Environmental Engineering Reference
In-Depth Information
endocytosis.may.be.the.most.important.transport.mechanism.because.of.the.predicted.
low.diffusion.rates.for.materials.with.volume.on.the.order.of.hundreds.to.thousands.
of.cubic.nanometers..Endocytosis.tends.to.follow.the.concentration.gradient,.in.that.
high.exogenous.particle.concentrations.result.in.high.rates.of.endocytotic.transport..
However,.the.capability.to.initiate.endocytosis.is.chemical.and.cell-speciic,.and.the.
kinetics.do.not.follow.a.diffusion.relation..This.necessitates.the.use.of.speciic.empir-
ical.expressions.for.the.derivation.of.
P
.that.cannot.be.derived.thermodynamically.
Nanoparticles.have.been.shown.to.be.transported.by.endocytosis.into.the.central.
compartment. with. a. size. cut-off. of. about. 300. nm. [5].. It. is. known. that. particulate.
matter.is.transported.from.the.intestinal.lumen.into.the.lymphatic.system.via.Peyer's.
patches.that.contain.specialized.endocytes.called.M-cells..Uptake.via.the.intestinal.
epithelium.or.intestinal.lymphatic.tissue.results.from.an.induced.cellular.response.
and.therefore.would.be.expected.to.vary.by.nanomaterial.size,.partition.characteris-
tics,.and.charge.distribution.
Few.data.describe.the.potential.for.ultraine.or.nanomaterials.to.impact.the.gas-
trointestinal.tract..Particulate.metals.in.high.concentrations.can.disrupt.the.luid.bal-
ance.in.the.colon..Some.evidence.indicates.that.ultraine.particles.may.be.involved.
in. inlammatory. conditions. such. as. irritable. bowel. syndrome. and. Crohn's. disease.
[6].. However,. a. genetic. predisposition. appears. to. be. required. for. the. condition. to.
manifest. itself,. thereby. making. population-based. generalizations. dificult. in. risk.
assessment.. Nanoparticles. of. zinc. have. reportedly. induced. both. contact. and. sys-
temic.toxicity.upon.ingestion.[7]..However,.it.is.unclear.whether.these.are.particle.
effects.or.the.result.of.zinc.dissolution.from.the.particle.surface.
.
exPosuRe and eFFeCts thRough deRMal absoRPtion
To.date,.no.speciic.reports.have.indicated.dermal.toxicity.resulting.from.exposure.to.
an.identiied.nanoproduct..However,.ultraine.metal.particles.have.been.known.to.cause.
contact.dermatitis,.as.have.polyaromatic.hydrocarbon-contaminated.soots.[8,.9].
Reportedly,.nanoparticles.of.titanium.oxide.[10],.transition.metals.[11],.liposomes.
[12],.and.functionalized.fullerenes.[13].can.penetrate.through.the.outer.layers.of.the.
skin.(stratum.corneum).into.the.viable.epidermis.and.dermis..The.rates.and.amounts.
vary.with.the.material.as.well.as.the.health.of.the.receptor..Conditions.such.as.age,.
site.of.exposure,.and.certain.chronic.disease.conditions.mediate.the.rate.and.extent.
of.penetration..Secondary.exposure.factors.such.as.vehicle,.pH,.and.even.humidity.
can. dramatically. affect. particulate. penetration. [14].. Past. research. on. particle. pen-
etration. has. involved. the. movement. of. particles. through. the. stratum. corneum. via.
impromptu.channels.formed.between.the.subsequent.layers.[15]..The.thickness.and.
permeability.of.stratum.corneum.varies.with.location.on.an.individual..Hair.follicles.
also.may.act.as.a.conduit.for.the.movement.of.materials.from.the.environment.into.
the.dermal.layers..Similar.to.the.stratum.corneum,.hair.follicles.are.also.protected.
by. a. horny. layer,. although. it. tends. to. be. thinner. than. that. present. on. surface. skin.
[14]..Studies.with.micro-scale.titanium.dioxide.(TiO
2
).particles.indicate.penetration.
of.the.epidermal.layers.with.the.greatest.concentrations.clustered.about.the.hair.fol-
licles.[10].
