Biomethylation of Arsenic in Contaminated Soils - Environmental Contamination: Health Risks and Ecological Restoration - page 253

Amendment. of. soils. with. phosphate. could. potentially. be. a. means. of.
displacing.As.from.solid.phases.and.thus.making.it.more.biologically.avail-
able.for.biomethylation..Indeed,.Signes-Pastor.et.al..(2007).showed.that.with.
increased.rates.of.P.addition.there.were.increased.levels.of.soluble.As..Since.
phosphate.fertilizers.are.routinely.added.to.soil,.this.amendment.might.be.
a. practical. means. for. increasing. As. volatilization. from. As-contaminated.
soils..Unfortunately,.even.though.phosphate.might.increase.the.uptake.of.As.
by.microorganism,.because.of.its.similar.chemical.properties.to.phosphate,.
phosphate.interferes.with.the.biomethylation.
This. was. shown. by. Cox. and. Alexander. (1973). who. studied. phosphate.
effect.on.TMA.formation.by.fungi,. C. humicola ..They.found.phosphate.inhib-
its.TMA.formation.from.arsenite,.arsenate,.and.monomethylarsonate,.but.not.
from.dimethylarsinate..Hyperphosphite.will.lead.to.temporary.reduction.or.
even.a.cessation.of.TMA.evolution.and.phosphite.suppresses.TMA.produc-
tion. from. monomethylarsonate.. They. postulated. phosphate. blocks. TMA.
formation.at.the.stage.between.the.mono-.and.dimethylarsenic.compounds,.
which.then.inhibits.biomethylation..Meanwhile,.their.research.showed.that.
high. concentrations. of. antimonite,. selenite,. selenate,. and. tellurate. affected.
conversion.rate.of.arsenate.while.nitrate.had.no.effect.
Frankenberger. (1998). reported. novel. results. on. the. effect. of. trace. ele-
ments.on.As.volatilization..He.tested.21.trace.elements.to.determine.their.
inhibition. or. activation. on. As. biomethylation. by. Penicillium . sp.. Results.
showed.at.10.or.100.μM,.only.four.trace.elements,.Co,.Fe,.Al,.and.As.(III),.
stimulated.volatilization..At.the.higher.concentration.of.1000.μM,.17.trace.
elements.completely.inhibited.biomethylation..Only.As(III).As.(V),.Se(IV).
and. Se(VI). didn't. show. complete. inhibition. and. As(III). surprisingly.
enhanced. As. volatilization. by. the. magnitude. of. 3.48-fold.. Conversely,. at.
low.concentrations,.Al,.Cu,.Fe,.Hg,.Se,.and.Zn.stimulated.biomethylation.
(Frankenberger.1998).
Perspectives
Biomethylation. may. be. a. useful,. natural. attenuation. method. for. bioreme-
diation. of. soils. and. water. contaminated. by. heavy. metals. and. metalloids.
(Frankenberger. et. al.. 1991).. Volatilization. via. methylation. could. be. used.
to. remove. As. contamination. from. soil. and. water.. Biomethylation. as. a. As.
bioremediation. technology. has. many. advantages. over. other. remediation.
approaches.. First,. As. biomethylation. is. a. naturally. occurring. process. and.
there.is.no.need.to.inoculate.speciic.microorganisms.to.contaminated.soils.
for.As.removal.(Cernansky.et.al..2007)..Second,.although.the.arsine.conver-
sion. rate. in. soils. are. considered. to. be. low. to. moderate,. especially. in. those.
soils.that.have.been.contaminated.for.a.long.time.(Edvantoro.et.al..2004),.this.