Environmental Engineering Reference
In-Depth Information
most.particulates,.making.the.material.unavailable.to.the.rest.of.the.body..Too.much.
exposure,. however,. will. overwhelm. the. RES. and. the. lung. will. become. ibrotic,.
calciied,. or. emphysematous,. losing. its. elasticity. and. eventually. resulting. in. lung.
disease..Nanomaterials.may.pose.the.greatest.risk.to.the.lung.because.they.can.be.
transported.like.a.gas.and.reach.the.deepest.portion.of.the.lungs,.the.alveoli..The.
latter.structures.are.crucial.for.the.transport.of.oxygen.to.the.arterial.blood.and.the.
exchange.of.carbon.dioxide.from.the.venous.blood.supply..One.of.the.biggest.chal-
lenges.in.solving.the.puzzle.of.the.toxicity.of.nanotechnology.will.be.to.evaluate.the.
toxicity.of.nanomaterials.to.the.respiratory.system.
Another.important.factor.affecting.toxicity.is.particle.shape..Nanomaterials.can.
be.all.types.of.shapes:.amorphous,.rods,.wires,.sheets,.spheres,.horns,.dendrimers.….
the.list.can.be.as.long.as.the.imagination.of.the.inventor.or.engineer.seeking.a.new.
product.or.function..It.is.already.known,.for.microscale.particles.such.as.asbestos,.
exhaust.fumes,.or.smoke,.that.shape.strongly.inluences.the.toxicity.due.to.particle-
surface-catalyzed.reactions.or.the.induction.of.stress,.such.as.lipid.oxidation,.stress.
proteins,.or.ROS.
The.particulate.nature.of.nanomaterials.also.limits.their.distribution.in.the.food.
chain.. Should these. materials. make. their. way. into. the. environment. in. signiicant.
amounts,. they. may. bioconcentrate. to. some. degree;. however,. it. is. anticipated. that.
they.would.not.bioaccumulate.or.biomagnify.in.the.food.chain.because.they.are.still.
solid.particles.and.may.not.become.a.truly.dissolved.species.(which.is.a.prerequisite.
for.conventional.toxics.today,.particularly.in.aquatic.systems.where.macroinverte-
brates.and.ish.are.exposed.on.a.constant.basis.and.linked.via.a.food.web)..Colloids,.
humic.and.fulvic.acids,.and.hydrophilic.acids.are.in.the.same.size.range.(as.may.be.
some.naturally.occurring.nanomaterials,.such.as.volcanic.dusts.and.silts),.yet.they.do.
not. biomagnify.. Chemicals. like. dioxins/furans,. polychlorinated. biphenyls. (PCBs),.
methyl. mercury,. perluorooctanoic. acids. (PFOAs,. an. ingredient. of. Telon ),. and.
other.persistent,.bioaccumulative.and.toxic.contaminants.require.both.a.long-term.
residence.in.an.aquatic.system.and.a.high.order.of.fugacity.in.order.to.accumulate.
and.biomagnify.up.a.food.chain..The.tendency.for.nanomaterials.to.aggregate.and.
sorb.onto.environmental.media.limits.their.bioaccessibility..Although.it.is.possible,.it.
is.therefore.improbable.that.nanomaterials.would.pose.a.risk.to.the.environment.as.a.
result.of.a.passive.cumulative.mechanism..An.exception.may.occur.if.a.nanomaterial.
contains.elements.or.compounds.that.are.already.known.to.be.either.extremely.toxic.
or.biomagnify,.such.as.mercury,.selenium,.or.highly.halogenated.substances.
The. composition. of. a. particular. nanomaterial. also. is. very. important. in. three.
respects.. First,. the. characteristics. of. a. nanomaterial. can. differ. from. laboratory. to.
laboratory.or.from.manufacturer.to.manufacturer..For.example,.it.is.already.known.
that.single-.or.double-walled.carbon.nanotubes.(SWCNTs.or.DWCNTs,.respectively).
can. differ. in. size,. shape,. and. even. composition,. depending. on. the. process. and/or.
manufacturer.that.produced.the.material.[5]..It.therefore.can.be.dificult.to.general-
ize.bioassay.results.
Second,. many. bulk. nanomaterials. contain. impurities. or. byproducts. that. can.
signiicantly.inluence.toxicity.to.an.organism.in.the.laboratory.[5]..Similar.to.the.
production.of.new.materials.in.the.early.to.mid-20th.century,.the.production.of.new.
nanoproducts. differs. from. country. to. country,. and. byproducts. may. be. introduced.
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