Environmental Engineering Reference
In-Depth Information
also.come.into.play..The.bioaccessible.fraction.of.a.substance.like.a.nanomaterial.
would.be.the.amount.of.material.that.can.be.presented.to.a.tissue.or.organ.for.uptake..
For.example,.if.a.nanomaterial.agglomerates,.organisms.cannot.access.the.inner.por-
tion.of.an.intact.clump..The.outside.(exposed).portion.of.the.clumped.material.may.
be.able.to.react.with.receptors.on.a.cell.surface.or.penetrate.a.cell.membrane,.and.
thus.would.be.bioavailable.
Although.the.degree.of.risk.or.hazard.that.a.nanomaterial.may.pose.to.an.ani-
mal.is.clearly.a.function.of.both.the.degree.of.exposure.and.the.inherent.toxicity.of.
the.material,.deining.the.latter.two.parameters.can.be.quite.complex..In.bioassays,.
some.researchers.will.hold.the.exposure.or.dose.at.a.steady.concentration.and.then.
evaluate.the.effects.of.the.material.over.time,.while.others.will.vary.the.exposure.or.
dose.and.stop.the.experiment.or.study.after.a.speciied.time.period..The.latter.gener-
ally.is.preferred.as.demonstrating.dose.dependence,.a.key.principle.in.the.science.of.
toxicology..Because.nanomaterials.can.be.unique.compounds,.many.of.which.will.
be.water.insoluble.and.therefore.dificult.to.ind.a.dosing.vehicle.for,.the.science.of.
toxicology.may.have.to.adapt.new.and.innovative.methods.for.testing.many.of.these.
distinctive.materials.as.they.come.into.the.marketplace.
. FaCtoRs that Can aFFeCt the
toxiCologY oF nanoMateRials
Will.traditional.toxicology.testing.protocols.allow.for.the.proper.evaluation.of.the.
hazard.of.a.nanomaterial?.The.answer.depends.on.toxicity.and.exposure..This.sec-
tion.describes.the.factors.that.can.affect.the.toxicology.of.nanomaterials..Sections.
8.3.and.8.4.present.the.results.of.laboratory.studies.to.date.
8.2.1 t
OxiCity
OF
n
anOmaterials
Toxicity. depends,. in. part,. on. particle. size,. shape,. and. chemical. composition.. As.
discussed. previously,. a. nanomaterial. is. deined. as. a. substance. that. measures. less.
than.100.nanometers.(nm).in.any.one.of.three.dimensions..Relatively.speaking,.that.
is.100.to.1000.times.smaller.than.most.living.cells.[4]..For.another.perspective,.the.
size.of.nanomaterials.falls.in.between.the.wavelength.range.of.ultraviolet.light.(450.
to.10.nm).and.x-rays.(<10.nm)..Nanomaterials,.therefore,.are.dificult.to.observe.or.
to.detect.in.the.laboratory.[5]..As.particles.get.smaller,.the.surface-to-volume.ratio.
increases.dramatically..This.large.amount.of.area.presents.many.surfaces.that.can.
interact.with,.and.possibly.interrupt,.normal.cellular.physiological.mechanisms..For.
example,. titanium. dioxide. (TiO
2
). is. a. relatively. inert. substance. at. the. microscale,.
but.nanoscale.TiO
2
.has.been.shown.to.produce.reactive.oxygen.species.(ROS).with.
consequent. potential. for. cellular. damage. in. both. prokaryotic. and. eukaryotic. cell.
cultures.[6-8].
Size.and.shape.also.determine.where.a.material.might.end.up.in.the.body..Upon.
autopsy,.a.normal.individual's.lung.will.show.a.pepper-like.coloration,.both.at.the.
surface.and.upon.incision..This.coloration.results.from.a.lifetime's.accumulation.of.
both.natural.and.anthropogenic.dusts.and.soots..The.reticulo-endothelial.system.(or.
the.RES,.comprising.macrophages,.white.blood.cells,.and.lymph.nodes).sequesters.
