Cadmium

C a d m iu m M e t a b o l is m & P a t h o g e n e s is E f f e c t s
Is f a h a n U n iv e r s it y o f M e d ic a l S c ie n c e , S c h o o l o f P h a r m a c y
D e p a r t m e n t o f C lin ic a l B io c h e m is t r y

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C a d m iu m
B io lo g y

(An
O v e r v ie w )

B y: A .N . E m a m i


Outlines

 Introduction
 Pharmacokinetics
 Molecular mechanism of toxicity
 Pathogenesis effects
 Detoxification
 Summery

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C a d m iu m

In t r o d u c t io n


silver ← cadmium → indiumn
Zn
↑
Cd
↓
Hg
Periodic Table - Extended Periodic Table

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Cadmium:
A Co-product of Zinc Smelting

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Notable characteristics

 Cadmium is a soft, malleable, ductile, toxic, bluish-white
bivalent metal. It is similar in many respects to zinc but
reacts to form more complex compounds.

 The most common oxidation state of cadmium is +2, though
rare examples of +1 can be found.

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Properties of cadmium
 Boiling point=765° C

 Melting point=320.9° C

 Silvery metal soft enough
to be easily cut with a
knife

 Density=8.65g/cm³

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Cadmium facts

 Date of discovery = 1817

 Discoverer = Fredrich Stromeyer

 Atomic number = 48

 Atomic mass = 112.41
1776 - 1835

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Sources:
 Natural rock weathering
 Copper, lead and zinc smelting auto exhaust
 Cigarette smoke (a cigarette contains 1-2 ug Cd)

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Small rocks - Cadmium (Cd)

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Cadmium base, Cd

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Industrially produced cadmium

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Cadmium sifide

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Cadmium smithsonite contains cadmium impurities and is
yellow to yellow-green.

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The Name 'Smithsonite
 Smithsonite was named after James
Smithson in 1832. James Smithson was an
English scientist, often referred to as the best
chemist and mineralogist of his year. He
was an active member of many scientific
organizations that benefited society and
advanced scientific research. James
published at least 27 papers with topics in
chemistry, geology, and mineralogy. In
1802 James Smithson proved that zinc
carbonates were true carbonate minerals, not
zinc oxides. This discovery lead to the
breakdown of calamine into two separate
minerals hemimorphite and smithsonite.
After James Smithson's death in 1829 the
bulk of his estate was given to his nephew.
Since his nephew died without any heirs the
Smithson Estate was then given to the
United States of America to found the
Smithsonian Institution.

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Cadmium Production

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Cadmium Consumption

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The Application of Cadmium

 metal plating
 nickel-cadmium batteries
 solders
 paint pigments
 plastic stabilizers
 photographic chemicals
 fungicides

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Cadmium Plating

 COMMERCIAL

 Cadmium has long been used for its superior corrosion protection.
Cadmium as deposited is bright silver finish to which a clear or yellow
chromate can be applied. The deposit is soft, ductile and solderable. Here
at DeTray Plating Works we have both rack and barrel capabilities
depending on your needs.

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Nickel Cadmium Batteries

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Cadmium in paints

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Chrome yellow and Cadmium yellow

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Cadmium Orange Poppies Art Print

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C a d m iu m

p h a r m a c o k in e t ic
s


Inhalation
 Smelters, cigarette smoke
 15-50% absorbed

Shenyang Copper Smelter

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 Cigarette smokers, however, typically
sustain significantly higher exposure.
Cadmium inhaled through cigarette
smoke is more easily taken up by the
body than cadmium in food or water.
From 40 to 60 percent of the cadmium
inhaled in smoke is absorbed into the
bloodstream as opposed to the 5 to 10
percent absorbed through foods. Each
cigarette contains roughly 1 to 2
micrograms of cadmium, and smokers
absorb an additional 1 to 3 micrograms
of cadmium into their systems daily
for every pack they smoke. Studies
have shown that smoking more than
20 cigarettes daily can increase
cadmium levels in the body tenfold.

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Ingestion

 Main source is liver and
kidney of meats

 6% absorbed, greater if
deficient in calcium, zinc
or iron

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Distribution

 bound to albumin in plasma
and red blood cells
 transported to liver,
pancreas, prostate and
kidney, with eventual
transfer to kidney
 50-75% of total body Cd is
found in liver and kidney

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Metallothionein
protein rich in cysteine

 Traps Cd esp. in kidney

 Synthesis induced by Cd

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Elimination
Urine
 half-life in humans is 20 - 30 years

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C a d m iu m

M o l e c u l a r m e c h a n is m
o f t o x ic it y


Classification of metals
Class A Borderline Class B
(oxygen-seeking) (sulphur- or nitrogen-
seeking)
Calcium Zinc Cadmium
Magnesium Lead Copper
Iron Mercury
Manganese
Chromium Silver
Potassium Cobalt
Strontium Nickel
Sodium Arsenic
Vanadium

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Borderline and Class B metals and
metalloids are important pollutants
 Nitrogen- and sulphur-seeking

 High affinity to proteins and other biological ligands

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Cadmium is a heavy metal
 Heavy metals are chemical elements that have
a specific gravity (a measure of density) at
least five times that of water.

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Basis of toxicity of metals
 Substitution of essential metals in active centers of enzymes

 Interference with intracellular signaling pathways and Ca2+
metabolism

 Oxidative stress (excessive production of free radicals)

 Interference with DNA transcription, translation and repair

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Toxic effects of heavy metals
 Heavy metals (HM) exert their toxic effects by combining
with one or more reactive groups (ligands) essential for
normal physiological functions

 Nearly all organ systems are involved in heavy metal toxicity;
however, the most commonly involved organ systems include
the CNS, PNS, GI, hematopoietic, renal, and cardiovascular
(CV).

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Mechanisms of uptake and transport
of metals
 Lipid route
 Plays limited role in metal transport
 Hg may diffuse through the membrane in the form of neutrally charged
chlorocomplexes
 Hg2++2Cl- ↔ HgCl2

 Aqueous routes
 Simple diffusion
 Yes
 Facilitated diffusion
 Very much so
 Active transport
 Little or no role

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Simple and facilitated diffusion

 Ion channels
 Ca2+ channels
 can transport Zn2+, Cd2+, Hg2+, Pb2+
 SH-rich Zn2+ channels
 can transport Cd2+

 Carrier proteins
 Divalent cation transporter 1 (DCT1)
 Major carrier protein for uptake of Fe2+, Zn2+ but can also
transport Cd2+, Hg2+, Pb2+

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Endocytosis
 Receptor-mediated endocytosis
 Iron-binding proteins - transferrin, ferritin,
lactoferrin can bind other metals

Out In Out In Out In
Fe3+

Apotransferrin

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Take-home messages
 There are multiple pathways of metal uptake into the
cell

 No specific pathways of uptake exist for “toxic”
metals

 Toxic metals use uptake routes, which have evolved
for uptake of essential metals such as iron, copper and
zinc

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General mechanisms of metal toxicity
 Metals have multiple intracellular targets
 Proteins
 Substitution of essential metals in active centers of enzymes
 Binding to thiol (SH) groups
 Oxidative damage
 Membranes
 Membrane permeability
 Oxidative stress
 DNA
 Interference with transcription, translation and repair
 Oxidative damage
 Interference with intracellular signaling pathways and Ca2+
metabolism

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Oxidative damage
A hallmark of heavy metal toxicity

Free radical (ROS,
RNS)

Increase in free radical Decrease
production in antioxidants

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Heavy metals increase ROS production
 Direct effects
 Haber-Weiss reactions

Meox+O2•-→ Mered+O2
Mered+H2O2→ Meox+ OH• +OH-
Net: H2O2+O2•-→ O2+OH• +OH-

 Indirect (inhibition of the mitochondrial electron
transfer chain)

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Oxidative damage to DNA

 Single Cell Comet
Assay (single cell gel
electrophoresis)
SCGE

 Detects DNA
fragmentation

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Oxidative damage to DNA
TUNEL (TdT-mediated X-dUTP nick-end labeling) assay

Terminal uridine deoxynucleotidyl transferase

dUTP nick end labeling (TUNEL) is a common
Detects free –OH method for detecting DNA fragmentation that

groups created by results from apoptotic signaling cascades. The

assay relies on the presence of nicks in the
strand breakage DNA which can be identified by terminal

deoxynucleotidyl transferase, an enzyme that

will catalyze the addition of dUTPs that are

secondarily labeled with a marker. It may also

label cells undergoing necrosis or cells that

have suffered severe DNA damage.

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TUNEL-detected DNA damage in Cd-exposed
zebra fish embryos

Control

100 µ M Cd

Chan & Cheng (2002)
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Cd-induced apoptosis in zebrafish

Control embryo

Cd-exposed embryos

Cd-exposed embryo

Chan & Cheng (2002)

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Oxidative DNA damage may lead to
mutations
 AT –GC transitions
 Deamination of adenine or cytosine
 G—C → G - - U (deamination) → G—C + A - -U (replication) →
G—C+ A—T (replication)

 GC-TA transversions
 8-hydroxyguanine
 G—C → 8HOG—C → 8HOG - - A + G—C → T—A + G—C
(replication)

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Oxidative damage to proteins and lipids
 Lipids
 Malondialdehyde (MDA)
 Lipofuscin

 Proteins
 Carbonylation
 Loss of iron from

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Mutagenicity of cadmium

Jin et al., 2003 Nature Genetics

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Inhibition of DNA repair

Isolated human cells exposed
to Cd in vitro

Jin et al., 2003 Nature Genetics

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Toxic metal can affect function of zinc-
finger proteins

Hartwig (2001)

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Take-home messages

 Heavy metals affect a wide variety of intracellular
molecules and functions.

 Two major mechanisms of heavy metal toxicity are:
 Binding to –SH and nitro-groups of biomolecules
 Cofactor substitution, conformational changes, etc.
 Oxidative damage due to direct catalysis of ROS
production and/or to inhibition of ETC in mitochondria

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C a d m iu m

Pat h o g e n e s is
effects


Cadmium and renal effects

 Cadmium accumulates especially in the kidneys leading to
dysfunction of the kidney with increased secretion of e.g.
proteins in urine (proteinuri) and other effects.

 The proximal renal tubular dysfunction creates low phosphate
levels in the blood hypophosphatemia, causing muscle
weaknesses and coma. The dysfunction also causes Gout, a
form of arthritis due to the accumulation of sodium urate
crystals in the joints because of high blood levels of uric
acid (hyperuricemia). Another side effect are increased levels
of chloride in the blood (hyperchloremia). The kidneys can
also shrink up to 30%.

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 Markers of kidney
function:
tubular function:
Urinary excretion of

 NAG
 RBP
 ß2-microglobulin
 AA
 Ca

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Cadmium and liver toxicity
 Intraperitoneal injection of CdCl2 in animals
cause:
 Elevation of hepatic enzymes
 Morphological changes in mitochondry and
endoplasmic reticulum of hepatocytes
 Decrease of intracellular pH from 6.8 to 6.6
due to:
 Cadmium interaction with Cl-/HCO3 channels

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Cadmium and fractures
 Chronic exposure to cadmium may
promote urinary calcium loss

 Cadmium may interfere with the
metabolism of calcium, vit. D,
collagen

 Severe cadmium poisoning is
associated with ostemalacia or
osteoporosis

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Cadmium and fractures
 In postmenopausal women, urinary
cadmium correlated negatively with
bone density.

 The population-based risk for
fractures in districts near the smelters
was 35%.

Conclusion: cadmium may promote
skeletal demineralisation, which may
lead to increased bone fragility and
raised risk of fractures.

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Cadmium and placenta
 Cadmium induces placental necrosis at lower doses than renal
toxicity

 Deposited in placenta, little into fetus

 Blocks nutrient and blood flow: growth retardation, fetal death

 Interferes with zinc

 Responsible for the growth retardation caused by smoking

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Cadmium and lung toxicity

 edema and emphysema by killing lung
macrophages

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Cadmium and cancer risk
 Several occupational studies have reported an excess risk of
lung cancer in humans from exposure to inhaled cadmium.

 Animal studies have reported cancer resulting from inhalation
exposure to several forms of cadmium, while animal ingestion
studies have not demonstrated cancer resulting from exposure
to cadmium compounds.

 EPA(Environmental Protection Agency) considers cadmium to
be a probable human carcinogen (cancer-causing agent) and
has classified it as a Group B1 carcinogen

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Itai itai

Itai itai

Itai itai
Itai itai Itai itai
Itai itai

Itai itai
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itai-itai disease
 The itai-itai disease (Japanese: イタイイタイ病 , literally: ouch-ouch-
disease) From 1939 to 1954, some two hundred people near Fuchu, Japan
suffered from a condition termed 'Itai-itai‘

 There are a number of symptoms associated with cadmium poisoning. The
two main organs affected are the bones and the kidneys. The bones get soft
(osteomalacia) and lose bone mass and become weaker (Osteoporosis).
This causes the pain in the joints and the back, and also increases the risk
of fractures. In extreme cases of cadmium poisoning the body weight alone
might cause a fracture.

 The second affected organ is the kidney, which loses its function to remove
acids from the blood, a so called proximal renal tubular dysfunction. The
kidney damage due to cadmium poisoning is irreversible and does not heal
over time, and the victims of the itai-itai disease still have this disorder.

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Is there a test for cadmium exposure?

 There are several tests that indicate if someone has been
exposed to or been harmed by cadmium exposure. Urine or
blood samples can be tested to indicate current and past
exposure and may even be useful in determining if kidney
damage has occurred. Hair and fingernails or toenails are also
excellent biomarkers — biological indicators — for cadmium
exposure and can reveal past exposure to the metal

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Cadmium health effects

 Long-term exposure to cadmium at levels around 0.1
milligrams per cubic meter of air may cause kidney stones and
lung damage, and have been linked to lung cancer and high
blood pressure.

 Short-term exposure at ten times that level may irritate the
lungs. Our everyday diet, however, only gives one-tenth the
amount that could possibly affect long-term health, but if you
eat large amounts of shellfish, liver and kidneys, or if you
smoke, you may consume more cadmium than you should.

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Cadmium health effects

 The EPA has set a limit of 5 parts of cadmium per billion parts
of drinking water (5 ppb). EPA doesn't allow cadmium in
pesticides.

 The Food and Drug Administration (FDA) limits the amount
of cadmium in food colors to 15 parts per million (15 ppm).

 The Occupational Safety and Health Administration (OSHA)
limits workplace air to 100 micrograms cadmium per cubic
meter (100 µg/m³) as cadmium fumes and 200 µg cadmium/m³
as cadmium dust.

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C a d m iu m

D e t o x if ic at io n

de
to
xi
fi

Detoxification of metals
ca
ti
on

 Biotransformation
 Not possible for most metals
 Biotransformation (methylation) of Hg makes it more toxic

 Binding to intracellular ligands
 Reduces the amount of biologically active form (free ion)

 Deposition of insoluble metal granules

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de

Intracellular ligands for metal
to
xi
fi
ca
ti
on

binding
Histidine
 Metallothioneins

 Glutathione

 CRP(cysteine rich proteins)

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de
to
xi
fi

Metallothioneins
ca
ti
on

 Low molecular weight (60-68 aa,
6-7 kDa)

 Cysteine-rich

 In mammals – 20 Cys, bind
eqiuvalent of 7 bivalent metals

 Cys positions are highly conserved

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de
to
xi
fi
ca
ti
on

Rat MT I

Blue crab MT II

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de

Cadmium bound to metallothionein
to
xi
fi
ca
ti
on

subunit

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de
to

Metallothionein is induced by exposure to
xi
fi
ca
ti
on

heavy metals

Nucella lapillus

Leung & Furness (1998)

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de
to
xi
fi
ca

Metallothionein protects from Cd toxicity
ti
on

Experimental
exposure to
toxic Cd levels

Survival:
Cd-
pretreated>control

Liver damage:
Control>Cd-
pretreated

Klaasen & Liu (1998)

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de
t ox

MT-knockout mice studies support protective role
if
ic
a ti
on

of MT against Cd toxicity

5 weeks 10 weeks

Liu et al., 1999

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de
t ox

MT-knockout mice studies support protective role
if
ic
a ti
on

of MT against Cd toxicity

Liu et al., 1999

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de
to
xi
fi

Cellular functions of metallothionein
ca
ti
on

 Storehouse for Zn

 Protection against Cd-toxicity

 Free-radical scavenger

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de
to
xi
fi

Short peptide metal chelators
ca
ti
on

 Glutathione

 Phytochelatins

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de
to
xi
fi

Phytochelatines
ca
ti
on

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de
to
xi
fi

Cysteine-rich (intestinal) protein
ca
ti
on

Zn2+

Zn2+

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de

Deposition of insoluble granules
to
xi
fi
ca
ti
on

(invertebrates only)

Lysosome-derived granule in a snail Littorina littorea Marigomez et al. (2002)

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Take-home messages
 Specialized proteins (metallothioneins) and polypeptides can
protect cells from heavy metal toxicity by binding metals

 Cysteine has high affinity for metals and therefore is a key
amino acid in metal-binding proteins

 Some invertebrates (mollusks, crustaceans, annelids) can
detoxify metals by deposition and excretion of insoluble
metal-containing granules

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discoverer=
crystal structure= nickel-cadmium
Fredrich color=bluish white
hexagonal batteries
Stromeyer

date of
discovery poisonous
=1817

boiling point= Cadmium paint pigments
765°C properties & application

atomic
number solders
=48

compounds
atomic
Are
mass= density=8.65g/cm³ oxidation state=2
toxic
112.41

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Respiratory System Kidney
Pneumonitis, Proteinuria, kidney stones,
destruction of glomerular & tubular
mucous membranes damage

Cancer Placenta
Excess risk of lung cancer Cadmium Deposition & necrosis
Classified in group B1 Block nutrient & blood flow
carcinogens
effects Growth retardation & fetal death

Reproductive System Skeletal System
Testicular necrosis, Loss of bone density and
estrogen-like effects, mineralisation,
affection of steroid-hormon Itai-Itai disease
synthesis
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Do we need cadmium for health?

Though trace amounts of many metals are
essential for the health of living things, there is
no scientific evidence showing a nutritional
role for cadmium.

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The First Cadmium Enzyme – Carbonic Anhydrase 2 from the
Marine Diatom Thalassiosira weissflogii

Cadmium is generally thought to be toxic and
was not thought to be used by nature in
anyway. X-ray absorption experiments on a
marine diatom showed that Cadmium is
not only of biological importance, but
plays an important role in the global
carbon cycle.

Lane, T.; Saito, M. A.; George, G. N.;
Pickering, I. J.; Prince, R. C.; Morel, F. F.
M. "Isolation and Preliminary
Characterization of a Cadmium Carbonic
Anhydrase from a Marine Diatom" Nature,
2005, 435, 42

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Cadmium

In this document

Cadmium

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Cadmium

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