Inverse Relationship between Urinary Retinol-Binding Protein, Beta-2- Microglobulin, and Blood Manganese Levels in School-Age Children from an E-Waste Recycling Town - Environmental Contamination: Health Risks and Ecological Restoration - page 184

is.an.increasing.global.environmental.problem..The.current.global.produc-
tion. of. e-waste. is. estimated. to. be. 20-25. million. tons. per. year,. and. it. has.
become.the.fastest.growing.waste.stream.in.the.world.(Robinson.2009)..The.
techniques. used. in. recycling. of. e-waste. are. often. primitive.. Guiyu,. which.
is.located.in.Shantou.City,.South.China,.is.infamous.for.its.involvement.in.
primitive.e-waste.processing.and.recycling.activities.that.cause.severe.dam-
age. to. the. environment. and. the. health. of. local. residents.. Several. studies.
reported.elevated.levels.of.toxic.heavy.metals.in.air,.road.dust,.soil,.and.sedi-
ment.of.Guiyu.(Deng.et.al..2006,.Wong.et.al..2007b,c,.Leung.et.al..2008)..In.our.
previous. investigations,. we. found. that. children. and. neonates. from. Guiyu.
had.elevated.levels.of.blood.lead.and.other.metals.(Huo.et.al..2007,.Li.et.al..
2008,. Zheng. et. al.. 2008).. It. was. reported. that. dissolved. Mn. concentrations.
were.higher.in.Lianjiang.(206-246.μg/L).and.Nanyang.River.(188-217.μg/L).
within.Guiyu.than.in.the.reservoir.(2-6.μg/L).outside.of.Guiyu.(Wong.et.al..
2007a)..Elevated.levels.of.Mn.in.human.hair.were.found.in.Taizhou,.another.
e-waste.recycling.area.in.Zhejiang.province.in.China.(Wang.et.al..2009).
Mn.is.an.essential.element..Deiciencies.of.Mn.have.been.reported.to.cause.
weight. loss,. dermatitis,. nausea,. slow. growth,. skeletal. deformities,. sterility,.
and.neonatal.deaths.in.animal.(Wedler.1993)..The.biological.actions.of.Mn.
are.quite.diverse.as.conirmed.by.its.wide-ranging.role.as.an.essential.com-
ponent.for.a.variety.of.enzymes.involved.in.the.basic.metabolic.regulation.
of. the. cell.. It. is. required. for. normal. immune. function,. regulation. of. blood.
sugar. levels,. cellular. energy,. reproduction,. digestion,. bone. growth,. and.
defense.mechanisms.against.free.radicals.(Aschner.and.Aschner.2005)..Low.
levels.of.Mn.can.have.a.protective.effect..However,.excess.Mn.is.toxic,.and.
its.effects.can.lead.to.physiological.damage..Exposure.to.high.oral.or.ambi-
ent.air..concentrations.of.Mn.can.result.in.elevations.of.tissue.Mn.levels.and.
neurological.effects.(Santamaria.2008).
In. most. living. environments,. people. are. exposed. to. a. variety. of. chemi-
cals,. including. both. organic. and. inorganic. agents.. Among. possible. target.
organs.of.environmental.chemicals,.the.kidney.appears.to.be.the.most.sen-
sitive. one.. The. release.of.cytoplasmic.proteins.and.other. constituents.into.
the.urine.following.injury.to.tubular. cells.has. been. clinically.exploited.to.
assess. the. site. and. severity. of. renal. tubular. damage. associated. with. dis-
ease. and. toxic. exposures. (Bernard. and. Lauwerys. 1991,. Zhou. et. al.. 2008)..
One. of. the. most. sensitive. measures. of. renal. toxicity. is. the. excretion. of.
low-molecular-weight. proteins. in. the. urine,. such. as. beta-2-microglobulin.
(β 2 -MG).and.retinol-binding.protein.(RBP)..Elevated.levels.relect.dysfunc-
tion.of.the.proximal.tubule.as.RBP.is.a.low-molecular-weight.protein.freely.
iltered. at. the. glomerulus.. The. fractional. tubular. reabsorption. of. RBP. is.
99.97%,.and.increased.excretion.is,.therefore,.a.sensitive.marker.of.tubular.
dysfunction.(Smith.et.al..1994)..β 2 -MG,.identiied.as.a.low-molecular-weight.
protein.of.11,800.Da,.is.a.light.chain.of.HLA.class.I.molecule..It.also.is.iltered.
by.glomerulus,.and.reabsorbed.and.catabolized.by.proximal.tubules..Based.
on.extensive.clinical.and.experimental.studies,.elevated.levels.of.these.two.