Waste Management xxx (2015) xxx–xxx
Contents lists available at ScienceDirect
Waste Management journal homepage: www.elsevier.com/locate/wasman
Use of engineered nanomaterials in the construction industry with specific emphasis on paints and their flows in construction and demolition waste in Switzerland Ingrid Hincapié a, Alejandro Caballero-Guzman a, David Hiltbrunner b, Bernd Nowack a,⇑ a b
EMPA, Swiss Federal Laboratories for Materials Science and Technology, Technology and Society Laboratory, Lerchenfeldstrasse 5, CH-9014 St. Gallen, Switzerland FOEN, Swiss Federal Office for the Environment, Waste and Resources Division, Worblentalstrasse 68, CH-3063 Ittigen, Switzerland
a r t i c l e
i n f o
Article history: Received 27 January 2015 Revised 30 June 2015 Accepted 2 July 2015 Available online xxxx Keywords: Engineered nanomaterials Construction and demolition waste Recycling Landfills Paints Material flow modeling
a b s t r a c t One sector where the use of engineered nanomaterials (ENMs) is supposed to offer novel or improved functionalities is the construction industry. During the renovation or demolition of buildings, ENMs contained in former construction materials will enter recycling systems or become construction waste. Currently, information about ENM flows in these processes is insufficient. The potential for the release of ENMs from this waste into the environment is unknown, as are the environmental impacts. To evaluate whether there is currently any nano-relevant construction and demolition waste (C&DW) originating from buildings, we evaluated the sources and flows of ENMs in C&DW and identified their potential exposure pathways. A survey of business representatives of Swiss companies in this sector found that ENMs are mainly used in paints and cement. The most frequently used ENMs in the Swiss housing construction industry are nano-TiO2, nano-SiO2, nano-ZnO, and nano-Ag. Using a bottom-up, semi-quantitative approach, we estimated the flows of ENMs contained in paints along the product’s life cycle from buildings to recycling and landfill. The flows of ENMs are determined by their associated flows of building materials. We estimated an annual amount of ENMs used in paints of 14 t of TiO2, 12 t of SiO2, 5 t of ZnO, and 0.2 t of Ag. The majority of ENMs contained in paints in Switzerland enter recycling systems (23 t/y), a smaller amount is disposed directly in landfills (7 t/y), and a tiny fraction of ENM waste is incinerated (0.01 t/y). Our results allow a qualitative determination of the potential release of ENMs into technical or environmental compartments, with the highest potential release expected during recycling. Ó 2015 Elsevier Ltd. All rights reserved.
1. Introduction The construction sector requires products like cement, steel, paints, insulation materials, window glass, and many others. The quest for sustainable development, including the construction of greener buildings, influences innovation and encourages the use of products exploiting the unique properties of nanomaterials. Engineered nanomaterials (ENMs) are used either to improve the quality of existing conventional products or to create completely novel products, functionalities, and applications. For instance ENMs tested in cement include SiO2, Al2O3, Fe2O3, ZrO2 and CNT (van Broekhuizen et al., 2011), they are used mainly to improve the quality and longevity of structures (Hanus and Harris, 2013). In insulation materials, nano-SiO2 (aerogel) is used as a noise barrier and for heat loss reduction (Jelle et al., 2012). Properties such ⇑ Corresponding author. E-mail address: [email protected] (B. Nowack).
as easy-clean, antibacterial, scratch resistance, fire retardant, UV-protection, wood preservation and anti-corrosion can be introduced or improved in paints and coatings using the following ENMs: Ag, CeO2, CNT, Fe2O3, SiO2, TiO2, ZnO (Hanus and Harris, 2013; Kaiser et al., 2013b; Lee et al., 2010a; Teizer et al., 2012; van Broekhuizen and van Broekhuizen, 2009). In windows, ENMs such as SiO2, TiO2 are used for anti-reflection, anti-fogging, heat loss reduction and easy-clean properties (Lee et al., 2010b). However, most of the potential applications for ENMs (e.g. concrete, asphalt or insulation materials) have not yet reached large-scale commercial production, and rather represent niche market segments (van Broekhuizen and van Broekhuizen, 2009). In some cases, applications containing ENMs have only been developed on a pilot scale or are only to be found as experimental results in the scientific literature. Reasons for the limited spread of nano-applications include their high prices compared to conventional products, uncertainties related to their safety, and uncertainties related to their technical performance (van Broekhuizen
http://dx.doi.org/10.1016/j.wasman.2015.07.004 0956-053X/Ó 2015 Elsevier Ltd. All rights reserved.
Please cite this article in press as: Hincapié, I., et al. Use of engineered nanomaterials in the construction industry with specific emphasis on paints and their flows in construction and demolition waste in Switzerland. Waste Management (2015), http://dx.doi.org/10.1016/j.wasman.2015.07.004
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et al., 2011). In the near future, it is presumed that nanotechnology applications will help the construction sector to reach the following goals (Hanus and Harris, 2013; Kaiser et al., 2013b; Lee et al., 2010a; Teizer et al., 2012; van Broekhuizen and van Broekhuizen, 2009): development of stronger concrete structures; generation of healthier environments; protection of structural appearance and durability; and reduction of energy consumption and other resource use. According to van Broekhuizen et al. (2011), the current applications of ENMs in Europe’s construction sector are mainly in cement (concrete’s basic additives), paints, and insulation materials. These authors also reported that nano-TiO2, nano-ZnO, nano-Al2O3, and nano-SiO2 were the predominant ENMs used in construction materials and that there was no evidence of the current use of carbon nanotubes (CNTs). However, further investigations showed that CNTs are potential candidates for enhancing the mechanical properties of cement-based materials and their resistance to crack propagation while providing such novel properties as electromagnetic field shielding and self-sensing (Sanchez and Sobolev, 2010). Silica fume is used in cement mainly to improve the quality and durability of structures (Hanus and Harris, 2013). However, the costs associated to the nanomaterial production process and the special equipment required to handle it make the cement more expensive than conventional types (van Broekhuizen and van Broekhuizen, 2009). The paint and coating industry has successfully adopted nanotechnology (Evans et al., 2008; Kaiser et al., 2013b). Although there is an ongoing debate about whether or not the expected benefits of nanomaterials in these applications will materialize in the long run (Kaiser et al., 2013b), it is estimated that paints and coatings currently represent the biggest market for nanotechnology in the construction industry (NanoHouse, 2013; van Broekhuizen et al., 2011). Although official recommendations on the definition of nanomaterials (i.e. at least 50% of the particles must be in the size range of 1–100 nm) were just published (EU-Commission, 2011), nanomaterials have been produced and used before the development of nanotechnology industries as we know them today, for instance, SiO2 (Bosch et al., 2012), nano-Ag (Nowack et al., 2011), and carbon black (CB). In some cases, therefore, it may be difficult to confirm whether a given product contains nanomaterials or not. In some of these substances, e.g., SiO2 or CB, primary nanoparticles of less than 100 nm are fused together into aggregates of more than 100 nm. Because EU definitions are based on primary particle size, these substances are now considered nanomaterials although they have been considered and used as conventional materials for many decades. Despite the aforementioned benefits of integrating ENMs into construction materials, concerns about their use still remain open, including their effects on environmental and human health following potential release to air, water and soil. The currently available information makes it possible to quantify the flows of nanomaterials and to evaluate their potential releases during the whole products life cycle. A study by Müller et al. (2013) analyzed the flows of ENMs in the waste flows. The results provided the first estimate of the amount of ENMs in waste streams in Switzerland. The modeling suggested that an important flow of nanomaterials goes directly from construction waste into landfills and indirectly from waste incineration plants to the landfills as bottom ash. Based on that work and the Swiss waste management system regulations, the present study aimed to investigate what amounts of nanomaterials exist in the C&DW flows originating from buildings in Switzerland (i.e. we did not considered C&DW from roads, underground constructions and hazardous construction waste), and to analyze whether there is currently any nano-relevance in construction waste. We estimated the flow of ENMs in waste originating
from building construction, renovations, and demolitions as well as the potential release of ENMs during recycling, with focus on paint applications. On one hand, paints appeared to be the most important application containing ENMs in the construction sector. On the other hand, only for this application enough data was available to carry out a quantitative modeling. The steps performed in this estimation were: 1. Collect data on sources of ENMs and flows of C&DW to landfill, waste incineration, and recycling, within the Swiss waste management system. 2. Estimate the current amounts of nanomaterials in Swiss C&DW originating from buildings. 3. Model ENM flows from buildings to landfill and the environment, according to the Swiss waste management system. 4. Evaluate the potential release of nanomaterials based on studies on ENMs release. Only data for 2012 were available and collected for the application paint. Subsequently, we focused on the following nanomaterials: TiO2, SiO2, ZnO, and Ag, which are the ENMs most used in paints for the construction industry. 2. Materials and methods 2.1. Data collection To obtain information about ENM applications and the amounts used in the Swiss construction industry, we surveyed a group of expert representatives from companies in this sector. The survey questionnaire was designed using the Internet-based platform, Surveymonkey, and was sent out to 60 construction sector experts between February 12 and March 13, 2014. The questionnaire asked for estimates of ENM use in the Swiss construction industry (i.e., use/non-use of nanomaterials, market sizes, and shares and amounts of ENM used in different construction materials). The specific questions of the survey are shown in the supplementary information, Section 1. Questions were specifically related to the use of nano-TiO2, nano-SiO2, nano-ZnO, nano-Ag, nano-CuO, and nano-CuCO3, and to the following materials used in the construction sector: adhesives, architectural membranes, asphalt, cement, coatings, flooring materials, geosynthetic barriers, insulation materials, paints, pipes, sealants, solar panels, steel, other metals, windows, and wood. Besides our survey, additional information on the mass content of ENMs in construction applications (i.e. stocks of ENMs in the applications) was taken from Hischier et al. (2015), NanoHouse (2013) and van Broekhuizen et al. (2011), as well as from official registrations of nanomaterials (ANSES, 2013) where paints and cement were the main applications. In order to estimate the amount of paint containing ENMs sold in Switzerland, this information was complemented by data from the 2012 market reports of the Swiss Association for the Lacquer and Paint Industry, and other sources (Burkhardt and Dietschweiler, 2013; McCulloch, 2012; VdL, 2012; VSLF, 2013). As a result, the market data (i.e. sold amounts in 2012) of paint in Switzerland are the base data for our modeling. 2.2. Disposal and amounts of C&DW in Switzerland According to the Swiss waste management system, C&DW is generated from the changes in infrastructure stocks (i.e., buildings, roads and underground constructions), and it also includes hazardous construction waste. For this study, we only considered the C&DW originated from buildings. According to the Swiss waste
Please cite this article in press as: Hincapié, I., et al. Use of engineered nanomaterials in the construction industry with specific emphasis on paints and their flows in construction and demolition waste in Switzerland. Waste Management (2015), http://dx.doi.org/10.1016/j.wasman.2015.07.004
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regulation, C&DW is coded with number 17 (UVEK, 2010). The final disposal of construction waste in Switzerland is regulated by the technical ordinance on waste (TVA, 2011). The waste treatments options are: direct recycling, sorting/collection, recycling (REC); waste incineration plant (WIP); landfill (LF) and export. For instance, mineral construction waste is mainly re-used on-site or treated and transformed to recycling products. Combustible parts of the construction waste must be incinerated. The residues generated during recycling and treatment processes of C&DW as well as overcapacities of construction waste are further disposed using landfills for inert materials, for stabilized residues or bioactive landfills. The quantities of C&DW for 2012 were determined using the available information provided by the Swiss Federal Office for the Environment’s (FOEN) 2001 and 2008 models. These models estimated the relevant construction waste flows originating from buildings, based on temporal changes of the building stock and indicators of construction activity (FOEN, 2001, 2008). From a total of 6.46 million metric tons (mio. t) of C&DW disposed from building work in Switzerland in 2012, 51% was recycled (3.3 mio. t), 26% went to landfill (1.7 mio. t), 8% was incinerated (0.49 mio. t), and 15% (0.97 mio. t) was re-used on-site (for more details see supplementary information, Section 2, Table S1). C&DW was classified into different categories, and each category included a set of different materials (Table 1).
2.3. Estimation of ENMs containing C&DW in Switzerland We describe the fate routes of the materials that are covered with paints. The fate of paints containing ENMs in construction waste depends entirely on the fate of the material to which they were applied. Paints in construction are usually applied to stone surfaces; additionally, cement and gypsum plasters are used to cover both the interior and exterior walls of buildings, and are then usually painted in a successive stage. Thus, these waste materials also correspond to the ‘‘mixed demolition’’ category (Table 1). We also allocated the application of paints on concrete surfaces, wood, metallic surfaces (ferrous metals) and plastic (‘‘combustible waste’’ category).
Table 1 Construction and demolition waste (C&DW) categories originating from buildings (FOEN, 2001, 2008). C&DW group
Materials
Road construction waste Asphalt Concrete demolition Mixed demolition
Sand, gravel, other road construction waste
Combustible waste Wood Metalsc Mineral fraction Mixed C&DW
Asphalt Concrete, cementa Breakage, brick masonry, artificial & natural stone (facades also covered with plasters), architectural membranesa, coatings & paintsa ‘‘New’’ insulationb, ‘‘old’’ insulation, plastics, textiles, paper, packaging, adhesivesa, sealantsa Construction, timber and residual wood Steel, light metals, aluminum, other metals (including steel)a Roofing materials, ceramics, stoneware, slag, gypsum, plaster, glass, windowsa Backfill (refilling with construction waste), flooring materiala,
a Applications added from the survey on ENMs in the construction sector in Switzerland. b ‘‘New’’ insulation materials include polystyrene as well as mineral wool, foam, glass, etc. c Includes iron armoring.
Table 2 Fate of C&DW from the most relevant ENM containing construction applications used in the Swiss construction industry. Applicationsa
Paints On stone surfaces (walls or facades of buildings, also covered with plaster) On concrete On wood On window glass On ferrous metals On non-ferrous metals On plastics
Fate
b
REC
WIP
LF
Exported
0.77
0
0.23
0
0.90 0.10 0.03 0.98 0 0.28
0 0.90 0 0 0 0.64
0.10 0 0.97 0.02 0.02 0.08
0 0 0 0 0.98 0.00
a Sources: According to the waste categories given in Table 1, we assumed that paints are applied on the mentioned surfaces. The waste classification is taken from FOEN (2001) and FOEN (2008). b Fate routes: to recycling, REC; to waste incineration plant, WIP; to landfill, LF. Data estimated from FOEN (2001, 2008) and Caballero-Guzman et al. (2015).
The values in Table 2 represent the fate of construction materials (i.e. in this case of paints) that might contain ENMs during the end-of-life stage of their life cycle. We calculated these transfer coefficients (i.e. the fate, based on temporal changes of the building stock and indicators of construction activity (FOEN, 2001, 2008)) by dividing the amount of waste allocated per category (i.e., REC, WIP, LF, Exported) by the total amount of waste per application produced in 2012 (FOEN, 2001, 2008) (see Table S1 in the supplementary information, Section 2). For the reason of simplicity and because of limited data availability, it was further assumed that the system was in a steady state (i.e. estimations for year 2012). In this case, the transfer coefficients of ENM contained in C&DW were the same for all ENMs according to the given allocation. Subsequently they were used to estimate the ENM flows within the Swiss system.
2.4. Nanomaterial flows originating from buildings to landfill and the environment To assess the flows of ENMs within the system, we used a bottom-up approach (i.e., beginning with existing knowledge about nano-products). This approach included the following steps: 1. Determine the quantities sold of each nano-application (market penetration) in the construction sector; 2. Estimate the ENM content of that application (ENM stock in the application) and, if necessary, the fraction of the material containing the nanomaterial (metal, wood, glass, cement, etc.); 3. Determine the fate of the fraction containing the nanomaterial, based on waste management regulations; 4. If possible, determine any potential release of ENMs from the waste treatments into technical or environmental compartments. Usually, materials and applications in buildings have long useful life, ranging from a couple of years (lightbulbs) to decades, or even centuries if we look at some historic constructions. Because of this, the nature of the present analysis is prospective. The dynamics of the system were not considered, but it is rather an estimation of how the ENMs currently present in the system will flow under the current legal and technological framework if they become waste. Using this semi-quantitative, bottom-up approach (i.e., combining data collected from the survey, market reports, and the fate of C&DW produced in Switzerland), the flows of ENM contained in paints were estimated through the Swiss waste system.
Please cite this article in press as: Hincapié, I., et al. Use of engineered nanomaterials in the construction industry with specific emphasis on paints and their flows in construction and demolition waste in Switzerland. Waste Management (2015), http://dx.doi.org/10.1016/j.wasman.2015.07.004
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We compared these results with those of a top-down approach used by Sun et al. (2014) (i.e., beginning the estimations with the total production amount of a specific ENM) to validate our approach, and to provide the best method to assess the ENM flows. The flows of different ENMs in C&DW were then calculated. Finally, we made a qualitative evaluation of the potential release of ENMs contained in paint residues from the technical and environmental compartments. 3. Results 3.1. Market survey Eighteen experts answered the questionnaire (30% return). An evaluation of online surveys concluded that the average response rate to such surveys was 32.5% (Hamilton, 2009), indicating that the response rate of this survey was reliable. Seventeen (94%) of all respondents answered the question, ‘‘Are ENMs used in the following products in Switzerland?’’ One person skipped the question. Their answers (see Fig. 1) indicated that ENMs are used most in coatings and paints (78% and 72%, respectively), followed by applications in solar panels (50%), flooring materials (44%), and then insulation material, sealants, and windows (39%). Three participants (17%) answered the question, ‘‘Which ENMs are used in the following products in Switzerland?’’ Nano-Ag was mentioned as used in many products, even for architectural membranes, pipes, and solar panels (Fig. 2). Answers indicated that all of the ENMs considered were used in paints, which were once again the most mentioned products. Paints were followed by flooring materials and windows, which use nano-TiO2, nano-SiO2, and nano-Ag. Fig. 2 also shows a distribution of the amounts of ENMs used in paints, with a larger relative share for TiO2 and ZnO than for SiO2 and Ag. According to these results and the data availability, we used the construction application paint and the following ENMs for our flow modeling: nano-TiO2, nano-SiO2, and nano-Ag. Other applications were not considered mainly due to the lack of information about the used amounts. Although solar panels were mentioned, their end-of-life is considered rather as WEEE (Waste Electrical and Electronic Equipment), therefore it does not belong to C&DW.
Fig. 2. ENMs used in construction products in Switzerland: based on survey replies to the question, ‘‘Which ENMs are used in the following products in Switzerland?’’.
3.2. Amounts of nanomaterials in construction materials In order to understand the construction business and estimate the amounts of ENMs used in Switzerland, we used 2012 market development data from the Swiss Association for the Lacquer and Paint Industry (VSLF, 2013). The paint market is divided into different application segments (i.e., paint and plaster products for construction, wood coatings, printing inks, wood preservatives and industrial coatings); the respective market distributions are shown in Table 3, column A. Indeed, the majority of paint industry sales revenue comes from the construction sector, however, as data about the volumes of paint sold in Switzerland were not available, amounts were estimated using a market study carried out by McCulloch (2012). This study analyzed the market behavior of the top 25 paint manufacturers in Europe in different regions. In
Table 3 Calculated and estimated quantity of paint containing ENMs sold in Switzerland (t/y), assuming a market penetration of 1% for 2012 (information was available only for this year). Application segment
Paint productsa and plasters for construction Wood coatings Othersb Total
A
B
C
Market distribution in Switzerland (%)
Amount of paints sold in Switzerlandc (td)
Nano-paint amount using 2012 market penetration of 1%e (t)
76.3
139,445
1394
3.3 20.4
6107 37,302
61 373
182,854
1829
100
a
Fig. 1. Number of positive answers to the question, ‘‘Are ENMs used in the following products in Switzerland?’’.
Paint products for construction include indoor and outdoor paints and other types of coatings. b Other application segments include printing inks, wood preservatives, and industrial coatings. c Estimation based on GDP PPP data per capita, the conversion factor from EMEA to Switzerland was 0.0121. d Density of paint is assumed to be 1.5 kg/L according to ISO (2011) and several product data sheets for paints. e 1% based on our survey results and the findings from van Broekhuizen and van Broekhuizen (2009).
Please cite this article in press as: Hincapié, I., et al. Use of engineered nanomaterials in the construction industry with specific emphasis on paints and their flows in construction and demolition waste in Switzerland. Waste Management (2015), http://dx.doi.org/10.1016/j.wasman.2015.07.004
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the combined Europe, Middle East, and Africa region (EMEA), 9860 million liters (mio. L) of paint were sold in 2012 (McCulloch, 2012). Based on this information and on the gross domestic product at purchasing power parity (GDP PPP) per capita (World-Bank, 2012), we adjusted overall EMEA sales to Switzerland and estimated the size of the Swiss paint market in 2012 to be 45 mio. L. This volume was distributed proportionately to the Swiss market’s segmentation for different paint applications to obtain the amount of paints sold (in t) to Switzerland’s construction sector (Table 3, column B). We estimated an amount of 139,000 t of paints. According to Burkhardt and Dietschweiler (2013), the Swiss paint market is assumed to be 10 times smaller than the German market (based on statistics by VdL (2012), i.e., 90,000 t of paints and plaster—i.e., gypsum, stucco, or a mixture of them—for construction sold in Switzerland). These values are comparable despite the fact that there are large market uncertainties and different density values for paints (i.e., according to the paint type, the density varies from 0.9 up to 1.5 kg/L). Here, we used the upper value of 139,000 t for the flow estimations. For wood coatings (Burkhardt and Dietschweiler, 2013) who based their study on VdL (2012), reported almost the same value as that estimated in the present study (i.e., 6200 t). To estimate the quantities of nano-paint sold in Switzerland (Table 3, column C), we used an estimated of 1% market penetration in 2012. This assumption, however, agrees with the findings by van Broekhuizen and van Broekhuizen (2009), who showed that actual market penetration was still low and limited to a few niche products that are only applied upon request. A low market penetration for nano-products was also reported in our survey. Using this analysis, we estimated the amount of paints (in t) containing ENMs sold in Switzerland in 2012. The next step was to collect information on nanoparticle content in paint. We used the values reported in Table 3, column C, and the mass contents of different ENMs that are reported for paints: nano-TiO2, 3 wt%; nano-SiO2, 5 wt%; nano-ZnO, 1 wt%; and nano-Ag, around 0.1 wt% (Al-Kattan et al., 2013; Hischier et al., 2015; NanoHouse, 2013). The same ranges of mass content were reported in the present study’s survey (1–5 wt% was reported for nano-TiO2 and nano-SiO2, and less than 0.1 wt% for nano-Ag). To obtain a more realistic scenario, we used the distribution of ENM amounts used in paints from our survey (see Fig. 2) (nano-TiO2 and nano-ZnO (33.3%), and for nano-SiO2 and nano-Ag (16.7%)). Combining this information for 2012, we were able to estimate the different total nano-content of paints (Table 4) for each separate nanomaterial: nano-TiO2, nano-SiO2, nano-ZnO, or nano-Ag. We compared the amounts of ENMs in paints obtained for Switzerland in 2012 by our bottom-up estimation (i.e., takes into account the data on amounts of nano-applications) with a top-down approach (i.e., takes into account the total production data of a specific ENM) published by Sun et al. (2014) (Table 5).
Table 4 Estimated distribution of the amount of ENMs (t/y) used in paints, considering the distribution of the various ENMs according to our survey. Application segment
Amount of ENMsa in paint in 2012 (t/y) TiO2
SiO2
ZnO
Ag
Paint products and plasters for construction Wood coatings Others
14 – n.a.
12 – n.a.
5 – n.a.
0.2 0.01 n.a.
Total
14
12
5
0.2
(–), ENMs were not used in the application segment. n.a., data not available. a The ENM mass content used were: nano-TiO2, 3 wt%; nano-SiO2, 5 wt%; nanoZnO, 1 wt%; and nano-Ag, 0.1 wt%.
Table 5 Amount of ENMs in paint in Switzerland based on the top-down approach by Sun et al. (2014), and comparison with the weights calculated in this study. Sun et al. (2014)
This study
Amount of ENM paint in CH (t)
ENM share of paint weight
Amount of ENMs in paint in CH (t)
Estimated amount of ENMs in paint in CH (t)
Nano-TiO2 Nano-ZnO Nano-Ag Nano-SiO2 Others
337 48.4 1.1 n.a. 13.3
8.9% 14.3% 3% n.a. 1%
30 7 0.03 n.a. 0.2
14 5 0.2 12 n.a.
Total
400
28%
37
31
This comparison showed that the estimated ENM masses in paints obtained in this study using a bottom-up approach are in the same order of magnitude as the top-down estimates by Sun et al. (2014) , except for nano-Ag, which is 7 times higher in our estimate. Nano-Ag was the most frequently mentioned nanomaterial in our survey (56% of the answers; it was even mentioned as used for pipes, windows, and solar panels), yet its use seems to have been overestimated. In contrast, the French Agency for Food, Environmental and Occupational Health and Safety (ANSES, 2013) reported that between 0.1 and 1 kg/y nano-Ag was used in France, and this mainly for scientific purposes. Burkhardt et al. (2009) and Kemper (2008) reported an amount of
Contents lists available at ScienceDirect
Waste Management journal homepage: www.elsevier.com/locate/wasman
Use of engineered nanomaterials in the construction industry with specific emphasis on paints and their flows in construction and demolition waste in Switzerland Ingrid Hincapié a, Alejandro Caballero-Guzman a, David Hiltbrunner b, Bernd Nowack a,⇑ a b
EMPA, Swiss Federal Laboratories for Materials Science and Technology, Technology and Society Laboratory, Lerchenfeldstrasse 5, CH-9014 St. Gallen, Switzerland FOEN, Swiss Federal Office for the Environment, Waste and Resources Division, Worblentalstrasse 68, CH-3063 Ittigen, Switzerland
a r t i c l e
i n f o
Article history: Received 27 January 2015 Revised 30 June 2015 Accepted 2 July 2015 Available online xxxx Keywords: Engineered nanomaterials Construction and demolition waste Recycling Landfills Paints Material flow modeling
a b s t r a c t One sector where the use of engineered nanomaterials (ENMs) is supposed to offer novel or improved functionalities is the construction industry. During the renovation or demolition of buildings, ENMs contained in former construction materials will enter recycling systems or become construction waste. Currently, information about ENM flows in these processes is insufficient. The potential for the release of ENMs from this waste into the environment is unknown, as are the environmental impacts. To evaluate whether there is currently any nano-relevant construction and demolition waste (C&DW) originating from buildings, we evaluated the sources and flows of ENMs in C&DW and identified their potential exposure pathways. A survey of business representatives of Swiss companies in this sector found that ENMs are mainly used in paints and cement. The most frequently used ENMs in the Swiss housing construction industry are nano-TiO2, nano-SiO2, nano-ZnO, and nano-Ag. Using a bottom-up, semi-quantitative approach, we estimated the flows of ENMs contained in paints along the product’s life cycle from buildings to recycling and landfill. The flows of ENMs are determined by their associated flows of building materials. We estimated an annual amount of ENMs used in paints of 14 t of TiO2, 12 t of SiO2, 5 t of ZnO, and 0.2 t of Ag. The majority of ENMs contained in paints in Switzerland enter recycling systems (23 t/y), a smaller amount is disposed directly in landfills (7 t/y), and a tiny fraction of ENM waste is incinerated (0.01 t/y). Our results allow a qualitative determination of the potential release of ENMs into technical or environmental compartments, with the highest potential release expected during recycling. Ó 2015 Elsevier Ltd. All rights reserved.
1. Introduction The construction sector requires products like cement, steel, paints, insulation materials, window glass, and many others. The quest for sustainable development, including the construction of greener buildings, influences innovation and encourages the use of products exploiting the unique properties of nanomaterials. Engineered nanomaterials (ENMs) are used either to improve the quality of existing conventional products or to create completely novel products, functionalities, and applications. For instance ENMs tested in cement include SiO2, Al2O3, Fe2O3, ZrO2 and CNT (van Broekhuizen et al., 2011), they are used mainly to improve the quality and longevity of structures (Hanus and Harris, 2013). In insulation materials, nano-SiO2 (aerogel) is used as a noise barrier and for heat loss reduction (Jelle et al., 2012). Properties such ⇑ Corresponding author. E-mail address: [email protected] (B. Nowack).
as easy-clean, antibacterial, scratch resistance, fire retardant, UV-protection, wood preservation and anti-corrosion can be introduced or improved in paints and coatings using the following ENMs: Ag, CeO2, CNT, Fe2O3, SiO2, TiO2, ZnO (Hanus and Harris, 2013; Kaiser et al., 2013b; Lee et al., 2010a; Teizer et al., 2012; van Broekhuizen and van Broekhuizen, 2009). In windows, ENMs such as SiO2, TiO2 are used for anti-reflection, anti-fogging, heat loss reduction and easy-clean properties (Lee et al., 2010b). However, most of the potential applications for ENMs (e.g. concrete, asphalt or insulation materials) have not yet reached large-scale commercial production, and rather represent niche market segments (van Broekhuizen and van Broekhuizen, 2009). In some cases, applications containing ENMs have only been developed on a pilot scale or are only to be found as experimental results in the scientific literature. Reasons for the limited spread of nano-applications include their high prices compared to conventional products, uncertainties related to their safety, and uncertainties related to their technical performance (van Broekhuizen
http://dx.doi.org/10.1016/j.wasman.2015.07.004 0956-053X/Ó 2015 Elsevier Ltd. All rights reserved.
Please cite this article in press as: Hincapié, I., et al. Use of engineered nanomaterials in the construction industry with specific emphasis on paints and their flows in construction and demolition waste in Switzerland. Waste Management (2015), http://dx.doi.org/10.1016/j.wasman.2015.07.004
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et al., 2011). In the near future, it is presumed that nanotechnology applications will help the construction sector to reach the following goals (Hanus and Harris, 2013; Kaiser et al., 2013b; Lee et al., 2010a; Teizer et al., 2012; van Broekhuizen and van Broekhuizen, 2009): development of stronger concrete structures; generation of healthier environments; protection of structural appearance and durability; and reduction of energy consumption and other resource use. According to van Broekhuizen et al. (2011), the current applications of ENMs in Europe’s construction sector are mainly in cement (concrete’s basic additives), paints, and insulation materials. These authors also reported that nano-TiO2, nano-ZnO, nano-Al2O3, and nano-SiO2 were the predominant ENMs used in construction materials and that there was no evidence of the current use of carbon nanotubes (CNTs). However, further investigations showed that CNTs are potential candidates for enhancing the mechanical properties of cement-based materials and their resistance to crack propagation while providing such novel properties as electromagnetic field shielding and self-sensing (Sanchez and Sobolev, 2010). Silica fume is used in cement mainly to improve the quality and durability of structures (Hanus and Harris, 2013). However, the costs associated to the nanomaterial production process and the special equipment required to handle it make the cement more expensive than conventional types (van Broekhuizen and van Broekhuizen, 2009). The paint and coating industry has successfully adopted nanotechnology (Evans et al., 2008; Kaiser et al., 2013b). Although there is an ongoing debate about whether or not the expected benefits of nanomaterials in these applications will materialize in the long run (Kaiser et al., 2013b), it is estimated that paints and coatings currently represent the biggest market for nanotechnology in the construction industry (NanoHouse, 2013; van Broekhuizen et al., 2011). Although official recommendations on the definition of nanomaterials (i.e. at least 50% of the particles must be in the size range of 1–100 nm) were just published (EU-Commission, 2011), nanomaterials have been produced and used before the development of nanotechnology industries as we know them today, for instance, SiO2 (Bosch et al., 2012), nano-Ag (Nowack et al., 2011), and carbon black (CB). In some cases, therefore, it may be difficult to confirm whether a given product contains nanomaterials or not. In some of these substances, e.g., SiO2 or CB, primary nanoparticles of less than 100 nm are fused together into aggregates of more than 100 nm. Because EU definitions are based on primary particle size, these substances are now considered nanomaterials although they have been considered and used as conventional materials for many decades. Despite the aforementioned benefits of integrating ENMs into construction materials, concerns about their use still remain open, including their effects on environmental and human health following potential release to air, water and soil. The currently available information makes it possible to quantify the flows of nanomaterials and to evaluate their potential releases during the whole products life cycle. A study by Müller et al. (2013) analyzed the flows of ENMs in the waste flows. The results provided the first estimate of the amount of ENMs in waste streams in Switzerland. The modeling suggested that an important flow of nanomaterials goes directly from construction waste into landfills and indirectly from waste incineration plants to the landfills as bottom ash. Based on that work and the Swiss waste management system regulations, the present study aimed to investigate what amounts of nanomaterials exist in the C&DW flows originating from buildings in Switzerland (i.e. we did not considered C&DW from roads, underground constructions and hazardous construction waste), and to analyze whether there is currently any nano-relevance in construction waste. We estimated the flow of ENMs in waste originating
from building construction, renovations, and demolitions as well as the potential release of ENMs during recycling, with focus on paint applications. On one hand, paints appeared to be the most important application containing ENMs in the construction sector. On the other hand, only for this application enough data was available to carry out a quantitative modeling. The steps performed in this estimation were: 1. Collect data on sources of ENMs and flows of C&DW to landfill, waste incineration, and recycling, within the Swiss waste management system. 2. Estimate the current amounts of nanomaterials in Swiss C&DW originating from buildings. 3. Model ENM flows from buildings to landfill and the environment, according to the Swiss waste management system. 4. Evaluate the potential release of nanomaterials based on studies on ENMs release. Only data for 2012 were available and collected for the application paint. Subsequently, we focused on the following nanomaterials: TiO2, SiO2, ZnO, and Ag, which are the ENMs most used in paints for the construction industry. 2. Materials and methods 2.1. Data collection To obtain information about ENM applications and the amounts used in the Swiss construction industry, we surveyed a group of expert representatives from companies in this sector. The survey questionnaire was designed using the Internet-based platform, Surveymonkey, and was sent out to 60 construction sector experts between February 12 and March 13, 2014. The questionnaire asked for estimates of ENM use in the Swiss construction industry (i.e., use/non-use of nanomaterials, market sizes, and shares and amounts of ENM used in different construction materials). The specific questions of the survey are shown in the supplementary information, Section 1. Questions were specifically related to the use of nano-TiO2, nano-SiO2, nano-ZnO, nano-Ag, nano-CuO, and nano-CuCO3, and to the following materials used in the construction sector: adhesives, architectural membranes, asphalt, cement, coatings, flooring materials, geosynthetic barriers, insulation materials, paints, pipes, sealants, solar panels, steel, other metals, windows, and wood. Besides our survey, additional information on the mass content of ENMs in construction applications (i.e. stocks of ENMs in the applications) was taken from Hischier et al. (2015), NanoHouse (2013) and van Broekhuizen et al. (2011), as well as from official registrations of nanomaterials (ANSES, 2013) where paints and cement were the main applications. In order to estimate the amount of paint containing ENMs sold in Switzerland, this information was complemented by data from the 2012 market reports of the Swiss Association for the Lacquer and Paint Industry, and other sources (Burkhardt and Dietschweiler, 2013; McCulloch, 2012; VdL, 2012; VSLF, 2013). As a result, the market data (i.e. sold amounts in 2012) of paint in Switzerland are the base data for our modeling. 2.2. Disposal and amounts of C&DW in Switzerland According to the Swiss waste management system, C&DW is generated from the changes in infrastructure stocks (i.e., buildings, roads and underground constructions), and it also includes hazardous construction waste. For this study, we only considered the C&DW originated from buildings. According to the Swiss waste
Please cite this article in press as: Hincapié, I., et al. Use of engineered nanomaterials in the construction industry with specific emphasis on paints and their flows in construction and demolition waste in Switzerland. Waste Management (2015), http://dx.doi.org/10.1016/j.wasman.2015.07.004
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regulation, C&DW is coded with number 17 (UVEK, 2010). The final disposal of construction waste in Switzerland is regulated by the technical ordinance on waste (TVA, 2011). The waste treatments options are: direct recycling, sorting/collection, recycling (REC); waste incineration plant (WIP); landfill (LF) and export. For instance, mineral construction waste is mainly re-used on-site or treated and transformed to recycling products. Combustible parts of the construction waste must be incinerated. The residues generated during recycling and treatment processes of C&DW as well as overcapacities of construction waste are further disposed using landfills for inert materials, for stabilized residues or bioactive landfills. The quantities of C&DW for 2012 were determined using the available information provided by the Swiss Federal Office for the Environment’s (FOEN) 2001 and 2008 models. These models estimated the relevant construction waste flows originating from buildings, based on temporal changes of the building stock and indicators of construction activity (FOEN, 2001, 2008). From a total of 6.46 million metric tons (mio. t) of C&DW disposed from building work in Switzerland in 2012, 51% was recycled (3.3 mio. t), 26% went to landfill (1.7 mio. t), 8% was incinerated (0.49 mio. t), and 15% (0.97 mio. t) was re-used on-site (for more details see supplementary information, Section 2, Table S1). C&DW was classified into different categories, and each category included a set of different materials (Table 1).
2.3. Estimation of ENMs containing C&DW in Switzerland We describe the fate routes of the materials that are covered with paints. The fate of paints containing ENMs in construction waste depends entirely on the fate of the material to which they were applied. Paints in construction are usually applied to stone surfaces; additionally, cement and gypsum plasters are used to cover both the interior and exterior walls of buildings, and are then usually painted in a successive stage. Thus, these waste materials also correspond to the ‘‘mixed demolition’’ category (Table 1). We also allocated the application of paints on concrete surfaces, wood, metallic surfaces (ferrous metals) and plastic (‘‘combustible waste’’ category).
Table 1 Construction and demolition waste (C&DW) categories originating from buildings (FOEN, 2001, 2008). C&DW group
Materials
Road construction waste Asphalt Concrete demolition Mixed demolition
Sand, gravel, other road construction waste
Combustible waste Wood Metalsc Mineral fraction Mixed C&DW
Asphalt Concrete, cementa Breakage, brick masonry, artificial & natural stone (facades also covered with plasters), architectural membranesa, coatings & paintsa ‘‘New’’ insulationb, ‘‘old’’ insulation, plastics, textiles, paper, packaging, adhesivesa, sealantsa Construction, timber and residual wood Steel, light metals, aluminum, other metals (including steel)a Roofing materials, ceramics, stoneware, slag, gypsum, plaster, glass, windowsa Backfill (refilling with construction waste), flooring materiala,
a Applications added from the survey on ENMs in the construction sector in Switzerland. b ‘‘New’’ insulation materials include polystyrene as well as mineral wool, foam, glass, etc. c Includes iron armoring.
Table 2 Fate of C&DW from the most relevant ENM containing construction applications used in the Swiss construction industry. Applicationsa
Paints On stone surfaces (walls or facades of buildings, also covered with plaster) On concrete On wood On window glass On ferrous metals On non-ferrous metals On plastics
Fate
b
REC
WIP
LF
Exported
0.77
0
0.23
0
0.90 0.10 0.03 0.98 0 0.28
0 0.90 0 0 0 0.64
0.10 0 0.97 0.02 0.02 0.08
0 0 0 0 0.98 0.00
a Sources: According to the waste categories given in Table 1, we assumed that paints are applied on the mentioned surfaces. The waste classification is taken from FOEN (2001) and FOEN (2008). b Fate routes: to recycling, REC; to waste incineration plant, WIP; to landfill, LF. Data estimated from FOEN (2001, 2008) and Caballero-Guzman et al. (2015).
The values in Table 2 represent the fate of construction materials (i.e. in this case of paints) that might contain ENMs during the end-of-life stage of their life cycle. We calculated these transfer coefficients (i.e. the fate, based on temporal changes of the building stock and indicators of construction activity (FOEN, 2001, 2008)) by dividing the amount of waste allocated per category (i.e., REC, WIP, LF, Exported) by the total amount of waste per application produced in 2012 (FOEN, 2001, 2008) (see Table S1 in the supplementary information, Section 2). For the reason of simplicity and because of limited data availability, it was further assumed that the system was in a steady state (i.e. estimations for year 2012). In this case, the transfer coefficients of ENM contained in C&DW were the same for all ENMs according to the given allocation. Subsequently they were used to estimate the ENM flows within the Swiss system.
2.4. Nanomaterial flows originating from buildings to landfill and the environment To assess the flows of ENMs within the system, we used a bottom-up approach (i.e., beginning with existing knowledge about nano-products). This approach included the following steps: 1. Determine the quantities sold of each nano-application (market penetration) in the construction sector; 2. Estimate the ENM content of that application (ENM stock in the application) and, if necessary, the fraction of the material containing the nanomaterial (metal, wood, glass, cement, etc.); 3. Determine the fate of the fraction containing the nanomaterial, based on waste management regulations; 4. If possible, determine any potential release of ENMs from the waste treatments into technical or environmental compartments. Usually, materials and applications in buildings have long useful life, ranging from a couple of years (lightbulbs) to decades, or even centuries if we look at some historic constructions. Because of this, the nature of the present analysis is prospective. The dynamics of the system were not considered, but it is rather an estimation of how the ENMs currently present in the system will flow under the current legal and technological framework if they become waste. Using this semi-quantitative, bottom-up approach (i.e., combining data collected from the survey, market reports, and the fate of C&DW produced in Switzerland), the flows of ENM contained in paints were estimated through the Swiss waste system.
Please cite this article in press as: Hincapié, I., et al. Use of engineered nanomaterials in the construction industry with specific emphasis on paints and their flows in construction and demolition waste in Switzerland. Waste Management (2015), http://dx.doi.org/10.1016/j.wasman.2015.07.004
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We compared these results with those of a top-down approach used by Sun et al. (2014) (i.e., beginning the estimations with the total production amount of a specific ENM) to validate our approach, and to provide the best method to assess the ENM flows. The flows of different ENMs in C&DW were then calculated. Finally, we made a qualitative evaluation of the potential release of ENMs contained in paint residues from the technical and environmental compartments. 3. Results 3.1. Market survey Eighteen experts answered the questionnaire (30% return). An evaluation of online surveys concluded that the average response rate to such surveys was 32.5% (Hamilton, 2009), indicating that the response rate of this survey was reliable. Seventeen (94%) of all respondents answered the question, ‘‘Are ENMs used in the following products in Switzerland?’’ One person skipped the question. Their answers (see Fig. 1) indicated that ENMs are used most in coatings and paints (78% and 72%, respectively), followed by applications in solar panels (50%), flooring materials (44%), and then insulation material, sealants, and windows (39%). Three participants (17%) answered the question, ‘‘Which ENMs are used in the following products in Switzerland?’’ Nano-Ag was mentioned as used in many products, even for architectural membranes, pipes, and solar panels (Fig. 2). Answers indicated that all of the ENMs considered were used in paints, which were once again the most mentioned products. Paints were followed by flooring materials and windows, which use nano-TiO2, nano-SiO2, and nano-Ag. Fig. 2 also shows a distribution of the amounts of ENMs used in paints, with a larger relative share for TiO2 and ZnO than for SiO2 and Ag. According to these results and the data availability, we used the construction application paint and the following ENMs for our flow modeling: nano-TiO2, nano-SiO2, and nano-Ag. Other applications were not considered mainly due to the lack of information about the used amounts. Although solar panels were mentioned, their end-of-life is considered rather as WEEE (Waste Electrical and Electronic Equipment), therefore it does not belong to C&DW.
Fig. 2. ENMs used in construction products in Switzerland: based on survey replies to the question, ‘‘Which ENMs are used in the following products in Switzerland?’’.
3.2. Amounts of nanomaterials in construction materials In order to understand the construction business and estimate the amounts of ENMs used in Switzerland, we used 2012 market development data from the Swiss Association for the Lacquer and Paint Industry (VSLF, 2013). The paint market is divided into different application segments (i.e., paint and plaster products for construction, wood coatings, printing inks, wood preservatives and industrial coatings); the respective market distributions are shown in Table 3, column A. Indeed, the majority of paint industry sales revenue comes from the construction sector, however, as data about the volumes of paint sold in Switzerland were not available, amounts were estimated using a market study carried out by McCulloch (2012). This study analyzed the market behavior of the top 25 paint manufacturers in Europe in different regions. In
Table 3 Calculated and estimated quantity of paint containing ENMs sold in Switzerland (t/y), assuming a market penetration of 1% for 2012 (information was available only for this year). Application segment
Paint productsa and plasters for construction Wood coatings Othersb Total
A
B
C
Market distribution in Switzerland (%)
Amount of paints sold in Switzerlandc (td)
Nano-paint amount using 2012 market penetration of 1%e (t)
76.3
139,445
1394
3.3 20.4
6107 37,302
61 373
182,854
1829
100
a
Fig. 1. Number of positive answers to the question, ‘‘Are ENMs used in the following products in Switzerland?’’.
Paint products for construction include indoor and outdoor paints and other types of coatings. b Other application segments include printing inks, wood preservatives, and industrial coatings. c Estimation based on GDP PPP data per capita, the conversion factor from EMEA to Switzerland was 0.0121. d Density of paint is assumed to be 1.5 kg/L according to ISO (2011) and several product data sheets for paints. e 1% based on our survey results and the findings from van Broekhuizen and van Broekhuizen (2009).
Please cite this article in press as: Hincapié, I., et al. Use of engineered nanomaterials in the construction industry with specific emphasis on paints and their flows in construction and demolition waste in Switzerland. Waste Management (2015), http://dx.doi.org/10.1016/j.wasman.2015.07.004
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the combined Europe, Middle East, and Africa region (EMEA), 9860 million liters (mio. L) of paint were sold in 2012 (McCulloch, 2012). Based on this information and on the gross domestic product at purchasing power parity (GDP PPP) per capita (World-Bank, 2012), we adjusted overall EMEA sales to Switzerland and estimated the size of the Swiss paint market in 2012 to be 45 mio. L. This volume was distributed proportionately to the Swiss market’s segmentation for different paint applications to obtain the amount of paints sold (in t) to Switzerland’s construction sector (Table 3, column B). We estimated an amount of 139,000 t of paints. According to Burkhardt and Dietschweiler (2013), the Swiss paint market is assumed to be 10 times smaller than the German market (based on statistics by VdL (2012), i.e., 90,000 t of paints and plaster—i.e., gypsum, stucco, or a mixture of them—for construction sold in Switzerland). These values are comparable despite the fact that there are large market uncertainties and different density values for paints (i.e., according to the paint type, the density varies from 0.9 up to 1.5 kg/L). Here, we used the upper value of 139,000 t for the flow estimations. For wood coatings (Burkhardt and Dietschweiler, 2013) who based their study on VdL (2012), reported almost the same value as that estimated in the present study (i.e., 6200 t). To estimate the quantities of nano-paint sold in Switzerland (Table 3, column C), we used an estimated of 1% market penetration in 2012. This assumption, however, agrees with the findings by van Broekhuizen and van Broekhuizen (2009), who showed that actual market penetration was still low and limited to a few niche products that are only applied upon request. A low market penetration for nano-products was also reported in our survey. Using this analysis, we estimated the amount of paints (in t) containing ENMs sold in Switzerland in 2012. The next step was to collect information on nanoparticle content in paint. We used the values reported in Table 3, column C, and the mass contents of different ENMs that are reported for paints: nano-TiO2, 3 wt%; nano-SiO2, 5 wt%; nano-ZnO, 1 wt%; and nano-Ag, around 0.1 wt% (Al-Kattan et al., 2013; Hischier et al., 2015; NanoHouse, 2013). The same ranges of mass content were reported in the present study’s survey (1–5 wt% was reported for nano-TiO2 and nano-SiO2, and less than 0.1 wt% for nano-Ag). To obtain a more realistic scenario, we used the distribution of ENM amounts used in paints from our survey (see Fig. 2) (nano-TiO2 and nano-ZnO (33.3%), and for nano-SiO2 and nano-Ag (16.7%)). Combining this information for 2012, we were able to estimate the different total nano-content of paints (Table 4) for each separate nanomaterial: nano-TiO2, nano-SiO2, nano-ZnO, or nano-Ag. We compared the amounts of ENMs in paints obtained for Switzerland in 2012 by our bottom-up estimation (i.e., takes into account the data on amounts of nano-applications) with a top-down approach (i.e., takes into account the total production data of a specific ENM) published by Sun et al. (2014) (Table 5).
Table 4 Estimated distribution of the amount of ENMs (t/y) used in paints, considering the distribution of the various ENMs according to our survey. Application segment
Amount of ENMsa in paint in 2012 (t/y) TiO2
SiO2
ZnO
Ag
Paint products and plasters for construction Wood coatings Others
14 – n.a.
12 – n.a.
5 – n.a.
0.2 0.01 n.a.
Total
14
12
5
0.2
(–), ENMs were not used in the application segment. n.a., data not available. a The ENM mass content used were: nano-TiO2, 3 wt%; nano-SiO2, 5 wt%; nanoZnO, 1 wt%; and nano-Ag, 0.1 wt%.
Table 5 Amount of ENMs in paint in Switzerland based on the top-down approach by Sun et al. (2014), and comparison with the weights calculated in this study. Sun et al. (2014)
This study
Amount of ENM paint in CH (t)
ENM share of paint weight
Amount of ENMs in paint in CH (t)
Estimated amount of ENMs in paint in CH (t)
Nano-TiO2 Nano-ZnO Nano-Ag Nano-SiO2 Others
337 48.4 1.1 n.a. 13.3
8.9% 14.3% 3% n.a. 1%
30 7 0.03 n.a. 0.2
14 5 0.2 12 n.a.
Total
400
28%
37
31
This comparison showed that the estimated ENM masses in paints obtained in this study using a bottom-up approach are in the same order of magnitude as the top-down estimates by Sun et al. (2014) , except for nano-Ag, which is 7 times higher in our estimate. Nano-Ag was the most frequently mentioned nanomaterial in our survey (56% of the answers; it was even mentioned as used for pipes, windows, and solar panels), yet its use seems to have been overestimated. In contrast, the French Agency for Food, Environmental and Occupational Health and Safety (ANSES, 2013) reported that between 0.1 and 1 kg/y nano-Ag was used in France, and this mainly for scientific purposes. Burkhardt et al. (2009) and Kemper (2008) reported an amount of
