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Cadmium

DESIGNATIONS

CAS No.: 7440-43-9
Registry name: Cadmium
Chemical name: Cadmium
Synonyms, Trade names: Cadmium
Chemical name (German): Cadmium
Chemical name (French): Cadmium
Appearance: soft heavy metal with silvery white sheen

BASIC CHEMICAL AND PHYSICAL DATA

Chemical symbol: Cd
Rel. atomic mass: 112.41 g
Density: 8.642 g/cm3 at 20C
Boiling point: 767C
Melting point:
320.9C
Vapour pressure:
0.013 Pa at 180C
Solvolysis/solubility: Cd readily dissolves in nitric acid, but only slowly in hydrochloric and sulphuric acid

Basic data of selected compounds

CAS No: 1306-19-0 10108-64-2
Chemical name: Cadmium oxide Cadmium chloride
Synonyms, Trade names: Cadmium orange, Cadmium yellow, Aurora yellow Cadmium dichloride, Caddy
Chemical name (German): Cadmiumoxid Cadmiumchlorid
Chemical name (French): Oxyde de cadmium Chlorure de cadmium
Appearance: yellow to brown solid colourless, crystalline solid
Empirical formula: CdO CdCl2
Rel. molecular mass: 128.41 g 183.32 g
Density: 6.95 g/cm3 4.05 g/cm3
Boiling point:   967C
Melting point: sublimation above 700C 568C
Solvolysis/solubility: in water: very slightly (0.005 wt%)

readily soluble in diluted acids

in water: readily soluble (1,400 g/l)

ORIGIN AND USE

Usage:
Metallic cadmium is used to coat iron in order to improve corrosion resistance and in alloys in the automobile industry. Its compounds are used as pigments (primarily as cadmium sulphide) and as plastic stabilisers in PVC, in batteries and in fungicides; also applied for Ni-Cd batteries as well as moderators and control elements in nuclear reactors.

Origin/derivation:
Cadmium minerals are rare; frequently found in isomorphic form in nearly all zinc ores (95 % of cadmium production). Cadmium is separated from Zn by distillation or precipitation from sulphate solution using zinc dust.

Production figures:
1980 = 18 x 103 t (worldwide); MERIAN, 1984

Toxicity

Mammals:
Rat LDLo 15 mg/kg, ims acc. KOCH, 1989
Rat TDLo 70 mg/kg, ims acc. KOCH, 1989
Rat LD50 88 mg/kg , (cadmium chloride) acc. DVGW, 1988
Rat LD50 72 mg/kg , (cadmium oxide) acc. DVGW, 1988
Rabbit LD50 70-150 mg/kg , (cadmium chloride) acc. DVGW, 1988
Guinea pig LD 150 mg/kg , cadmium fluoride acc. DVGW, 1988
Aquatic organisms:
Daphnia 0.1 mg/l (harmful) acc. DVGW, 1988
Stickleback 0.3 mg/l (harmful) acc. DVGW, 1988
Minnow LD 5600 mg/l (1 h) acc. DVGW, 1988
Goldfish LD 0.017 mg/l (9-18 h) acc. DVGW, 1988
Fish (without spec. differentiation) LC50 minimal 23 ppm (over 264 h) acc. KOCH, 1989
LC50 average 140 ppm (over 24 h) acc. KOCH, 1989

Characteristic effects:

Humans/mammals: Apart from the gastro-intestinal tract and the lungs, the organ most susceptible to chronic cadmium exposure is the kidney. Cadmium is a cumulative poison; the ready solvolyse of the element in weak acids is an important precondition for its absorption in the organism: 5 % of cadmium is resorbed via the gastro-intestinal tract and accumulated in liver and kidneys. In Asia, "Itai-Itai" disease is caused by high cadmium concentrations in rice. Damage is caused by erythrocyte destruction, proteinuria, rhinitis, emphysema and chronic bronchitis. Cadmium and its compounds are carcinogenic. A typical symptom of chronic poisoning is the excretion of -microglobulin in the urine due to the impairment of the kidney function. Bone deformation may also result.

Plants: Cadmium reduces the photosynthesis and transpiration rate whilst increasing the respiratory rate. Small cadmium concentrations in the soil are sufficient to produce marked damage such as shortening of the shoot axis and intensive yellowing of older leaves. Absorption not only takes place via the roots but also through shoots and leaves. In addition to yield shortfalls the main hazard results from the contamination of (accumulation in) crop plants since this is how cadmium as a cumulative poison enters the food chain.

ENVIRONMENTAL BEHAVIOUR

Water:
2/3 - 3/4 of the cadmium in surface water and groundwater is adsorbed on suspended matter. It can be remobilised from sediment by complexing agents. Fish toxicity is dependent amongst other things on the calcium content of the water. Generally speaking, a high calcium content in water reduces the toxic effect of cadmium on fish.
The biological self-purification of surface water and groundwater is impaired from 0.1 mg/l (DVGW, 1988).

Air:
Cadmium is stable in air since it forms an oxide layer.

Soil:
The cadmium retention capacity is a function of the number of exchangeable alkalis. There is hardly any elution because of the adsorption on organic soil components. The accumulation horizon for cadmium is in the rhizosphere (roots). The minimum availability is at pH 6.5. The cadmium absorption by plants increases with a decreasing pH of the soil.

Degradation, decomposition products, half-life:
Cadmium accumulates in the organism. 50 % of the accumulated amount is found in the liver and the kidneys. Cadmium is primarily excreted in urine (2 m g/d on average (0.2 - 3.1 m g/l)). The biological half-life of cadmium in the human body is between 15 and 25 years (measured in the kidneys; GROKLAUS, 1989).

Food chain:
Humans consume roughly one third of the cadmium to which they are exposed in animal foodstuffs and two thirds in vegetable foodstuffs. Smoking significantly increases the cadmium impact.

Note: 1) The biological half-life is the time taken for a specified element concentration in the body to be reduced to half its original value by way of degradation and excretion processes.

ENVIRONMENTAL STANDARDS

Medium/acceptor Sector Country/organ.

Status

Value Cat. Remarks Source
Water: Drinkw AUS

(L)

10 g/l     acc. MERIAN, 1984
Drinkw CH

(L)

5 g/l     acc. MERIAN, 1984
Drinkw D

L

5 g/l   Amendment, 1985 acc. DVGW, 1988
Drinkw EC

G

5 g/l     acc. LAU-BW, 1989
Drinkw SU

(L)

10 g/l     acc. MERIAN, 1984
Drinkw USA

(L)

0.01 mg/l     acc. DVGW, 1988
Drinkw WHO

G

5 g/l     acc. MERIAN, 1984
Surface D

L

50 g/m3   Investigation acc. LAU-BW, 1989
Surface D

L

100 g/m3   Rehabilitation acc. LAU-BW, 1989
Surface D

G

0.005 mg/l   1) A acc. DVGW, 1988
Surface D

G

0.01 mg/l   2) B acc. DVGW, 1988
Groundw D(HH)

G

2.5 g/l   Investigation acc. LAU-BW, 1989
Groundw D(HH)

G

10 g/l   Rehabilitation acc. LAU-BW, 1989
Groundw NL

G

0.4 g/l   Reference acc. TERRA TECH 6/94
Groundw NL

L

6 g/l   Intervention acc. TERRA TECH 6/94
Waste water CH

(L)

0.10 g/m3   Direct/indirect introduc. acc. LAU-BW, 1989
Waste water CH

G

0.005 g/m3   Quality aim acc. LAU-BW, 1989
Waste water D(BW)

G

1 g/m3     acc. LAU-BW, 1989
Trough water D

L

6 g/l     acc. DVGW, 1988
Soil:   CH

G

0.8 mg/kg AD     acc. LAU-BW, 1989
  CH

G

0.03 mg/kg   Sol. content acc. LAU-BW, 1989
  D(HH)

G

8 mg/kg DS   Investigation acc. LAU-BW, 1989
  NL

G

0.8 mg/kg AD   Reference acc. TERRA TECH 6/94
  NL

L

12 mg/kg AD   Intervention acc. TERRA TECH 6/94
Sewage sludge CH

L

30 mg/kg DS   Sludge acc. LAU-BW, 1989
Sewage sludge D

L

3 mg/kg AD   Soil acc. LAU-BW, 1989
Sewage sludge D

L

20 mg/kg DS   Sludge DS acc. LAU-BW, 1989
Sewage sludge EC

L

1-3 mg/kg DS   Soil DS acc. LAU-BW, 1989
Sewage sludge EC

L

20 -.40 mg/kg DS   Sludge DS acc. LAU-BW, 1989
Fertiliser D

L

4 mg/kg   3) acc. LAU-BW, 1989
Fertiliser D

L

3 mg/kg   Soil AD acc. LAU-BW, 1989
Fertiliser D

L

20 mg/kg   Sludge acc. LAU-BW, 1989
Compost A

G

1-6 ppm     acc. LAU-BW, 1989
Compost CH

L

3 mg/kg     acc. LAU-BW, 1989
Compost D

G

3 mg/kg   Soil AD acc. LAU-BW, 1989
Compost D

G

33 g/ha and a     acc. LAU-BW, 1989

Air:

  CH

L

10 ng/m3   7) acc. LAU-BW, 1989
  CH

L

2 g/m3 and d   In dust deposition acc. LAU-BW, 1989
  D

L

0.04 g/m3 IW1 5) 6) acc. TA Luft, 1986
  D

L

5 g/m3 and d IW1 5) 7) acc. TA Luft, 1986
  WHO

G

1-5 ng/m3   8) acc. LAU-BW, 1989
  WHO

G

10-20 ng/m3   9) acc. LAU-BW, 1989
Emiss. D L 0.2 mg/m3   mass flow > 50 g/h10) acc. TA Luft, 1986
Workp AUS

L

0.05 mg/m3   Dust and sol. salts acc. MERIAN, 1984
Workp AUS

L

0.05 mg/m3   Cd oxide, smoke, as Cd acc. MERIAN, 1984
Workp B

L

0.05 mg/m3   Dust and sol. salts acc. MERIAN, 1984
Workp B

L

0.05 mg/m3   Manufacture, Cd oxide acc. MERIAN, 1984
Workp B

L

0.05 mg/m3   Cd oxide, smoke, as Cd acc. MERIAN, 1984
Workp BG

L

0.1 mg/m3   Cd oxide, smoke, as Cd acc. MERIAN, 1984
Workp CS

L

0.1 mg/m3   Cd oxide, smoke, Cd 11) acc. MERIAN, 1984
Workp CS

L

0.5 mg/m3   Cd oxide, smoke, Cd 12) acc. MERIAN, 1984
Workp CH

L

0.1 mg/m3   Cd oxide, smoke, as Cd acc. MERIAN, 1984
Workp CH

L

0.2 mg/m3   Dust and sol. salts acc. MERIAN, 1984
Workp D

L

1.5 g/dl BAT Whole blood acc. DVGW, 1988
Workp D

L

15 g/l BAT Urine acc. DVGW, 1988
Workp DDR

L

0.1 mg/m3   Dust and sol. salts 11) acc. MERIAN, 1984
Workp DDR

L

0.2 mg/m3   Dust and sol. salts 12) acc. MERIAN, 1984
Workp NL

L

0.05 mg/m3   Manufacture, Cd oxide acc. MERIAN, 1984
Workp NL

L

0.05 mg/m3   Dust and sol. salts acc. MERIAN, 1984
Workp NL

L

0.05 mg/m3   Cd oxide, smoke, as Cd acc. MERIAN, 1984
Workp H

L

0.1 mg/m3   Cd oxide, smoke, as Cd acc. MERIAN, 1984
Workp I

L

0.05 mg/m3   Dust and sol. salts acc. MERIAN, 1984
Workp I

L

0.01 mg/m3   Cd oxide, smoke, as Cd acc. MERIAN, 1984
Workp J

L

0.1 mg/m3   Cd oxide, smoke, as Cd acc. MERIAN, 1984
Workp PL

L

0.1 mg/m3   Cd oxide, smoke, as Cd acc. MERIAN, 1984
Workp RO

L

0.2 mg/m3   Cd oxide, smoke, Cd 12) acc. MERIAN, 1984
Workp S

L

0.05 mg/m3   Dust and sol. salts acc. MERIAN, 1984
Workp S

L

0.02 mg/m3   Cd oxide, smoke, as Cd acc. MERIAN, 1984
Workp SF

L

0.02 mg/m3   Dust and sol. salts acc. MERIAN, 1984
Workp SF

L

0.01 mg/m3   Cd oxide, smoke, as Cd acc. MERIAN, 1984
Workp SU

L

0.1 mg/m3   Cd oxide acc. KETTNER, 1979
Workp SU

L

0.3 mg/m3   Cd hydroxide acc. KETTNER, 1979
Workp SU

L

0.1 mg/m3   Cd oxide, smoke, as Cd acc. MERIAN, 1984
Workp USA

L

0.1 mg/m3   Cd oxide, smoke, Cd 11) acc. MERIAN, 1984
Workp USA

L

0.3 mg/m3   Cd oxide, smoke, Cd 12) acc. MERIAN, 1984
Workp USA

(L)

0.05 mg/m3 TWA   acc. DVGW, 1988
Workp USA

L

0.2 mg/m3   Dust and sol. salts 11) acc. MERIAN, 1984
Workp USA

L

0.6 mg/m3   Dust and sol. salts 12) acc. MERIAN, 1984
Workp USA

(L)

0.05 mg/m3 TWA Smoke, Cd oxide acc. ACGIH, 1986
Workp USA

(L)

0.05 mg/m3 TWA Manufacture, Cd oxide acc. ACGIH, 1986
Workp WHO

L

0.01 mg/m3   Dust and sol. salts 13) acc. MERIAN, 1984
Workp WHO

L

0.25 mg/m3   Dust and sol. salts 12) acc. MERIAN, 1984
Workp YU

L

0.1 mg/m3   Cd oxide, smoke, as Cd acc. MERIAN, 1984
Foodstuffs:   WHO

G

0.07 mg/d     acc. RMPP, 1979
  D

L

0.005 mg/l   Mineral water acc. DVGW, 1988
  D

G

0.0025 mg/kg   Milk acc. GROKLAUS, 1989
  D

G

0.05 mg/kg   Cheese acc. GROKLAUS, 1989
  D

G

0.1 mg/kg   Beef acc. GROKLAUS, 1989
  D

G

0.1 mg/kg   Sausage meat acc. GROKLAUS, 1989

Notes:

1) For drinking water treatment in each case: A = signifies pollution limits up to which water can be used as drinking water
2) For drinking water treatment in each case: B = signifies pollution limits up to which drinking water can be produced with the assistance of currently known and proven chemophysical methods
3) In organ.-mineral, mixed fertiliser
4) Annual arithmetic mean, in suspended dust
5) Annual arithmetic mean on the basis of daily mean values, protection of humans
6)
Cd and its anorganic compounds as suspended dust, stated as Cd
7) Cd and its anorganic compounds within dust sediments, stated as Cd
8) Averaging period: 1 year (rural areas); protection of humans
9) Averaging period: 1 year (urban areas); protection of humans
10) dustlike Cd ist and anorganic compounds, stated as Cd
11) Mean value
12) Short-time value
13) Long-time value
14) Tolerable weekly absorption

Further regulations in: Order Governing Cosmetics, 1985: Ban on usage; Law Governing Paints, 1987. Usage prohibited in the manufacture of foodstuffs, semi-luxury goods and consumer goods; the utilisation of Cd compounds as pesticides is prohibited in Germany.

Comparison/reference values

Medium/origin Country Value Source
Surface water
Rhine (Cologne): D 0.03 - 0.2 g/l acc. DVGW, 1988
Rhine (Duisburg): D 0.05 - 0.5 g/l acc. DVGW, 1988
Ruhr (Witten): D 0.2 - 2.1 g/l acc. DVGW, 1988
Ruhr (Duisburg): D 0.4 - 0.6 g/l acc. DVGW, 1988
Fertiliser (in 100 kg P2O5): USA 1.2 - 2.4 g Cd/ha acc. BREMER UMWELT INST., 1985
Morocco 3.5 - 7 g Cd/ha acc. BREMER UMWELT INST., 1985
SU 3.6 - 7.2 g Cd/ha acc. BREMER UMWELT INST., 1985
Senegal 11.4 - 22.8 g Cd/ha acc. BREMER UMWELT INST., 1985
Fly ash (coal) USA 0.1-3.9 mg/kg acc. HOCK, 1988
Plants   0.05-0.2 mg/kg acc. HOCK, 1988

Assessment/comments

As a trace element, cadmium is subject to constant circulation in biological and non-biological environmental structures. The impact on the environment which cadmium causes by natural means (approx. 40 t/a worldwide) is slight compared to the estimated anthropologically-induced emissions. Cadmium is regarded as one of the most poisonous metals. There have been documented cases of acute and chronic poisoning due to workplace exposure. Cadmium is one of the trace elements for which there is proof of poisoning of certain groups of people as a consequence of chronic, environment-related exposure.
The proven accumulation of the element in sediments, the associated possibility of remobilisation and the tendency towards bioaccumulation are the major environmental hazards. If possible, waste products containing cadmium should be reprocessed.


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