Environmental Engineering Reference
In-Depth Information
(A)
(B)
(C)
FIGURE 17.3
Formation.of.Fe.plaque.and.immobilization.of.heavy.metals:.(A).oxygen.release.from.the.root.
and.oxidation.of.Fe
2+
,.(B).formation.of.Fe.plaque.on.the.root.surface,.and.(C).immobilization.of.
heavy.metals.in.Fe.plaque.
barrier. reduced. metal. mobility. and. bioavailability,. thus. preventing. trace.
metals. from. reaching. the. more. sensitive. parts. of. the. plant.. Moorthy. and.
Kathiresan.(1998).also.reported.that.heavy.metal.concentrations.in.
Rhizophora
apiculata
.seedlings.decreased.from.roots.to.stems.and.from.stems.to.leaves..
In.terms.of.phytoremediation,.Fe.plaque.may.play.an.important.role.in.the.
removal.and.detoxiication.of.wastewater-borne.heavy.metals,.which.how-
ever. is. far. from. fully. evaluated. because. of. limited. published. materials.. Pi.
et. al.. (2010c). found. that. after. 75. days. of. exposure,. Fe. plaque. formation. on.
the.root.of.1.year.old.seedlings.of.
B. gymnorrhiza
,.
E. agallocha
,.and.
Acanthus
ilicifolius
. was. enhanced. with. increasing. concentrations. of. wastewater-
borne. heavy. metals. (synthetic. wastewater. having. 5-10. times. the. strength.
(5-10.MW).of.primarily.settled.municipal.sewage.in.Hong.Kong.containing.
DOC,.
NH -N
4
3
−
,.Fe
3+
,.Ni
2+
,.Cu
2+
,.Zn
2+
,.Mn
2+
,.Pb
2+
,.Cr
6+
,.
and.Cd
2+
.at.60,.25,.0.5,.45,.5,.30,.1,.2,.5,.5,.1,.0.5,.and.0.1.mg/L,.respectively),.
but. the. extent. of. enhancement. was. species. speciic.. The. concentrations. of.
trace. metals. immobilized. in. Fe. plaque. were. also. increased. signiicantly.
with. wastewater. strength. and. were. positively. correlated. with. the. concen-
tration.of.Fe.plaque.formed.on.the.root.surface.for.all.three.species..These.
results. conirmed. that. Fe. plaque. could. act. as. a. reservoir. to. immobilize.
metals,.thus.reducing.their.bioavailability.and.contributing.to.the.removal.
and. detoxiication. of. wastewater-borne. heavy. metals.. These. results,. how-
ever,.also.indicated.that.metal.immobilization.via.Fe.plaque.formation.may.
have.a.negative.relationship.with.metal.tolerance,.as.the.most.metal-tolerant.
,.
NO -N
3
,.TKN,.
PO -P
4
+
−
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