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Chemical characterisation, antibacterial activity, and (nano)silver transformation of commercial personal care products exposed to household greywater
Citation:
Khaksar, M., S. Vasileiadis, R. Sekine, G. Brunetti, Kirk G. Scheckel, K. Vasilev, E. Lombi, AND E. Donner. Chemical characterisation, antibacterial activity, and (nano)silver transformation of commercial personal care products exposed to household greywater. Environmental Science: Nano. RSC Publishing, Cambridge, Uk, 6(10):3027-3038, (2019). https://doi.org/10.1039/c9en00738e
Impact/Purpose:
Due to its antibacterial and antifungal properties, silver (Ag) is an increasingly common active ingredient in commercial products. Previous research has established that these products contain various forms of Ag, such as ionic Ag (Ag+), silver nanoparticles (Ag-NPs) and/or their derivatives (e.g. AgCl, Ag2S), and the use of these products inadvertently release Ag, whether ionic, nano-particulate or otherwise, to the wider environment. Current research estimating the environmental releases of Ag from these products are reliant on the manufacturers’ (largely voluntary) labelling of Ag form and concentration, but the reliability of this data is typically unknown. There is a need for more rigorous testing and independent verification of labelled contents. The environmental risks associated with nano-products also depend on the chemical, physical, and biological transformations that nanoparticles (NPs) undergo upon use and release. For example, Ag from antibacterial textiles used in socks and sports-shirts is released into laundry greywater during washing. The speciation of Ag and its transformation during washing is complex and depends on the initial form present, the nature of the textile, and the washing conditions. The regulations and guidelines for greywater reuse vary considerably by country, and also differ between jurisdictions within a single country, with reuse practices ranging from having few or no legal restrictions to being prohibited in all situations. Moreover, greywater treatment systems are extremely diverse, including technologies such as constructed wetlands, infiltration systems, rotating biological contactors, membrane bioreactors (MBR), and small scale household systems. In some areas onsite greywater reuse for garden irrigation may be practiced (with or without prior treatment). This is increasingly common in water-stressed countries (e.g. USA, Israel, Australia, etc.), and especially in times of drought when household water restrictions are in place. Most commonly however, greywater from well-serviced urban areas is released into the combined wastewater stream destined for treatment at a municipal wastewater treatment plant. The objective of this study was to test the original speciation of Ag in eight different commercially available PCPs and to investigate the subsequent chemical transformation of this Ag following exposure to two different greywater mixtures. The Ag content of each product was quantified by inductively coupled plasma mass spectrometry (ICP-MS), and X-ray absorption near edge spectroscopy (XANES) was used to investigate the initial Ag speciation in the products and the changes occurring upon mixing with greywater. In addition, the antimicrobial activity of these Ag PCPs was examined using a standard culture-based method (EN 1276) in an effort to relate Ag content and speciation to the antibacterial functionality of the products.
Description:
The objective of this study was to test the original speciation of silver (Ag) in eight different commercially available personal care products and investigate the chemical transformation of Ag during exposure to two types of synthetic greywater. The antimicrobial activity of the products was examined to determine the relationship between Ag content and speciation with the antibacterial functionality of the products. The Ag content of each product was quantified and X-ray absorption near-edge structure (XANES) analysis was used to investigate the initial speciation in the products and the changes occurring upon mixture with greywater. The results showed that the total Ag concentration in the products ranged from 17 to 30 mg kg−1, and was usually below the value reported on the label. Analyses revealed the complexity of Ag speciation in these products and highlighted the importance of characterisation studies to help elucidate the potential risks of nano-Ag in the environment. The antibacterial results confirmed that the antibacterial efficacy of the products depends on the concentration, form and speciation of Ag in the products, but is also significantly affected by product formulation. For instance, many of the products contained additional bactericidal ingredients, making it difficult to determine how much of the bactericidal effect was due directly to the Ag content/species. This paper offers some suggestions for standard methodologies to facilitate cross-comparison of potential risks across different studies and nano-enabled products.
URLs/Downloads:
DOI: Chemical characterisation, antibacterial activity, and (nano)silver transformation of commercial personal care products exposed to household greywater
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