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Carbon monoxide

DESIGNATIONS

CAS No.: 630-08-0
Registry name: Carbon monoxide
Chemical name: Carbon monoxide
Synonyms, Trade names: Carbon oxide, carbon(II) oxide
Chemical name (German): Kohlenmonoxid, Kohlenoxid
Chemical name (French): Oxyde de carbone, monoxyde de carbone
Appearance: colourless, odourless gas

BASIC CHEMICAL AND PHYSICAL DATA

Empirical formula: CO
Rel. molecular mass: 28.01 g
Density: 1.25 g/l at 0C
Relative gas density: 0.97
Boiling point: -191.5C
Melting point: -199C
Ignition temperature: 605C
Explosion limit: 12.5 - 74 vol.%
Max. explosion pressure: 7.3 x 105 Pa
Odour threshold: none
Solvolysis/solubility: in water: 33 ml/l (at 0C)
23 ml/l (at 20C)
soluble in ethyl acetate, chloroform, glacial acetic acid, ethyl acetate and other organic solvents
Conversion factors: 1ppm = 1.164 mg/m3
1 mg/m3 = 0.859 ppm

ORIGIN AND USE

Usage:
The most important use of CO in production involves its reaction with steam at elevated temperature to form syngas which is e.g. used to produce methanol. Carbon monoxide is also used in the reduction of oxides to form pure metals. It is, however, used on a very small scale.

Origin/derivation:
Carbon monoxide is an unwanted by-product of numerous thermal processes. It is produced in the course of all oxygen-undersaturated combustion processes involving carbon and its compounds. The natural sources of carbon monoxide predominate (90% of total emissions); the remaining 10% are made up of motor-vehicle emissions (55%), industry (11%) and other emitters (HORN, 1989).
Carbon monoxide is a component of "town gas".

Toxicity

Humans: LCLo 4,000 ppm, inhalation (30 min) acc. UBA, 1986
TCLo 650 ppm, inhalation (45 min) acc. UBA, 1986
Mammals:
Rat: LC50 1,807 ppm, inhalation (4 h) acc. UBA, 1986
Mouse: LC50 2,444 ppm, inhalation (4 h) acc. UBA, 1986
Cat: MLC 10,040 mg/m3, inhalation (35 min) acc. HORN, 1989
Guinea pig: LC50 2,811 mg/m3, inhalation (4 h) acc. HORN, 1989
Aquatic organisms:
Fish: LD > 1.2 mg/l acc. UBA, 1986

Characteristic effects:

Humans/mammals: The toxicity in humans and animals is caused by the extraordinary affinity of carbon monoxide for haemoglobin which is responsible for the oxygen transport (approx. 250 times greater affinity of carbon monoxide compared to oxygen [ULLMANN/RMPP]). Intake is exclusively by way of inhalation. Carbon monoxide cannot be perceived on the basis of odour, colour, taste, irritation of the mucous membranes or other effects. Thus, poisoning due to town gas or vehicle emissions may take place (frequently suicide results).

Acute poisoning takes the form of headaches, retching, muscular weakness, loss of consciousness, shortness of breath and finally death, depending on the concentration and time of exposure.

Plants: Carbon monoxide does not poison plants since it is rapidly oxidised to form carbon dioxide which is used for photosynthesis.

ENVIRONMENTAL BEHAVIOUR

Water:
Carbon monoxide is only slightly soluble in water. Depressurizing the compressed gas quickly leads to the formation of explosive mixtures over the surface of the water. Carbon monoxide is listed under water hazard class 0 in the Federal Republic of Germany (no hazard to water). It has a toxic effect on fish.

Air:
Carbon monoxide is about as dense as air. It ingresses into the atmosphere by way of exhaust gases and is rapidly oxidised to form carbon dioxide. The substance is particularly hazardous because of ist widespread dispersion and the high toxicity level for humans and animals. Particular attention is therefore to be paid to the CO concentration in breathing air in smog areas.

Soil:
Oxygen-undersaturated soils have been found to have a higher concentration of carbon dioxide oxidised from carbon monoxide. CO accelerates the oxidation of NO to form NO2. Roughly 80 t CO/km2 are converted every year by soil bacteria.

Half-life:
The dwell time of CO in the atmosphere is between 1 and 2 months on average (HORN, 1989). The half-life of carbon monoxide bonded in blood is about 250 minutes (HORN, 1989).

Degradation, decomposition products:
Carbon monoxide rapidly oxidises to form carbon dioxide. Especially at higher temperatures, it reacts explosively with numerous substances (e.g. aluminium dust, potassium, nitrogen dioxide) with heat being produced (e.g. bromine trifluoride, silver oxide). Plants metabolise CO to form CO2 or methane.

Food chain:
There is no evidence of residues in foodstuffs or semi-luxury goods. Smokers inhale considerable quantities of carbon monoxide in cigarette smoke.

ENVIRONMENTAL STANDARDS

Medium/ acceptor Sector Country/ organ. Status Value Cat. Remarks Source
Air:   AUS

(L)

30 ppm   2 h acc. STERN, 1986
  AUS

(L)

10 ppm   8 h acc. STERN, 1986
  B

(L)

6 mg/m3   8 h acc. MEINL et al., 1985
  B

(L)

15 mg/m3   1 h acc. MEINL et al., 1985
  BG

(L)

3 mg/m3   30 min1) acc. STERN, 1986
  BG

(L)

1 mg/m3   24 h1) acc. STERN, 1986
  CH

(L)

8 mg/m3   24 h acc. BUB, 1986
  CDN

(L)

35 mg/m3   2 h acc. STERN, 1986
  CDN

(L)

15 mg/m3   8 h acc. STERN, 1986
  CS

(L)

6 mg/m3   30 min acc. STERN, 1986
  CS

(L)

1 mg/m3   24 h acc. STERN, 1986
  D

L

10 mg/m3 MIK Long-time value2) acc. BAUM, 1988
  D

L

50 mg/m3 MIK Short-time value3) acc. BAUM, 1988
  D

L

10 mg/m3 IW 1   acc. TA Luft, 1986
  D

L

30 mg/m3 IW 2   acc. TA Luft, 1986
  DDR

(L)

3 mg/m3 MIKD   acc. HORN, 1989
  DDR

(L)

5 mg/m3 MIKK   acc. HORN, 1989
  E

(L)

45 mg/m3   30 min acc. STERN, 1986
  E

(L)

15 mg/m3   8 h acc. STERN, 1986
  GB

(L)

10 mg/m3   8 h acc. BUB, 1986
  GB

(L)

40 mg/m3   1 h acc. BUB, 1986
  GR

(L)

15 mg/m3   8 h, smog warning acc. MEINL et al., 1985
  GR

(L)

25 mg/m3   8 h, smog alarm stage 1 acc. MEINL et al., 1985
  GR

(L)

35 mg/m3   8 h, smog alarm stage II acc. MEINL et al., 1985
  H

(L)

1 mg/m3   30 min5) acc. STERN, 1986
  H

(L)

3 mg/m3   30 min1) acc. STERN, 1986
  H

(L)

6 mg/m3   30 min6) acc. STERN, 1986
  I

(L)

40 mg/m3   2 h acc. STERN, 1986
  I

(L)

10 mg/m3   8 h acc. MEINL et al., 1985
  IL

(L)

30 ppm   30 min acc. STERN, 1986
  IL

(L)

10 ppm   8 h acc. STERN, 1986
  J

(L)

10 ppm   24 h acc.STERN, 1986
  J

(L)

20 ppm   8 h acc. STERN, 1986
  J

(L)

58 mg/m3   1 h, priority stage II acc. MEINL et al., 1985
  N

(L)

25 mg/m3   3 h acc. STERN, 1986
  N

(L)

10 mg/m3   8 h acc. STERN, 1986
  NL

(L)

40 mg/m3   2 h acc. STERN, 1986
  NZ

(L)

30 ppm   2 h acc. STERN, 1986
  NZ

(L)

10 ppm   24 h acc. STERN, 1986
  RC

(L)

1 ppm   60 min acc. STERN, 1986
  RP

(L)

30 ppm   2 h acc. STERN, 1986
  RP

(L)

9 ppm   8 h acc. STERN, 1986
  SA

(L)

40 mg/m3   2 h acc. STERN, 1986
  SA

(L)

10 mg/m3   8 h acc. STERN, 1986
  SF

(L)

40 mg/m3   2 h acc. STERN, 1986
  SF

(L)

10 mg/m3   8 h acc. STERN, 1986
  SU

(L)

3 mg/m3   30 min1) acc. STERN, 1986
  TJ

(L)

6 mg/m3   6 min acc. STERN, 1986
  TJ

(L)

2 mg/m3   24 h acc. STERN, 1986
  WHO

G

10 mg/m3   8 h acc. UBA, 1988
  WHO

G

30 mg/m3   1 h acc. UBA, 1988
  WHO

G

60 mg/m3   1/2 h acc. UBA, 1988
  YU

(L)

10 mg/m3   30 min3) acc. STERN, 1986
  YU

(L)

30 mg/m3   30 min4) acc. STERN, 1986
  YU

(L)

40 mg/m3   1 h acc. STERN, 1986
  YU

(L)

10 mg/m3   8 h acc. STERN, 1986
  YV

(L)

10 mg/m3   8 h acc. STERN, 1986
Workp D

L

33 mg/m3 MAK   DFG, 1989
Workp DDR

(L)

55 mg/m3   Long-time value acc. HORN, 1989
Workp DDR

(L)

110 mg/m3   Short-time value acc. HORN, 1989
Workp SU

(L)

20 mg/m3     acc. SORBE, 1989
Workp USA

(L)

55 mg/m3 TWA   ACGIH, 1986
Workp USA

(L)

440 mg/m3 STEL   ACGIH, 1986
Workp D

L

5 %7) BAT Whole blood, end of shift DFG, 1989

Notes:

1) Designated protection areas
2) 1/2 hour mean value (may be exceeded once per month at most)
3)
Annual arithmetic mean for human health
4) 98% value of 1/2 hour mean values in one year
5) Specially designated protection areas
6) Areas other than those designated/specially designated as protection areas
7) CO haemoglobin

Comparison/reference values

Medium/origin Country Value Source
Air:
Rural areas DDR 0.01-0.9 mg/m3 acc. HORN, 1989
Atmosphere up to altitude of 10 km   0.15 mg/m3 acc. HORN, 1989
Urban areas DDR 10-60 mg/m3 (daily average) acc. HORN, 1989
Berlin, daily mean value D 15 mg/m3 acc. UBA, 1977
Cologne, daily mean value D 12 mg/m3 acc. UBA, 1977
Tunnels, garages DDR 115-570 mg/m3 acc. HORN, 1989
Gasworks, mines DDR < 660 mg/m3 acc. HORN, 1989

Assessment/comments

Carbon monoxide is released into the environment by combustion processes particularly in road traffic. In view of the fact that inhaled carbon monoxide does considerable harm to humans and animals, the emissions must be regulated by filters and catalysts. In addition to its toxic effect, carbon monoxide is probably partly responsible for changes in the world climate (higher atmospheric temperatures) due to its rapid oxidation to form carbon dioxide.


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