Pragmatic Approach for Health Risk Assessment of Bauxite Tailing Waste Materials - Environmental Contamination: Health Risks and Ecological Restoration - page 100

by. similarity. of. particle. distribution. proiles. between. the. house. dust. and.
BT3.tailings.
Metal. concentrations. in. bulk. tailings. and. PM 10 . fractions. are. shown. in.
Table.6.5..The.metal.concentrations.of.the.house.dust.sample.are.similar.to.
those.found.in.the.tailings.for.some.key.elements..PM 10 .fractions.had.higher.
Al.levels.than.the.bulk.tailings,.but.there.were.exceptions..It.is,.therefore,.dif-
icult.to.conclude.which.storage.dam.the.house.dust.derived.from,.based.on.
the.concentrations.of.metals.alone..The.metal.concentrations.of.house.dust.
could. have. been. mixed. with. other. sources. of. contamination,. for. example,.
garden.soil.and.road.dust.
Bioaccessibility
All. bauxite. samples. (bulk. tailings. and. PM 10 . tailings). and. the. house. dust.
were.tested.for.solubilized.fraction.(bioaccessibility).under.various.pH.val-
ues. in. a. synthetic. gastric. luid. system,. using. a. PBET. method. (Ruby. et. al..
1996)..PBETs.were.analyzed.in.duplicates.across.pH.values.of.1.3,.2.5,.and.4.0.
over.various.time.intervals.for.up.to.3.h.when.each.pH.was.adjusted.to.7.0.to.
simulate.the.intestinal.phase..Average.percentages.of.bioaccessibility.(based.
on.the.24.individual.readings.that.form.part.of.the.duplicate.set.of.results).of.
various.targeted.elements.are.shown.in.Table.6.6..Only.the.PBET.results.for.
harmful. metal/metalloids. and/or. elements. with. signiicant. concentrations.
in.the.original.samples.are.shown.here.and.considered.for.risk.assessment.
(see.the.following.section).
Risk Assessment
Aluminum
There. is. no. National. Environmental. Protection. Measure. (NEPM). health.
investigation.level.(HIL).for.aluminum.(Al).(NEPC.1999)..However,.because.
of.its.high.concentration.in.bauxite.tailings.and.in.PM 10 .dust,.this.element.is.
taken.into.consideration.for.the.risk.assessment.activity.
A. pragmatic. approach. is. to. treat. the. house. dust. as. the. same. as. bauxite.
tailings. in. terms. of. risk. assessment.. In. addition,. there. are. several. reasons.
to.believe.that.west.dam.tailings.(BT3).are.a.major.contributor.to.the.house.
dust. based. on. characterization. of. its. particle. size. proile,. mineralogy,. and.
metal.concentrations..Aluminum.is.the.third.most.abundant.element.in.the.
earth's. crust,. exceeded. only. by. oxygen. and. silicon.. U.S.. Geological. Survey.
reported.soil.aluminum.ranged.from.700.to.100,000.mg/kg.with.an.average.
of.72,000.mg/kg.(Shacklette.and.Bolerngen.1984).
Aluminum. (Al). is. poorly. absorbed. (0.1%-0.3%). via. the. gastrointestinal.
tract,.with.soluble. citrate.complexes.reaching.as.high.as.1%.bioavailability..
The. bioavailability. of. Al.is. about. 3%. in. water. of. 100.μg/L.. The. addition. of.
silica.can.reduce.Al.bioavailability.by.sevenfolds.(IPCS.1997).