Textile Functionalization and Its Effects on the Release of SilverNanoparticles into Artificial SweatSandra Wagener,*,† Nils Dommershausen,† Harald Jungnickel,† Peter Laux,† Denise Mitrano,‡

Bernd Nowack,‡ Gregor Schneider,§ and Andreas Luch†

†Department of Chemical and Product Safety, German Federal Institute for Risk Assessment (BfR), Max-Dohrn-Straße 8-10,D-10589, Berlin, Germany‡Technology and Society Laboratory, EMPA − Swiss Federal Laboratories for Materials Science and Technology, Lerchenfeldstrasse5, CH-9014, St. Gallen, Switzerland§rent a scientist GmbH, An der Irler Hohe 3a, D-93055, Regensburg, Germany

ABSTRACT: This study addresses the release of total silver (Ag) and silver nanoparticles(Ag-NPs) from textiles into artificial sweat, particularly considering the functionalizationtechnology used in textile finishing. Migration experiments were conducted for fourcommercially available textiles and for six laboratory-prepared textiles. Two among theselab-prepared textiles represent materials in which Ag-NPs were embedded within the textilefibers (composites), whereas the other lab-prepared textiles contain Ag particles on therespective fiber surfaces (coatings). The results indicate a smaller release of total Ag fromcomposites in comparison to surface-coated textiles. The particulate fraction determinedwithin the artificial sweat was negligible for most textiles, meaning that the majority of thereleased Ag is present as dissolved Ag. It is also relevant to note that nanotextiles do not releasemore particulate Ag than conventional Ag textiles. The results rather indicate that thefunctionalization type is the most important parameter affecting the migration. Furthermore,after measuring different Ag-NP types in their pristine form with inductively coupled plasmamass spectrometry in the single particle mode, there is evidence that particle modifications, like surface coating, may alsoinfluence the dissolution behavior of the Ag-NPs in the sweat solutions. These factors are important when discussing thelikelihood of consumer exposure.

■ INTRODUCTIONThe use of nanosized particles in consumer products isconstantly increasing, but up-to-date knowledge whether and towhat extent nanoparticles (NPs) are released from theseproducts is sparse. Especially, the influence of differentfunctionalization technologies on NP release is not definitive.Nowadays, textiles possess a multitude of different specificproperties, e.g., UV protection, self-cleaning features, orantimicrobial activity. To achieve these functions, nano-technology is more and more applied in manufacturing ofmodern textiles.1−4 Textile fibers may be equipped with NPs bydifferent functionalization technologies, e.g., by coating or bydirect integration of particles in the spinning polymer solution(nanocomposite).1,3,5 Currently, labeling obligations for textilesworldwide are marginal. For nanomaterials in Europe, labelingis so far only intended for biocides like nano-silver (Ag)regarding the new EU directive Nr. 528/2012, thus making itdifficult for the consumer to follow if a textile is nano-functionalized. The increased application of NPs, especially intextiles, has raised concerns about consumer exposure.6

Whereas at least some data on the release of silver (Ag) andtitanium dioxide (TiO2) NPs from textiles into water or washwater, respectively, are available,7−12 data on consumerexposure are sparse.13−16 For surface functionalized fibers, ithas already been described that particles might be released into

simulated human sweat or during washing within a certain timeframe.7,15,17 Kulthong et al.17 determined the Ag release intoartificial sweat from different Asian fabrics, ranging from 0 toabout 322 mg kg−1 of fabric weight, with the amount releasedcorrelated with the concentration in the initial coating. vonGoetz et al.15 described the release of nano-TiO2 and nano-Agfrom several commercial textiles after application of mechanicalstress. The results obtained corresponded to an overall dermalexposure of 8.2 μg Ag kg−1 body weight for adults. Bianco etal.18 demonstrated in their study that the use of Ag-containingtextiles leads not only to the release of Ag but also to itspenetration across the skin, thus highlighting the importancealso for the consumer. It is supposed that NPs integrated intonanocomposites are more efficiently retained than NPs insurface coatings. However, only little information exists aboutthe influence of textile modification on the release and fate ofparticles. Initial investigations were done by Stefaniak et al.,comparing the Ag migration into sweat and saliva between twotextiles, one coated with nano-Ag and one nanocomposite,confirming a lower Ag release for the composite.19

Received: December 15, 2015Revised: April 19, 2016Accepted: April 29, 2016Published: April 29, 2016

Article

pubs.acs.org/est

© 2016 American Chemical Society 5927 DOI: 10.1021/acs.est.5b06137Environ. Sci. Technol. 2016, 50, 5927−5934

Here, we present results on the release of Ag into artificialsweat from ten textiles. By comparing textiles with silvernanoparticles (Ag-NPs) and “conventional” Ag embedded in asurface coating with NPs fully integrated into the fiber (i.e.,nanocomposites), a detailed investigation on the influence offunctionalization technologies on NP release into sweat anddermal exposure is provided. Whereas one part of theinvestigated textiles was laboratory-prepared (lab-prepared)textiles with known NP contents, the other textiles werecommercially available in Europe, providing a useful comple-ment to the results presented for textiles from the Asianmarket.17 Optical methods for the visualization of NPs locatedat the fiber’s surface before migration experiments, such asenvironmental scanning electron microscopy (ESEM) withenergy dispersive X-ray spectroscopy (EDX), were used toidentify the chemical composition of the NPs used for textilefunctionalization. In addition, time-of-flight secondary ion massspectrometry (ToF-SIMS) was used as it allows for massspectrometric identification of particle composition andimaging of the particle distribution. This technique, which isalready established for structural and chemical characterizationof other solid materials, has hardly been used for textilecharacterization and therefore presents a quite novel approach.The total Ag content in the textile material and in artificialsweat upon migration was further determined. With the use ofsingle particle ICP-MS (spICP-MS), element specific informa-tion on particle size distribution in artificial sweat solutions wasobtained.

■ MATERIALS AND METHODSCharacterization of Textiles. Experiments were con-

ducted with four commercial textiles (T-C) modified withAg, as declared by the manufacturer, and six lab-preparedmaterials (T-L) containing Ag in different specifications (Table1). The lab-prepared textile T-L-1 was obtained from thecompany RAS materials (Regensburg, Germany). Theproduction of the lab-prepared textiles T-L-2 to T-L-5 hasbeen described by Mitrano et al.10 All of these samples werepreviously analyzed for their total Ag content and the release ofAg in various size fractions upon laundering the fabrics.Information regarding the commercial textiles such as elementspeciation, particle size, and functionalization was sparse. ToF-SIMS (IONTOF GmbH, Munster, Germany) was performed

for the identification of the chemical composition anddistribution patterns of particles on the fibers for two of thetextiles. In ToF-SIMS, samples are bombarded with a focused,energetic ion beam that sputters atoms, clusters, or largemolecules off the surface. A fraction is ejected as secondaryions, and their mass is analyzed. This enables an image of thedistribution of the trace elemental and chemical composition ofinterest comprising the whole selected area. It enables high-resolution (below 100 nm20) imaging of both physiological andincorporated compounds such as NPs inside fibers. Textileswere cut into pieces of 2 cm × 2 cm and analyzed. Ion imagesand spectra measurements were performed using a ToF-SIMSV instrument with a 30 keV nanobismuth primary ion beamsource. The ion currents were measured to be 0.5 pA at 5 kHzusing a Faraday cup. A pulse of 0.7 ns from the bunchingsystem resulted in a mass resolution that usually exceeded 6000(full width at half-maximum) at m/z <500 in positive mode.The primary ion dose was controlled below 1012 ions cm−2 toensure static SIMS conditions.The other textiles were difficult to measure with ToF-SIMS

due to charging processes and the rough nature of the fibers.For these textiles, ESEM (XL30ESEM FA FEI) with EDX(Amtek, FA EDAX) was performed. Textiles were cut intopieces of 1 cm × 1 cm and measured in the ESEM without anysputtering under low vacuum.

Quantification of the Total Ag Content. Before themigration experiments, the total content of Ag in the textileswas determined with ICP-MS (X-Series II, FA Thermo). To0.2−0.3 g of textile, 8 mL of nitric acid (HNO3) and 2 mL ofhydrogen peroxide (H2O2) were added in PTFE tubes.Subsequently, samples were digested in a microwave oven(FA MLS, Ethos.start) following a temperature programsuitable for textile fibers (step 1: heating up to 140° in 3.5min; step 2: heating up to 200° in 3.5 min; step 3: heating up to270° in 6 min: step 4: holding at 270° for 15 min). Therecovery rate for the digestion, which was determined withstandard solutions, was ∼95%. The limit of detection (LOD)was determined by taking the mean + 3 times the standarddeviation of HNO3 blanks which were produced following thesame procedure as the sample preparation and were measuredbefore and after measurements of textile samples. The LODwas 1.7 ppb, corresponding to 0.7 mg kg−1 textile when using atextile sample of 250 mg.

Table 1. Overview of Textiles Used for Migration Experimentsa

product product labelingnano-labeled

Ag particles confirmed withESEM-EDX application process

T-L-1 lab-preparedb nano-Ag, Ø 20 nm (NM-300K) X X integration into the fiber(nanocomposite)

T-L-2 lab-preparedc Ag/SiO2, composite, Ø ∼ 1 μm integration intothe fiber

X n.d.h integration into the fiber(nanocomposite)

T-L-3 lab-preparedc nano-Ag, Ø 20 nm (NM-300K) X Xf coatingT-L-4 lab-preparedc Ag/SiO2, Ø ∼ 1 μm X n.d.h coatingT-L-5 lab-preparedc AgCl, Ø >100 nm − Xf coatingT-L-6 lab-preparedc untreated n.d.h −T-C-1 pillowd nano-Ag, antibacterial X X coatingg

T-C-2 towelb nano, antibacterial X n.f.i −T-C-3 sockse Ag, antibacterial − X coatingg

T-C-4 sports shirtc Ag, antibacterial − X coatingg

aThe large X’s indicate that the textile was nano-labeled or that Ag was detected on the samples using ESEM-EDX, respectively. bFibers arecomposed of polyester and polyamide. cFibers are composed of polyester. dFibers are composed of cotton. eFibers are composed of cotton andpolyester. fToF-SIMS was used instead of ESEM-EDX. gProduction technology was assumed on the basis of ESEM-EDX results. hn.d. = notdetermined. in.f. = silver was not found on the sample.

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Migration Experiments. To determine the release of Aginto artificial sweat, migration experiments were conductedfollowing the procedure described by Kulthong et al.17 Artificialsweat solutions (pH 8 and 5.5) were made according to ISO105-E04 protocol for color fastness testing.21 Approximately0.2−0.3 mg of each textile was covered with acid and alkalinesweat solutions in a ratio of 1:50 (w/v) and incubated in awater bath at 37 °C for 24 h. For each textile, three replicateswere subjected to migration at each pH exposure point. Onereplicate per sample set was subjected to an additional 24 hexposure with fresh artificial sweat (48 h in total). Before ICP-MS analysis, the solutions were filtered through a PTFE-filterwith a pore size of 0.45 μm to remove any residues of textilefibers. For the discrimination between the particulate and thedissolved fraction, samples of one replicate per textile wereadditionally centrifuged at 4500 rpm using 3 K Amicon filtersfor 30 min. The migration solutions were analyzed with ICP-MS. The recovery rate was determined with standard solutionsand was between 75% and 90%, depending on the Agconcentration. However, the Ag content was calculated onthe basis of a calibration conducted with the sweat solution,following the same procedure as the sample preparation toconsider the loss of Ag which may occur, e.g., by precipitationof insoluble Ag like AgCl formed in the artificial sweat. TheLOD for Ag was determined by taking the mean + 3 times thestandard deviation of artificial sweat blanks which wereproduced following the same procedure as the samplepreparation and were measured before and after measurementsof textile samples. The LOD was 3.1 ppb, corresponding to aminimum release of 1.2 mg kg−1 textile.Single Particle Analysis. ICP-MS was additionally

operated in the single particle mode (spICP-MS). Using thismethod, it is possible to determine not only the particle mass

but also the number and particle size distribution of theparticulate fraction. SpICP-MS therefore provides moredetailed information compared to ultracentrifugation, which isnormally used for the determination of the particulate massfraction. Further, an elemental identification is obtained,representing a major advantage over other analytical methodslike dynamic light scattering or nano tracking analysis. Particlesdown to a size of ∼20 nm can be detected. The number ofparticles has to represent 2% to 10% of all detected signals.SpICP-MS uses very short dwell times (here: 3 ms). Thenumber of NPs was calculated by the frequency of signalsdetected above the background signals (detection limit) whichis equivalent to the dissolved element species.22,23 The particlemass is, among others, dependent on the signal intensity of theparticles, the dwell time, the transport efficiency, and theresponse of the ion standard. Information about the response ofthe ion standard is attained from a calibration with dissolved Ag(AgNO3) in the sweat solution. The transport efficiency iscalculated by particle number and mass of a reference standard.In this study, gold (Au) NPs were used as reference standard(NIST RM 8013, 60 nm). Finally, the size of the NPs can becalculated from the particle mass and the element-specificparticle density. The calculation is based on the assumptionthat particles are spherical. Besides the migration solutions,citrate-coated Ag-NPs (FA NanoComposix, 80 nm) anduncoated Ag-NPs of NM-300K (20 nm24) dispersed in waterand artificial sweat were measured for comparison and to testthe influence of particle coating on the presence of particulateAg in sweat solutions.

■ RESULTS AND DISCUSSIONIdentification of NPs and Functionalization Technique

in the Raw Textiles. Seven out of 10 textiles were analyzed

Figure 1. (a) ESEM images with EDX-spectra of a laboratory-prepared textile (T-L-1), a pillow (T-C-1), and a sports shirt (T-C-4). (b) ToF-SIMSimages of T-L-3 (NM-300K) and T-L-5 (AgCl). The light regions reflect the Ag signal.

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with either ESEM-EDX or ToF-SIMS. For 6 of 7 textilesexamined, the presence of Ag was verified in accordance to thestated product contents. For textile T-C-2, the presence of Agcould not be confirmed by these methods (Table 1).If particles are yarned into the fibers, a rather low number of

particles are expected to be located on the surface of the fibers.However, for all commercial textiles investigated, Ag particleswere detectable on the fiber surface (Figure 1a), indicating theapplication of fiber coating for functionalization. According tothe manufacturer of the lab-prepared materials T-L-1 and T-L-2, particles were yarned into the fiber (nanocomposites).Nevertheless, in textile T-L-1, individual particles could bedetected (Figure 1a), especially at the fiber endings where thetextile was cut. For the textiles coated with Ag-NPs <20 nm(NM-300K, T-L-3) and with AgCl (T-L-5), a significantdifference was detected by ToF-SIMS. While for textile T-L-3,large aggregates were found on the fiber surfaces, and a verythin film was observed in case of the fiber T-L-5 (Figure 1b).Despite these findings, according to Mitrano et al.10 total Agconcentrations of both fabrics were quite similar (15.5 and 14.6mg kg−1, respectively). These results demonstrate that ToF-SIMS not only can assess the chemical composition of Agspecies in functionalized textiles but provides additionalinformation on the spatial distribution of the material on thefiber surface.On the basis of our findings, it can be concluded that fibers

were coated in the case of commercial textiles, as a clearly largernumber of particles could be detected at the surface comparedto the lab-prepared textile T-L-1. Particles were found unevenlyall over the fiber surfaces rather than predominantly at the fiberendings. They often showed diameters >100 nm, and theformation of agglomerates could be observed (Figure 1a).Total Content of Ag in Textiles. Table 2 gives the total

concentrations of Ag in the fabric before migration experimentsas determined by ICP-MS. The results are in accordance withthe observations made by ESEM-EDX or ToF-SIMS: elementalanalysis confirmed the presence of Ag for almost all textiles, inwhich the elements were already identified. For textile T-C-2,Ag could be detected neither by EDX nor by ICP-MS. Fortextile T-C-3, few particles containing Ag could be observedwith ESEM-EDX, but concentrations were below the LOD ofthe ICP-MS method. With 23.5 mg kg−1, the pillow (T-C-1)showed the highest Ag concentrations of all purchased textilesinvestigated. The lab-prepared composites T-L-1 and T-L-2showed the highest Ag concentrations of all textiles (128 and132.8 mg kg−1, respectively). The results obtained for thetextiles T-L-2 to T-L-5 are generally comparable with the

concentrations previously determined for these fabrics byMitrano et al.10 Only for textile T-L-5, significantly higherconcentrations were measured in our study.

Release of Total Ag into Sweat Solutions. Table 2shows the Ag concentrations (±SD) detected in artificial sweatas analyzed and quantified with ICP-MS after two 24 hmigration cycles. The amounts presented include the dissolvedas well as the particulate fraction of Ag <0.45 μm. Hence, Agparticles larger than 0.45 μm were not considered. Acidic (pH5.5) and alkaline (pH 8) sweat solutions were used.Concentrations after 24 h of migration varied between 1.7and 21.9 ppm (mg kg−1 textile), corresponding to 7% and 75%of the total Ag content, respectively (Figure 2). Most of the

release occurred during the first 24 h. However, calculating thereleased amount after the second migration cycle in relation tothe remaining content after the first 24 h of migration, thepercentages of Ag release after the first and the second 24 hmigration were comparable (Figure 3). Textile T-L-5 lostnearly the total Ag content within 48 h when exposed to thealkaline solution. In general, no significant pH-related influencewas observed in terms of Ag release into artificial sweatsolution. It should be kept in mind that some of the released Agmay have precipitated during the experiment due to theformation of insoluble Ag, e.g., as AgCl. In this case, theamount of Ag released would have been underestimated.However, as the concentrations were quantified against acalibration also conducted in the artificial sweat solution, the

Table 2. Total Levels and Migrate Concentrations of Ag Given in mg kg−1 Textile (± SD)a

migrate concentration

textile product total concentration acid 1st 24 h acid 2nd 24 h alk 1st 24 h alk 2nd 24 h

T-L-1 C lab-prepared 128.0 (±12.3) 8.9 (±1.4) 2.5 10.5 (±2.1) 2.7T-L-2 C lab-prepared 132.8 (±1.5) <LOD n.d. <LOD n.d.T-L-3 S lab-prepared 12.4 (±0.3) 1.9 (±0.3) n.d. 2.1 (±0.3) n.d.T-L-4 S lab-prepared 14.9 (±0.3) 1.7 (±0.9) <LOD 2.0 (±0.2) n.d.T-L-5 S lab-prepared 26.6 (±3.0) 19.9 (±0.4) 4.5 21.9 (±5.6) 4.6T-L-6 − lab-prepared 1.0 (±0.7) <LOD n.d. <LOD n.d.T-C-1 S pillow 23.5 (±1.9) 5.1 (±0.4) 1.3 5.2 (±0.7) 1.5T-C-2 − towel <LOD n.d. n.d. n.d. n.d.T-C-3 S socks <LOD n.d. n.d. n.d. n.d.T-C-4 S sports shirt 14.2 (±0.9) 5.5 (±0.2) 1.4 5.2 (±0.1) 1.6

aC = composite; S = surface modification; n.d. = not determined; acid = acidic simulant; alk = alkaline simulant.

Figure 2. Relative Ag release of textiles. Left bars refer to acidic andright bars to alkaline sweat solution.

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precipitated amount was tried to be considered. Furthermore,as seen at the example of textile T-L-5, which contained AgClalready in the textile, the quantified amount of released Ag wasfound to be close to the total amount of Ag determined in thetextile following digestion. Therefore, it can be assumed thatmost of the released Ag is determined.Kulthong et al.17 who investigated textiles purchased from

the Thai market as well as textiles coated with Ag suspensionsin the laboratory, determined an Ag release into artificial sweatranging from 42% to nearly 100%. The release, however, wasmainly calculated from the lab-prepared textiles. These valueswere higher than the ones observed in our study. Furthermore,Kulthong et al.17 found a significant influence of the type ofsweat (pH value and composition) on the Ag release, whereasthe influence of these parameters was found negligible in ourstudy. Balakumaran et al.25 also investigated the Ag release ofan Ag-coated textile subjected to the pH value of a sweatsolution. They reported an influence of the pH value of thesweat solution on the Ag release, too. However, in contrast toKulthong et al.,17 they found an increasing Ag release withdecreasing pH value. von Goetz et al.15 conducted migrationexperiments for titanium (Ti) and Ag release for ninecommercially available textiles also using sweat solutions that

followed the ISO 104-E04 protocol.21 However, migrationexperiments were performed with additional simulation ofmechanical stress. For this purpose, the protocol of the ISOmethod 105-C06,26 normally used for washing experiments,was slightly modified. Besides the replacement of the washingsolution by artificial sweat, a shorter migration time (30 min)than in the study presented here was applied. In the study ofvon Goetz et al.,15 two out of four textiles released Ag rangingfrom 5% to 14%, one of them also in the particulate form.While Kulthong et al.17 observed a weak correlation between

Ag contents and migration rates, this could not be confirmed inour study (R2= −0.08, Figure 4a). On the other hand, ourresults point to an impact of the functionalization technologyon the Ag release into artificial sweat (Figure 4b). While textileswith Ag coatings released 8−75% of their total contents intoartificial sweat within 24 h, the composite T-L-1 retained mostof the Ag within its fibers (Ag release <8%), and composite T-L-2 did not release any detectable amount of Ag at all. Similarfindings were reported by Stefaniak et al.,19 where one textilewith an Ag coating released more Ag into artificial sweat andsaliva than the composite textile. A further observation is thatthe textile with AgCl-coating (T-L-5), which does not representa nanocoating, released most of the total Ag content. Thisindicates that the starting form of Ag in the textile, i.e., Ag orAgCl, has a strong influence on its release.The textiles T-L-2 to T-L-5 had already been examined for

the release of Ag into wash water during laboratory washingconditions by Mitrano et al.10 The quantities released are quitecomparable, where only textile T-L-5 showed a clearly higherrelease of Ag into sweat solution. It can be summarized thatnanocomposites release a smaller amount of Ag in comparisonto surface-coated textiles.

Release of Particulate Ag into Sweat Solutions. Toinvestigate the release of the particulate fraction (<0.45 μm)into artificial sweat, the concentration of Ag in the migrationfiltrate after ultracentrifugation was subtracted from the totalamount released. Furthermore, the particle number and massconcentration of Ag particles was determined by spICP-MS.Results are summarized in Table 3.

Results Obtained after Ultracentrifugation. For most ofthose textiles releasing Ag into artificial sweat (Table 2), aparticulate fraction could be calculated (Table 3). However,most of these values were below the LOD of the ICP-MSmethod, which is why they have to be considered as

Figure 3. Comparison of the relative Ag release after 24 h of migrationto the original Ag content of the material and of the relative Ag releaseafter 48 h of migration to the remaining contents after 24 h ofmigration. As only one sample was investigated for the 48 h timepoint, no standard deviations are presented in this case.

Figure 4. Ag release (migration time of 24 h, acidic solution) as a function of the total Ag contents (a). Relative releases of Ag as a function of thetotal contents (b), differentiated for textiles representing nanocomposites and those with surface coatings. The circle marks the textile with the non-nanocoating.

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Table 3. Determination of the Particulate Fraction in Migration Solutions

centrifugation (Ag in mg kg−1 textile) spICP-MS (part. kg−1 textile/mg kg−1 textile) particle size

textile acidic alkaline acidic alkaline (spICP-MS)

T-C-1 − 0.02 (0.1%)a 7.6 × 109/0.01 7.6 × 109/0.01 60 nmT-C-4 − 0.09 (0.6%)a − −T-L-1 0.2 (0.2%)a 0.02 (0.02%)a − −T-L-2 − − − −T-L-3 − − − −T-L-4 1.7 (1.7%) − − −T-L-5 1.8 (1.8%) 7.7 (7.7%) 3 × 1012/0.5 3 × 1012/0.5 40 nm

aAccording to the LOD of the ICP-MS method, calculated values have to be considered “nonsignificant”.

Figure 5. Signal intensities (top) and size distribution (bottom) of Ag as measured by spICP-MS for (a) two commercial textiles and (b) coated anduncoated Ag in distilled water or acidic sweat.

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nonsignificant. Whereas for textile T-L-4, a particulate fractioncould be found in the acidic solution only, and in case of textileT-L-5, particles were identified in both acidic and alkalinesolution. In general, however, it can be concluded that the Agrelease from textiles predominantly occurs in the form of ions(>99% in most cases).Results Obtained Using spICP-MS. Figure 5a gives the signal

intensities and size distributions of Ag released from the twocommercial textiles T-C-1 and T-C-4. Results achieved withcitrate-coated Ag-NPs of 80 nm diameter, dispersed in water oracidic sweat solution, are displayed for comparison purposes(Figure 5b). As a further reference, uncoated Ag-NPs of NM-300K, which were also integrated in textiles T-L-1 and T-L-3,were also analyzed as dispersed in water and in acidic sweatsolution. All dispersions had a concentration of 0.1 μg l−1. Forthe sample with dissolved Ag (AgNO3) in the sweat solutionused for calibration, no particles were detected. This is incontrast to the results presented by Mitrano et al.,10 whoreported a formation of Ag particles of different species afterspiking AgNO3 directly into the washing solution. This may beexplained with different pH values and a different compositionof the agents. In the case of citrate-coated Ag-NPs in water, alow background of dissolved Ag was observed (Figure 5b). Theparticle number distribution is normally distributed. Thecitrate-coated Ag-NPs in sweat solution, however, are notnormally distributed and a decrease of the particle size wasobserved, pointing to the dissolution of the Ag-NPs. In the caseof the uncoated NPs NM-300K, the particle numbers decreasedclearly in contrast to the coated particles, in water (notpresented in the figure) as well as in acidic sweat. This showsthat in general a very small number of NPs is to be expected,especially in sweat if particles are not protected againstdissolution by coating. The Ag release of the textilesinvestigated occurs almost completely in the form of dissolvedions (exemplarily shown for textile T-C-4). However, fortextiles T-C-1 (Figure 5a) and T-L-5 (Table 3), single NPswere also detected with estimated particle sizes of 60 and 40nm, respectively. In the case of textile T-L-5, coated with non-nano-AgCl, Mitrano et al.10 showed that Ag-NPs were formedafter the washing process in the washing liquid, proving that anoccurrence of Ag particles in the liquid does not necessarilyindicate a release of NPs arising from the textiles. Thus, it ispossible that the Ag-NPs detected here also arise from anindirect formation after release of AgCl. However, the particlesize presented applies exclusively to the Ag fraction of theparticles and does not provide a proof that the particlesdetected are pure Ag-NPs. In light of the complex compositionof both, the inserted Ag particles and the sweat solution, whichdiffers from the washing solution (pH 10.5) used in Mitrano etal.,10 it can not be excluded that particles detected in themigration solution are of different chemical compositions, asdifferent liquids may cause different particle formation,11 asalready seen for the formation of Ag containing particles afterspiking AgNO3 in artificial sweat or washing solution,respectively. In the case of a complex particle composition,the diameter of the actual particle sizes would be under-estimated.The results of spICP-MS analysis further do not completely

mirror the results of migration filtrate measurements afterultracentrifugation. According to Table 3, only in the migratesof textiles T-L-4 (only acidic solution) and T-L-5, significantamounts of particulate Ag were detected. However, accordingto the spICP-MS results, a particulate fraction could be

observed also for textile T-C-1. Contrastingly, for textile T-L-4,no particles were detected with spICP-MS. It can be supposedthat the filtrate subtraction method was too insensitive for sucha small concentration of the particulate fraction, making itdifficult to compare results. In the cases of textiles T-C-1 and T-L-5, which are coated textiles, it can be summarized that Agcontaining particles were observed using both methods, eventhough concentrations were close or even below the detectionlimit. In respect to the filtrate subtraction method, it can not beexcluded that a certain portion of the Ag content of the filtratemigrated into the supernatant right after ultracentrifugation, asit was no longer saturated with Ag ions (Ag+). This is generallya critical step in the quantification of Ag when using thismethod. Thus, at least for textile T-C-1, for which a particulatefraction could be confirmed in artificial sweat simulant viaspICP-MS, it can be supposed that the particulate fraction hasbeen underestimated by the filtrate subtraction method. On theother side, another concern with regard to spICP-MS analysis isthe requirement of a very low particle concentration. Eventhough all samples were measured shortly after dilution, it cannot be excluded that the necessary dilution is facilitating furtherdissolution, leading to an underestimation of the amounts ofparticulate Ag. This would explain why for textiles T-L-4 and T-L-5 no or a lower amount of particles compared to filtratesubtraction were observed.Mitrano et al.,10 who also investigated the release of Ag into

wash water for textiles T-L-2 to T-L-5, reported a higherpresence of particulate Ag. The high amount of dissolvedfraction found in our study is also in contrast to other previousresults on the release of Ag particles into washing solutions.7,27

However, Benn and Westerhoff9 found up to 86% of thereleased Ag from socks into distilled water to occur in thedissolved form. Concerning migration studies into sweatsolutions, Stefaniak et al.19 reported an Ag release occurringmostly in the dissolved form. von Goetz et al.15 reported amigration of particulate Ag and found that the concentrationsof the particulate fraction were similar or even higher comparedto the dissolved fraction. Similar to the results presented herefor one textile, NPs were only detected in the alkaline, but notin the acidic, solution. It is questionable if the mechanical stressexerted on the textiles conducted by von Goetz et al.15

influenced the release of particulate Ag from the textile, but atleast it can be supposed that exerting mechanical stressfacilitates total Ag release. As seen in Figure 5b, the impactof the particle type, e.g., if a particle is coated or not, on the Agrelease is quite large. Therefore, it can not be excluded thatdifferences between the results from von Goetz et al.15 and ourstudy might be due to the different types of NPs used. Adifferent particle composition or coating could further explainwhy, e.g., for textile T-C-1, for which the particle type isunknown, a higher particle number was detected in the sweatsolution when compared to textile T-L-3, which is coated withpristine NM-300K NPs. However, as also discussed in Mitranoet al.10 and Hedberg et al.,11 the composition and pH value ofthe respective agent have a large impact on the release ofparticulate Ag or the subsequent formation of variousparticulate Ag species within the liquid, respectively.It can be concluded that a consumer may be exposed against

Ag, predominantly in the dissolved form, when wearing textilesmodified with Ag-NPs. The data presented here indicate thatthe functionalization type is an important parameter influencingthe amount migrated and therefore also consumer exposure.Furthermore, there is evidence that particle modifications, such

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as surface coatings, may affect the dissolution of the Ag-NPs insweat. As the largest amount of total and particulate Ag releasedwas found for the textile coated with non-nano-AgCl, it isindicated on the one hand that Ag-NPs detected in themigration do not necessarily originate from the textiles but canalso be formed in the migration liquid. On the other hand, thiscould indicate that the starting form of Ag in the textile has asignificant influence on Ag release and that textiles with non-nanocoatings release more Ag than textiles with nanocoatings.Further research on nanofurnished textiles should focus on theidentification of the main factors determining particle releaseduring daily life conditions, including different types of binder,the particle type, and the type of textile material. A systematicmanufacturing of reference textiles using different NP types orwhich have been finished using different functionalizationtechnologies needs to be promoted. As demonstrated here byusing two different methods for the determination of theparticulate fraction in the sweat solutions, ultrafiltration has itslimitations. This is why it is important to conduct techniquesdetermining not only particle mass but also the size distributionspecific for the element of interest. SpICP-MS could be shownto be a valuable method to do so. Further, ToF-SIMS wasshown to provide suitable information about the distribution ofAg particles throughout the fiber area and should be used forstructural material characterization alongside with ESEM-EDXor transmission electron microscopy to investigate humanexposure in relation to material properties.

■ AUTHOR INFORMATIONCorresponding Author*Phone: +49-(0)30-18412 4164; fax: +49-(0)30-18412 4741;e-mail: sandra.wagener@bfr.bund.de.NotesThe authors declare no competing financial interest.

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