o-xylene

95-47-6

Manufacture of phthalic anhydride; vitamin and pharmaceutical
syntheses; dyes; insecticides; motor fuels. 
Manufacturing
terephalic acid for polyester, solvent recovery plants;
specialty chemical manufacture; manufacturing of isophthalic
acid, aviation gasoline, and protective coatings. 
As a solvent
for alkyd resins, lacquers, enamels, and rubber cements. 
In dye
manufacturing, and as an asphalt and naphtha constituent. 
As a
solvent for sterilizing catgut; and in microscopy as a cleaning
agent and with Canada balsam as an oil-immersent in microscopy;
intermediate. 

Colourless liquid. 
Will float and form slick on the surface.

Sweet odour.

Odour threshold: 
lower 0.26 ppm 
medium 2.21 ppm 
upper 4.13 ppm
(Sax 1986).

Odour threshold, air: 0.08 ppm; 0.17 ppm;
odour threshold, water: 1.8 ppm
(Sax 1986).

106.18

Based on a mass transfer equation to estimate evaporation rates
for assumed conditions of 25 °C, and 1 m depth of water, the
evaporation half-life for o-xylene was calculated to be 38.8
months (Sax 1986).

The concentration of o-xylene was measured in test aquaria
being used to conduct static bioassays. 
An initial
concentration of 1.3 µl/l measured 32 %, 82 %, and > 99 % loss
after 24, 48 and 96 hours, respectively. 
An initial
concentration of 4.6 µl/l measured losses of 33 %, 85 %, and >
99 % after the same intervals, respectively; 9.3 µl/l measured
losses of 23 %, 49 %, 95 % and > 99 % after 24, 48, 72, and 96
hours. 
These losses were believed to be primarily due to
volatilization although other variables included changes in
aquaria biomass, bacterial degradation and sorption (Sax 1986).

A mass transfer equation was developed consistent with the
conceptual model employed by Liss and Slater, with the
resulting estimated volatilization half-life at 25 °C and 1 m
water depth of 5.61 hours (Sax 1986).

Equilibrium distribution:
        mass %
air     98.92
water    0.89
solid    0.19
(Anon 1988)

Soluble in alcohol and ether; soluble in acetone, benzene,
carbon tetrachloride and petroleum ether (Sax 1986).

Photooxidation half-life in air:
1.8d - 4.4hr, based upon measured rate data for vapor phase 
reaction with hydroxyl radicals in air (Howard 1991).

Aerobic half-life:
4w - 1w, scientific judgement based upon soil column study 
simulating an aerobic river/ground water infiltration system 
and aqueous screening test data (Howard 1991).

Anaerobic half-life:
12mo - 6mo, scientific judgement based upon acclimated grab
sample data for anaerobic soil from a ground water aquifer
receiving landfill leachate and a soil column study simulating
an anaerobic river/ground water infiltration system (Howard 
1991).

Pseudomonas aeruginosa was cultured in a synthetic medium
containing o-xylene as the sole carbon source, no growth was
observed. o-Xylene was oxidized to o-hydroxymethylbenzoic acid
(Sax 1986).

None of the microorganisms obtained from 364 soil samples were
found to utilize o-xylene as a sole carbon source (Sax 1986).

Degradation of o-xylene:
*-------------------------------------------------------------*
ENVIRONMENT  INIT.CONC     REDOX-      TEMP   DEGRADATION  REF.
               mg/l          COND.      °C     %/day
*-------------------------------------------------------------*
water          0.510       aerobic      -       86/17      a
groundwater    0.0016      aerobic      13     100/8       b
groundwater   10           aerobic      10     100/12      c
soil           0.000042    aerobic      20       0/14      d
soil           0.04        aerobic      -       95/18      e
soil           0.257       methanogen   17      78/280     f
soil           0.257       methanogen   17     >99/840     f
sterile soil   0.257       methanogen   17       0/280     f
sterile soil   0.257       methanogen   17      34/840     f
soil           0.5         nitrate reducing 20 100/37      g
*--------------------------------------------------------------*
a) Battermann 1984           e) Zehnder 1984
b) Jamison et al. 1976       f) Wilson et al. 1986
c) Kappeler & Whurman 1978   g) Kuhn et al. 1985
d) Hutchins & Ward 1984      (Anon 1987b).

The penetration of o-xylene through the abdominal skin of rats
was low (Sax 1986).

Adult male Wistar rats were administered ipr injections of
o-xylene. 
A 75 % decrease in hepatic glutathione resulted
within 3 hr after treatment, however, this level returned to
normal after 24 hr. 
The result revealed direct conjugation of
o-xylene with GSH does not occur, and therefore, the chemical
must be bio-activated by other cellular enzymes before it
reacts with GSH. 
In another experiment, the rats were given ipr
injections of 3 mmoles/kg in 0.5 arachis oil to determine the
excretion of thioethers in the urine. 
Ten percent of the dose
was excreted and identified as
N-acetyl-S-(o-methylbenzyl)-L-cysteine. 
A dose 0.5 mmole/kg
resulted in 21 % excreted. 
For both dosages, the excretion was
almost complete within 24 hr after administration (Sax 1986).

Rats and guinea pigs excreted phenol in the urine after a
subcutaneous injection of 0.1 ml o-xylene (Sax 1986).

The absorption, metabolism and excretion of o-xylene was
studied in four healthy men, aged 28 - 50, who were exposed to
vapors (0.2 or 0.4 mg/l) for 8 hr. 
The pulmonary retention was
found to be independent of the level and duration of exposure
with a mean value of 62.4 %. 
The total amount exhaled after
exposure was calculated by determining the percent retained in
the subjects, approximately 5.3 % for o-xylene. 
Urinary
metabolites included unchanged o-xylene, glycine-bound toluic
acids, 2,3-xylenol and 3,4-xylenol. 
Hydroxytoluic acids;
toluylglucoronic acids, and free toluic acids were not detected
in the urine. 
Concentrations of unchanged o-xylene in the urine
increased slightly following the first 2 hr of exposure, and
were not detected following termination of exposure. 
The total
amount (of unchanged xylene) excreted was ascertained to be
0.005 % of the amount retained during exposure. 
The levels of
toluric acid reached a maximum at the end of the exposure and
then decreased rapidly, although, trace amounts were still
detected after 4 - 5 d. 
The total amount of toluric acid
excreted was 97.1 % of the o-xylene retained during exposure.

Of this amount, 68.5 % was excreted eithin 24 hr. 
Total
excretion of the xylenol metabolites occurred within 1 - 2 d,
following exposure and was calculated to be 0.86 % of the
retained o-xylene dose (Sax 1986).

Ortho-xylene (900 mg/kg) was given orally to rats and
metabolized to phenol, showing up in the blood approximately 6
hr later. 
When benzene (300 mg/kg) was given with o-xylene, the
amount of phenol formed increased and was in the blood
approximately 18 hr and excreted in the urine approximately 36
hr later. 
Blood hippuric acid levels also increased after
administration of combination of benzene and another solvent
(Sax 1986).

O-xylene, 100 mg/kg dissolved in 1 ml propylene glycol, was
administered by stomach tube to rats. 
Exretion in the urine
within 48 hr showed 0.1 % of the dose converted to
3,4-dimethylphenol. 
Small amounts of 2,3-dimethylphenol were
also excreted. 2-methylbenzyl alcohol was detected as another
metabolite (Sax 1986).

Inhaled o-xylene vapors are either exhaled unchanged or
oxidized to o-tolyglucuronic acid. 
A minor metabolic pathway is
hydroxylation to o-xylenol which is excreted either unchanged
or after conjugation with sulfate and glucuronic acid (Sax 
1986).

Following an 8 hr inhalation of approximately 0.2 - 0.4 mg/l,
the pulmonary retention by humans was 63.6 %. 
Approximately 95
% of the dose was metabolized, and another 5 % was eliminated
by the lungs during a 3 d desaturation period. 
Urinary
elimination was negligible (Sax 1986).

Noradrenaline-induced respiration was inhibited by 31 % in
isolated hamster brown fat cells exposed to 1mM o-xylene in
vitro. 
The cell consentration was approximately 1E5 cells/ml
and the temperature 37 °C. 
Ehrlich-Ladschutz diploid ascites
tumor cells were incubated for 5 hours in vitro at 37 °C with
50 or 100 ppm o-xylene. 
The ability of o-xylene to induce an
increase in the frequency of irreversibly injured cells at
these consentrations was comparable to controls (Sax 1986).

A long-term inhalation study of ortho-xylene in several species
failed to show significant changes in body weight or
hematological parameters after continuous exposure to 78 ppm
of xylene vapour for 90 days, or after 30 repeated exposures to
780 ppm of xylene (Jenkins et al. 1970).

Can be absorbed through skin at slightly hazardous chronic
levels. 
Recognition odour 1.8 ppm in air. 
May be narcotic at
high concentrations (Sax 1986).

Gene mutation - negative references (Sax 1986).

Mammals negative references (Sax 1986).

Southern armyworm (Prodenia eridania) in groups of 12 worms (5
th or 6 th instar) were fed 0.0135 mmole/g diet ad libitum for
3 days. 
Worms were sacrificed and analyzed for the effects on
the microsomal oxidase activities in the gut tissue. 
The
epoxidase (222 %), N-demethylase (201 %), NADPH-sytochrome c
reductase (128 %) and cytochrome P-450 (169 %) enzyme
activities were all greatly increased as compared to controls
(100 %) (Sax 1986).

The rate at which electrolytes were lost from sunflower leaves
(Helianthus annus) after treatment with o-xylene was
proportional to the phytotoxicity. 
Plants 3 - 5 weeks old were
administered 2 ml o-xylene by pipette onto the abaxial surfaces
of 5 g of the plant leaves. 
Leaves were the immersed in 100 ml
deionized water. 
The leakage of salts was measured by
electrodes and the changes in conductance. 
The rate of
electrolyte loss was 255E4 per min; the value for the untreated
controls was 16E4 per min (Sax 1986).

0.1 % seriously retarded sewage digestion (Sax 1986).

Aplexa hypnorum; LC50, > 22.4 mg/l, 4d (Holcombe et al. 1987).

The algal Chorella vulgaris had a 50 % reduction of cell
numbers vs. controls after 1 day incubation at 20 °C  with
exposure to 55 ppm o-xylene. 
A log period of 1 day between
inoculation and commencement of growth existed at concentration
of 25 and 50 ppm, however, no recovery of growth was observed
at 171 ppm. 
These cells differed morphologically: the
chloroplast was bleached and was aggregated in the center of
the cell, as were other cell contents (Sax 1986).