Environmental Engineering Reference
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bacteria. can. convert. inorganic. As. into. DMA,. which. is. very. stable. in. the.
absence.of.oxygen.(McBride.and.Wolfe.1971,.Cullen.et.al..1977,.Woolson.1983,.
Bentley.and.Chasteen.2002).(Table.12.2)..Methanogens.are.morphologically.
diverse.and.are.found.in.large.numbers.in.biosolids,.composts,.and.freshwa-
ter.sediments.(McBride.et.al..1978)..At.least.one.species.of. Methanobacterium .
can.form.DMA.from.arsenate,.arsenite,.and.methanearsonic.acid.substrates.
(McBride. et. al.. 1978). with. biomethylation. being. completely. inhibited. by.
heat.treatment.of. Methanobacterium .cells.(McBride.and.Wolf.1971)..Michalke.
et. al.. (2000). with. isolates. from. sewage. sludge. showed. one. bacterial. spe-
cies. ( Clostridium collagenovorans ). and. several. methanogenic. archaea. species.
(Table.12.2).could.volatilize.arsenate.to.methylated.As.forms.(AsH 3 ,.MMA,.
DMA,. TMA). under. anaerobic. conditions.. They. found. the. methanogenic.
archaea,. Methanobacterium formicicum ,.to. be. the. most.eficient.at.As. volatil-
ization.of.the.anaerobic.microorganism.tested.
Early.work.by.Cheng.and.Focht.(1979).showed.that. Pseudomonas .sp..and.
an. Alcaligenes . sp.. isolated. from. soil. produced. only. arsine. from. arsenate.
or.arsenite.when.incubated.anaerobically..The.bacteria. Corynebacterium .sp.,.
Escherichia coli ,. Flavobacterium .sp.,. Proteus .sp.,.and. Pseudomonas .sp..isolated.
by.Shariatpanahi.et.al..(1981).from.the.environment.produced.DMA.from.
the.pesticide,.sodium.arsenate..But.only. Pseudomonas .sp..formed.MMA.and.
TMA..MMA.and.DMA.were.produced.from.the.organic.pesticide.methyl-
arsonate.by. Achromobacter .sp.,. Aeromonas .sp.,. Alcaligenes .sp.,. Flavobacterium .
sp.,. Nocardia . sp.,. and. Pseudomonas with Norcardi . sp.. also. producing. TMA.
(Shariatpanahi. et. al.. 1983).. Others. have. been. found. that. TMA. oxide. can.
be.converted.to.TMA.by. Fusobacterium nucleatum ,. Veillonella alcalescens ,.and.
Staphylococcus aureus . by. Pickett. et. al.. (1988,. 1981).. Honshopp. et. al.. (1996).
isolated. Flavobacterium-Cytophaga . groups. from. soils. that. only. produced.
volatile.TMA.
Michalke. et. al.. (2000). found. that. Clostridium collagenovorans ,. Desulfovibrio
vulgaris ,.and. Desulfovibrio gigas .formed.detectable.levels.of.TMA..They.also.
showed.that.methanogenic.archaea.can.produce.arsine.( Methanobacterium for-
micium ).and.MMA,.DMA,.and.TMA.( Methanosarcina barkeri, Methanobacterium
thermoautotrophicum ).
The. bacteria. isolated. thus. far. that. can. methylate. organic. and. inorganic.
forms. of. As. aerobically. have. greater. diversity. than. those. isolated. from.
anaerobic.environments. (Frankenberger.and.Huysmans.1991)..A.cross.sec-
tion.of.bacteria.that.can.volatilize.As.under.aerobic.conditions.are.shown.in.
Table.12.2.
The.report.by.Islam.et.al..(2007).provides.an.estimate.of.the.populations.of.
bacteria.that.can.volatize.As.in.soils..They.found.that.As.methylating.bacte-
ria.(AsMB).from.ten.As-contaminated.sites.in.Bangladesh.had.from.0.2.×.10 4 .
to.7.8.×.10 4 .AsMB.(MPN)/kg.dry.soil.
It.worth.noting.that.As.volatilization.can.proceed.under.anaerobic.condi-
tions..One.of.the.irst.reports.was.by.McBride.and.Wolfe.(1971).who.found.
Methanobacterium bryantii . produced. dimethylarsine.. Isolates. from. various.
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