Environmental Engineering Reference
In-Depth Information
8.4.1 m
ethOdOlOgies
FOr
e
valuating
h
aZards
and
their
l
imitatiOns
From.a.regulatory.perspective,.characterizing.the.toxicity.of.xenobiotics.has.become.
easier.for.aquatic.systems.than.terrestrial.systems,.mainly.due.to.the.fact.that.both.
acute.and.chronic.bioassays.have.become.standardized.over.time..These.traditional.
bioassays.employ.a.wide.range.of.species.that.are.easily.maintained.and.cultured,.
whose.life.cycles.are.well.characterized,.and.which.will.reproduce.in.the.laboratory..
Both.government.and.private.laboratories.have.used.these.species.for.bioassays.for.
decades..Indeed,.almost.all.nonnarrative.water.quality.standards.for.individual.com-
pounds,.whether.for.fresh-.or.saltwater.ecosystems,.are.based.on.a.plethora.of.tests.
on.a.wide.variety.of.organisms,.from.engineered.strains.of.bacteria.to.rainbow.trout..
The.results.of.these.tests.are.then.ranked.and.prioritized.to.determine.the.most.sen-
sitive.species,.and.to.then.obtain.the.most.sensitive.endpoint.for.the.most.sensitive.
life.stage.(usually.a.chronic,.reproductive.endpoint).for.that.species..Classic.bioassay.
techniques.have.several.limitations.when.it.comes.to.testing.nanomaterials,.includ-
ing.the.limited.solubility.of.many.materials.
What.if.a.nanomaterial.were.to.ind.its.way.into.a.waterbody.via.an.industrial.
waste. stream. and. be. able. to. resist. the. processes. of. agglomeration,. sedimentation,.
adsorption,. and. reaction?. What. would. be. the. anticipated. effects. on. individual.
organisms,.communities,.or.populations?.Unlike.terrestrial.ecotoxicity,.where.few.
data.exist,.scientists.have.studied.the.effects.of.several.classes.of.nanomaterials.on.
selected. aquatic. organisms.. Most. of. these. studies. have. focused. on. carbon-based.
nanomaterials,.and.critical.issues.such.as.the.purity.of.the.materials.and.dificulty.in.
deining.the.units.of.dose.
Table.8.1.lists.published.studies.that.have.used.various.test.species.to.bioassay.
various.types.of.nanomaterials..This.list.focuses.on.the.six.materials.examined.in.
this.topic:.carbon.black,.C60.fullerenes.and.derivatives,.single-.and.double-walled.
carbon.nanotubes,.silver,.titanium.dioxide,.and.zero-valent.iron..In.perusing.these.
articles,.it.becomes.immediately.clear.that.the.irst.obstacle.many.researchers.had.to.
overcome.was.that.of.getting.a.water-insoluble.nanomaterial.into.solution,.generally.
using.either.sonication.or.a.solvent.vehicle.
For.example,.several.researchers.[25-29].used.the.solvent.tetrahydrofuran.(THF).
as.an.initial.treatment.to.overcome.the.insolubility.of.C60.fullerenes..A.later.study.
conducted.by.Henry.et.al..[30].showed.that.the.resulting.toxicity.may.not.be.due.to.
the.nanomaterial.being.tested,.but.rather.result.from.the.toxic.effects.of.the.decom-
position.products.of.THF,.namely.γ-butyrolactone.and.tetrahydro-2-furanol..These.
treatments.alone.lead.to.the.observation.that,.if.it.is.so.dificult.to.get.an.“insoluble”.
material.into.solution.to.test.it.on.aquatic.organisms,.then.it.is.unlikely.that.fresh-.or.
saltwater. organisms. in. the. natural. environment. could. be. exposed. to. the. material.
should.it.be.released.into.an.aqueous.waste.stream..A.relatively.insoluble.nanoma-
terial. would. sorb. or. bind. to. other. insoluble. material,. which. would. eventually. be.
removed.from.the.water.column.by.natural.deposition.onto.bed.sediments..As.noted.
in.Chapter.6,.however,.adsorption.to.natural.organic.material.can.keep.some.nano-
materials.in.suspension.in.river.water.
If.this.were.the.case,.it.also.might.be.evident.that.the.nanoparticulate.in.ques-
tion. may. pose. a. risk. to. sediment-dwelling. organisms,. such. as. infaunal. benthic.
