Environmental Engineering Reference
In-Depth Information
8.2.2 e
xpOsure
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anOmaterials
The. sources. and. routes. of. exposure. to. nanomaterials. are. discussed. below,. as. are.
the.natural.defenses.that.limit.the.dose.to.organisms.once.exposed..Two.key.factors.
can.limit.exposure..First,.most.nanomaterials.are.expensive.to.produce..To.prevent.
waste.and.therefore.loss.of.capital,.manufacturers.can.carefully.contain.their.prod-
ucts.. Sound. economics. therefore. can. help. an. industry. police. the. life. cycle. of. its.
own.product.and.thereby.limit.exposures..Second,.many.nanomaterials.form.much.
larger.agglomerates,.which.would.eventually.settle.out.of.the.atmosphere.or.a.sur-
face.waterbody.onto.soil.or.sediment..Over.time,.these.agglomerations.might.bind.
irreversibly.to.these.matrices.
...
sources and Routes of exposure
Various. authors. have. developed. conceptual. models,. some. complex,. of. how. nano-
materials.might.work.their.way.into.the.terrestrial.environment..The.most.obvious.
source,.based.on.historical.precedent,.would.be.via.emission.from.an.industrial.stack.
or.hood.ventilation.system..Nanomaterials'.small.size.precludes.them.from.behav-
ing. like. their. microscale. counterparts. (e.g.,. ibers. of. asbestos,. iberglass,. cotton)..
They.are.thus.expected.to.behave.more.similarly.to.a.gas,.dissipating.via.advection.
and.diffusion.processes,.and.thus.decreasing.logarithmically.in.concentration.with.
distance. from. a. source.. Depending. on. weather. conditions,. the. nanomaterials. or.
nanoparticles.could.either.be.carried.aloft,.possibly.high.up.into.the.stratosphere,.or,.
be.washed.down.to.the.surrounding.soils.or.waterbodies.during.a.rainstorm.
For.terrestrial.receptors.to.be.exposed.to.airborne.nanomaterials,.a.source.would.
have.to.be.fairly.close.by.for.exposure.to.be.probable.and,.even.then,.luctuations.in.
meteorological.conditions.would.facilitate.periods.when.animals.whose.home.range.
fell.on.the.upwind.side.of.a.potential.air.source.were.not.exposed.
Similar.to.traditionally.toxic.materials,.concentrations.in.soils.would.have.to.be.
relatively.high.(high.part-per-million.to.percent.range).to.overcome.the.fate.and.trans-
port.processes.that.tend.to.ameliorate.toxicity.over.time..Adsorption.to.and.reactions.
within.the.soil.matrix.are.anticipated.to.cause.nanoparticles.to.eventually.degrade,.
become.less.bioaccessible,.or.become.less.biologically.active.than.the.parent.mate-
rial..Because.like.dissolves.like,.carbon-based.nanomaterials.would,.based.on.what.
we.know.about.the.behavior.of.other.carbon-based.compounds,.bind.to.the.organic.
fraction. of. the. soil.. The. smallest. nanomaterials. could. be. bound. up. by. irregular.
surface.micropores.of.the.soil.matrix.(unless.the.concentration.of.the.nanomaterial.
exceeds.the.sorptive.capacity.of.the.soil)..Future.research,.particularly.experiments.
employing.many.different.types.of.soil.matrices,.will.be.able.to.resolve.whether.this.
phenomenon.will.occur.with.carbon-,.metal-,.or.metalloid-based.nanomaterials.
Nanomaterials.also.can.enter.the.environment. through.wastewater.discharges,.
whether. from. aqueous. industrial. waste. streams,. efluent. from. wet. scrubbers. used.
in.air.pollution.control,.or.in.domestic.wastewater..The.latter.is.discussed.further.in.
Chapter.7.
