Citation:

Potter, P., J. Navratilova, K. Rogers, AND S. Al-Abed. Transformation of silver nanoparticle consumer products during simulated usage and disposal. Environmental Science: Nano. RSC Publishing, Cambridge, Uk, 6(2):592-598, (2019).

Impact/Purpose:

Silver nanoparticles are known to exhibit antimicrobial properties that can affect people, plants, and microbes that are vital to wastewater treatment. While the transformations that pristine silver nanoparticles undergo have been extensively studied, the nanoparticles that reach the waste stream are likely changed by processes involved in their use. For example, silver nanoparticle dietary supplements will pass through the gastrointestinal tract and interact with stomach acid before reaching the waste stream. This research used actual consumer products containing silver nanoparticles and individually and sequentially exposed them to synthetic stomach fluid and wastewater sludge to simulate a usage and disposal scenario. While all the consumer products and silver nanoparticle standards showed significant conversion of silver to silver sulfide when exposed only to wastewater sludge, pretreatment to synthetic stomach fluid led to reduced formation of silver sulfide in wastewater sludge. This is likely due to reaction with stomach fluid forming a protective shell of silver chloride around the nanoparticles and possible allowing them to transport further before undergoing further reaction. These findings should influence future studies on the environmental fate of nanomaterials to include actual consumer products and incorporate sequential exposures that more accurately simulate usage and disposal. The presented results will be useful in evaluating chemicals in consumer products and will be used by Regional and Program Office partners to determine fate and risk of silver in consumer products.

Description:

Twenty-two silver nanoparticle (AgNP) consumer products (CPs) were analyzed with respect to their silver speciation. Three CPs and three lab-synthesized particles were selected to simulate environmental fate and transport by simulating their intended usage and disposal methods. Since many of these products are meant for ingestion, we simulated their usage by exposing them to human synthetic stomach fluid followed by exposure to wastewater sludge. We found that during the products' individual exposure to wastewater sludge, the conversion rate of silver to AgCl and Ag2S was affected by both the amount of silver ion present and the properties of the AgNP. The rates of conversion of metallic silver to silver sulfide was heavily dependent on the particle size for the lab-synthesized particles, with 90 nm PVP-capped particles reacting to a much lesser extent than the 15 nm PVP-capped or the citrate-capped particles. We observed similar sulfidation rates on two of the tested CPs with the 15 nm lab-synthesized particles despite containing silver nanoparticles >5 times larger, indicating the presence of other influencing factors. Pre-treatment with synthetic stomach fluid modified the rates of Ag2S formation. Due to the variable composition of CPs and the conditions they are exposed to between manufacture, sale, use, and disposal, their final composition may be somewhat unpredictable in the environment. In the present study, we have achieved a more accurate approximation of the expected interactions between silver nanoparticle-containing CPs and environmental media by utilizing real CPs and evaluating them with solid phase and aqueous phase analytical techniques.

URLs/Downloads:

Record Details: