Environmental Engineering Reference
In-Depth Information
particles. because. smaller. particles. are. “kicked”. further. by. the. solvent. molecules.
and.move.more.rapidly..With.a.multi-exponential.analysis.of.the.scattered.light,.a.
particle.size.distribution.can.be.calculated..The.diameter.obtained.by.this.technique,.
called.the.hydrodynamic.diameter,.is.that.of.a.sphere.that.would.move.with.the.same.
velocity.and.to.the.same.distance.as.the.particle.being.measured..For.nonspherical.
nanoparticles,.this.diameter.will.depend.on.not.only.the.physical.dimensions.of.the.
particle,. but. also. on. its. surface. structure. and. on. effects. from. any. dissolved. mate-
rial.in.the.sample..The.size.calculated.from.DLS.measurements.is.often.larger.than.
the. dimensions. measured. by. electron. microscopy.. DLS. instrumentation. is. readily.
available.and.relatively.straightforward.to.use,.and.the.technique.can.be.applied.in.a.
dynamic.fashion.to.monitor.changes.in.the.degree.of.clustering.or.agglomeration.of.
nanoparticles
in situ
.
DLS.also.can.be.referred.to.as.photon.correlation.spectroscopy.(PLS).or.quasi-
elastic. light. scattering. (QELS).. The. newest. instrumentation. allows. measurements.
down.to.1.nm.
DLS.is.used.in.studies.to.predict.toxicity.or.environmental.effects,.and.to.con-
irm.the.size.distribution.of.material.before.use.and.to.monitor.changes..It.has.been.
used.to.determine.the.particle.size.of.TiO
2
.and.fullerene.prior.to.their.use.in.experi-
ments.to.determine.the.effect.of.low.on.transport.and.deposition.in.porous.media.
[38],.and.to.monitor.the.aggregation.of.zero-valent.iron.particles.[39].and.TiO
2
.[40].
in.laboratory.experiments.designed.to.investigate.reasons.for.the.limited.mobility.of.
these.in.environmental.settings.
. woRkPlaCe aiR MonitoRing
The.irst.of.ive.challenges.for.the.safe.handling.of.nanotechnology.as.identiied.by.
scientists.in.the.ield.[41].is.to.“develop.instruments.to.assess.exposure.to.engineered.
nanomaterials.in.air.and.water,.within.the.next.3.to.10.years.”.The.exposure.of.work-
ers.to.engineered.nanoparticles.during.their.production.and.direct.use.is.of.particular.
concern,.and.the.challenge.cites.the.need.for.inexpensive.personal.aerosol.samplers.
capable.of.measuring.and.logging.the.number.of.nanoparticulates,.their.surface.area,.
and.overall.mass.concentration.in.order.to.assess.exposure..As.discussed.in.Chapter.
9,.nanoparticles.can.enter.the.body.through.respiratory,.dermal,.and.ingestion.expo-
sure.and.then.be.transported.through.intercellular.pathways..Because.the.physical.
characteristics. of. a. nanoparticle. (such. as. size,. shape,. structure,. surface. area,. and.
surface.activity).determine.the.body's.response,.knowing.the.chemical.composition.
and.overall.air.concentrations.solely.in.terms.of.any.one.of.these.parameters.is.not.
enough..Maynard.[42].reviews.the.challenges.and.technologies.for.workplace.moni-
toring.as.was.current.in.2005.
In.some.instances,.the.occupational.setting.may.offer.the.advantages.of.limited.
complexity.and.available.reference.material.—.when.the.engineered.nanoparticles.of.
concern.are.available.in.adequate.amounts.for.complete.characterization,.when.there.
is.minimal.variability.in.their.physical.properties,.and.when.few.interferences.from.
other. sources. in. the. workplace. air. are. expected.. In. these. instances,. the. measure-
ment.challenge.can.be.separated.into.two.distinct.approaches:.(1).physical.and.chemi-
cal.characterization,.which.can.be.completed.on.the.source.material.by.appropriate.
