Case Study Challenges in Human Health Hazard and Risk Assessment of Nanoscale Silver - Safety of Nanomaterials along Their Lifecycle - page 419

Lorenz et al. 2012). In addition, a washing machine releasing silver nanoparticle
has been investigated (Farkas et al. 2011). It uses a patented mechanism (Patent
WO/2005/056908) to generate and release silver nanoparticles during the washing
cycle. Release of nanoparticulate silver was found in the wastewater as well as depos-
ited on the laundry (Farkas et al. 2011).
Food contact materials have been investigated in the form of food storage bags
(Huang et al. 2011) and food storage containers (von Goetz et al. 2013). Using four
different food simulating solutions on bags, silver was released in nanoparticulate
form in a time- and temperature-dependent manner (Huang et al. 2011). Silver was
detected in two of four tested bodies of plastic food storage containers (von Goetz
et al. 2013). Both containers released silver into food-simulating solution with a
comparable rate to the bags.
Human exposure may also occur at the workplace, during production and han-
dling of nanosilver, its formulation into products, or the fabrication of goods from
nanosilver-treated material.
A study monitoring workplace air in nanosilver production facilities measured
silver metal concentrations from 0.00002 to 0.00118 mg/m 3 , depending on the
type of workplace, the operation state, and the manufacturing method. When sil-
ver nanoparticles were generated using induced coupled plasma, particle numbers
reached 535-25,022 per cm³ at the workplace outside the reactor. A broad range of
particle sizes was observed, presumably as a result of agglomeration or aggregation.
When a wet method was used for manufacturing, particle numbers in the work-
place air were significantly lower with 393-3,526 particles per cm³ (Lee et al. 2011).
Particle numbers during production, postproduction handling, and processing in a
test facility producing a silica-nanosilver microcomposite powder were monitored
using SMPS by Demou et al. (2008). In the size range from 6 to 673 nm an increase
over background of approx. 9,000 particles per cm³ to a maximum of 50,000 par-
ticles per cm³ was observed during production, and a maximum of 15,000 particles
per cm³ was determined during processing and handling. Although measurements
were limited to particle size and numbers, not discriminating between silver and
other materials, these results were interpreted as to indicate the potential for break-
away of silver nanoparticles from the microcomposite (US EPA 2011). In addition,
information from health surveillance of two male individuals with a 7-year history
of work in nanosilver manufacturing was reported. For the first individual, a level of
0.34 μg/L silver in blood and 0.43 μg/L in urine were associated with an estimated
exposure at the workplace of 0.35 µg/m³. For the other individual, blood and urine
silver levels were 0.30 μg/L and not detectable (<0.1 μg/L), respectively, at an esti-
mated occupational exposure of 1.35 µg/m³ (Lee et al. 2012). For comparison, blood
silver levels in an unexposed control group ranged from not detectable (<0.1 µg/L)
in 11 of 15 individuals to 0.2 µg/L in the remaining four workers (Armitage et al.
1996). In conclusion, occupational exposures during nanosilver production and han-
dling may result in significant inhalation exposures that are reflected by increases in
blood silver levels. Finally, spraying or roll-on application of paints or other coatings,
manipulation, and handling of treated materials, for example, cutting and sewing
nanosilver-treated textiles, as well as secondary tasks including cleaning and others
may provide potential sources of nanosilver exposure.