Environmental Engineering Reference
In-Depth Information
Arsenic. methylation. has. been. observed. for. a. long. time.. Reports. of. mys-
terious.poisonings.from.moldy.wallpaper.in.damp.rooms.began.as.early.as.
1815.(Thom.and.Raper.1932)..Later.in.the.nineteenth.century,.people.found.
the. poisoning. was. related. to. As. in. coloring. substances. used. as. Scheele's.
green. (cupric. arsenite). and. Schweinfurth's. green. (copper. acetoarsenite). in.
wallpaper.(Challenger.et.al..1933,.Woolson.1983).
Gasio.was.the.irst.to.link.fungal.metabolism.to.the.formation.of.As.gas..
He.isolated.several.fungi.strains.from.an.As-containing.potato.medium.that.
produced. a. garlic-like. odor. gas. which. was. named. “Gasio. Gas”. after. him..
He.suggested.this. gas.was.dimethylarsine.(DMA).(Gasio.1893,.1901),.while.
Challenger.later.showed.that.the.“Gasio.Gas”.was.actually.trimethylarsine.
(TMA).(Challenger.et.al..1933,.Challenger.1945).
Challenger.established.the.metabolic.pathways.for.As.methylation.which.
came.to.be.known.as.the.Challenger's.mechanism.(Challenger.1945)..These.
pathways. are. a. series. of. reactions. where. there. is. a. reduction. of. the. pen-
tavalent. form. of. As. that. is. followed. by. the. oxidative. addition. of. a. methyl.
group.(Dombrowski.et.al..2005,.Wang.and.Mulligan.2006)..This.results.in.As.
chemical.species.that.are.increasingly.methylated.as.follows:.methyl.arsenite.
(MMA),. dimethyl. arsenate,. dimethyl. arsenite,. and. trimethyl. arsine. oxide.
which. is. shown. in. Figure. 12.1.. McBride. and. Wolfe. (1971). went. on. to. show.
that.under.anaerobic.condition,.bacteria.can.also.do.As.methylation.as.well.
The.biomethylation.process.requires.a.methyl-donor.or.precursor.(Cullen.
et. al.. 1977,. Cullen. and. Reimer. 1989,. Tamaki. and. Frankenberger. 1992),. and.
three. major. co-enzymes. including. (1). S-adenosylmethionine. (SAM),. the.
most. important. methylating. agent,. (2). N5-methyltetrahydrofolate. deriva-
tives,. and. (3). vitamin. B12. derivatives. (Fatoki. 1997,. Mohapatra. et. al.. 2008)..
Methylation
Arsenate
OH
Monomethylarsonite
Dimethylarsinate
Trimethylarsine
CH
3
CH
3
CH
3
Methylation
CH
3
CH
3
CH
3
HO
As
OH
HO
As
OH
HO
As
As
O
O
CH
3
CH
3
Methylation
Methylation
HO
As
OH
HO
As
OH
HO As
CH
3
CH
3
As
CH
3
OH
CH
3
O
O
Arsenite
Monomethylarsonate
Dimethylarsinite
Trimethylarsine oxide
FIGURE 12.1
Revised. Challenger. Mechanism. for. arsenic. methylation. pathway.. (Based. on. Wang,. S.. and.
Mulligan,.C.N.,.
J. Hazard. Mater
.,.138,.459,.2006.)
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