Environmental Engineering Reference
In-Depth Information
As. removal. as. arsenical. gases. via. methanogenic. bacteria. under. anaerobic.
conditions.. The. initial. rate. of. As. volatilization. was. large,. which. suggested.
that.the.microorganisms.were.well.adapted.to.grow.in.the.presence.of.As..At.
later.stages.of.incubation,.the.biomethylation.rate.was.reduced.correspond-
ing.to.the.gradual.decrease.of.substrate..The.biomethylation.rate.was.a.irst-
order. linear. kinetics. up. to. 40. days. and. thereafter. biomethylation. rate. was.
negligible,.likely.due.to.the.lack.of.substrate.or.auto.poisoning.
Some.experiments.have.reported.relatively.low.rates.of.As.volatilization..
This.includes.Rodriguez.(1998).who.found.only.0.0005%.of.total.As.content.
was.lost.over.a.20.week.period..Similarly,.Turpeinen.et.al..(2002).under.both.
aerobic.and.anaerobic.conditions.showed.that.of.the.arsenate.added.to.soil,.
only.0.02%-0.3%.As.was.lost.as.volatile.TMA.over.a.10.day.lab.incubation..
They.reported.that.these.results.were.similar.to.what.they.found.in.the.ield.
in.soil.contaminated.by.industrial.As.pollution.from.a.wood.As.impregnat-
ing.factory..Islam.et.al..(2007).found.that.in.soil.contaminated.naturally.with.
As.from.geologically.contaminated.water.lost.0.4%.of.the.total.As.over.a.100.
day.incubation.
Gao. and. Burau. (1997). found. that. As. evolved. as. arsines. was. <1%. of. the.
incorporated. As. after. a. 70. day. incubation. period. for. all. treatments. in. this.
study.(<0.01%/day)..The.maximum.fractional.release.over.70.days.of.added.
As. as. arsines. (0.4%). occurred. in. the. soil. treated. with. 10.mg. As/kg. soil. as.
sodium.cacodylate.(CA),.plus.5%.cellulose.and.where.the.system.was.main-
tained.at.−0.03.MPa.
The.aforementioned.volatilization.rates.are.much.lower.than.other.reports.
in. the. literature.. Values. reported. by. Woolson. (1977b). were. in. the. range. of.
0.033%-0.386%/day. for. CA. volatilization. as. alkylarsines.. Woolson. (1977a).
observed. an. 18%. loss. from. a. CA-amended. soil. after. 160. days. when. lush-
ing.the.system.with.air..The.soil.had.a.pH.of.5.3,.a.loam.texture.and.the.soil.
moisture.was.maintained.at.25%-35%.of.ield.capacity..Addition.of.animal.
manure.to.soil.(30%.wet.wt.).with.moisture.at.75%.of.ield.capacity.resulted.
in. 8.3%. of. the. As. being. volatilized. over. a. 5. month. incubation. (Edvantoro.
et.al..2004)
A. factor. to. consider. for. rates. of. and. transformations. of. As. volatilization.
is. the. “aging”. of. As. that. occurs. in. soils. after. soils. receive. As. compounds..
Onken.and.Adriano.(1997).showed.that.As.volatilization.rate.from.sodium.
arsenate. or. sodium. arsenite. added. to. soil,. declined. to. zero. after. 68. days..
They. explained. these. results. were. due. to. the. conversion. of. bioavailable.
forms.to.insoluble.As.compounds.and.this.happened.in.both.saturated.and.
subsaturated.soils.
Anions and Trace Elements
Phosphate. and. arsenate. are. chemical. analogs.. Because. of. the. similarity.
between. these. two. anions,. competition. between. phosphate. and. arsenate.
uptake.by.microorganisms.is.likely.to.occur.(Kertulis.et.al..2004).
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