Mixed Contamination of Polyaromatic Hydrocarbons and Metals at Manufactured Gas Plant Sites: Toxicity and Implications to Bioremediation - Environmental Contamination: Health Risks and Ecological Restoration - page 359

sheep.dip.sites,.could.have.the.capacity.of.tolerating.toxic.concentrations.of.
metals. and,. at. the. same. time,. capacity. of. degrading. organic. contaminants.
and.utilizing.carbon.as.source..These.changes.in.community.structure.are.
important. and. may. lead. to. the. development. of. successful. bioremediation.
strategies..To.our.knowledge,.there.are.no.reports.on.the.successful.isolation.
and.characterization.of.microorganisms.that.are.metal.resistant.and.capable.
of.degrading.organic.pollutants.
InhibitionofPAHsDegradationbyMetals
Signiicant.associations.between.metals.and.PAHs.in.soil.exert.an.inluence.
on.microbes.that.manifests.itself.in.drastic.changes.in.microbial.diversity..It.
has. been.reported.that.the. presence.of.metals. impedes. the.biodegradation.
of.PAHs.(Table.16.4),.although.microorganisms.require.some.of.these.heavy.
metals.at.trace.levels.for.growth.(Wong.et.al..2005,.Atagana.2006)..Maslin.and.
Maier.(2000).examined.the.impact.of.Cd.on.phenanthrene.biodegradation.by.
indigenous.soil.community.in.two.desert.soils.over.a.9.day.period..Results.
showed.an.increase.in.lag.period.by.5.days.for.phenanthrene.degradation.in.
the.presence.of.1.and.2.mg.solution-phase.Cd/L.and.complete.inhibition.at.
3.mg. solution-phase.Cd/L..The. inluence. of.trace.metals. on. microbial. deg-
radation. of. aromatic. and. aliphatic. hydrocarbons,. either. in. solution. (Amor.
et. al.. 2001). or. in. soil. (Baldrian. et. al.. 2000),. has. been. investigated.. Baldrian.
et. al.. (2000). observed. degradation. of. PAH. molecules. up. to. ive. to. six. aro-
matic. rings. by. the. white. rot. fungus,. Pleurotus ostreatus ,. in. the. presence. of.
100.mg/kg.Cd. in.nonsterile.soil,.but.Cd.at.500.mg/kg.completely.inhibited.
the.PAH.biodegradation..Although.the.rate.of.PAH.degradation.by.the.fun-
gus.was.not.affected,.presence.of.Cd.was.inhibitory.to.the.activity.of.lignino-
lytic.enzymes,.laccase,.and.Mn-dependent.peroxides..The.biodegradation.of.
PAHs.was.reduced.by.free.Cd.species.between.0.002.and.1.mg/L.(Springael.
et.al..1993,.Sandrin.et.al..2000,.Sandrin.and.Maier.2003).
Riis.et.al..(2002).studied.the.degradation.of.diesel.fuel.by.a.microbial.com-
munity.from.a.soil.polluted.with.heavy.metals.such.as.Cu,.Ni,.Zn,.Pb,.Cd,.
Hg,. and. Cr.. The. degradation. was. greatly. inhibited. by. the. concentrations.
of. metals,. and. toxicity. of. the. metals. followed. the. order:. Hg.>.Cr(VI).>.Cu.>.
Cd.>.Ni.>.Pb.>.Zn.. Fluoranthene. degradation. by. bacteria. grown. on. agar.
plates. was. totally. inhibited. by. 10.mg/L. of. Cd. and. 50.mg/L. of. Zn. and. Cu.
(Gogolev. and. Wilke. 1997).. Since. metal. complexing. ligands. are. present. in.
agar,. the. concentration. of. bioavailable. metal. in. agar. plates. might. be. very.
low.or.totally.zero..Shen.et.al..(2005).spiked.the.mixtures.of.PAHs.(phenan-
threne,. luoranthene,.benzo(a)pyrene).and. metals.(Cd,.Pb,. Zn). to. study. the.
effect.of.mixed.contaminants.on.soil.urease.activity..The.results.showed.that.
Zn.interacted.more.easily.with.PAHs.than.Pb.or.Cd;.the.combined.effect.of.