DOI: 10.14457/tu.the.2016.1766
title: The fate of nanosilver during in-use and disposal phases under landfill conditions

description: The usage of nanosilver (nano-Ag) as an antibacterial agent in various products has increased, especially in textiles, and this nano-Ag can enter the environment during the use and disposal phases of such products. This study aims to investigate the potential leaching of Ag from nano-Ag commercial products during the use and disposal phases. A washing test was carried out following the ISO standard 105-C06: 2010 Textiles - Tests for color fastness. The test was aimed at simulating the aging of nano-Ag particles on textiles before the latter’s disposal. The Toxicity Characteristic Leaching Procedure (TCLP) test was followed by USEPA method 1311. Different types of fabrics (cotton, polyester (PES), and cotton blended with PES called TC), loaded with different concentrations of nano-Ag (20 to 1,000 mg/L) and different sizes of nano-Ag (4-5 nm, 60 nm, and 100 nm), were prepared on a laboratory scale and were used to perform the washing and TCLP tests. Bactericidal experiments were performed to confirm the antibacterial properties of the prepared fabrics. For the washing experiments, Milli-Q water at neutral pH and detergents from the market, which are in the alkaline range, were used. Two types of detergents (with strong oxidizing agents called detergent A and without an oxidizing agent called detergent B) were employed. The initial testing of nano-Ag dissolution into the leaching extract and Milli-Q water was done to understand the physiochemical changes of nano-Ag embedded in the extraction fluid, which simulates acid conditions in a landfill. Gold nanoparticles (AuNPs) at 60 nm were used as the non-reactive particle to compare to the Ag, which can dissolve. The Field Emission Scanning Electron Microscope (FE-SEM) with Energy Dispersive X-Ray Spectroscopy (EDS) and scanning electron microscope (SEM-EDS) were used to characterize the size and form of Ag on the surfaces of the products. Transmission Electron Microscopy (TEM), equipped with EDS (Energy Dispersive X-Ray Spectroscopy) and SEM-EDS, was used to characterize the size and form of Ag in the liquid solution.The Ag content was quantified by Inductively Coupled Plasma - Mass Spectroscopy (ICP-MS) and it ranged from 1 to 44 µg/g of the product in the commercial products, and from 1.49 to 350 µg/g of the product in the lab prepared fabrics. In the TCLP test, Ag concentrations ranged from 4.3 to 276 µg/L in the commercial products and from 28.9 to 28381 µg/L in the lab prepared fabrics.  SEM-EDS and TEM-EDS showed that the Ag released is nano sized. In the washing test, after 20 wash cycles, 48 to 72 % of Ag was lost from the fabrics washed with Milli-Q water, while a greater loss of 84 to 94 % of Ag occurred after washing with detergent B. Among the commercial products, household cleaning cloth released more than 92 percent of its Ag content into the wash water. There was no significant difference in the amount of Ag released between washing with Milli-Q water and tap water. PES fabrics showed a higher release of Ag into the wash water than other fabrics did, but blended PES with cotton (TC) was able to retard the released amount of Ag even after 20 washes. The results obtained from the exponential fitting curve in MATLAB also confirmed that PES released the most Ag, followed by cotton, and then TC. Using a 10 kDa ultrafiltration membrane, it was determined that only 0.1 to 12 % of nano-Ag was found in ion form in the first and second washes.  It can be concluded that Ag was mostly released in particulate form.    The antibacterial tests showed that one commercial product have a bactericidal effect on Staphylococcus aureus (S. aureus) with a 96 % reduction in bacterial growth after a 48 h incubation period. All the lab-prepared fabrics showed a high percent reduction of bacterial growth at ≥ 99 %. The results from sequential washing with the two types of detergents, followed by the TCLP test, showed that fabrics washed with detergent A (containing strong oxidants) resulted in a total of  83% loss of nano-Ag compared to that washed with detergent B (without oxidants) with less than 21% loss. The results from the testing of nano-Ag dissolution in the leaching extract and Milli-Q showed that around 76 to 91 % of Ag can be recovered in the test media. This would indicate that some of the particles were attached to the wall of sample bottle.During in-use phase, the washing conditions promoted a higher likelihood of metallic release from the textiles than when the textile reached the disposal phase in the landfill. The result suggests nano-Ag would not be mainly released from landfills because the release of nano-Ag from textiles were mostly complete during the in-use phase of the life cycle. From the results, it can be implied that the Ag remaining on the products after washing (in-use phase) can increase only a small portion of their appearance in the landfill when disposed. The amount of Ag released depends on the type of the fabric as the percent released was different for different prepared fabrics. The use of a binder reduced the release of Ag. Nano-Ag particles of small size incorporated in fabrics were released more than larger sized nano-Ag, indicating that the release amount also depends on the size of nano-Ag in the fabric. The estimation of the existing amounts and forms of Ag in washing and leaching solutions is crucial for understanding the fate of the environment into which these products finally end.