Environmental Engineering Reference
In-Depth Information
macroinvertebrates.. The. authors. are. aware. of. only. limited. ongoing. studies. of. the.
fate,.transport,.or.effects.of.nanomaterials.in.sediments,.or.on.benthic.faunal.inver-
tebrates.. Due. to. their. extremely. small. size,. nanoparticles. would. it. easily. into. the.
micropores.of.a.sediment.particle.or,.over.time,.could.bind.irreversibly.to.organic.
carbon.and.not,.therefore,.be.bioavailable.to.the.organism.in.question.
Other. researchers. also. have. questioned. the. purity. of. nanomaterials. in. aquatic.
bioassays. because. metals. and. other. byproducts. used. in. their. production. may. be.
responsible.for.toxicity,.rather.than.the.parent.nanomaterial.that.makes.up.the.major-
ity.of.the.product..One.study.suggested.that.metal.byproduct.impurities.caused.toxic-
ity.to.zebraish.embryos.in.a.bioassay.of.SWCNTs..Cheng.et.al..[31].observed.that.
the.hatching.delay.of.the.embryos.(Table.8.1).“likely.was.induced.by.the.Co.and.Ni.
catalysts.used.in.the.production.of.SWCNTs.that.remained.as.trace.concentrations.
after.puriication.”
An.unsettling.aspect.of.using.conventional.aquatic.testing.protocols.to.identify.
the. hazard. of. nanomaterials. is. dosimetry.. No. standard. yet. exists. for. deining. the.
units.of.dose.for.nanomaterials..Table.8.1.presents.doses.that.were.cited.in.units.of.
milligrams.per.liter.(mg/L)..Nanomaterials,.however,.are.particulates.that.can.actu-
ally.be.counted..Without.knowing.the.density.of.the.material.and/or.the.number.of.
particles.per.unit.weight.of.the.nanomaterial,.the.reader.is.left.without.a.frame.of.
reference. against. which. to. compare. the. dose.. Further,. surface. area. may. inluence.
reactivity..Thus,.dose.units.such.as.nanoparticles.per.milliliter.or.surface.area.units.
per.milliliter.may.be.more.relevant.to.toxicity.than.units.of.milligrams.per.liter.or.a.
molar.unit.such.as.micromolar.(µM)..If.no.standard.metric(s).are.adopted.to.ensure.
consistency. from. material. to. material. and. from. test. to. test,. then. comparing. two.
scientiic. studies. performed. using. the. same. bioassay. but. with. nanomaterials. from.
different.suppliers.will.simply.be.“comparing.apples.to.oranges.”
Note.in.Table.8.1.that.the.concentrations.employed.in. in vivo .tests.range.from.
0.1.to.360.mg/L..For.conventional.materials,.concentrations.in.the.part-per-million.
range.generally.are.not.considered.to.be.environmentally.relevant.from.the.stand-
point.of.a.realistic.concentration.in.surface.water..For.many.trace.metals,.for.exam-
ple,.regulators.will.only.be.very.concerned.with.concentrations.that.start.to.exceed.
10,.50,.or,.for.some.less.potent.metals,.100.µg/L.
These.factors.are.important.because.a.research.study,.to.be.scientiically.valid,.
must.also.be.able.to.be. reproduced .by.another.laboratory..This.includes.using.(1).the.
same.type.of.nanomaterial,.(2).the.same.method.of.test.solution.preparation,.(3).the.
same.dosing.metric,.and.(4).the.same.toxicological.testing.conditions..If.a.second.
laboratory. cannot. reproduce. the. results. of. a. study. under. the. same. environmental.
testing.conditions,.then.the.results.of.the.original.study.will.be.thrown.into.doubt.
8.4.2  d isCussiOn OF  r esults
In. reviewing. Table.8.1,. it. irst. becomes. clear. that. the. unsubstituted. carbon-based.
compounds. (e.g.,. single-. and. multi-walled. carbon. nanotubes,. C60. fullerenes,. car-
bon. black). are. dificult. to. get. into. aqueous. solution. and. thus. it. is. dificult. to. dose.
test.organisms.without.introducing.another.test.variable..Measures.taken.to.get.the.
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