Biomethylation of Arsenic in Contaminated Soils - Environmental Contamination: Health Risks and Ecological Restoration - page 250

Thomas. and. Rhue. (1997). showed. there. was. an. interaction. between. a.
readily.available.energy.source.(glucose).and.redox.conditions..They.found.
that.under.more.aerobic.conditions,.addition.of.glucose.had.no.effect.on.As.
volatilization. compared. to. anoxic. conditions. when. glucose. stimulated. As.
volatilization.
These. somewhat. conlicting. results. between. aerobic. and. anaerobic. con-
ditions. might. be. explained. by. the. lack. of. control. or. accounting. for. the.
exact. level. of. redox. potential. in. previous. experiments. (e.g.,. anaerobic. vs..
aerobic.but.no.measurement.of.the.actual.redox.potential.across.treatments)..
A.potential.insight.for.the.role.of.redox.potential.on.biomethylation.may.be.
related.to.the.solubility.or.bioavailability.of.As.as.a.function.of.Eh..Signes-
Pastor. et. al.. (2007). showed. that. As. was. most. soluble. under. moderately.
reducing. conditions. (0. to. −150.mV). due. to. dissolution. of. iron. oxy-hydrox-
ides..Interestingly.upon.reduction.to.−250.mV,.As.solubility.decreased.and.
was. controlled. by. the. formation. of. insoluble. sulides.. This. is. important.
because. if. redox. potential. controls. soluble. As. (biologically. available),. it.
therefore.also.controls.biomethylation.and.rates.of.As.volatilization.
Although.most.of.the.research.on.speciic.microbial.anaerobic.isolates.(as.
described.previously).has.been.done.in.relation.to.anaerobic.sewage.sludge.
or. in. pure. cultures. (see. review. by. Bentley. and. Chasteen. [2002]),. anaerobic.
bacteria.could.be.important.in.remediating.As.contaminated..For.example,.
when.local.conditions.allow,.it.might.be.possible.to.lood.As-contaminated.
sites.or.to.have.pulsing.systems.that.result.in.luctuating.redox.potential.to.
drive.anaerobic.As.
Indeed,.luctuating.between.low.and.high.redox.potential.may.be.impor-
tant. in. making. As. more. biologically. available.. This. was. shown. by. Frohne.
et.al..(2010).and.others.(Masscheleyn.et.al..1991,.Chiu.et.al..1998,.Mitsunobu.
et. al.. 2006). that. soluble. As. (as. III. species). increased. with. decreasing. redox.
potential..The.mechanism.is.that.under.low.redox.potential,.Fe.(hydr)oxides.
are.reduced.which.results.in.concurrent.release.of.associated.As.(Mitsunobu.
et.al..2006)..Thus,.one.could.imagine.subjecting.soils.to.reducing.conditions.
to. increase. As. in. soil. solution. followed. by. induction. of. aerobic. conditions.
that.would.be.a.more.favorable.environment.for.fungi.which.typically.do.not.
thrive.under.anaerobic.condition..But.stimulated.under.aerobic.conditions,.
fungi.can.be.dominant.players.in.driving.As.volatilization.
Non-Arsenic Substrates
Soil Amendments
Nutritional.support.of.microorganisms.has.been.shown.to.be.related.to.As.
biomethylation.. This. was. irst. supported. by. Atkins. and. Lewis. (1976). who.
investigated. As. release. from. soils. that. had. a. range. of. soil. organic. matter.
levels.. In. this. case. the. highest. level. of. release. was. 11%. of. the. isotopically.
labeled.As.soil.(100.μg.As/g).in.the.soil.with.the.highest.organic.matter.con-
tent. (11%). after.60.days.. From.this. it. would. follow. that. addition.of.organic.