Skip to main content

Leaching of nanoparticles from nano-enabled products for the protection of cultural heritage surfaces: a review


The development of highly innovative techniques and technologies to enhance performance and technical sustainability of materials used in the field of cultural heritage conservation is providing conservators with innovative nanocomposites materials, including protective coatings, by merging the performances of engineered nanoparticles (NPs) with conventional chemicals. However, the human health and environmental risks that may potentially arise from these new materials are still largely unknown, requiring an adequate assessment and management along their entire life cycle. Concerns could emerge due to the leaching of the material containing NPs or of the NPs alone, especially during their use (exposure of the treated object to, e.g., heavy or acid rain) and disposal (when the wasted product is processed in, e.g., waste water treatment plants). To date, no standard leaching test methods have been specifically developed for nano-enabled products, with the consequent lack of data on the NPs potential exposure also in the field of cultural heritage. Therefore, an extensive review over the last 10 years by querying to the Scopus database “nanoparticles”, “leaching” and “coatings” has been herein reported to clearly highlight (i) the standard test methods used or adapted to estimate the NPs leaching from nano-based coatings; (ii) the available studies in which the NPs leaching from nano-based coatings was estimated without following any specific standard test method; (iii) the works focusing on other nanocomposite materials performances than leaching, in which standard test methods were applied, potentially useful to indirectly estimate NPs leaching. All the information gathered by this bibliographic search have been used to identify the most promising leaching tests for NPs estimation to be applied in the field of cultural heritage, especially for both large, e.g., building façades, and small, e.g., bronze works of art, surface areas from which the leaching of nano-based materials could be significant in terms of human health and ecological risks, based also on the (eco)toxicity of the leachate. The derived information can thus ultimately support effective risk management of innovative nano-enabled products, including the implementation of Safe by Design approaches.


Regardless of their nature, movable and immovable cultural heritage assets, especially those located outdoors, are irremediably exposed to several degradation agents such as temperature, humidity, light, microorganisms and air pollutants, all accounting for the natural aging of art materials [1, 2]. In recent years, engineered nanoparticles (NPs), consisting of particles deliberately designed with all the three dimensions in size between 1 and 100 nm, are emerging as a successful solution for the preservation of cultural heritage because of their capability in enhancing performances, e.g., by improving transparency, resistance, cleaning and anti-microbial properties, ensuring greater durability of art materials [3]. Because of the variety and complexity of artistic and historical substrates, conservation science has explored different routes, developing several technical approaches for solving conservation issues. In the field of stone conservation, colloidal Ca(OH)2 is one of the most promising products for stone’s consolidation because it is easily converted into calcium carbonate (CaCO3) as result of carbonation when exposed to atmospheric CO2 under moist conditions [4]. Another example is provided by coatings incorporating SiO2 NPs for improving abrasion resistance and for adding hydrophobic properties to the stone surface [5, 6]. Both hydrophilic and hydrophobic silica are used in solvent-borne coatings to enhance the anti-settling additives for pigments [7]. The addition of Ag NPs to paints for outdoor applications on building façades, instead, determines an antimicrobial effect derived from the activity of silver [8], while photoactive TiO2 NPs are used to optimize the mechanical properties of the products and to give the paint self-cleaning properties through photocatalytic and hydrophilic properties [9]. The addition of zirconia NPs to coatings for metal substrates showed to remarkably improve their properties, such as strength and fracture toughness, wear resistance, hardness, chemical and corrosion resistance [10]. Recently, further innovative nano-based products for the conservation of movable and immovable property have been developed within H2020 projects such as NANORESTART (Grant agreement no: 646063) and NanoCathedral (Grant agreement no: 646178). Some examples from the NANORESTART project are nano-based fluids for undesired graffiti removal [11, 12], alkaline NP dispersions for restoration of alum-treated archaeological wood [13], layered double hydroxide nanocarriers in protecting bronze artworks [14] or nanocellulose-based materials for canvas consolidation [15, 16]. In addition, nanocomposite materials have been specifically developed in the field of stone protection within the NanoCathedral project [17, 18].

However, similarly to other market sectors benefitting from nanotechnology innovation, the design and use of nano-enabled products in the conservation field raise issues concerning human health and environmental risks that could emerge from exposure to NPs embedded in conservation products and into innovative materials used in the construction field and that need to be carefully assessed to satisfy current European regulatory provisions. According to the revision of Annexes of the EU REACH regulation with regards to nanomaterials, effective from the 1st of January 2020 [19], manufacturers and importers must register a nanomaterial if the total amount per year (including both nanoforms and potential bulk form) is above one tonne and submit a complete Chemical Safety Assessment (CSA) report if this quantity exceeds 10 tonnes. The CSA shall identify and describe the risks associated with the bulk form and the nanoform(s) along the life cycle of the substance and document that these risks are adequately controlled. Therefore, human and ecological exposure assessment requires the investigation of possible release scenarios of NPs along the life cycle of nano-enabled products, including: (1) release during NPs production; (2) release from the manufacturing processes of products containing NPs; (3) release into the environment during use (including release from the objects treated with such products), re-use and recycling of nano-enabled products, and (4) indirect release at the end-of-life stage as consequence of processes within wastewater treatment plants or waste incineration plants, to different environmental compartments (i.e. surface water, soil, air, and groundwater) [20]. In parallel, (eco)toxicological testing should also be carried out at each of the different stages of the life cycle, to provide information useful of real exposure scenarios.

On this regard, a recent review by Reyes-Estebanez et al. [21] collected numerous studies dealing with the impacts of the most used and widespread NPs in cultural heritage on biota at both the biochemical and organism levels for different environmental compartments.

Such data and information would also support the development of “green” or “Safe by Design” approaches, which are still in their infancy in the field of cultural heritage conservation [22, 23]. In particular, Semenzin et al. [23] recently proposed a sustainability framework implementing the Safe by Design concept to support product’s developers in the early steps of product development, with the aim to provide safer nano-formulations for conservation, while retaining their functionality. Such framework takes into account the current EU legislative context (i.e. CLP and REACH regulations) as well as the specific features of the innovation process in the cultural heritage conservation field, which demands a high interaction between the product developers and the restorers [24]. In detail, starting from the development of a nano-based formulation (step 1), the following main steps of the framework are the: screening hazard assessment (step 2); advanced hazard assessment (step 3); safety assessment (step 4) and, finally, sustainability assessment (step 5). While the hazard assessment in step 1 is mainly based on the EU CLP self-classification approach for health and environmental hazards of the mixture, step 2 can include computational (e.g., in silico models) as well as experimental [e.g., in vitro and in vivo (eco)toxicological tests] approaches according to an Integrated Testing Strategy (ITS), where information about relevant exposure scenarios for both human health (i.e. occupational and public health) and the environment (i.e. technical compartments such as waste systems and environmental compartments such as soil and water systems) along the life cycle of the innovative products should also be collected or generated. More specifically, in order to allow safety assessment (i.e. integration of risk assessment and risk control as required by the EU REACH regulation; (step 3), data/information on product degradation and/or release throughout their life cycle should be collected, to evaluate medium and long-term behaviour of nano-based products [9].

Indeed, NPs that reach the environment may be completely different from the materials originally produced by industry because of aging processes that may cause transformations [25, 26], making the monitoring and quantification of the NPs release highly challenging, especially when they are present at trace levels in environmental compartments (e.g., freshwater, soil) [27]. In this context, leaching tests could provide a valuable support to exposure assessment, particularly in the post-application phase of nano-enabled products, i.e. when the treated work of art is exposed to outdoor conditions (e.g., heavy rain) or the wasted product is processed in waste systems, and therefore NPs can reach the surrounding environment.

To the best of our knowledge, only recently the release of hazardous substances from nano-based products has been studied in depth. Froggett et al. [28] reviewed the literature on releases from solid, non-food commercial nanocomposites during use, disposal, or recycling, claiming that there is a paucity of data on release of NPs from solid nanocomposites under the five scenarios considered: machining, weathering, washing, contact and incineration. Among the 54 nanorelease studies identified, most of them detected only the particles from the matrix alone, followed by matrix debris embedding NPs. Far less frequently the added NPs entirely dissociated from the matrix were determined, and even more rarely dissolved ionic forms of the added NPs. Besides this review, Koivisto et al. [29] provided a library for nano-based products, calculating the quantitative NPs release from the literature. Following the approach suggested by Froggett et al. [28], the 96 peer-reviewed scientific publications identified by Koivisto and et al. [29] were divided into six groups: (1) thermosets; (2) thermoplastics; (3) coated surfaces; (4) sprays; (5) textiles; (6) other articles. The quantitative release was defined as “the amount of mass released from a nano-application under experimental setups (scenarios) that intend to simulate situations that result in the liberation of material, calculating it from the measured average concentration levels and volumes of immersion fluid or dilution air”. The authors underlined the lack of general available guidance to measure quantitative release under various release scenarios and called for developing systematic experimental methods to support hazard and exposure assessment of nano-based products.

In this context, the overarching objective of this review was to provide an analysis of the available leaching standard test methods already used for different nano-enabled products to support the environmental exposure assessment of NPs from innovative products employed for surface protection in cultural heritage conservation. In addition to standardized leaching test, non-standardized leaching procedures, as well as standard tests used to evaluate technical performances of nano-enabled products, have been collected and investigated, with the aim to provide all the procedures that can be suitable in the field of cultural heritage, where more sensitive substrates could require less invasive testing. This work can therefore contribute to the assessment of human health and ecological risks as well as to the implementation of Safe by Design approaches for effective risk management of innovative nano-enabled products, especially taking into account their use (application and post-application phases, including exposure of the treated object to heavy or acid rain or other weather conditions) and disposal (when the wasted product is processed, e.g., in waste water treatment plants).

Materials and methods—literature search approach

The leaching of hazardous substances from a material is often investigated under the broader topic of materials’ performances (e.g., assessment of hardness/flexibility, resistance to abrasion, resistance to a falling weight, adhesion, artificial weathering, release). The systematic search herein reported was performed by querying the Scopus database, from 2010 to present, using three broad search terms: nanoparticles, leaching, and coatings.

This analysis identified 930 documents, among which 53 relevant studies focus on NPs leaching from different nanocomposite materials, including nano-based paints and preservatives materials, nanoscale fillers as well as photocatalytic coatings, nanopigments and antibacterial nano-based products. The studies selected were divided into: (i) leaching tests of nano-enabled products in which standard methods (e.g., ISO and ASTM standards) have been applied or adapted; (ii) leaching tests from nano-enabled products without any standardized test methods; (iii) assessment of performances other than the direct assessment of leaching, useful to indirectly estimate the NPs leaching from nano-enabled products.

Results and discussion

The bibliographic search performed highlighted that no specific standard leaching test methods properly designed to estimate the NPs leaching from nano-enabled products are present in the literature. Nevertheless, all the outcomes potentially linked to this aim have been considered and discussed. The results of this literature analysis were divided into three tables: Table 1 includes seven studies in which four different standard leaching test methods were used, i.e. two for nano-based paints and coatings and two for nano-based wood preservatives; Table 2 lists 35 studies for evaluating leaching of NPs from products by using only standard preparation test methods but without any specific standard leaching test; Table 3 summarizes additional ten works, in which eight more standards for evaluating other nano-based materials’ performances than leaching have been applied and could be adapted for developing useful leaching tests in the field of cultural heritage. A schematic representation of the available methods is reported in Fig. 1.

Table 1 Studies including standard leaching testing methods for NPs estimation from nano-enabled products
Table 2 Studies with non-standardized procedures to estimate NPs leaching from nano-enabled products
Table 3 Studies evaluating other nano-based materials’ performances than leaching by standard test methods
Fig. 1

Schematic representation of the available test methods to investigate the leaching of NPs, divided by: standard leaching tests, non-standard leaching tests and other standards used to investigate the performances of materials that could be useful for the NPs’ leaching evaluation

Besides the standards already mentioned, other two standard leaching test methods for the determination of the release of dangerous substances from non-nano coatings and construction products have been considered and discussed.

Lastly, specific information from the studies listed in Table 1 on the estimated amount of species detected in the leachate has been collected in Additional file 1: Table S1.

Standardized testing to estimate NPs leaching from nanocomposite materials

Nano-based paints

The leaching of NPs from nano-based paints was assessed by following two standard tests, i.e. ISO 2812-2:2007 [30] on paints and varnishes, focusing on the determination of resistance to liquids by water immersion method and 12457-3:2002 [31], related to leaching of granular waste materials and sludges. The first standard leaching test was employed by Zuin et al. [9], Zhang et al. [26] and Lopez-Ortega et al. [32] while Zuin et al. [7] estimated the nano-based paint debris leaching according to the second one. In detail, both Zuin et al. [9] and Zhang et al. [26] investigated the leaching of TiO2, SiO2 and Ag NPs embedded in paints applied on fibre cement panels. Zuin et al. [9] adapted this standard method, collecting leachates after UV exposure (according to ISO 11507:2007 [33], currently revised by ISO 16474-1:2013 [34]) and Taber Abraser test (using ISO 7784-2:2006 [35]), by immersing ¾ of the length of the panels and with a surface/volume ratio equal to 2. Leachates were collected after 4, 8, 24, 120 h and analysed by inductively coupled plasma-optical emission spectroscopy (ICP-OES). After the water immersion test, a small amount of acetic acid was added to the leaching solution to simulate acid rain effect on coated panels. Surface degradation was investigated by transmission electron microscopy (TEM), energy dispersive X-ray analysis (EDX) and X-ray fluorescence (XRF). The results highlighted that only very little Si migration from SiO2 NPs-based paints occurred in these accelerated tests. With regard to TiO2 NPs-based paint and its reference based on bulk TiO2 pigment, it was observed that both paints released only very low amounts of Ti into the leachates during the immersion test, without any increase of Ti concentration over time and no TiO2 particles were identified in the leachate by TEM. As far as the Ag NPs-based paint, the Ag concentration from Ag NPs-based paint in leachates was below the detection limit of the ICP-OES (0.1 µg/l).

Zhang et al. [26] also applied ISO 2812-2:2007 standard [30] for determining the resistance of single-layer or multi-layer systems of coating materials to the effects of water by partial or full immersion, analysing the leachates after 100, 150, 200, 250, 300, 350, 400 and 500 h of weathering chamber. The role of pH on the releases was also investigated by varying the pH from 3 to 10. As far as weathering before obtaining leachates, EN 1062-11:2002 standard [36] was used for conditioning the samples before testing and ISO 11507:2007 standard [33] was followed for UV weathering. Particles size distribution of the leached NPs was evaluated by means of Dynamic Light Scattering (DLS) technique, the NPs’ release by inductively coupled plasma-mass spectrometry (ICP-MS), while scanning electron microscopy (SEM) and TEM were employed to identify size and shape of NPs in the matrix before and after leaching. The results obtained showed that the duration of weathering test and rainfall are more important in controlling the NPs’ release than the variation of pH.

The evaluation of SiO2 NPs leaching from paint debris was carried out by Zuin et al. [7], following 12457-3:2002 [31]. Polyvinyl chloride panels were coated with different paints containing the same amount of SiO2 NPs, but different pigment volume concentrations and different amount and type of binder and pigment. After 24 h of drying in indoor environment, paints were taken off from panels and mechanically milled until a fine powder in the range of approx. 100 μm to a few mm was obtained. The leaching test involved approx. 300 g d.w. of paint debris added into a high-density polyethylene bottle. Deionized water (DW) was used to obtain a liquid-to-solid (L/S) ratio of 2:1 and of 8:1 (cumulative L/S of 10:1). The mixture at L/S of 2:1 was shaken by end-over-end rotation at 10 rotation per minute (rpm) for 6 h, while the mixture at L/S of 8:1 was agitated for 18 h. The supernatant was collected for analysis after 24 h of agitation, filtered at 0.45 μm under vacuum on a standard cellulose nitrate filter and acidified (1% v/v) to determine the “dissolved” SiO2 by ICP-MS according to ISO 17294-2:2003 standard [37]. Total Si was also quantified via acidification with nitric acid of unfiltered samples. Following the procedure of the standards method 2540C of the American Public Health Association, both total dissolved solids and total suspended solids were also determined. The NPs detection was carried out by TEM–EDX. The main outcomes of this study were that: (i) the Si leached out was 1.8% with respect to the initial amount of Si in paint; (ii) some agglomerates of SiO2 NPs were detected in some leachates; (iii) the pigment volume concentration is a crucial factor for SiO2 NPs leaching, and (iv) by balancing the binder to pigment ratio, it would be possible to reduce the SiO2 NPs leaching.

Within the field of antifouling paints for offshore structures, Lopez-Ortega et al. [32] compared the water resistance of an aluminium layer treated with Carboguard® epoxy mastic coating with one coated with a product functionalized by NPs. The evaluation of water resistance was assessed according to several standards, such as ISO 6270-2:2018 [38] on water condensation test, ISO 9227:2017 [39] on salt-fog test and ISO 4628 1-5:2016 [40] on the evaluation of degradation of coatings, including the ISO 2812-2:2007 [30] on leaching test. In detail, an organic topcoat paint was functionalized with a SiO2 NPs dispersion to enhance hydrophobicity and with three different biocides, including Cu2O NPs. Briefly, the panels were immersed in 1 l of synthetic seawater and stirred over 28 days. Unlike the first two studies, here the NPs leaching was assessed only indirectly by determining the release rate of copper and other main elements present in the painted samples by ICP-OES every 24 h. After this step, a set of new samples was tested under the same experimental conditions, till reaching the plateau of copper maximum release. The leaching results highlighted the presence of Si and negligible Cu release for both original and nano-based topcoat paints, with the silicon content in the modified paint decreasing with time to lower values than those of the original paint at the end of the test. Following the marine algal growth inhibition test (ISO 10253 [41]), in accordance with the OECD Guidance Document no: 23 [42], the ecotoxicity assessment with the algae Phaeodactylum tricornutum showed a toxicity level of the leachate which fulfilled the legislation requirements for modified nano-based paint and lower than that of the bulk material.

Wood preservatives

Two different standard test methods for NPs leaching investigation from wood were applied in three studies. The AWPA E11-97 standard method [43] for accelerated laboratory evaluation of the leachability of waterborne wood preservatives was employed by Ding et al. [44]. The nano-based wood preservatives tested included (i) CuO NPs with an average particle size of 10 or 50 nm (CuO-10 and CuO-50) and (ii) CuO NPs stabilized by weakly acidic or weakly basic polymer-stabilizers, i.e. [(2-hydroxy-3-trimethylammonium)propyl] chitosan chloride (HTCC-CuO-10 and HTCC-CuO-50) and Poly(vinylpyrrolidone) (PVP-CuO-10). The description of the leaching method applied clearly states that the data collected are not intended to, nor shall it be used to predict environmental impacts of treated wood. The test involved the leachate collection over 500 h, followed on one side by TEM–EDS analysis, revealing the presence of NPs, and, on the other side, by heating at 80 °C and by acid digestion to dissolve solid NPs and determine Cu2+ via Atomic Absorption Spectrophotometry (AAS). Ding et al. [44] concluded that the size was the most significant factor affecting leaching, showing the highest Cu2+ concentration derived from the smallest NPs tested. Moreover, the authors found that the polymer stabilizers used enhanced leaching with respect to the unstabilized CuO NPs, hypothesizing that aggregation of bare CuO NPs prevents the leaching.

The other standard test method for the NPs leaching assessment was EN 84:1997 [45], employed in Pantano et al. [46] by comparing nano-enabled and molecular copper-based formulations for wood preservative. The test was conducted at 4 kPa vacuum-atmospheric pressure cycle in DW, by maintaining the wood blocks (DW:wood 5:1 v/v) for 14 days with nine water changes at 20 °C and 65% of relative humidity. The leachate was analysed by ICP-MS for the total copper content determination and by single particle ICP-MS (spICP-MS) to detect any NPs. The results indicated that the highest Cu leaching rate was about 3 orders of magnitude higher for molecular Cu-based formulations than for nano-based preservatives. Furthermore, NPs leaching was assessed by a combination of analytical methods, i.e. filtration-ICP-MS, TEM–EDX and spICP-MS, allowing to conclude that the nano-enabled micronized Cu formulation released only ionic Cu, with a rate nearly identical to the conventional no-nano formulation.

The same leaching test standard method used by Pantano et al. [46], was applied in Bak and Németh [47] by employing ZnO NPs, Zn-borate NPs, Ag NPs, Cu NPs and Cu-borate NPs dispersions to beech and pine planks. However, the authors investigated the NPs leaching only by indirectly measuring the weight variations before and after NPs suspensions impregnation. By comparing the weight variations, they supposed that zinc-oxide, copper and silver NPs showed much higher resistance to leaching with respect to zinc- and copper-borate dispersions.

NPs’ leaching estimation

For the studies listed in Table 1, information on both qualitative and quantitative estimation of NPs’ leaching from nano-enabled products by applying a standard leaching test method has been included in Additional file 1: Table S1. When specified, the data provided about NPs’ leaching were quite scattered in terms of the metric used for the species detected in the leachate, providing the results as mg/m2 or as a percentage of a species of interest. The studies in Additional file 1: Table S1 highlighted that the experimental conditions (e.g., immersion cycles, weathering time, duration) and the matrix in which NPs were embedded are key parameters in driving the amount of NPs leaching from nano-enabled products.

Non-standardized procedures to estimate NPs leaching from nanocomposites materials

Among the 34 studies listed in Table 2 in which no specific standard leaching test was used, a wide set of type and size of treated substrates have been considered, assessing NPs leaching in several aqueous-based solutions, ranging from deionized water, to simulated and natural rain, saline solutions, synthetic and natural seawater, as well as phosphate buffer saline and biological media. The only standard test methods followed by the authors mentioned in Table 2 were related to UV weathering before performing any leaching experiment. By analysing the similarities and the differences among these studies, they can be further divided into four different sub-groups. The largest group (22 studies) includes works where different sample immersion test procedures were employed, estimating the leaching of targeted compounds at different time points: most of the authors analysed the leachate after the typical exposure time points of bacterial growth (till 96 h), up to days (maximum 10) or weeks (maximum 4), while only in Künninger et al. [48] and Azimzada et al. [49] the leaching test was carried out under natural weather conditions. Within this first sub-group, besides determining the concentration of the targeted elements, only Olabarrieta et al. [50], Al-Kattan et al. [51], Künninger et al. [48], Neubauer et al. [52], Ruggiero et al. [53], Wohlleben et al. [54] and Azimzada et al. [49] directly focused on the NPs detection in the leachate, by using electron microscopy techniques (SEM or TEM–EDX), spectroscopy or spectrometry techniques (UV–Vis, or spICP-MS) or centrifugation techniques (AUC). The other three sub-groups consist of: 5 studies where water spray or/and outdoor runoff methods were used, including Kaegi et al. [8], Shandyla et al. [55] and Jimenez-Relinque et al. [56] that directly assessed the amount of NPs after leaching experiments by electron microscopy techniques; 3 studies investigating leaching from milled paint/aged particles in contact with a liquid, providing an estimation of the NPs in the leachate only in the works by Al-Kattan et al. [5, 57] again by electron microscopy techniques; other 5 studies focused on the leachate from nanocomposite materials when in contact with a water-based liquid by flushing, dripping or spreading it, investigating the presence of NPs after leaching test only in Agnihotri et al. [58], Sassoni et al. [59] and Nam et al. [60] by employing either electron microscopy or spectroscopy (surface enhanced Raman spectroscopy, SERS) techniques.

Standard test methods for evaluating nanocomposite performances potentially useful for NPs leaching estimations

The leaching of NPs from coatings and materials can be heavily influenced by their mechanical performances (e.g., permeability, wettability, durability, thermal stability, and resistance to abrasion and corrosion), thus standardized test methods investigating them can give very useful information to indirectly estimate NPs leaching under different conditions. Considering for example a nano-based material with high abrasion or corrosion resistance that is also chemically and biologically inert, good leaching resistance could also be assumed. Therefore, besides the information reported in Tables 1 and 2, 10 additional studies investigating other performances of nanocomposite materials are listed in Table 3. Among all the standard methods included within these works, the most suitable ones for obtaining indirect information on a potential NPs leaching were: (a) ASTM B117-19 [61] and ASTM G154-16 [62] for artificial weathering; (b) ASTM standards D6037 [63], D4060 [64], D968 [65] and the ISO 2409:2007 [66] for resistance to abrasion; (c) ASTM D638 [67] and ISO 14125:1998 [68] for tensile and flexural properties. Moreover, the resistance of coated materials to water by partial or full immersion test described in ISO 2812-2:2007 [30], followed by Zuin et al. [9], Zhang et al. [26] and Lopez-Ortega et al. [32] (as reported in Table 1), has also been used by Luangtriratana et al. [69] (Table 3), but only for determining the weight loss of coated samples instead of analysing the potential presence of NPs in the leachate. Most of the studies included in Table 3 tested these performances on SiO2 NPs-based materials.

General remarks and conclusions

In the field of cultural heritage conservation, nano-enabled products that are thermally stable, biologically and chemically non- or little-reactive, are effective to prevent and/or mitigate the effect of weathering (e.g., rainfall, relative humidity, temperature, wind, sunlight, microorganisms and air pollution) [70]. However, safety and sustainability assessment of nano-enabled materials and products have not kept pace with their rapid commercialization [71], calling for further efforts in assessing the potential release of NPs by leaching to support the comprehensive investigation of potential risks along their life cycle.

The new technical data requirements for NMs, as clarified in the revised Annexes of REACH regulation in force since 1st of January 2020 (and corresponding guidance manuals), include a comprehensive set of information on physico-chemical properties of NMs (e.g., particle size distribution, shape, crystallinity, surface area, solubility/dissolution rate), as well as knowledge on environmental fate and toxicity. In particular, 20 additional nano-specific information requirements must be satisfied in order to register substances as nanoforms in REACH [72]. If for some information requirements standard methods are available or under development (see [72] for a critical appraisal), current technical guidance entail no assistance on how to measure and report transformations that nanoforms and related nano-enabled products can experience when considering all stages of the life cycle and with regard to their environmental behaviour and fate [73]. Therefore, especially in the case when a Chemical Safety Assessment would be required, methods to identify and investigate relevant exposure scenarios (including the justification of “no exposure” or “low exposure” evaluations) are needed. In this context, this review covers experimental methods that can effectively support the overall exposure assessment by identifying and, where possible, quantifying the releases from nano-enabled products especially during the use and end-of-life stages. Moreover, the identification of a variety of approaches and some difficulties in comparing the results revealed the need to move towards agreed and standardized methodologies to provide risk assessors with quantitative, comparable results, easy to interpret and to be integrated with hazard data.

Summarizing all the information gathered throughout the studies reviewed, to date, the standard leaching test methods used to assess the NPs leaching from nano-enabled products are ISO 2812-2:2007 [30] (nowadays replaced by ISO 2812:2018 [74]) and ISO 12457-3:2004 [31], applied to nano-based paints and paints debris, respectively. As far as nano-based wood preservatives, AWPA E11-97 [43] and EN 84-1997 [45] have been employed.

In addition to these standards, two further standard leaching test methods could contribute to NPs leaching investigation. The first one is EN 16105:2011 [75], a standard method for the determination of the leaching of substances from coatings, validated by Schoknecht et al. [76], by carrying out an interlaboratory comparison with eight EU participants. Panels of extruded polystyrene were coated with different coatings and exposed in intermittent contact with water over 1 h, to simulate the alternation of rain events and dry seasons. Analysis of leached substances were conducted by applying high-performance liquid chromatography (HPLC) combined with UV detection, liquid chromatography-mass spectrometry (LC/MS) and LC/MS/MS. Results revealed that the procedure described by this standard leaching test method was suitable to investigate the potential released substances with good reproducibility.

Furthermore, the Technical Committee CEN/TC 351 “Construction products: assessment of release of dangerous substances”, developed some technical specifications concerning the release of hazardous materials under Construction Products Regulation. Among these specifications, as mentioned in Bandow et al. [77], CEN/TS 16637-1:2018 [78] allows identifying suitable leaching tests for the release of dangerous substances from construction products into soil, surface water and groundwater. Bandow et al. [77] stated that, since lab-scale experiments usually employed artificial conditions (e.g., deionized water, which has no buffering capacity and it is prone to changes of the pH value if products with high alkaline or acidic potential are investigated), standardized leaching test conditions have not to be considered as a simulation of reality but rather as inputs for data modelling. Moreover, they underlined that, due to the matrix complexity, a complete release assessment of hazardous substances from construction products should combine chemical analytical methods with standardized ecotoxicity tests, referring to the CEN/TR 17105:2017 guidance [79].

Since all these standards involve a partial or full immersion of test samples to obtain a leachate to be analysed, their applicability to cultural heritage could be limited to specific mock-up samples, such as treated building façades or artworks that need artificial specimens opportunely prepared which reproduce the original ones. Moreover, some other standard test methods evaluating, e.g., abrasion and corrosion resistance or tensile and flexural properties on mock-up samples could also be potentially useful to indirectly provide insights on NPs leaching, becoming potential alternatives to standard leaching test methods. In general, all these standard test methods show applicability limitations related to the size of the treated sample (especially for immovable artworks) and to their artistic value.

In addition to standard methods, non-standard procedures reported in Table 2 could be a valuable support to NPs’ leaching evaluation. In particular, besides non-standardized immersion methods used, which represent a worst-case scenario, other weathering conditions such as water spray or outdoor runoff have been tested, which constitute an alternative exposure scenario.

Moreover, according to some studies performed by the National Institute of Standards and Technology (NIST), as reported in Jacobs et al. [80], NPs’ leaching as a function of UV dose exposure, combined with simulated washings of rainwater by applying a water spray protocol described in Sung et al. [81], could be another alternative for estimating NPs’ leaching at more realistic environmental conditions. This approach could provide the advantage of simulating further exposure scenarios by testing several UV irradiations (W/m2) and wavelengths as well as relative humidity ranges, representative of different real environmental conditions. However, one of the main limitations of this approach could be related to the complexity of the experimental design, also considering the costs of the equipment needed (e.g., climate chamber, UV lamps).

To advance the environmental exposure assessment of NPs from nano-enabled products, not necessarily limited to the field of cultural heritage, taking into account the complexity and the variety of the nano-based products available on the market, besides all the conventional parameters of a standard leaching test (e.g., the size of the sample under testing, the chemistry of the leaching solution or the duration of the test), the main information of a study designed for an NPs’ leaching evaluation should include: (i) the initial amount of NPs present in the product; (ii) the amount of nano-based product applied; (iii) the area of the surface treated; (iv) the time considered for the leaching test; (v) the cumulative loss of targeted species in the leachate (as for example mg/m2 or %/m2), vi) the form of the released substances in the leachate (i.e., ionic form, free NPs or matrix fragments containing NPs). A good starting point could be the review by Koivisto et al. [29], in which the NPs release was expressed by mg/m2 and, similar also to Froggett et al. [28], there was a clear distinction of release among ionic forms, matrix containing NPs, NPs alone and matrix alone. Lastly, as suggested by Bandow et al. [77], a standardized leaching test, by describing the analytical methods used to detect any NPs, alone or embedded in their matrix, should also give indications on performing standardized ecotoxicological tests to allow a comparison of the results.

Moreover, if we consider analytical issues, a tiered multi-method approach could be proposed to estimate the NPs’ leaching, suitable to balance the degree of detail in leachate characterization and operational costs. For example, a preliminary assessment to qualitatively verify the presence of NPs in the leachate could be performed by employing simple-to-use and fast techniques, such as ICP-OES or UV–Vis, following the procedure reported by Lopez-Ortega et al. [32] and Regiel et al. [82]. A more comprehensive NPs’ leaching evaluation could instead be achieved by the combination of spICP-MS with TEM/SEM + EDX techniques (such as described, e.g., by Pantano et al. [46] or Neubauer et al. [52]), to clearly distinguish the form potentially present in the leachate, i.e. ions, free NPs and the matrix containing NPs.

From the information collected through this literature review we might argue that, within the boundaries of the tested experimental conditions, the presence of free NPs detected in the leachate is very limited and does not provide evidence for expected significant concentrations in environmental media. Nevertheless, case-by-case conclusions based on a deep knowledge of tested materials/products and specific environmental conditions and proved through robust experimental methods are needed to effectively inform risk assessment and management.

The information extracted and elaborated from literature together with the recommendations provided in this work, concerning the methodological approach for leaching testing as well as possible analytical solutions, could provide useful inputs to guide the assessment of human health and ecological exposure due to releases from nano-enabled products. This review focused on nanotechnology applications for cultural heritage conservation but possible benefits to wider fields are foreseen (including the potential release of nano and microplastics from commercial thermoplastic products), with the appropriate adaptations based on the types and applications of nano-enabled products, potential environmental conditions and aging and weathering processes of interest, different exposure targets. Once release mechanisms and exposure scenarios are better characterized, this information could contribute to the development of innovative, safe and sustainable nano-enabled products, within a Safe by Design perspective to ensure an effective risk management of nanocomposite materials.

Availability of data and materials

Data sharing is not applicable to this article as no datasets were generated or analysed during the current study.



Asymmetric flow field flow fractionation


Atomic absorption spectroscopy


American Society for Testing and Materials


Analytical ultracentrifugation


American Wood Protection Association


Classification, labelling and packaging


Dynamic light scattering


Deionized water


Energy dispersive X-ray


Electrochemical impedance spectroscopy


Environmental Protection Agency


Field emission scanning electron microscopy


Field emission gun-transmission electron microscopy


Fourier-transform infrared spectroscopy


[(2-Hydroxy-3-trimethylammonium) propyl] chitosan chloride


Inductively coupled plasma atomic emission spectroscopy


Inductively coupled plasma-mass spectrometry


Inductively coupled plasma-optical emission spectrometry


International Organization for Standardization


Integrated testing strategy


Linear low-density polyethylene


Liquid to solid


Multi-walled carbon nanotubes


Engineered nanoparticles


Organisation for Economic Co-operation and Development




Registration, evaluation, authorization of chemicals


Rotation per minute


Single particle inductively coupled plasma-mass spectrometry


Surface enhanced Raman spectroscopy


Thermogravimetric analysis


Time of flight-secondary ion mass spectrometry


Total reflection X-ray fluorescence


Ultra violet–visible spectroscopy


X-ray diffraction


X-ray fluorescence


X-ray photoelectron spectroscopy


X-ray absorbance fine structure


  1. 1.

    Varotsos C, Tzanis C, Cracknell A (2009) The enhanced deterioration of the cultural heritage monuments due to air pollution. Environ Sci Pollut Res 16:590–592.

    Article  Google Scholar 

  2. 2.

    Lee C, Kim Y, Nagajyothi PC et al (2011) Cultural heritage: a potential pollution source in museum. Environ Sci Pollut Res Int 18:743–755.

    CAS  Article  Google Scholar 

  3. 3.

    Giorgi R, Ambrosi M, Toccafondi N, Baglioni P (2010) Nanoparticles for cultural heritage conservation: calcium and barium hydroxide nanoparticles for wall painting consolidation. Chem Eur J 16:9374–9382.

    CAS  Article  Google Scholar 

  4. 4.

    Ambrosi M, Dei L, Giorgi R et al (2001) Colloidal particles of Ca(OH)2: properties and applications to restoration of frescoes. Langmuir 17:4251–4255.

    CAS  Article  Google Scholar 

  5. 5.

    Al-Kattan A, Wichser A, Vonbank R et al (2015) Characterization of materials released into water from paint containing nano-SiO2. Chemosphere 119:1314–1321.

    CAS  Article  Google Scholar 

  6. 6.

    Gheno G, Badetti E, Brunelli A et al (2018) Consolidation of Vicenza, Arenaria and Istria stones: a comparison between nano-based products and acrylate derivatives. J Cult Herit 32:44–52.

    Article  Google Scholar 

  7. 7.

    Zuin S, Massari A, Ferrari A, Golanski L (2014) Formulation effects on the release of silica dioxide nanoparticles from paint debris to water. Sci Total Environ 476–477:298–307.

    CAS  Article  Google Scholar 

  8. 8.

    Kaegi R, Sinnet B, Zuleeg S et al (2010) Release of silver nanoparticles from outdoor facades. Environ Pollut 158:2900–2905.

    CAS  Article  Google Scholar 

  9. 9.

    Zuin S, Gaiani M, Ferrari A, Golanski L (2014) Leaching of nanoparticles from experimental water-borne paints under laboratory test conditions. J Nanopart Res 16:2185.

    CAS  Article  Google Scholar 

  10. 10.

    Mirabedini SM, Behzadnasab M, Kabiri K (2012) Effect of various combinations of zirconia and organoclay nanoparticles on mechanical and thermal properties of an epoxy nanocomposite coating. Compos Part A Appl Sci Manuf 43:2095–2106.

    CAS  Article  Google Scholar 

  11. 11.

    Giorgi R, Baglioni M, Baglioni P (2017) Nanofluids and chemical highly retentive hydrogels for controlled and selective removal of overpaintings and undesired graffiti from street art. Anal Bioanal Chem 409:3707–3712.

    CAS  Article  Google Scholar 

  12. 12.

    Baglioni M, Poggi G, Jaidar Benavides Y et al (2018) Nanostructured fluids for the removal of graffiti—a survey on 17 commercial spray-can paints. J Cult Herit 34:218–226.

    Article  Google Scholar 

  13. 13.

    Andriulo F, Braovac S, Kutzke H et al (2016) Nanotechnologies for the restoration of alum-treated archaeological wood. Appl Phys A 122:322.

    CAS  Article  Google Scholar 

  14. 14.

    Salzano de Luna M, Buonocore GG, Giuliani C et al (2018) Long-lasting efficacy of coatings for bronze artwork conservation: the key role of layered double hydroxide nanocarriers in protecting corrosion inhibitors from photodegradation. Angew Chemie Int Ed 57:7380–7384.

    CAS  Article  Google Scholar 

  15. 15.

    Bridarolli A, Nechyporchuk O, Odlyha M et al (2018) Nanocellulose-based materials for the reinforcement of modern canvas-supported paintings. Stud Conserv 63:332–334.

    CAS  Article  Google Scholar 

  16. 16.

    Kolman K, Nechyporchuk O, Persson M et al (2018) Combined nanocellulose/nanosilica approach for multiscale consolidation of painting canvases. ACS Appl Nano Mater 1:2036–2040.

    CAS  Article  Google Scholar 

  17. 17.

    Gherardi F, Roveri M, Goidanich S, Toniolo L (2018) Photocatalytic nanocomposites for the protection of European architectural heritage. Materials.

    Article  Google Scholar 

  18. 18.

    Roveri M, Gherardi F, Goidanich S et al (2018) Self-cleaning and antifouling nanocomposites for stone protection: properties and performances of stone-nanomaterial systems. IOP Conf Ser Mater Sci Eng 364:12070.

    CAS  Article  Google Scholar 

  19. 19.

    ECHA (European CHemicals Agency) (2020) Overview of REACH information requirements and available methods.

  20. 20.

    Gottschalk F, Nowack B (2011) The release of engineered nanomaterials to the environment. J Environ Monit 13:1145–1155.

    CAS  Article  Google Scholar 

  21. 21.

    Reyes-Estebanez M, Ortega-Morales BO, Chan-Bacab M et al (2018) Antimicrobial engineered nanoparticles in the built cultural heritage context and their ecotoxicological impact on animals and plants: a brief review. Herit Sci 6:52.

    CAS  Article  Google Scholar 

  22. 22.

    Balliana E, Ricci G, Pesce C, Zendri E (2015) Assessing the value of green conservation for cultural heritage: positive and critical aspects of already available methodologies. Int J Conserv Sci 7:185–202

    Google Scholar 

  23. 23.

    Semenzin E, Giubilato E, Badetti E et al (2019) Guiding the development of sustainable nano-enabled products for the conservation of works of art: proposal for a framework implementing the safe by design concept. Environ Sci Pollut Res 26:26146–26158.

    Article  Google Scholar 

  24. 24.

    Baglioni P, Chelazzi D, Giorgi R (2015) Nanotechnologies in the conservation of cultural heritage. Springer, Netherlands

    Book  Google Scholar 

  25. 25.

    Mitrano DM, Motellier S, Clavaguera S, Nowack B (2015) Review of nanomaterial aging and transformations through the life cycle of nano-enhanced products. Environ Int 77:132–147.

    CAS  Article  Google Scholar 

  26. 26.

    Zhang X, Wang M, Guo S et al (2017) Effects of weathering and rainfall conditions on the release of SiO2, Ag, and TiO2 engineered nanoparticles from paints. J Nanopart Res 19:338.

    CAS  Article  Google Scholar 

  27. 27.

    Zhang M, Yang J, Cai Z et al (2019) Detection of engineered nanoparticles in aquatic environments: current status and challenges in enrichment, separation, and analysis. Environ Sci Nano 6:709–735.

    CAS  Article  Google Scholar 

  28. 28.

    Froggett SJ, Clancy SF, Boverhof DR, Canady RA (2014) A review and perspective of existing research on the release of nanomaterials from solid nanocomposites. Part Fibre Toxicol 11:17.

    CAS  Article  Google Scholar 

  29. 29.

    Koivisto AJ, Jensen ACØ, Kling KI et al (2017) Quantitative material releases from products and articles containing manufactured nanomaterials: towards a release library. NanoImpact 5:119–132.

    Article  Google Scholar 

  30. 30.

    ISO (International Standard Organization) (2007) ISO 2812-2 Paints and varnishes-Determination of resistance to liquids—part 2: Water immersion method.

  31. 31.

    BSI (British Standard Institution) (2004) BSI EN 12457-3 Characterization of waste-leaching-compliance test for leaching of granular waste materials and sludges-part 3: two stage batch test at a liquid to solid ratio of 2 l/kg and 8 l/ kg for materials with high solid content and with particle size below.

  32. 32.

    López-Ortega A, Areitioaurtena O, Alves SA et al (2019) Development of a superhydrophobic and bactericide organic topcoat to be applied on thermally sprayed aluminum coatings in offshore submerged components. Prog Org Coatings 137:105376.

    CAS  Article  Google Scholar 

  33. 33.

    ISO (International Standard Organization) (2007) ISO 11507 Paints and varnishes-exposure of coatings to artificial weathering—exposure to fluorescent UV lamps and water.

  34. 34.

    ISO (International Standard Organization) (2013) ISO 16474-1 Paints and varnishes—methods of exposure to laboratory light sources general guidance.

  35. 35.

    ISO (International Standard Organization) (2006) ISO 7784-2 Paints and varnishes—determination of resistance to abrasion—part 2: rotating abrasive rubber wheel method.

  36. 36.

    CEN (European Committee for Standardization) (2003) EN 1062-11 Paints and varnishes—coating materials and coating systems for exterior masonry and concrete-methods of conditioning before testing.

  37. 37.

    ISO (International Standard Organization) (2003) ISO 17294-2 Water quality—application of inductively coupled plasma mass spectrometry (ICP-MS)—part 2: determination of 62 elements.

  38. 38.

    ISO (International Standard Organization) (2018) ISO 6270-2 Paints and varnishes—determination of resistance to humidity—part 2: condensation (in-cabinet exposure with heated water reservoir).

  39. 39.

    ISO (International Standard Organization) (2017) ISO 9227 Corrosion tests in artificial atmospheres—salt spray tests.

  40. 40.

    ISO (International Standard Organization) (2016) ISO 4628–1 Paints and varnishes-evaluation of degradation of coatings—designation of quantity and size of defects, and of intensity of uniform changes in appearance-part 1: general introduction and designation system.

  41. 41.

    ISO (International Standard Organization) (2017) ISO 10253 Water quality—marine algal growth inhibition test with Skeletonema sp. and Phaeodactylum tricornutum.

  42. 42.

    OECD (Organization for Economic Co-operation and Development) (2018) OECD no. 23 Guidance document on aqueous—phase aquatic toxicity testing of difficult test chemicals.

  43. 43.

    AWPA (American Wood Protection Association) (1997) E11 Standard method of determining the leachability of wood preservatives.

  44. 44.

    Ding X, Meneses MB, Albukhari SM et al (2013) Comparing leaching of different copper oxide nanoparticles and ammoniacal copper salt from wood. Macromol Mater Eng 298:1335–1343.

    CAS  Article  Google Scholar 

  45. 45.

    CEN (European Committee for Standardization) (1997) EN 84 Wood preservatives—accelerated ageing of treated wood prior to biological testing—leaching procedure. Eur Stand 1–8

  46. 46.

    Pantano D, Neubauer N, Navratilova J et al (2018) Transformations of nanoenabled copper formulations govern release, antifungal effectiveness, and sustainability throughout the wood protection lifecycle. Environ Sci Technol.

    Article  Google Scholar 

  47. 47.

    Bak M, Németh R (2018) Effect of different nanoparticle treatments on the decay resistance of wood. Bioresources.

    Article  Google Scholar 

  48. 48.

    Künniger T, Gerecke AC, Ulrich A et al (2014) Release and environmental impact of silver nanoparticles and conventional organic biocides from coated wooden façades. Environ Pollut 184:464–471.

    CAS  Article  Google Scholar 

  49. 49.

    Azimzada A, Farner JM, Jreije I et al (2020) Single- and multi-element quantification and characterization of TiO2 nanoparticles released from outdoor stains and paints. Front Environ Sci 8:91

    Article  Google Scholar 

  50. 50.

    Olabarrieta J, Zorita S, Peña I et al (2012) Aging of photocatalytic coatings under a water flow: long run performance and TiO2 nanoparticles release. Appl Catal B Environ 123:182–192.

    CAS  Article  Google Scholar 

  51. 51.

    Al-Kattan A, Wichser A, Vonbank R et al (2013) Release of TiO2 from paints containing pigment-TiO2 or nano-TiO2 by weathering. Environ Sci Process Impacts 15:2186–2193.

    CAS  Article  Google Scholar 

  52. 52.

    Neubauer N, Scifo L, Navratilova J et al (2017) Nanoscale coloristic pigments: upper limits on releases from pigmented plastic during environmental aging, in food contact, and by leaching. Environ Sci Technol 51:11669–11680.

    CAS  Article  Google Scholar 

  53. 53.

    Ruggiero E, Vilsmeier K, Mueller P et al (2019) Environmental release from automotive coatings are similar for different (nano) forms of pigments. Environ Sci Nano 6:3039–3048.

    CAS  Article  Google Scholar 

  54. 54.

    Wohlleben W, Kingston C, Carter J et al (2017) NanoRelease: pilot interlaboratory comparison of a weathering protocol applied to resilient and labile polymers with and without embedded carbon nanotubes. Carbon NY 113:346–360.

    CAS  Article  Google Scholar 

  55. 55.

    Shandilya N, Le Bihan O, Bressot C, Morgeneyer M (2015) Emission of titanium dioxide nanoparticles from building materials to the environment by wear and weather. Environ Sci Technol 49:2163–2170.

    CAS  Article  Google Scholar 

  56. 56.

    Jimenez-Relinque E, Grande M, Duran T et al (2020) Environmental impact of nano-functionalized construction materials: leaching of titanium and nitrates from photocatalytic pavements under outdoor conditions. Sci Total Environ 744:140817.

    CAS  Article  Google Scholar 

  57. 57.

    Al-Kattan A, Wichser A, Zuin S et al (2014) Behavior of TiO2 released from nano-TiO2-containing paint and comparison to pristine nano-TiO2. Environ Sci Technol 48:6710–6718.

    CAS  Article  Google Scholar 

  58. 58.

    Agnihotri S, Mukherji S, Mukherji S (2013) Immobilized silver nanoparticles enhance contact killing and show highest efficacy: elucidation of the mechanism of bactericidal action of silver. Nanoscale 5:7328–7340.

    CAS  Article  Google Scholar 

  59. 59.

    Sassoni E, D’Amen E, Roveri N et al (2018) Durable self-cleaning coatings for architectural surfaces by incorporation of TiO2 nano-particles into hydroxyapatite films. Materials.

    Article  Google Scholar 

  60. 60.

    Nam S, Ernst N, Chavez SE et al (2020) Practical SERS method for assessment of the washing durability of textiles containing silver nanoparticles. Anal Methods 12:1186–1196.

    CAS  Article  Google Scholar 

  61. 61.

    ASTM (American Society for Testing and Materials) (2019) ASTM B117-19 Standard practice for operating salt spray (fog) apparatus.

  62. 62.

    ASTM (American Society for Testing and Materials) (2016) ASTM G154-16 Standard practice for operating fluorescent ultraviolet (UV) lamp apparatus for exposure of nonmetallic materials.

  63. 63.

    ASTM (American Society for Testing and Materials) (2018) ASTM D6037-18 Standard test methods for dry abrasion mar resistance of high gloss coatings.

  64. 64.

    ASTM (American Society for Testing and Materials) (2019) ASTM D4060-19 Standard test method for abrasion resistance of organic coatings by the taber abraser.

  65. 65.

    ASTM (American Society for Testing and Materials) (2017) ASTM D968-17 Standard test methods for abrasion resistance of organic coatings by falling abrasive.

  66. 66.

    ISO (International Standard Organization) (2007) ISO 2409 Paints and varnishes—cross-cut test.

  67. 67.

    ASTM (American Society for Testing and Materials) (2014) ASTM D638-14 Standard test method for tensile properties of plastics.

  68. 68.

    ISO (International Standard Organization) (1998) ISO 14125 Fibre-reinforced plastic composites—determination of flexural properties.

  69. 69.

    Luangtriratana P, Kandola BK, Myler P (2015) Ceramic particulate thermal barrier surface coatings for glass fibre-reinforced epoxy composites. Mater Des 68:232–244.

    CAS  Article  Google Scholar 

  70. 70.

    David ME, Ion R-M, Grigorescu RM et al (2020) Nanomaterials used in conservation and restoration of cultural heritage: an up-to-date overview. Materials 13:2064.

    CAS  Article  Google Scholar 

  71. 71.

    Johnston LJ, Gonzalez-Rojano N, Wilkinson KJ, Xing B (2020) Key challenges for evaluation of the safety of engineered nanomaterials. NanoImpact 18:100219.

    Article  Google Scholar 

  72. 72.

    Nielsen MB, Baun A, Mackevica A et al (2021) Nanomaterials in the European chemicals legislation—methodological challenges for registration and environmental safety assessment. Environ Sci Nano.

    Article  Google Scholar 

  73. 73.

    Clausen LPW, Hansen SF (2018) The ten decrees of nanomaterials regulations. Nat Nanotechnol 13:766–768.

    CAS  Article  Google Scholar 

  74. 74.

    ISO (International Standard Organization) (2018) ISO 2812-1 Paints and varnishes—determination of resistance to liquids—part 1: immersion in liquids other than water

  75. 75.

    CEN (European Committee for Standardization) (2011) EN 16105 Paints and varnishes—laboratory method for determination of release of substances from coatings in intermittent contact with water

  76. 76.

    Schoknecht U, Sommerfeld T, Borho N, Bagda E (2013) Interlaboratory comparison for a laboratory leaching test procedure with façade coatings. Prog Org Coatings 76:351–359.

    CAS  Article  Google Scholar 

  77. 77.

    Bandow N, Gartiser S, Ilvonen O, Schoknecht U (2018) Evaluation of the impact of construction products on the environment by leaching of possibly hazardous substances. Environ Sci Eur 30:14.

    CAS  Article  Google Scholar 

  78. 78.

    CEN (European Committee for Standardization) (2018) CEN/TS 16637-1 Construction products-assessment of release of dangerous substances—part 1: guidance for the determination of leaching tests and additional testing step

  79. 79.

    CEN (European Committee for Standardization) (2017) CEN/TR 17105 Construction products-assessment of release of dangerous substances—guidance on the use of ecotoxicity tests applied to construction products

  80. 80.

    Jacobs DS, Huang S-R, Cheng Y-L et al (2016) Surface degradation and nanoparticle release of a commercial nanosilica/polyurethane coating under UV exposure. J Coatings Technol Res 13:735–751.

    CAS  Article  Google Scholar 

  81. 81.

    Sung L, Stanley D, Gorham JM et al (2015) A quantitative study of nanoparticle release from nanocoatings exposed to UV radiation. J Coatings Technol Res 12:121–135.

    CAS  Article  Google Scholar 

  82. 82.

    Regiel A, Irusta S, Arruebo AKM, Santamaria J (2012) Preparation and characterization of chitosan–silver nanocomposite films and their antibacterial activity against Staphylococcus aureus. Nanotechnology 24:15101.

    CAS  Article  Google Scholar 

  83. 83.

    Zanna S, Saulou C, Mercier-Bonin M et al (2010) Ageing of plasma-mediated coatings with embedded silver nanoparticles on stainless steel: an XPS and ToF-SIMS investigation. Appl Surf Sci 256:6499–6505.

    CAS  Article  Google Scholar 

  84. 84.

    Barua S, Chattopadhyay P, Phukan MM et al (2014) Biocompatible hyperbranched epoxy/silver-reduced graphene oxide–curcumin nanocomposite as an advanced antimicrobial material. RSC Adv 4:47797–47805.

    CAS  Article  Google Scholar 

  85. 85.

    Ren J, Han P, Wei H, Jia L (2014) Fouling-resistant behavior of silver nanoparticle-modified surfaces against the bioadhesion of microalgae. ACS Appl Mater Interfaces 6:3829–3838.

    CAS  Article  Google Scholar 

  86. 86.

    Al-Naamani L, Dobretsov S, Dutta J, Burgess JG (2017) Chitosan-zinc oxide nanocomposite coatings for the prevention of marine biofouling. Chemosphere 168:408–417.

    CAS  Article  Google Scholar 

  87. 87.

    Cedillo-González EI, Barbieri V, Falcaro P et al (2018) Influence of domestic and environmental weathering in the self-cleaning performance and durability of TiO2 photocatalytic coatings. Build Environ 132:96–103.

    Article  Google Scholar 

  88. 88.

    Clar JG, Platten WE, Baumann EJ et al (2018) Dermal transfer and environmental release of CeO2 nanoparticles used as UV inhibitors on outdoor surfaces: implications for human and environmental health. Sci Total Environ 613–614:714–723.

    CAS  Article  Google Scholar 

  89. 89.

    Parks AN, Cantwell MG, Katz DR et al (2018) Assessing the release of copper from nanocopper-treated and conventional copper-treated lumber into marine waters I: concentrations and rates. Environ Toxicol Chem 37:1956–1968.

    CAS  Article  Google Scholar 

  90. 90.

    Clar JG, Platten WE, Baumann E et al (2019) Release and transformation of ZnO nanoparticles used in outdoor surface coatings for UV protection. Sci Total Environ 670:78–86.

    CAS  Article  Google Scholar 

  91. 91.

    Clar JG, Platten WE, Baumann E et al (2019) Transformation and release of nanoparticle additives & byproducts from commercially available surface coatings on pressure treated lumber via dermal contact. Sci Total Environ 694:133669.

    CAS  Article  Google Scholar 

  92. 92.

    Zhang J, Zhang L (2019) Polystyrene/TiO2 Nanocomposite coatings to inhibit corrosion of aluminum alloy 2024–T3. ACS Appl Nano Mater 2:6368–6377.

    CAS  Article  Google Scholar 

  93. 93.

    Gadkari RR, Ali W, Das A, Alagirusamy R (2020) Configuration of a unique antibacterial needle-punched nonwoven fabric from silver impregnated polyester nanocomposite fibres. J Ind Text.

    Article  Google Scholar 

  94. 94.

    Hanif Z, Khan ZA, Siddiqui MF et al (2020) Tannic acid-mediated rapid layer-by-layer deposited non-leaching silver nanoparticles hybridized cellulose membranes for point-of-use water disinfection. Carbohydr Polym 231:115746.

    CAS  Article  Google Scholar 

  95. 95.

    Thornton SB, Boggins SJ, Peloquin DM et al (2020) Release and transformation of nanoparticle additives from surface coatings on pristine & weathered pressure treated lumber. Sci Total Environ 737:139451.

    CAS  Article  Google Scholar 

  96. 96.

    Valenzuela L, Iglesias-Juez A, Bachiller-Baeza B et al (2020) Biocide mechanism of highly efficient and stable antimicrobial surfaces based on zinc oxide-reduced graphene oxide photocatalytic coatings. J Mater Chem B 8:8294–8304.

    CAS  Article  Google Scholar 

  97. 97.

    Jolin WC, Oster C, Kaminski MD (2019) Silicate coating to prevent leaching from radiolabeled surrogate far-field fallout in aqueous environments. Chemosphere 222:106–113.

    CAS  Article  Google Scholar 

  98. 98.

    Golanski L, Gaborieau A, Guiot A et al (2011) Characterization of abrasion-induced nanoparticle release from paints into liquids and air. J Phys Conf Ser 304:12062.

    CAS  Article  Google Scholar 

  99. 99.

    Arakawa FS, Shimabuku-Biadola QL, Fernandes Silva M, Bergamasco R (2020) Development of a new vacuum impregnation method at room atmosphere to produce silver–copper oxide nanoparticles on activated carbon for antibacterial applications. Environ Technol 41:2400–2411.

    CAS  Article  Google Scholar 

  100. 100.

    Gurianov Y, Nakonechny F, Albo Y, Nisnevitch M (2020) LLDPE composites with nanosized copper and copper oxides for water disinfection. Polymers.

    Article  Google Scholar 

  101. 101.

    ASTM (American Society for Testing and Materials) (2018) ASTM D523-14 Standard test method for specular gloss

  102. 102.

    Scrinzi E, Rossi S, Kamarchik P, Deflorian F (2011) Evaluation of durability of nano-silica containing clear coats for automotive applications. Prog Org Coatings 71:384–390.

    CAS  Article  Google Scholar 

  103. 103.

    Stepien M, Chinga-Carrasco G, Saarinen JJ et al (2013) Wear resistance of nanoparticle coatings on paperboard. Wear 307:112–118.

    CAS  Article  Google Scholar 

  104. 104.

    ASTM (American Society for Testing and Materials) (2017) ASTM D3359-17 Standard test methods for rating adhesion by tape test

  105. 105.

    ASTM (American Society for Testing and Materials) (2020) ASTM D7136 Standard test method for measuring the damage resistance of a fiber-reinforced polymer matrix composite to a drop-weight impact event

  106. 106.

    ASTM (American Society for Testing and Materials) (2020) ASTM DC109/C109M Standard test method for compressive strength of hydraulic cement mortars [using 2-in. or (50 mm) cube specimens]

  107. 107.

    ASTM (American Society for Testing and Materials) (2019) ASTM C1202-19 Standard test method for electrical indication of concrete’s ability to resist chloride ion penetration

  108. 108.

    ASTM (American Society for Testing and Materials) (2020) ASTM C1585 Standard test method for measurement of rate of absorption of water by hydraulic-cement concretes

  109. 109.

    Mahdikhani M, Bamshad O, Fallah Shirvani M (2018) Mechanical properties and durability of concrete specimens containing nano silica in sulfuric acid rain condition. Constr Build Mater 167:929–935.

    CAS  Article  Google Scholar 

  110. 110.

    Shen H, Cao J, Jiang J, Xu J (2018) Antiweathering properties of a thermally treated wood surface by two-step treatment with titanium dioxide nanoparticle growth and polydimethylsiloxane coating. Prog Org Coatings 125(1):7.

    CAS  Article  Google Scholar 

  111. 111.

    ASTM (American Society for Testing and Materials) (2004) ASTM G99-04 Standard test method for wear testing with a pin-on-disk apparatus

  112. 112.

    Hou X, Hu Y, Hu X, Jiang D (2017) Poly (ether ether ketone) composites reinforced by graphene oxide and silicon dioxide nanoparticles: mechanical properties and sliding wear behavior. High Perform Polym 30:406–417.

    CAS  Article  Google Scholar 

  113. 113.

    ASTM (American Society for Testing and Materials) (2020) ASTM C230 Standard specification for flow table for use in tests of hydraulic cement

  114. 114.

    ASTM (American Society for Testing and Materials) (2019) ASTM C191 Standard test methods for time of setting of hydraulic cement by vicat needle

  115. 115.

    NT (NordTest) (1999) NT Build 492 Non-steady state chloride migration (diffusion coefficient)

  116. 116.

    ASTM (American Society for Testing and Materials) (2017) ASTM C490 Standard practice for use of apparatus for the determination of length change of hardened cement paste, mortar, and concrete

  117. 117.

    Kooshafar M, Madani H (2020) An investigation on the influence of nano silica morphology on the characteristics of cement composites. J Build Eng 30:101293.

    Article  Google Scholar 

  118. 118.

    ASTM (American Society for Testing and Materials) (2018) ASTM D1388 Standard test method for stiffness of fabrics

  119. 119.

    ISO (International Standard Organization) (1995) ISO 9237 Textiles—determination of permeability of fabrics to air

  120. 120.

    Talebi S, Montazer M (2020) Denim fabric with flame retardant, hydrophilic and self-cleaning properties conferring by in-situ synthesis of silica nanoparticles. Cellulose 27:6643–6661.

    CAS  Article  Google Scholar 

  121. 121.

    ASTM (American Society for Testing and Materials) (2017) ASTM D3039/D3039M Standard test method for tensile properties of polymer matrix composite materials

  122. 122.

    ASTM (American Society for Testing and Materials) (2015) ASTM D7264/D7264M Standard test method for flexural properties of polymer matrix composite materials

  123. 123.

    Zhang Y, Mi C (2020) Improved hydrothermal aging performance of glass fiber-reinforced polymer composites via silica nanoparticle coating. J Appl Polym Sci 137(19):48652.

    CAS  Article  Google Scholar 

Download references


The authors are grateful to the European Commission for funding NANORESTART project (H2020-NMP-21-2014, Grant agreement number 646063).


This work has received funding from the European Union’s Horizon 2020 Research and Innovation Programme under Grant agreement no. 646063 (NANORESTART—NANOmaterials for the REStoration of works of ART).

Author information




All authors helped in conceptualization of this review. AB, EB, LC and VC worked on data curation and data analysis. ES and AM recruited funding. AB, EB, LC, VG and ES were involved in the application of the methodology. EB, ES, EG and AM supervised the work and they contributed to the validation. AB, EB, LC and VC wrote the original draft. All authors helped in reviewing and editing the final draft. All authors read and approved the final manuscript.

Corresponding author

Correspondence to Elena Badetti.

Ethics declarations

Ethics approval and consent to participate

Not applicable.

Consent for publication

Not applicable.

Competing interests

The authors declare that they have no competing interests.

Additional information

Publisher's Note

Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Supplementary Information

Additional file 1: Table S1.

Information about estimated amount of species detected after leaching experiments by employing standard leaching test methods used in studies included in Table 1.

Rights and permissions

Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article's Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article's Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit

Reprints and Permissions

About this article

Verify currency and authenticity via CrossMark

Cite this article

Brunelli, A., Calgaro, L., Semenzin, E. et al. Leaching of nanoparticles from nano-enabled products for the protection of cultural heritage surfaces: a review. Environ Sci Eur 33, 48 (2021).

Download citation


  • Leaching test
  • Engineered nanoparticles
  • Coatings
  • Environmental exposure assessment
  • Cultural heritage