Handling Copper: A Paradigm for the Mechanisms of Metal Ion Homeostasis - Environmental Contamination: Health Risks and Ecological Restoration - page 264

averages.70.ppm.(Linder.and.Goode.1999,.Misra.2000)..Cobalt.and.lead.are.
found. in. similar. concentrations,. slightly. less. than. copper.. Cobalt. ranges.
2-47.ppm. with. an. average. of. 25.ppm,. whereas. lead. ranges. 7-48.ppm. and.
averages.13.ppm.in.the.Earth's.crust..Gold.is.the.least.abundant.averaging.
0.07.ppm.(Misra.2000).
In.nature,.the.common.major.ores.of.copper.are.bornite.(Cu 5 FeS 4 ),.chalco-
pyrite.(CuFeS 2 ),.chalcocite.(Cu 2 S),.and.malachite.(Cu 2 CO 3 (OH) 2 )..In.contrast,.
cuprite.(Cu 2 O),.covellite.(CuS),.and.native.copper.(Cu).are.found.in.smaller.
amounts. and. are. minor. ores. (Klein. et. al.. 2002).. Copper. has. two. different.
oxidation. states,. Cu + . (Cu(I)). and. Cu 2+ . (Cu(II)). (Linder. and. Goode. 1999)..
Copper.(I).ions.can.only.be.found.free.in.very.acidic.solutions.or.complexed.
with.other.molecules,.whereas.free.Cu(II).ions.are.stable.in.neutral,.aqueous.
solutions.that.are.exposed.to.the.atmosphere.(Klein.et.al..2002).
During.early.geologic.time.(before.2.5.×.10 9 .years.ago).both.the.atmosphere.
and.the.oceans.were.in.a.reduced.state.(Walker.et.al..1983)..The.dominant.
species. of. carbon,. nitrogen,. and. sulfur. in. this. environment. would. have.
been. CO,. CH 4 ,. N 2 ,. NH 3 ,. and. H 2 S. (Stevenson. 1983).. Metal. bioavailability.
would.be.limited.to.Fe,.Mn,.Zn,.Co,.Ni,.and.Mo.complexes.for.integration.
into.molecular.cofactors.(Chapman.and.Schopf.1983)..The.irst.oxygen.pro-
ducers,.cyanobacteria,.emerged.during.the.Early.Archean.time.period.and.
many. scientists. believe. that. these. photosynthesizing. organisms. were. the.
cause. of. the. oxidized. atmosphere. found. during. current. time. (Chapman.
and. Schopf. 1983).. Even. though. photosynthetic. organisms. appeared.
approximately. 3.5.×.10 9 . years. ago,. during. transitional. period. oxygen. was.
only.found.sporadically.in.microclimates..It.was.not.until.1.7.×.10 9 .years.ago.
that.the.accumulation.of.free.oxygen.resulted.in.widespread.aerobic.condi-
tions.in.the.Earth's.atmosphere.as.well.as.the.oceans. (Walker.et.al..1983)..
Within.this.newly.oxidized.environment,.iron.availability.decreased.dra-
matically.whereas.copper.became.available.as.Cu(II).(Chapman.and.Schopf.
1983)..This.change.in.the.availability.of.copper.is.arguably.the.second.most.
signiicant. event. in. geologic. history. after. the. evolution. of. oxygen,. giving.
rise.to.the.complex.photosynthetic.pathway.found.in.modern,.higher.plant.
systems.
Copper and Nutrition
Bioavailability. of. copper. to. plants. is. dependent. on. the. soil. type.. Copper,.
especially. as. Cu(II),. has. a. high. afinity. to. bind. to. organic. matter. with. an.
estimated. 98%. of. copper. found. as. a. complex. in. soil. solutions. (Marschner.
1995)..Therefore,.organic.soils.are.deined.copper.deicient.if.there.is.less.than.
20.ppm.whereas.inorganic.soils.are.deicient.if.there.is.less.than.4.ppm.(Linder.
and. Goode. 1991).. Most. plants. contain. copper. concentrations. ranging. from.
5.to.20.μg/g.(ppm).dry.weight.(Hemphill.1972,.Marschner.1995)..Symptoms.
of. deiciency.start.when.copper. decreases. below.5.μg/g. dry. weight. in.veg-
etative. tissues,. while. toxicity. levels. can. be. deined. as. 20.μg/g. dry. weight.