Environmental Engineering Reference
In-Depth Information
supports.the.evaluation.of.the.Assessment.Endpoint,.such.as:.“What.is.the.Concen-
tration. Y. of. Chemical. X. that. will. adversely. affect. 20%. of. a. known. population. of.
rainbow.trout.in.the.laboratory?”
The. main. endpoint. for. measuring. ecological. toxicology. is. the. LD50,. or. the.
lethal.dose.required.to.kill.50%.of.the.organisms.under.controlled.laboratory.testing.
conditions..For.aquatic.organisms,.the.LC50.and.EC50 . (or.the.respective.lethal.con-
centration.and.effect.concentration.required.to.kill.or.affect.50%.of.the.organisms).
are.the.more.appropriate.terms.used.for.a.toxicity.endpoint..When.dose.is.plotted.
versus.response,.the.slope.of.the.curve.is.a.general.indication.of.the.potency.of.the.
toxicant:.the.steeper.the.slope,.the.more.potent.the.toxicant.relative.to.chemicals.of.
a.similar.class.
One.can.generalize.about.how.these.criteria.will.relect.the.relative.toxicity.of.
a.substance.based.on.its.structure.and.the.principle.that.like.dissolves.like..Because.
cell.membranes.primarily.comprise.a.lipid.bilayer,.lipophilic.or.fat-loving.substances.
are,.as.a.general.rule.of.thumb,.more.toxic.than.hydrophilic.or.water-loving.(soluble).
substances..Lipophilic.substances.are.more.easily.absorbed.by.inhalation,.ingestion,.
or. dermal. exposure,. and. tend. to. have. a. longer. half-life. (i.e.,. the. time. required. to.
reduce. the. body. burden. of. a. toxicant. by. one-half,. either. by. metabolism. or. excre-
tion),.while.water-soluble.substances.are.more.easily.metabolized.by.the.liver.and/or.
excreted.by.the.kidney.and.thus.tend.to.have.a.shorter.residence.time.in.the.body.
In.the.ield.of.inhalation.toxicology,.foreign.matter.is.generally.categorized.as.
gas,.vapor,.or.particulate.(or.ibrous).matter..The.latter.can.affect.physically.the.elas-
ticity.of.the.lung..Examples.include.silicosis.in.concrete.and.quarry.workers,.asbes-
tosis.in.shipyard.workers,.and.pneumoconiosis.in.coal.miners..Nanoparticles.would.
be. classiied.as. particulate. matter,.but. because. these. particulates.are. so. extraordi-
narily.small,.they.fall.in.a.toxicological.gray.area..Some.comprise.potentially.toxic.
elements. that,. if. dissociated. or. dissolved,. may. cause. adverse. effects. inside. a. cell..
Therefore,. they. may. cause. adverse. extracellular. physical. effects. similar. to. those.
caused.by.larger.ibers.such.as.asbestos.or.iberglass.insulation,.or.may.be.actively.
or.passively.internalized.by.cells.and.cause.toxic.effects.by.interfering.with.cellular.
processes..Data.from.a.battery.of.both. in vitro .and. in vivo .bioassays.may.be.needed.
to.reveal.to.the.investigator.the.inherent.toxicity.of.the.various.elements.and.com-
pounds.that.comprise.nanomaterials.(for.some.of.which.there.are.little.to.no.toxico-
logical.data)..The.dificulty.will.lie.in.separating.whether.an.adverse.effect.relects.
a.physical.effect.induced.by.the.nanomaterial.or.a.direct.toxic.effect.resulting.from.
the.composition.of.the.material.itself.
For. example,. carbon. black,. a. common. nanomaterial. in. commercial. use. for.
decades,. is. considered. biologically. inert.. Although. it. may. remain. in. the. body. in.
a.sequestered.form,.it.is.expected.to.have.a.low.inherent.toxicity.[3]..In.contrast,.a.
unique. nanomaterial. constructed. from. one. (or. more). elements. may. be. inherently.
toxic.. Consider. cadmium,. a. highly. toxic. metal. used. to. make. quantum. dot. alloys.
of. cadmium. selenide. or. cadmium. telluride.. Toxic. effects. on. the. reproductive. sys-
tem. or. the. nervous. system. are. of. particular. concern.. The. response. of. these. sys-
tems,.in.general,.will.take.a.longer.time.to.unravel.than.other.biological.endpoints,.
because.the.endpoints.take.a.long.time.to.achieve,.are.expensive.to.characterize,.or.
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