Treatment of Nanoparticles in Wastewater - Nanotechnology and the Environment - page 159

wastewater.from.using.the.SilverCare™.system;.however,.as.noted.above,.that.upper.
bound.estimate.was.quite.conservative. As.described.below,.research.on.the.toxicity.
of.silver.nanoparticles.provides.further.relevant.information.
Rojo.et.al..[17].assayed.the.toxicity.of.colloidal.silver.nanoparticles.in.the.5-.to.
20-nm. size. range. to. zebraish. embryos. They. tested. solutions. containing. between.
1.and.5000.µg/L.silver.nanoparticles. Their.initial.tests.showed.no.effect.on.devel-
opment. or. survival. of. the. embryos. in. the. irst. 2. weeks. Subsequent. experiments.
monitored.effects.on.eight.selected.genes. At.the.highest.nanosilver.concentrations.
tested,.the.researchers.“found.a.clear.effect.on.gene.expression.in.most.cases.” Those.
concentrations.were,.however,.orders.of.magnitude.higher.than.the.estimated.levels.
of.silver.nanoparticles.in.wastewater.described.above.
Other.researchers.have.worked.with.mammalian.cell.lines.to.test.the.toxicity.of.
silver.nanoparticles. Hussain.et.al..[18].tested.the.effect.of.solutions.containing.10.to.
50.µg/L.silver.nanoparticles.(15.nm).on.PC-12.cells. This.neuroendocrine.cell.line.
originated. from. Rattus norvegicus (Norwegian. rat). The. research. team. observed.
decreased. mitochondrial. function. in. the. PC-12. cells. upon. exposure. to. the. silver.
nanoparticles. Skebo. et. al.. [15]. showed. that. rat. liver. cells. could. internalize. silver.
nanoparticles. (25,. 80,. 130. nm). but. that. agglomeration. of. nanoparticles. can. limit.
cell.penetration. Finally,.Braydich-Stolle.et.al..[19].tested.the.effects.of.15-nm.silver.
nanoparticles.on.a.cell.line.established.from.spermatogonia.isolated.from.mice. The.
nanoparticles. reduced. mitochondrial. function. and. cell. viability. at. a. concentration.
between.5.and.10.µg/mL.(or.5000.and.10,000.µg/L). The.researchers.estimated.the.
EC50,. or. the. concentration. that. would. provoke. a. response. half-way. between. the.
baseline. and. maximum. response,. at. 8750. µg/L. This. level. is. orders. of. magnitude.
higher.than.the.irst.approximation.estimates.of.silver.nanoparticles.in.wastewater.
from.using.the.SilverCare™.system.

7.1.2 C ase s tudy : s OCks with n anO s ilver

Several. manufacturers. market. socks. impregnated. with. nanosilver. particles. as. an.
antibacterial.agent. Westerhoff's.[20].team.at.Arizona.State.University.measured.the.
amount.of.silver.that.ive.different.brands.of.socks.could.release.when.washed. They.
simulated.washing.by.placing.the.socks.in.deionized.water.for.24.hours.(hr).on.an.
orbital.mixer,.removing,.drying,.and.then.rewashing.the.socks.three.times.(for.a.total.
of.four.wash.cycles). Four.of.the.test.socks.initially.contained.silver.at.2.0.to.1360.
µg/g.sock. The.ifth.sock.contained.no.measurable.silver. The.amount.of.silver.that.
leached.out.of.the.silver-bearing.socks.after.four.simulated.wash.cycles.ranged.from.
0.to.100%. The.concentration.of.silver.in.the.wash.water.ranged.from.less.than.1.to.
600.µg.in.500.mL.wash.water,.or.up.to.300.µg/L. The.research.team.noted.that.it.
was.dificult.to.distinguish.between.silver.ions,.silver.nanoparticles,.and.aggregated.
silver.nanoparticles.in.the.wash.water.
These.initial.laboratory.results.are.dificult.to.extrapolate.to.the.concentration.
of.silver.that.might.result.in.sewage.from.washing.socks.containing.silver.nanopar-
ticles. As. noted. above,. the. typical. wash. cycle. uses. more. than. 12. gallons. of. water.
(rather.than.500.mL).and.runs.for.much.less.than.24.hr,.suggesting.that.dilution.and.