Environmental Engineering Reference
In-Depth Information
This.diluted.slurry.can.be.injected.into.wells.under.pressure.or.by.direct.push.instal-
lation..The.term.“direct.push.installation”.refers.to.the.technique.of.using.hydraulic.
pressure.to.advance.a.tool.string.into.the.subsurface;.this.technique.removes.no.soil.
and.creates.only.a.small.borehole.through.which.reagents.can.be.injected.
Once.injected,.the.fate.and.transport.of.nZVI.depends.not.only.on.the.charac-
teristics.of.the.reagent,.but.also.on.the.low.of.groundwater.through.the.aquifer,.the.
groundwater.geochemistry,.and.the.nature.of.the.aquifer.materials..nZVI.can.oxi-
dize.rapidly.and.agglomerate.and.attach.to.soil.grains.readily,.reducing.its.reactivity.
and. mobility. [3,. 5,. 12,. 14-16].. The. mechanisms. and. rates. of. reaction. are. not. yet.
well.understood..Laboratory.studies.have.found.that.the.activity.of.nZVI.particles.
depends.on.the.particle.type,.pH,.presence.of.compounds.other.than.iron,.amount.
of.iron.available.in.the.particle.core.for.reaction,.oxide.coating.on.the.particle,.and.
other.aspects.of.geochemistry..Depending.on.these.factors,.the.reactivity.of.nZVI.
lasts.on.the.order.of.weeks.to.months..Field.data.are.limited,.as.the.technology.has.
been.commercially.available.only.since.2003..Some.reports.from.ield.applications.
suggest.that.nZVI.may.be.reactive.for.months.after.injection.
nZVI.particles.tend.to.agglomerate.and.attach.to.soil.grains,.reducing.their.effec-
tive.distribution.through.a.plume.of.contamination.[9,.10]..Attachment.to.soil.grains,.
according.to.some.estimates,.would.remove.99%.of.the.nanoparticles.within.a.travel.
distance.between.a.few.meters.and.a.few.tens.of.meters.under.typical.groundwater.
conditions.[3,.9]..Further.transport.might.be.possible.under.high-velocity.conditions.
or.in.bedrock.fractures.
10.1.5 p
Otential
r
isks
This.chapter.opened.with.one.authority's.caution.about.the.use.of.free.nanomaterials.
in.environmental.applications..The.paragraphs.below.describe.initial.data.regarding.
the.potential.hazards.of.nZVI.and.discuss.risk.management.positions.taken.regard-
ing.its.use.
Laboratory.studies.provide.some.information.on.the.potential.toxicity.of.nZVI..
In.one.
in vitro
.experiment,.central.nervous.system.microglia.cells.exposed.to.nano.
iron.at.2.to.30.mg/L.exhibited.oxidative.stress.response.and.assimilated.nZVI.into.
the.cells..Weisner.et.al..[9].characterized.these.data.as.“preliminary.results.”.Brun-
ner.et.al..[17].studied.the.
in vitro
.toxicity.of.nano.Fe
2
O
3
..(Recall.that.Fe
2
O
3
.can.be.
part.of.the.surface.coating.of.nZVI.).The.tests.used.human.(mesothelioma.MSTO-
211H).and.rodent.(3T3.ibroblast).cell.lines..The.researchers.measured.the.effects.on.
mean.cell.culture.activity.and.DNA.content.after.dosing.cell.cultures.with.particles.
at.concentrations.between.3.75.and.15.mg/L.for.a.6-day.exposure.period,.and.7.5.to.
30.mg/L.for.a.3-day.exposure.period..The.control.test.of.nano.tricalcium.phosphate.
did. not. show. any. effects.. At. concentrations. up. to. 30. mg/L,. nano. Fe
2
O
3
. affected.
slow-growing.3T3.cells.only.slightly..Faster-growing.MSTO.cells.showed.a.greater.
response..A.dose.as.low.as.3.75.mg/L.had.a.signiicant.effect.on.cell.culture.activity.
and.DNA.content,.and.a.dose.above.7.5.mg/L.was.lethal..Brunner.et.al..[17].con-
cluded.that.the.toxicity.was.approximately.40.times.greater.than.would.result.from.
iron. ions. alone,. and. attributed. that. increase. in. toxicity. to. a. nanoparticle-speciic.
