iso-Butanol

78-83-1

The major use of isobutanol is in the manufacture of isobutyl
acetate, which is employed in the lacquer industry.

Furthermore, isobutanol is used as a solvent in paint and
varnish removers and in the manufacture of isobutyl esters,
which serve as solvents, plasticizers, flavourings, and
perfumes. 
It is also used as a flavouring agent in butter,
cola, fruit, liquor, rum, and whisky (Hall & Oser 1965).

Isobutanol is one of the three main alcohols in fused oil, and
is present in large amounts in some alcoholic beverages
(Hedlund Kiessling 1969).

Natural isobutanol is produced by the fermentation of
carbohydrates. 
Isobutanol is found in some fruits. 
It also
occurs in beverages. 
Isobutanol has been identified in sundry
other foods including cheddar cheese and hop oil (WHO 1987).

Colourless liquid.

Sweet, similar to that of amyl alcohol, but weaker.

Odour threshold: approximately 4.6 mg/m3 (1.5 ppm).

Quality: sweet, musty
Hedonic tone: unpleasant to pleasant
Threshold odour concentration
absolute: 0.68 ppm
50 % recognition: 1.80 ppm
100 % recognition: 2.05 ppm
Odour index 100 % recognition: 5 131
(Hellman & Small 1974)

74.12

Biodegradation:
90% by BOD
period: 14d
substance: 100 mg/l
sludge: 30 mg/l
(MITI 1992)

Confirmed to be biodegradable (Anon. 1987).

Isobutanol is readily biodegradable. 
It is degraded in
significant amounts within a few hours, and degradation would
be expected to be complete within a few days (WHO 1987).

Nazarenko ( 1969) reports an oxygen requirement of
approximately 1.4 mg to oxidize 1 mg of isobutanol.

In animals, isobutanol is absorbed through the skin, lungs, and
gastrointestinal tract. 
Isobutanol is metabolized by alcohol
dehydrogenase to isobutyric acid via the aldehyde and may enter
the tricarboxylic acid cycle. 
Small amounts of isobutanol are
excreted unchanged, ot as the glucoronide in the urine. 
In
rabbits, metabolites found in the urine include acetaldehyde,
acetic acid, isobutyraldehyde, and isovaleric acid (Saito 
1975).

Isobutanol does no bioaccumulate (Chiou et al. 1977).

The acute toxic effects are alcoholic intoxication and
narcosis. 
Isobutanol is severely irritating to the eyes and
moderately irritating to the skin. 
A group of rats given an 1
mol/l solution of isobutanol as their sole drinking liquid for
4 months did not show any adverse effects in the liver; another
group given a 2 mol/l solution as their sole drinking liquid
for 2 months showed a reduction in fat, glycogen, ant RNA
content, and in the overall size of the cells in the liver.

Continuous inhalation exposure of rats to 3 mg/m3 for 4 months
resulted in depression of leg withdrawal response to electrical
stimulation, minor changes of formed elements of the blood and
serum enzymes. 
The estimated NOEC level was 0.1 mg/m3
(WHO 1987).

In a lifetime carcinogenicity study, groups of rats received
isobutanol subcutaneously (0.05 ml/kg body weight twice a week)
or orally (0.2 mg/kg). 
The animals exhibited toxic liver damage
ranging from steatosis to cirrhosis. 
Numbers of animals showing
malignant tumours totalled 8 in the subcutaneous group, 3 in
the oral group, and 0 in the control group. 
The majority of
treated animals also showed hyperplasia of blood-forming
tissues. 
Because of lack of mutagenicity studies, the Task 
Group could not determine whether isobutanol was a genetically 
active compound. 
The findings in the carcinogenicity study are 
a cause of concern. 
Because of methodological inadequacies 
and the manner of reporting the data, it was not possible to 
determine whether isobutanol should be regarded as an animal 
carcinogen. 
Thus it is not possible to extrapolate from this 
study to possible long-term effects in man (WHO 1987).

No adequate data are available to assess mutagenicity of
teratogenicity of isobutanol or effects on reproduction 
(WHO 1987).

Threshold for narcosis: 4000 mg/l,Tadpole (Rana sp.),
(Münch 1972).

Toxicity studies in plants indicate that germination will not
be affected by exposure to isobutanol at background levels. 
An
EC50 of 760 mg/l was reported by Reynolds (1977) for seed
germination in lettuce (Lactuca sativa). 

Smith & Siegel (1975) found an EC50 of 40800 mg/l for seed 
germination in cucumber (Cucumis sativus).

Table 1 Toxicity of isobutanol to microorganisms (WHO 1987).
_______________________________________________________________
Species      Conc.mg/l   Parameter       Reference
---------------------------------------------------------------
Protozoa
Chilomonas               NOEC 48hr       Bringmann & Kühn
paramaecium    22        total biomass   1981
(flagellate)
Uronema
parduczi      169        NOEC 20 hr      Bringmann & Kühn
(ciliate)                total biomass   1981
Entosiphon
sulcatum      296        NOEC 72hr       Bringmann & Kühn
(flagellate)             total biomass   1981
Bacteria
Pseudomonas              NOEC 16hr       Bringmann & Kühn
putida        280        total biomass   1981
Bacillus                 EC50            Yasuda-Yasaki et al.
subtilis     1180        spore germination               1978
_______________________________________________________________
Toxicity threshold (cell multiplication inhibition test):
bacteria (Pseudomonas putida): 280 mg/l
(Bringmann & Kühn 1980a)

Toxicity threshold (cell multiplication inhibition test):
green algae (Scenedesmus quadricauda): 350 mg/l
protozoa (Entosiphon sulcatum): 295 mg/l
(Bringmann & Kühn 1980a)