Field Application of the Stabilization Process for Arsenic-Contaminated Soil - Environmental Contamination: Health Risks and Ecological Restoration - page 455

from.intense.husbandry.(disinfectants);.compost.and.dung.(surplus.As.from.
animal.feeding);.household.waste.disposal;.glassware.production.(decolor-
ing. agent);. electronics. industries.(admixture. in.semiconductor.production,.
arsenide. as. laser. material. to. convert. electrical. energy. into. coherent. light);.
ore. production. and. processing. (melting. and. roasting. in. nonferrous. smelt-
ers,. melting.in.iron. works);. metal. treatment.(admixture. in. bronze.produc-
tion,.lead.and.copper.alloys);.galvanizing;.ammunition.factories.(hardening.
and.improvement.of.light.characteristics.of.projectiles);.chemistry.(dyes.and.
colors,. wood. preservatives,. pesticides,. pyrotechnics,. drying. agent. for. cot-
ton,. oil. and. dissolvent. recycling);. and. pharmaceutical. works. (medication).
(Reimann.and.Caritat.1998,.Matschullat.2000).
Geochemical Characteristics of Arsenic
Arsenic. belongs. to. group. 15. (N,. P,. As,. Sb,. Bi). of. the. periodic. table. ele-
ments,.and.it.has.an.outer.electronic.coniguration.of.4s 2 4p 3 .(Alloway.1995)..
Geochemically,. arsenic. is. present. in. close. association. with. the. transition.
metals,.namely,.Au,.W,.Sb,.Bi,.and.Mo,.and.is.commonly.present.as.an.impu-
rity.in.varieties.of.metallic.ferrous..Arsenic.is.a.toxic.element.and.is.classi-
ied.by.the.U.S.. Environmental.Protection.Agency.as.a.human.carcinogen..
Arsenic. occurs. in. the. environment. through. weathering. and. volcanism.
( Juillot.et.al..1999).and.can.form.various.oxidation.states,.such.as.−3,.0,.+3,.
and.+5..Arsine.(AsH 3 ).is.a.poisonous.and.lammable.gas,.but.rarely.occurs.
in.nature.(Cheng.et.al..2009)..Arsenic.is.toxic.to.both.plants.and.animals,.and.
inorganic.arsenicals.are.proven.carcinogens.in.humans.(Ng.2005)..The.toxic.
effects.of.arsenic.on.human.health.range.from.skin.lesions.to.cancer.of.the.
brain,.liver,.kidney,.and.stomach.(Smith.et.al..1992)..Arsenite.(As 3+ ).and.arse-
nate.(As 5+ ).are.the.most.common.species.in.natural.environments..Arsenite.
is.reported.to.be.more.mobile.than.arsenate.and.is.25-60.times.more.toxic.
(Conner.1990,.Pantsar-Kallio.and.Manninen.1997,.Corwin.et.al..1999,.Moon.
et.al..2008)..Monomethyl.arsenic.(MMA).and.dimethyl.arsenic.(DMA),.which.
are. organic. forms. of. arsenic,. have. low. toxicity. compared. with. their. inor-
ganic.forms.
Arsenic. is. mainly. present. as. arsenite. and. arsenate. under. the. natural.
conditions,. but. its. oxidation. state. can. change. with. pH,. Eh,. and. microbial.
activity..Figure.21.1.shows.the.Eh-pH.diagram.for.arsenic..Arsenite.species.
predominate.under.reducing.conditions.and.is.more.soluble.than.arsenate.
because. it. is. not. ionized. and. adsorbs. less. strongly. than. arsenate. species.
(Nordstrom. and. Archer. 2003).. Thermodynamic. calculations. and. experi-
mental. results. indicate. that. at. high. redox. levels. (pe.+.pH.>.10),. arsenate. is.
the. predominant. arsenic. species. whereas. under. moderately. reducing. and.
reducing.conditions.(pe.+.pH.<.8),.arsenite.is.the.most.abundant.form.of.arse-
nic.(Masscheleyn.et.al..1991,.Sadiq.1997,.Cheng.et.al..2009)..The.equilibria.for.
arsenous.acid.(As(III)).and.arsenic.acid.(As(V)).in.aqueous.solution.are.given.
as.follows.(Alloway.1995).