ARTICLE pubs.acs.org/est
Silver Nanoparticles and Total Aerosols Emitted by Nanotechnology-Related Consumer Spray Products Marina E. Quadros and Linsey C. Marr* Department of Civil and Environmental Engineering, Virginia Tech, 418 Durham Hall, Blacksburg, Virginia 24061, United States
bS Supporting Information ABSTRACT: Products containing silver nanoparticles are entering the market rapidly, but little is known about the potential for inhalation exposure to nanosilver. The objectives of this work were to characterize the emissions of airborne particles from consumer products that claim to contain silver nanoparticles or ions, determine the relationship between emissions and the products’ liquid characteristics, and assess the potential for inhalation exposure to silver during product use. Three products were investigated: an antiodor spray for hunters, a surface disinfectant, and a throat spray. Products emitted 0.24 56 ng of silver in aerosols per spray action. The plurality of silver was found in aerosols 1 2.5 μm in diameter for two products. Both the products’ liquid characteristics and the bottles’ spray mechanisms played roles in determining the size distribution of total aerosols, and the size of silver-containing aerosols emitted by the products was largely independent of the silver size distributions in the liquid phase. Silver was associated with chlorine in most samples. Results demonstrate that the normal use of silver-containing spray products carries the potential for inhalation of silvercontaining aerosols. Exposure modeling suggests that up to 70 ng of silver may deposit in the respiratory tract during product use.
’ INTRODUCTION Policies and regulations for responsible incorporation of nanomaterials into consumer products are still under development,1 4 yet the introduction of new products that have the potential to aerosolize engineered nanoparticles is proceeding swiftly.5 Silver nanoparticles (nanosilver) are increasingly popular additives to consumer products for antimicrobial purposes.6,7 Normal use of several types of nanotechnology-based consumer products, such as sprays, humidifiers, and hairdryers, may to lead to inhalation exposure of engineered nanoparticles, but the aerosol emission rates and characteristics—important for assessing risk— are largely unknown. Inhalation exposure to silver can cause respiratory tract irritation and an irreversible bluish-grayish discoloration of the skin (argyria) or eyes (argyrosis).8 10 Silver polishers exposed to silver and other metals developed bronchitis, emphysema, and a reduction in pulmonary volume.11 Occupational exposure to silver dusts and fumes via inhalation is regulated on the basis of mass concentration. The American Conference of Governmental Industrial Hygienists (ACGIH) recommends a threshold limit value (TLV) of 0.1 mg m 3 for metallic silver and 0.01 mg m 3 for soluble silver compounds, and the Occupational Safety and Health Administration (OSHA) has set a permissible exposure limit (PEL) 0.01 mg m 3 for metallic and soluble silver compounds combined. The Environmental Protection Agency (EPA) does not have an inhalation reference r 2011 American Chemical Society
concentration for silver, but its oral reference dose for silver is 0.005 mg kg 1 day 1. It is well established that inhalation of nanoparticles is associated with adverse health effects,5,12 and recent studies justify concern about exposure to nanosilver. Soto et al.13 found that nanoparticle cytotoxicity was greater for cells exposed to nanosilver than to other materials (e.g., titanium dioxide, iron oxide). Sung et al.14 reported chronic alveolar inflammation in rats exposed subchronically to airborne silver nanoparticles, with the lungs and liver as the main target organs for silver accumulation. These authors suggested a threshold of 0.1 mg m 3 for no adverse effects in rats for inhalation exposure to ∼20 nm silver nanoparticles. Even in those studies in which only minimal toxicity was found, authors suggested that chronic effects might arise following long-term exposure to nanosilver.15 We are aware of only two studies of aerosols generated from nanotechnology-related consumer products. Hagendorfer et al.16 reported no measurable release of nanoparticles from a product containing silver nanoparticles when it was dispensed from a pump spray bottle; aerosol emissions were only detected when this product was applied from a pressurized spray bottle. Received: August 8, 2011 Accepted: November 9, 2011 Revised: October 31, 2011 Published: November 09, 2011 10713
dx.doi.org/10.1021/es202770m | Environ. Sci. Technol. 2011, 45, 10713–10719
Environmental Science & Technology
Figure 1. Experimental setup and mass balance equations used to determine aerosol emission rates (further described in the Supporting Information).
Norgaard et al.17 assessed the VOC and aerosol emissions from four types of spray products used for surface-coatings (none containing silver), three of which used manual spray pumps and one of which used a pressurized gas can. More data on the rates and characteristics of nanoparticles that are released during the use of consumer products are needed for studies of the toxicity18 and environmental fate and transport of engineered nanomaterials.19 Although toxicity studies have been successful in assessing dose response relationships for specific types of nanoparticles, the use of laboratory-generated, monodisperse, high purity nanoparticles (for the most part, uncoated) carried by purified air streams may not represent realistic human exposure scenarios. There are concerns about the inhalation toxicity of silver nanoparticles, and there are consumer products that contain nanosilver, but we do not know the amount or characteristics of aerosols that may be released during use of the products. This gap in knowledge is addressed by the objectives of this work: to characterize the emissions of aerosols from consumer products that claim to contain silver nanoparticles or ions, determine the relationship between aerosol emissions and the products’ liquid characteristics, and assess the potential for inhalation exposure to silver during product use.
’ EXPERIMENTAL METHODS Products Tested. Three spray products were chosen for this study based on manufacturers’ claims that they contain silver and the products’ potential for generating aerosols during normal use. 1 An antiodor spray for hunters (16 ounces, Silver Scent, SilverScent Products, Mechanicsville, VA), which lists “patented nano-silver” and water as the only ingredients. The silver concentration was not advertised. Two different bottles were tested. 2 A surface disinfectant (4 ounces, SilverClene 24, Agion, Wakefield, MA), whose label advertises “electrolytically generated Ag+” (0.003%), citric acid (4.840%) and “other ingredients” (95.157%). The company’s Web site advertises the use of zeolite to deliver silver ions in its products. 3 A throat spray (2 ounces, Wellness Colloidal Silver Throat Spray, Source Naturals, Santa Cruz, CA). “Colloidal silver (30 ppm)” is the only ingredient listed. Real-Time Aerosol Characterization. To characterize aerosol emissions from products, we sprayed them inside a 0.52 m3 polyethylene chamber (Atmosbag, Sigma-Aldrich, St. Louis, MO) (Figure 1). The chamber was initially filled with air that was conditioned though a hydrocarbon trap, two desiccant dryers,
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and a high efficiency particulate air (HEPA) filter to a relative humidity
