Environmental Engineering Reference
In-Depth Information
et.al..[6].reported.this.phenomenon.for.fullerenes,.where.the.crystalline.properties.of.
the.agglomerated.material.vary.based.on.the.medium.from.which.it.condensed.
Because.polymorphism.can.cause.variations.in.physical.and.chemical.properties,.
care.must.be.taken.in.extrapolating.from.the.experimental.results.for.a.nanomaterial.
. PRediCting the behaVioR oF
nanoMateRials in the enViRonMent
The.interactions.of.any.given.nanomaterial.with.its.environment.depend.on.both.the.
physical. and. chemical. properties. described. above.. All. nanomaterials. will. behave.
differently. because. their. physical. and. chemical. natures. vary. with. composition. and.
structure..However,.by.placing.the.known.properties.of.the.materials.within.an.envi-
ronmental.context,.it.is.possible.to.generally.predict.a.material's.transport.within.the.
environment.and.the.thermodynamics.of.potential.interactions.with.the.environment.
Because.the.ultimate.purpose.for.predicting.the.fate.and.transport.of.a.material.
often.is.to.determine.the.potential.for.an.adverse.environmental.effect,.it.is.useful.to.
consider.the.environmental.interactions.within.the.context.of.the.risk.paradigm..For.
nanomaterials,.this.can.be.divided.into.three.principal.considerations:
.
1.. Potential.and.rate.of.dispersal.or.agglomeration.in.environmental.media.
.
2.. Potential.and.rate.of.interactions.with.environmental.constituents.
.
3.. Rate.and.form.that.a.nanomaterial.will.be.presented.to.an.environmental.recep-
tor.of.concern..(Chapters.8.and.9.discuss.the.potential.results.of.exposure.)
As.with.any.material,.nanomaterials.will.tend.toward.their.equilibrium.state.(∆
G
.
=.0).within.their.environment..While.this.makes.it.very.straightforward.to.determine.
the.equilibrium.conditions.for.a.given.situation,.complications.related.to.particulate.
properties.can.result.in.signiicant.variability.in.the.transient.states..In.consequence,.it.
can.be.dificult.to.predict.the.precise.kinetics.and.therefore.the.time.course.by.which.
a.nanomaterial.will.transform.from.the.state.in.which.it.enters.the.environment.to.its.
ultimate.equilibrium.state..For.example,.consider.dispersion.and.agglomeration.
Considerations.of.dispersion.and.agglomeration.are.akin.to.solubility.and.vapor.
pressure.for.non-nanomaterials,.in.that.they.form.the.basis.for.predicting.the.con-
centrations.of.materials.in.environmental.media.(air.or.water).relative.to.the.amounts.
released.. However,. while. vapor. pressure. and. solubility. are. equilibrium. measures,.
dispersion. and. agglomeration. are. dynamic. measures.. This. difference. results. from.
the. scale. of. events. involved.. For. example,. a. small. volatile. molecule. such. as. vinyl.
chloride. will. reach. equilibrium. vapor. pressure. very. quickly. such. that. the. period.
of.disequilibrium.becomes.insigniicant.within.an.environmental.context..An.aero-
sol. of. titanium. dioxide. in. nanoparticulate. form,. however,. may. take. hours. or. even.
days. to. reach. equilibrium.. Depending. on. the. nature. of. the. exposure,. generalizing.
equilibrium.in.such.cases.may.introduce.signiicant.uncertainty.that.may.be.over-.
or.under-predictive..In.risk.assessments.where.assumptions.of.equilibrium.are.not.
appropriate,. dynamic. prediction. methods. may. need. to. be. applied. to. develop. rea-
sonable.estimates.of.safety..Dynamic.prediction.differs.from.equilibrium.in.that.it.
requires. a. time-to-event. consideration.. The. changes. in. the. nature. of. nanomaterial.
