Environmental Engineering Reference
In-Depth Information
A.nanomaterial.is.a.particulate.manifestation.of.one.or.more.identiiable.chemi-
cals.combined.as.an.insoluble.entity.in.its.medium.of.transport..Because.covalent.
interactions.would.negate.the.particle's.identity.as.a.nanomaterial,.interactions.with.
the.suspending.medium.usually.involve.only.weak.or.Coulomb.forces..By.deinition,.
nanomaterials.range.in.size.from.1.to.100.nanometers.(nm)..The.uniqueness.of.nano-
materials. is. based. on. the. fact. that. they. present. an. environmentally. or. toxicologi-
cally.reactive.entity.with.a.multi-atomic.or.multi-molecular.surface.associated.with.
non-surface.constituents..The.surface.properties.of.these.particles.often.differ.from.
their.molecular.form.with.regard.to.photo-.and.electrochemistry.as.well.as.reactive.
thermodynamics. [1].. Furthermore,. their. size. imparts. to. nanomaterials. a. potential.
for. environmental. and. pharmacokinetic. distributions. that. differ. from. both. larger.
particulate.and.smaller.molecular.forms..These.departures.can.signiicantly.impact.
the.risk.assessment.by.altering.or.even.negating.inherent.assumptions.regarding.both.
exposure.and.toxicological.response.
At.the.time.of.publication.of.this.work,.the.understanding.of.the.actual.exposure.
and.toxicology.of.speciic.nanomaterials.was.still.in.its.infancy..To.aid.in.the.progress.
of.risk.assessment.for.nanomaterials.in.the.environment,.this.chapter.concentrates.
irst.on.aspects.of.the.assessment.process.that.would.be.speciic.and.unique.to.nano
-
materials,.and.second.on.how.to.integrate.these.considerations.within.a.risk.para-
digm.useful.for.the.evaluation.of.human.and.ecological.safety..(Note.that.Section.9.8.
lists.the.symbols.used.in.the.mathematical.models.in.these.discussions.).The.chapter.
concludes.with.a.brief.review.of.the.current.knowledge.base.
. Risk assessMent and nanoMateRials
Risk.assessment.is.the.quantitative.analysis.intended.to.predict.the.magnitude.of.a.
response.as.the.result.of.an.event..In.this.case,.the.event.is.the.presentation.of.a.nano-
material.at.a.given.rate.or.concentration,.and.the.response.is.a.physiological.impair-
ment.within.a.deined.receptor..This.type.of.toxicological.risk.assessment.originated.
in.medical.and.clinical.practices..Its.use.has.since.expanded.to.quantify.situations.
involving.matters.ranging.from.product.safety.to.environmental.pollution.
Application.of.toxicological.risk.assessment.to.nanomaterials.will.not.require.a.
signiicant.change.in.the.standard.paradigms..However,.it.will.entail.new.consider-
ations.that.previously.were.either.insigniicant.or.could. be. reasonably.generalized.
using.conservative.or.equilibrium-based.assumptions..For.nanomaterials,.such.gen-
eralizations.could.be.extremely.imprecise..Hence,.considerations.such.as.partition-
independent.penetration,.inlammatory.and.sensitivity.reactions,.and.disequilibrium.
dynamics.will.be.required.to.accurately.quantify.risk.
9.1.1 e
FFeCts
OF
s
teriC
h
indranCe
Nanomaterials,. like. ultraine. particles,. do. not. necessarily. follow. the. same. toxico-
logical.paradigms.as.molecular.toxicants..Differing.routes.and.altered.potential.for.
absorption.can.result.in.different.exposures..The.toxicological.response.to.particulate.
toxicants.may.not.always.follow.the.concentration.gradient.because.of.steric.limita-
tions.resulting.from.the.particle.size..Steric.limitations.arise.when.a.physiological.
