Environmental Engineering Reference
In-Depth Information
occur.frequently.and.arise.through.a.variety.of.mechanisms..The.differen-
tial.retention/eflux.of.contaminants.caused.by.these.mechanisms.may.alter.
exposure. and. hence. the. overall. toxicity. to. organisms. in. natural. environ-
ments..Most.of.the.studies.indicated.that.the.occurrence.of.synergistic.toxic-
ity.between.PAHs.and.metals.may.be.predominant.(Gust.2005)..Therefore,.
metals.may.facilitate.either.synergistic.or.antagonistic.toxic.effects.depend-
ing.on.which.reactions.they.affect.during.PAH.metabolism.
In.addition.to.metals.altering.the.toxicity.of.hydrocarbons,.interactive.tox-
icity.may.also.be.elicited.when.hydrocarbons.inluence.metal.toxicity..For.
example,.George.and.Young.(1986).showed.that.the.PAH.3-methylcholan-
threne.delayed.the.onset.of.metallothionein.induction.in.plaice..Also,.PAHs.
have. been. found. to. affect. the. bioaccumulation. of. metals.. Fair. and. Sick.
(1983).found.that.the.Black.Sea.bass,.
Centropristis striata
,.assimilated.higher.
concentrations.of.Cd.in.various.tissues.from.food.(spiked.oyster.tissue).con-
taining.Cd.and.naphthalene.compared.to.food.containing.Cd.alone..Babu.
et.al..(2001).found.synergistic.inhibitory.effects.on.photosynthetic.rate.and.
plant. growth. in. duckweed. (
Lemna gibba
). when. exposed. to. an. oxygenated.
PAH. (1,. 2-dihydroxyanthraquinone). and. Cu..The.combined.contaminants.
were.found.to.dismantle.the.function.of.photosynthetic.electron-transport.
chain,.thereby.severely.inhibiting.energy.metabolism.and.growth.
MicrobialMechanismsforMetalResistance
Microorganisms. have. coexisted. with. metals. since. the. beginning. of. life,.
and. essential. metals. are. used. for. catalyzing. key. metabolic. reactions. and.
maintaining.protein.structures..Although.metals.are.thought.to.inhibit.the.
ability. of. microorganisms. to. degrade. organic. pollutants,. several. microbial.
mechanisms.of.resistance.to.metal.are.known.to.exist.(Nies.and.Silver.1995)..
A.breadth.of.microbial.metabolic.function.is.presumed.to.enhance.resistance.
to. environmental. stress. and. disturbance.. For. protection. against. the. toxic.
effects. of. heavy. metals,. bacteria. can. adapt. diverse. resistance. systems. that.
confer.upon.them.a.certain.range.of.metal.tolerances.(Gadd.2010,.Valls.and.
Lorenzo.2002)..Resistant.mechanisms.include.intracellular.and.extracellular.
metal. sequestration,. metal. reduction,. metal. eflux. pumps,. and. production.
of.metal.chelators.such.as.metallothioneins.and.biosurfactants..Despite.the.
ubiquity. and. eficacy. of. microbial. mechanisms. for. metal. resistance,. a. few.
studies.have.attempted.to.exploit.them.to.increase.pollutant.biodegradation.
in.mixed.contaminated.systems.
Generally,. the. decrease. in. metal. concentration. in. microbial. experiments.
could.be.the.result.of.several.known.detoxiication.mechanisms.such.as.(1).
sorption.of.metals.by.the.bacterial.cells.(Bollag.and.Duszota.1984),.(2).energy-
dependent. accumulation. of. metals. by. the. cells. and. subsequent. interaction.
Search WWH ::
Custom Search