Environmental Engineering Reference
In-Depth Information
strain. isolated. from. the. contaminated. soil. having. made. adaptations. to.
reduce.toxicity.by.enhancing.melanin.production,.which.binds.As.(Fogarty.
and.Tobin.1996),.or.by.enzymatic.intracellular.transformation.of.As—all.of.
which.immobilizes.As.rather.than.allowing.for.biomethylation.and.volatile.
losses.of.As.
Of. the. fungi. studied. so. far. it. seems. C. humicola . may. be. one. of. the. most.
important.and.versatile.for.volatilizing.As..It.can.use.arsenate.or.arsenite.as.
a.substrate.to.produce.TMA.(Cullen.et.al..1979)..Additionally.it.can.methylate.
benzenearsonic. acid,. methylphenylarsinic. acid,. and. dimethylphenylarsine.
oxide.to.the.volatile.dimethylphenylarsine.(Cullen.et.al..1983)..And.as.men-
tioned.earlier.it.can.deplete.As.from.wood.impregnated.with.the.preserva-
tive.CCA.(Cullens.et.al..1984).
Microbial Inoculation of Soils
Inoculation. of. soil. with. As. methylating. microorganisms. can. enhance. bio-
methylation.rates..Edvantoro.et.al..(2004).reported.arsine.evolution.rates.for.
inoculated.( Penicillium .sp..and. Ulocladium .sp.).to.long-term.As-contaminated.
and.freshly.As.spiked.soils.were.approximately.3.7.and.8.3.orders.of.magni-
tude.greater.than.uninoculated.soils.(Table.12.1).
Pearce. et. al.. (1998). found. fungus. isolated. from. uncontaminated. sub-
strate. was. more. capable. of. methylating. As. than. fungus. isolated. from.
As-contaminated.substrate..They.attributed.this.inding.to.the.fact.that.fungi.
isolated. from. contaminated.soil.may. have. a. larger.ability. than.fungi. from.
uncontaminated.soil.to.produce.melanin,.a.compound.that.may.bind.As.and.
decrease.As.uptake.(Fogarty.and.Tobin.1996)..Similar.results.were.found.by.
Cernansky. et. al.. (2007). who. showed. that. A. niger . (B). strains. isolated. from.
uncontaminated.substrates.had.higher.ability.to.volatilize.As.than.the.strain.
from.an.uncontaminated.substrate..They.suggested.that.the.strain.isolated.
from.contaminated.substrate.may.shift.toward.As.absorbance.and.tolerance.
over.volatilization.
Though. conversion. rates. varied,. many. previous. studies. showed. most.
extractable. soil. As. can. be. transferred. to. the. atmosphere. by. this. microbial.
process.(Table.12.1).
Environmental Conditions
Soil Moisture and Temperature
It.stands.to.reason.that.favorable.moisture.and.temperature.regimes.would.
enhance. a. biologically. driven. process. such. as. As. volatilization.. Indeed,.
Woolson.(1977b).concluded.that.the.environmental.factors.of.adequate.mois-
ture. and. warm. temperatures. that. promote. microbial. activity. in. combina-
tion.with.high.organic.matter.enhance.biomethylation..Gao.and.Burau.(1997).
proposed.that.warmer.temperatures.and.an.optimum.soil.moisture.between.
250.and.350.g.H 2 O/kg.soil.can.enhance.arsine.evolution.
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