Toxicity and Bioavailability of Heavy Metals and Hydrocarbons in Mangrove Wetlands and Their Remediation - Environmental Contamination: Health Risks and Ecological Restoration - page 381

BioavailabilityandRemediation
Heavy Metals

Wetland.sediments.often.undergo.intermittent.looding.and.draining,.pro-
viding.an.alternating.anaerobic.and.aerobic.environment..The.high.levels.of.
reduction. in. sulide,. iron,. and. manganese. observed. favor.the.precipitation.
and.immobilization.of.heavy.metals.(Ambus.and.Lowrance.1991,.Dunbabin.
and. Bowmer. 1992).. On. the. other. hand,. the. ROL. of. wetland. plants. would.
aerate. the. rhizosphere. and. increase. the. mobilization. of. heavy. metals. due.
to. sulide. oxidation. and. dissolution.. ROL. would. also. cause. the. formation.
of.Fe.plaque,.which.provides.some.extra.binding.sites.for.heavy.metals.on.
root. surface. (Pi. et. al.. 2010c).. The. formation. of. Fe. plaque. was. found. to. be.
positively.correlated.to.the.amount.of.ROL.present.in.the.roots.of.mangrove.
plants.grown.in.the.freshwater.control.(Pi.et.al..2010b).as.well.as.to.the.immo-
bilization. of. wastewater-borne. heavy. metals. (Pi. et. al.. 2010c,. Figure. 17.4)..

Fe plaque formation vs. ROL

B. gymnorrhiza E. agallocha

2.5 2.5

Y = -0.035*X+ 2.415

2.0 2.0

1.5

Y = -0.052*X+ 3.376
R 2 = 0.891***

R 2 = 0.969***

1.5

FW

10 NW

1.0
0.5

1.0
0.5

Y = -0.014*X-0.086

Y = -0.014*X-0.086
R 2 = 0.982***

R 2 = 0.982***

0.0 0.0

0 10 20 30 40 0 15 30 45 60 75 90

(A) (B) Rate of ROL (1/ng cm 2 min)

Rate of ROL (1/ng cm 2 min)

Metal immobilization vs. Fe plaque formation

0.16

0.14
0.12
0.10
0.08
0.06
0.04
0.02
0.00

Zn Mn

0.14

FW

0.12
0.10
0.08
0.06
0.04
0.02
0.00 0

5 MW
10 MW

Y = -0.016*X+ 0.008
R 2 = 0.862***

Y = -0.010*X+ 0.042
R 2 = 0.797***

0 2 4 6 8 10

2 4 6 8 10

(C)

(D)

Fe plaque (mg/g root dry weight)

Fe plaque (mg/g root dry weight)

FIGURE 17.4
Relationships.between.Fe.plaque. formation. and. ROL. (A. and.B),.and.between.Fe. plaque. for-
mation. and. metal. immobilization. (C. and. D).. The. curves. were. itted. with. the. linear. regres-
sion.models.(y.=.y0.+.ax);.R 2 ,.regression.coeficients;.***.indicates.the.R 2 .values.are.signiicant.at.
P.≤.0.001;.FW,.freshwater.control;.10.NW,.10.times.normal.wastewater.without.heavy.metals;.
5.MW,.5.times.normal.wastewater.containing.heavy.metals;.10.MW,.10.times.normal.wastewa-
ter.containing.heavy.metals..Details.on.the.components.and.concentrations.of.NW.and.MW.
are.described.in.the.text..(Data.used.for.plotting.are.from.Pi,.N..et.al.,. Environ. Pollut .,.158,.381,.
2010b;.Pi,.N..et.al.,. Mar. Pollut. Bull .,.63,.402,.2010c.)