Biomethylation of Arsenic in Contaminated Soils - Environmental Contamination: Health Risks and Ecological Restoration - page 233

Arsenic.has.become.a.widespread.hazard.in.India,.Bangladesh,.Vietnam,.
Chile,. and. Taiwan.. In. some. cases. this. is. due. to. pollution. but. additionally.
vast. areas. of. these. countries. have. been. contaminated. by. As. of. geological.
origin.(Nordstrom.2002)..Epidemiological.studies.in.these.regions.indicated.
that. skin,. liver,. lung,. bladder,. and. other. cancers. are. highly. related. to. the.
exposure. to. As. (Abernathy. et. al.. 1999).. Of. further. concern,. particularly. in.
Bangladesh,.is.that.groundwater.containing.high.levels.of.geologic.As.was.
extensively.used.for.irrigation.water.between.the.1980s.and.2000s.(Meharg.
and. Rahman. 2002).. This. has. elevated. As. in. rice. soils. of. Bangladesh. from.
background.levels.of.10.to.as.much.as.46.μg.As/g.soil.and.caused.elevated.
levels.of.As.in.rice.grain.(Meharg.and.Rahman.2002).
A. major. concern. is. for. children. who. ingest. soil. contaminated. with. As..
This. is. based. on. human. or. animal. studies. that. have. shown. that. ingested.
inorganic.As.salts.are.absorbed.from.the.gastro-intestinal.tract.and.enter.the.
blood.stream..The.relative.bioavailability.of.dosed.sodium.arsenate.is.80%.
(Basta.et.al..2001,.Scheckel.et.al..2009)..This.is.a.much.higher.rate.than.most.
other.nonessential.elements.and,.in.part,.is.likely.due.to.arsenate's.(AsO 4 3− ).
chemical.similarity.to.the.essential.nutrient,.phosphate.(PO 4 3− ),.that.is.read-
ily. absorbed. through. the. gastric. intestinal. track. of. animals. (Caussy. and.
Priest.2008).
Remediation Strategies
There. are. potentially. a. number. of. approaches. for. remediating. As-conta-
minated. soils.. One. strategy. would. be. physical. removal. of. these. soils. to.
contained. landill. sites.. Although. this. may. be. appropriate. for. highly. con-
taminated. and. localized. pollution,. it. would. be. too. expensive. for. As. con-
tamination.over.large.areas.or.where.the.soil.would.need.to.be.replaced.for.
agricultural.or.landscape.vegetation.
Phyotoremediation.is.an. in situ .approach.whereby.hyperaccumulating.As.
plants. are. grown. and. As. is. removed. by. harvesting. plants.. Disadvantages.
of. this. approach. include. the. following:. As. accumulating. plants. must. be.
locally.adapted;.requiring.plant.management.and.repeated.harvests.over.an.
extended. period;. and. disposal. of. As.plant.biomass,.all.of.which. limits. the.
economic.feasibility.of.this.method.
An. alternative. As. remediation. approach. is. in situ . volatilization. of. As..
This. involves.As. biotransformation.by. reduction.and.methylation. of. As.in.
As-enriched. soils.. Microorganisms. can. release. volatile. derivatives. of. As.
(mainly.arsines,.mono-,.di-.or.tri-methylarsine,.and.As.oxides)..This.approach.
could.be.done.as.a.stand-alone.method.or.in.tandem.with.phytoremediation.
of.As-contaminated.soils.
A. concern. of. this. approach. is. the. dispersion. of. toxic. forms. of. As. in. the.
atmosphere..However,.it.irst.should.be.noted,.as.mentioned.earlier.that.As.
volatilization. is. a. natural. process.. As. gases. are. released. from. natural. and.
anthropogenic. sources. that. includes. sewage. treatment. plants,. lake. and.