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

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.

Photocatalytic and Protective Thin Films for Enhanced Self‐cleaning Activity and Durability of Painted Steel Roofings

“…Only a negligible level of leaching was reported with the magnitude of 0.0024 mg l −1 and 0.0038 mg l −1 respectively for the 24 weeks weathered DT40 and DK40 coating systems for the water samples that were collected under simulated rainfall conditions with the angle of 45° water falling angle. This value is within the safe limits of world health organization's drinking water quality standards [51] and hence there is no risk of leaching out of nano‐TiO 2 .…”

Physical and Antimicrobial Properties of Chitosan/Silver Nanoparticle Composite Hydrogels: Role of the Crosslinker

“…A solution of 0.1 M Ag NPs was prepared as a positive control according to previous studies , (further details can be found in the Supporting Information). Hydrogels were completely submerged in DI water and vortexed lightly for 1 min to emulate industrially relevant conditions such as weathering and mechanical strain . Hydrogels remained submerged for one week, and the wash solutions were then measured using a Carry 500 UV–vis–NIR spectrophotometer.…”

“…Hydrogels were completely submerged in DI water and vortexed lightly for 1 min to emulate industrially relevant conditions such as weathering and mechanical strain. 24 Hydrogels remained submerged for one week, and the wash solutions were then measured using a Carry 500 UV−vis−NIR spectrophotometer. The samples were compared to a stock Ag NP solution prepared as detailed in the Supporting Information due to the presence of the characteristic peak of silver around 400 nm, 25 which could be used for comparison with the experimental samples.…”

Identification of the safe(r) by design alternatives for nanosilver-enabled wound dressings

“…As explained in the review by Brunelli et al, 2021, leaching tests can be performed according to standard protocols (International Organization for Standardization, 2018;The British Standards Institution, 2004) by a partial or a total immersion of the nano-enabled product in a liquid, followed by the quantification of NPs and/or its ionic form at different time of immersion (for a maximum of 4 weeks). The reported standard protocols have been developed for nanobased paints and paints debris.…”