.37–198	1.68–351	ND–30.6
As	ND		0.04–8.39	ND–0.09	ND–0.30	ND–1.52							ND	ND	ND
Ba							2.05–102	ND–66.2					ND–9.46	ND–19.1	ND–2.78
Be			ND–6.37										ND	ND	ND–0.06
Bi			ND–7.29										ND–1.92	ND–0.10	ND
Cd	ND–0.2			ND–0.07									ND–0.04	ND–0.07	ND
Co	ND		0.02–5.07		ND–15.9	ND–0.96							ND–5.18	ND–20.4	ND
Cr	0.3–965	ND–3.2	0.09–10.71	ND–0.32	0.50–263	ND–1.12	ND–2.60	ND–0.48	ND–380.4	ND			ND–605	ND–754	ND–0.97
Cu	2.2–3.5		ND–98.9	0.05–1.95	0.29–113	ND–13.6	ND–273	ND–1.08	ND–246	ND–10.7			ND–287	ND-439	ND–0.99
Fe			5.26–325.9				12.1–66.1	ND–8.23					3.38–35.1	1.09–194	ND–7.57
Hg	ND												ND	ND	ND
Mg			4.22–450.6										3.75–716	ND–832	2.97–261
Mn				ND–2.17									0.10–13.3	0.07–5.77	ND–1.50
Mo			0.04–9.93										ND–0.38	ND–0.16	ND
Ni	0.9–3.3		1.15–23.0		0.08–2.23	ND–1.32	ND–5.10	ND–0.54					ND	ND–1.79	ND–0.24
Pb	ND–1.4				0.20–7.62	ND–2.5							0.03–0.32	ND–1.90	ND–0.22
Sb	ND												ND–204	ND–152	ND–5.67
Sc													ND–0.72	ND–0.93	ND
Sn													ND–0.20	ND–0.29	ND–0.14
Ti											ND–8543	ND–5.8		ND–37.8	ND–1.28
Tl													ND	ND–0.03	ND
Zn			2.44–9.56		1.29–955	ND–308	ND–10.9	ND-4.45	2.1–20180	2.52–1033			ND–256	ND–1185	ND–537

ND: Not detected.

Human exposure and risk assessment

Dermal exposure to a number of trace elements due to skin contact is summarized in Table 7. In addition, the contribution of each kind of clothing is also given. Dermal exposure ranged between 9.6·10^–10mg/(kg·day) for Tl in men, and 1.3·10^–3mg/(kg·day) for Zn in both men and women. No differences of human exposure were noted according to the gender, with mean:women exposure ratios between 0.33 and 1.88 (Ba and Co, respectively). In general terms, higher exposure levels were found in the present study with respect to values obtained in a previous investigation, in which migration rates of 0.5% had been assumed for all the elements.³¹ This finding emphasizes the importance of migration experiments to obtain a more realistic exposure assessment.

Table 7.

Human exposure to elements (mg/(kg·day)) due to contact with clothes. Elements below detection limit are not taken into account to assess the exposure

	Men				Women				<1 year Children
	Exposure	Contribution (%)			Exposure	Contribution (%)			Exposure
	mg/(kg·day)	T-shirt	Underwear	Socks	mg/(kg·day)	T-shirt/ Blouse	Underwear	Socks	mg/(kg·day)
Ag	1.0×10^–6	15	0	85	9.6×10^–7	8	0	92	NC
Al	2.9×10^–5	70	24	6	2.3×10^–5	62	30	8	2.2×10^–5
B	4.0×10^–6	1	0	99	4.1×10^–6	1	0	99	NC
Ba	8.8×10^–6	45	49	6	2.7×10^–5	82	16	2	3.9×10^–5
Bi	3.2×10^–9	0	0	100	4.8×10^–9	30	0	70	NC
Cd	2.4×10^–9	0	0	100	3.2×10^–9	22	0	78	NC
Co	1.8×10^–6	97	0	3	9.6×10^–7	94	0	6	NC
Cr	3.5×10^–6	1	94	4	5.0×10^–6	30	66	3	3.1×10^–8
Cu	2.5×10^–6	31	63	6	2.4×10^–6	24	69	7	2.8×10^–6
Fe	2.6×10^–5	41	43	17	2.6×10^–5	40	43	17	9.1×10^–5
Mg	1.9×10^–5	25	26	48	1.9×10^–5	20	28	52	2.1×10^–5
Mn	1.7×10^–5	43	29	28	1.5×10^–5	30	35	35	3.8×10^–5
Mo	2.8×10^–9	0	100	0	2.8×10^–9	0	100	0	NC
Ni	7.6×10^–7	95	1	4	4.1×10^–7	90	1	9	NC
Pb	3.5×10^–7	3	90	7	3.5×10^–7	3	90	7	4.4×10^–8
Sb	2.6×10^–5	73	0	27	2.0×10^–5	65	0	35	8.0×10^–6
Sc	4.6×10^–8	49	13	38	4.3×10^–8	43	15	43	1.2×10^–7
Sn	1.7×10^–8	79	0	21	1.2×10^–8	68	0	32	4.6×10^–8
Sr	2.8×10^–5	31	29	40	3.0×10^–5	32	28	40	8.7×10^–5
Ti	1.6×10^–6	47	30	22	2.7×10^–6	67	19	14	5.9×10^–7
Tl	9.6×10^–10	0	0	100	1.0×10^–9	0	0	100	NC
Zn	1.3×10^–3	7	0	92	1.3×10^–3	5	0	95	5.9×10^–5

NC: not calculated because all samples showed a concentration below the detection limit.

Contribution is the percentage to the exposure coming from each type of clothing.

For <1 year children, the contribution is 50% for both pajamas and body suits, since exposure was considered as an average between baby bodysuits and pajamas.

With respect to the non-carcinogenic risks due to exposure to trace elements through skin-contact clothes, the HQs were below 0.1, with the exception of Sb. For polyester clothes, the mean HQ levels for Sb were 0.44, 0.40 and 0.13 for adult males, adult females and children <1-year old, respectively. For one T-shirt (sample No. 1), showing the maximum Sb level (152 mg/kg) and the maximum migration rate (3.7%), the HQ was 1.2, clearly exceeding the safety limit (HQ = 1). In adults, around 73% and 65% for males and females, respectively, of these values came from polyester T-shirts due to the high Sb levels and migration rates (0.3–3.7%). The remaining contribution to Sb total exposure came from socks, made with some percentage of polyester, also with high Sb content and migration rates between 0.5% and 2.5%. The frequent and long periods of time that polyester clothes are worn could mean an Sb overexposure. It could also be the cause of health risks for some subpopulation groups (e.g. athletes). In addition, physical activity increases the transpiration and migration from polyester clothes to skin.³⁶

Carcinogenic risks were also calculated for Cr and Pb, the only detected metals for which an oral SF has been established. Carcinogenic risks for Cr were 4.9·10^–6 and 7.9·10^–6 for adult males and females, respectively. The Pb carcinogenic risk showed values below 10^–8. It must be taken into account that, currently, SF_o is only defined for Cr(VI), while total Cr was here the analyzed species. Therefore, we assumed that the level of Cr(VI) was a sixth of total Cr.

Although some nanomaterials, such as TiO nanoparticles, cannot pass through the skin, others such as Ag nanoparticles can penetrate it, especially when a large skin surface area is covered, which can cause a high skin absorption of Ag.^26,57 Nanoparticles with bactericide properties, as well as other substances with biocide activity such as ZnPT, could have inhibitory effects on skin flora. For example, the skin protective function may be compromised due to a prolonged and repetitive exposure.¹⁸ Moreover, Rudolf and Cervinka⁵⁸ reported cell death-apoptosis and cellular premature senescence, when dermal fibroblasts were exposed to different concentrations of ZnPT. In terms of environmental and human health risks, the product life cycle has been identified as a key process to estimate the real exposure to nanoparticles.⁵⁹

Conclusions

In the present study, we determined the concentrations of a number of trace elements in clothes and assessed the migration rates with acidic artificial sweat. The migration experiments were essential to work under more realistic exposure scenarios. Human dermal exposure was estimated and health risks were assessed. For polyester clothes, the mean HQs for Sb were 0.44, 0.40 and 0.13 for adult males, adult females and children <1-year old, respectively, for one polyester T-shirt reaching a value of 1.2. For the remaining trace elements and clothes, non-carcinogenic and carcinogenic risks were considered as safe (HQ < 1) and acceptable (<10^–5), respectively. ZnPT and Ag nanoparticles were also detected in some clothes. These substances with biocide activity could affect the natural skin micro flora and, consequently, could lead to adverse effects on the skin.

Footnotes

Acknowledgment

The authors are grateful for scientific and technical services from the Universitat Rovira i Virgili for their assistance with the ESEM.

Declaration of conflicting interests

The authors declared no potential conflicts of interest with respect to the research, authorship and/or publication of this article.

Funding

The authors disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: J Rovira was supported by the Spanish Ministry of Economy and Competitiveness (MINECO), under the Torres Quevedo Program (PTQ-13-06059), co-funded by the European Social Fund.

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