Environmental Engineering Reference
In-Depth Information
was.extremely.polluted..This.might.be.due.to.the.low-relief.topography.with.
organic-rich.Holocene.alluvial.sediment.deposits.(Buschmann.et.al..2007)..
14
C.dating.and.regional.history.showed.that.the.age.of.aquifer,.and.associ-
ated.sedimentary.organic.carbon,.was.greater.than.6000.years,.and.the.aver-
age.annual.clay.layer.deposit.was.found.to.be.3.3.mm.(Polizzotto.et.al..2008)..
Arsenic.concentrations.in.groundwater.ranged.from.247.08.to.1841.50.μg/L.
(n.=.46,. average. 846.14.μg/L),. with. all. of. the. observed. wells. exceeding. the.
Cambodian. drinking. water. standard. of. 50.μg/L;. Mn. concentrations. were.
584.23.±.516.49.μg/L.(mean.±.σ).with.52%.>.400.μg/L;.Fe.concentrations.were.
5901.93.±.3017.64.μg/L. (mean.±.σ),. with. 100%. exceeding. the. 300.μg/L. regu-
lation;. and. Ba. concentrations. were. 1028.26.±.477.75.μg/L. (mean.±.σ),. with.
74%.>.700.μg/L.. Out. of. the. 12. observed. wells. in. the. Kratie. province. study.
area,.a.quarter.were.found.with.elevated.arsenic.levels.and.another.quar-
ter. had. Mn.>.400.μg/L,. whereas. groundwater. samples. from. the. Kampong.
Cham. study. area. were. relatively. clean,. with. arsenic. concentrations. less.
than. WHO's. guideline. of. 10.μg/L. and. no. toxic. trace. elements. found. with.
elevated.levels.
Common. manganese. minerals. are. secondary. deposits. of. oxides. MnO
2
.
(pyrolusite). and. Mn
3
O
4
. (hausmanite). and. carbonates. MnCO
3
. (rhodochro-
site).(Greenwood.and.Earnshaw.1997)..However,.the.mechanisms.involved.
in.manganese.release.to.the.aqueous.phase.remain.unclear..Recently,.it.has.
been.reported.that,.under.anaerobic.conditions,.some.microorganisms.can.
utilize.Mn.(IV).as.an.electron.acceptor.to.oxidize.elemental.sulfur.to.sulfate.
(Prescott. et. al.. 2002).. This. microbial. activity. might. link. the. sulfur. cycle. to.
the. Mn. cycle.. This. inding. supports. the. notion. that. MnO
2
. is. reduced;. Mn.
(II). is. consequently. released. to. pore. water. under. the. reducing. conditions,.
which. could. be. harmful. to. human. beings,. as. in. the. cases. of. the. Kandal.
and.Kratie.province.study.areas..Moreover,. human.and.other. animals.can.
acquire.Mn,.an.essential.element.for.metabolism.pathways,.through.many.
food.sources.(WHO.2004)..However,.an.excess.or.deiciency.of.Mn.can.cause.
adverse. effects.. Neurological. disorders. resulting. from. drinking. very. high.
levels. of. Mn. have. been. reported. in. epidemiological. studies. (WHO. 2004)..
Barium. is. a. trace. element. present. in. igneous. and. sedimentary. rocks.. The.
most.common.barium.mineral.is.BaSO
4
.(Barite).(Greenwood.and.Earnshaw.
1997)..To.date,.barium.has.not.been.proven.to.be.carcinogenic.or.mutagenic,.
although.drinking.barium-contaminated.water.might.lead.to.hypertension.
(WHO.2004).
Arsenic Risk Assessment
A. health. risk. assessment. model. derived. from. the. USEPA. (Integrated. Risk.
Information.System—IRIS:.arsenic,.inorganic,.CASRN.7440-38-2,.1998).was.
applied. to. compute. the. noncarcinogenic. and. carcinogenic. effects. on. indi-
viduals.who.consume.groundwater.as.their.drinking.water.source:
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