Toxicity and Bioavailability of Heavy Metals and Hydrocarbons in Mangrove Wetlands and Their Remediation - Environmental Contamination: Health Risks and Ecological Restoration - page 384

Solubility.is.an.important.factor.limiting.biodegradation.of.toxic.organic.
pollutants,.such.as.oil.and.PAHs..Ke.et.al..(2009).showed.that.the.addition.of.
humic.acid.(0%-1.6%,.w/v).signiicantly.enhanced.the.solubility.of.all.PAHs.
in.both.liquid.medium.and.sediment.slurry,.but.only.the.biodegradation.of.
phenanthrene. and. pyrene. (and. not. benzo[a]pyrene). in. the. liquid. medium.
was. enhanced.. Solubility. is. related. to. the. sorption. and. desorption. behav-
ior. of. organic. pollutants,. which. in. turn. is. affected. by. the. physiochemical.
properties.of.sediment..Zhang.et.al..(2007a).found.that.the.lubricating.oil.in.
sandy.sediment.had.a.more.acute.toxic.effect.on.the.germination.and.early.
growth.of. B. gymnorrhiza .than.muddy.sediment,.but.the.lower.bioavailability.
and.biodegradation.of.hydrocarbons.in.muddy.sediment.made.the.oil.more.
persistent,. which. may. lead. to. more. chronic. toxicity. and. pose. a. long-term.
risk.to.the.environment..The.bioavailability.of.toxic.pollutants.such.as.PAHs.
was.linked.to.the.sorption-desorption.behavior,.which.was.closely.related.
to.sediment.properties..The.sorption-desorption.behaviors.of.PAHs.in.dif-
ferent. mangrove. sediment. slurries. were. best. described. by. a. linear. model..
The.muddy.sediment.had.a.higher.binding.afinity.to.PAHs.than.silty.sedi-
ment..The.sandy.sediment.had.the.least.binding.afinity.(unpublished.data)..
Sediments. with. high. contents. of. clay. and. total. organic. carbon. provided.
large.surface.areas.for.PAH.binding,.which.enhanced.the.sorption.of.PAHs.
into.sediments,.thus.decreasing.their.bioavailability.and.biodegradation.
ConcludingRemarks
Toxic. contaminants,. such. as. heavy. metals. and. petroleum. hydrocarbons,.
pose. signiicant. adverse. effects. on. the. establishment. and. initial. develop-
ment. of. mangrove. seedlings. and. are. found. to. alter. the. root. anatomy. and.
physiology.. Changes. in. the. areas. of. aerenchyma. tissues. and. thickness. of.
outer.layers.in.roots.due.to.these.contaminants.led.to.the.variations.in.the.
amount.and.spatial.pattern.of.ROL,.which.then.affected.Fe.plaque.formation.
on.the.root.surface.and.immobilization.of.heavy.metals..The.activity.of.anti-
oxidant.enzymes.and.other.biochemical.responses.in.the.roots.and.leaves.of.
mangrove. plants. were. also. changed. when. exposed. to. toxic. contaminants..
The. tolerance. level. of. mangroves. to. these. toxic. contaminants. was. species.
speciic.. B. gymnorrhiza . was. the. most. robust. and. tolerant. species. to. heavy.
metals.and.hydrocarbons,.as.it.had.(1).the.“tightest”.barrier.on.root.surface,.
(2).the.least.amount.of.Fe.plaque.on.root.surface,.(3).the.lowest.ROL.per.root.
dry.weight,.and.(4).the.least.modiication.in.root.anatomy.and.biochemical.
properties.. B. gymnorrhiza . might. be. the. most. ideal. candidate. for. phytore-
mediation. of. sediment. contaminated. with. heavy. metals. or. hydrocarbons.
among.the.mangrove.plants.found.in.Hong.Kong..The.success.of.bioremedi-
ation.depended.on.the.bioavailability.and.the.sorption-desorption.behavior.