Abstract
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.
Highlights
Regardless of their nature, movable and immovable cultural heritage assets, especially those located outdoors, are irremediably exposed to several degradation agentsBrunelli et al Environ Sci Eur (2021) 33:48 greater durability of art materials [3]
The bibliographic search performed highlighted that no specific standard leaching test methods properly designed to estimate the Engineered nanoparticles (NP) leaching from nano-enabled products are present in the literature
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
Summary
Regardless of their nature, movable and immovable cultural heritage assets, especially those located outdoors, are irremediably exposed to several degradation agentsBrunelli et al Environ Sci Eur (2021) 33:48 greater durability of art materials [3]. In the field of stone conservation, colloidal Ca(OH) is one of the most promising products for stone’s consolidation because it is converted into calcium carbonate (CaCO3) as result of carbonation when exposed to atmospheric C O2 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]. 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). Nanocomposite materials have been developed in the field of stone protection within the NanoCathedral project [17, 18]
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