Environmental Engineering Reference
In-Depth Information
Edvantoro.et.al..(2004).found.lower.rates.of.As.loss.with.a.soil.moisture.of.
75%.of.ield.capacity.than.a.dryer.soil.of.35%..In.this.case.over.5.month.incu-
bation,. the. higher. soil. moisture. content. had. only. about. 4%. total. As. losses.
compared.to.6%-8%.at.the.lower.water.content.of.two.soils.amended.with.
30%.animal.manure.
pH
Frankenberger.and.Huysmans.(1991).evaluated.conditions.most.suitable.for.
TMA. production. using. a.
Penicillium
. species. isolated. from. an. evaporation.
pond.in.California..They.suggested.pH.5-6,.temperatures.around.20°C,.and.
phosphate.concentration.of.0.1-50.mM.was.optimal.for.As.volatilization.
Cox.and.Alexander.(1973).tested.several.pH.conditions.for.TMA.produc-
tion. by.
C. humicola
,.indicating.the.optimum.pH. is.5.0..In.sediments,. Baker.
et.al..(1983).found.that.As.methylation.was.optimal.at.pH.3.5-5.5.which.was.
attributed.to.acidiication.causing.a.release.of.As.that.was.biologically.avail-
able.for.As.volatilization..This.mechanism.for.this.optimum.pH.was.demon-
strated.by.Signes-Pastor.et.al..(2007).who.found.that.the.lowest.pH.of.their.
experiment.(pH.5.5).had.the.highest.soluble.As.which.would.make.it.more.
biologically.available.
Redox Potential
The.results.on.the.effects.of.anaerobic.versus.aerobic.on.As.volatilization.are.
mixed.. However,. as. might. be. expected. fungi,. yeasts,. and. a. wide. range. of.
species.for.bacteria.dominate.under.oxic.conditions,.whereas.under.anaero-
bic.conditions.a.more.narrowly.focused.set.of.bacteria,.primarily.methano-
genic.bacteria.or.archaea.drive.volatilization.of.As.(Boyle.and.Jonasson.1973,.
Weinberg.1979).
Woolson.(1977a).added.isotope.labeled.As.into.soils.and.studied.As.meth-
ylation. under. both. aerobic. and. anaerobic. conditions. for. 160. days.. Results.
indicated.volatile.As.compounds.formed.most.quickly.under.aerobic.condi-
tions,. and. the. largest. As. loss. (18%). was. in. aerobically. treated. soil.. Similar.
indings.were.provided.by.Edvantoro.et.al..(2004).and.Turpeinen.et.al..(1999),.
but.all.reported.methylation.rates.in.aerobic.conditions.were.not.more.than.
18%.(Table.12.1).
Contrary. to. these. indings,. Atkins. and. Lewis. (1976). found. that. 8.1%. of.
the.
74
As. added.to.soil. was. lost. over. a. 60. day. incubation. under. anaerobic.
conditions. compared. to. 2.2%. losses. under. aerobic. conditions.. Similarly,.
Woolson. and. Kearney. (1973). showed. that. As. losses. from. sodium. caco-
dylate. added. to. soil. was. 35%. under. aerobic. conditions. whereas. under.
anaerobic. conditions. there. was. a. 61%. loss.. Interestingly,. the. form. of. As.
that.volatilized.was.different.due.to.redox.potential,.with.organic.arseni-
cals.dominating.under.aerobic.conditions.whereas.TMA.dominated.under.
aerobic.conditions.
Search WWH ::
Custom Search