Environmental Engineering Reference
In-Depth Information
(Burau.and.Gao.1997)..Studies.have.been.conducted.to.ind.out.the.optimum.
conditions.for.As.methylation,.and.both.very.small.and.very.large.amounts.
of.As.loss.via.methylation.have.been.reported.under.various.experimental.
conditions.(Table.12.1)..Many.factors,.including.As.sources,.microorganism.
species,. environmental. conditions. (soil. moisture,. temperature,. pH,. redox.
potential,.substrates,.etc.),.are.likely.to.affect.As.biomethylation.rates.
Arsenic Sources
Forms,. concentrations,. and. status. (freshly. added. or. residua). of. arseni-
cals. may. have. the. potential. to. affect. the. As. methylation. process.. Gao. and.
Burau. (1997). systemically. assessed. arsine. evolution. rates. of. four. different.
As.species..Under.the.same.treatments,.As.loss.followed.the.order:.sodium.
cacodylate. (dimethylarsenic. acid;. (CH
3
)
2
AsO
2
H). (CA).>.methanearsonic.
acid. (CH
3
AsO(OH)
2
).>.sodium. arsenite. [As(III)].=.sodium. arsenate. [As(V)].
(Table.12.1)..They.suggested.this.was.due.to.the.different.solubilities,.toxici-
ties,.as.well.as.methylation.mechanisms.related.to.these.species..Their.results.
were.consistent.with.Woolson's.inding.that.As.loss.from.CA-contaminated.
soil.was.about.18%,.while.only.1%.for.As(V)-contaminated.soil.after.160.days.
aerobic.incubation.(Woolson.1977a,.Table.12.1).
Cernansky.et.al..(2009).studied.the.effect.of.As.valence.on.its.biomethyl-
ation..Their.results.showed.the.average.amount.of.volatilized.As.for.all.tested.
fungal. strains. ranged. from. 10%. to. 36%. of. the. As. added. to. pure. cultures.
(Table. 12.1).. They. concluded. there. was. no. signiicant. difference. between.
As.(III).and.As.(V).on.As.biomethylation.rates..They.also.claimed.the.initial.
As.concentration.was.more.important.than.As.valence..Their.experimental.
results.showed.initial.As.concentration.of.5.or.20.mg/L.resulted.in.As.loss.
from. 0.010. to. 0.067.mg. and. 0.093. to. 1.00.mg,. respectively. (Table. 12.1).. They.
suggested.larger.initial.As.concentration.can.lead.to.higher.toxicity,.which.
will.result.in. more.intensive.microbial.detoxiication.activities.(Cernansky.
et.al..2007,.2009)..However,.Pearce.et.al..(1998).reported.no.correlation.between.
initial.As.concentration.and.As.loss.rate.under.their.test.conditions.
Arsenic. status. will. also. affect. methylation. process.. According. to.
Edvantoro. et. al.. (2004),. fungal-induced. arsine. production. was. more. pro-
nounced. (≥2.2-fold). in. soil. freshly. spiked. with. As. than. in. long-term. con-
taminated. soil,. and. the. authors. proposed. this. may. happen. as. the. freshly.
spiked. As. is. more. readily. bioavailable. (Table. 12.1).. There. is. evidence. that.
organic.arsenicals.are.more.readily.volatized.than.inorganic.forms.(Braman.
1975,.Woolson.1979).
Microorganisms
Early.work.to.identify.As.volatizing.microorganisms.was.based.on.the.pres-
ence.of.a.garlic.odor.or.known.as.“Gasio.Gas”.named.after.an.Italian.physi-
cian.Bartolomeo.Gosio.who.pioneered.research. on.the.microbiology.of.As.
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