Entry into the marine environment
Toluene has a large number of applications in both
industrial and consumer products.
The largest single use of unisolated toluene, as
BTX mixture, is the incorporation of the reformate
mixture into petrol to produce high octane fuel.
In addition, approximately 35% of isolated (technically
pure) toluene is backblended into petrol to increase
the octane ratings (Fishbein 1985). As the lead
content in petrol is reduced to 0.15 g l-1
and ultimately zero in EC member states, there will
be an increase in the use of catalytic reformate
(BTX mix) to maintain octane numbers, and it is
predicted that the content of aromatic hydrocarbons
in petrol will increase by approximately 20%, Clark
et al (1984a).
Isolated toluene has a diverse range of other applications.
An estimated 9.5% is used as a solvent (increasingly
as a 'safe' replacement for benzene) in paints and
coatings, adhesives, inks and dyes, pharmaceuticals
and aerosols (Fishbein 1985).
Furthermore, toluene is used as a raw material
in the chemical industry for the manufacture of
phenol and toluene diisocyanate (TDI), benzoic acid,
benzyl chloride, xylenes, vinyl toluene, benzaldehyde
and cresols and to a lesser extent, caprolactam.
Toluene is also important in the production of TNT,
saccharin and detergents (toluene sulphonates).
Fishbein (1985) estimated that more than 6 million
tons of toluene entered the environment annually.
The atmosphere provides the main sink for toluene
and relatively small amounts are lost to the aqueous
environment. The total amount of toluene lost world-wide
to the sea is estimated at 500,000 tons/y (Merian
and Zander 1982). The greatest loss of toluene,
approximately 3 to 4 million tons/y, occurs during
the production and transport of petroleum products,
with a further 2 million tons/y emitted in automobile
exhausts. The use of toluene as a solvent accounts
for losses of approximately 1 to 1.5 million tons/y.
Possible routes of entry for toluene into surface
waters include; direct discharges of industrial
effluents, especially from chemical production and
refinery sites; spillage; leaching and run-off and
Recorded levels in the marine
Jones and Zabel (1996) reviewed data on toluene.
Harland et al (1982) carried out a detailed
study of the toluene levels in the Tees estuary,
NE England. The estuary receives discharges from
many industries. At one site, toluene levels ranged
from 0.3 to 19.7 µg l-1,
whereas at Tees Dock, the levels ranged from 18.9
to 112.8 µg l-1. Highest
concentrations were found in samples taken from
the surface freshwater layer overlying the saline
Gschwend et al (1980) suggested that toluene
may originate from biogenic sources in coastal waters
as increased total volatile organic concentrations
near algal blooms were observed. However, concentrations
were low, at less than 0.01 µg l-1.
Harland et al (1982) took sediment samples
from two sites in the Tees estuary and found toluene
concentrations ranging from 2.2 to 3.7 µg kg-1
wet weight at one site and 1.2 to 6.4 µg kg-1
wet weight at the other. These values were not corrected
for recovery efficiency and actual levels may be
a factor of three greater than reported. Corresponding
water concentrations were up to 20 and 113 µg l-1
In rural Britain, Clark et al (1984a,b)
found levels of toluene in air ranging from a mean
of 1.27 ppb to a maximum of 6.4 ppb, whereas at
an urban site in south west London, the levels were
higher at 13.0 ppb (mean) with a maximum of 42.4
ppb. This demonstrated that increased toluene levels
occurred in areas with high exhaust emissions. The
proportion of toluene in emissions from vehicular
exhausts range from 3.1% to 16.3% of total emitted
hydrocarbons, depending on fuel and engine type
(Verschueren 1983; Fishbein 1985; Sigsby et al
1987). Levels at a motorway site off the M1 were
lower than at the urban site, probably because toluene
emissions at high and constant speed tend to be
lower than under urban traffic conditions.
Fate and behaviour in the marine
The solubility of toluene in fresh and salt waters
at 25 °C is 535 and 380
mg l-1 respectively. Volatilisation
is an important removal process for toluene present
in the aqueous environment. Particularly under conditions
when biodegradation is low, volatilisation is the
predominant removal process (Wakeham et al
(1983, 1985)). Maximum winter volatilisation rate
constants of 0.11/day were obtained for a controlled
marine ecosystem by Wakeham et al (1985).
This resulted in a half life of about 25 days which
was reduced to only 6 days under storm conditions.
Toluene is lipophilic and moderately adsorbed on
soils and sediments (Jones and Zabel 1996)
Effects on the marine environment
Toxicity to marine organisms
An exhaustive literature review on the toxicity
of toluene to marine organisms has not been carried
out for the purposes of this profile. The information
provided in this section is taken from existing
review documents (Jones and Zabel 1996). The most
sensitive groups of organisms have been identified.
Jones and Zabel (1996) reviewed the aquatic toxicity
data for toluene and found relatively few toxicity
data for marine organisms had been reported. Most
of the reported tests were carried out under static
conditions with nominal exposure concentrations.
Because of the high volatility of toluene and the
wide variation in saltwater solubility values reported
in the literature, the results of static tests with
no analysis of exposure concentrations are very
In acute tests, the crustacean Crago franciscorum
was found to be the most sensitive species with
a 96 hour LC50 of 3.7 mg l-1 (Benville
and Korn 1977). The results appear to be based on
mean analysed concentrations. However, as most deaths
seem to occur during the initial few hours of exposure,
the use of the mean concentration could lead to
an over-estimation of the toxicity. For the crustacean,
Palaeomonetes pugio a 24 hour LC50 of 9.5
mg l-1 (Tatem 1975) was obtained
in a static test based on initial concentrations.
In this case, the results could be an underestimation
Similar acute toxicities have been obtained for
fish species - a 24 hour LC50 of 5.4 mg l-1
(Thomas and Rice 1979) and a 96 hour LC50 of 6.4
mg l-1 (Korn et al 1979)
for the pink salmon, and 24 and 96 hour LC50s of
6.3 mg l-1 (Benville and Korn 1979)
for the striped bass. The results are based on initial
concentrations and the true values could be lower
by more than 50%.
Bacteria and algae seem to be more resistant to
the acute effects of toluene than fish and crustaceans
(Jones and Zabel 1986).
The only reported chronic test was for the early
life stage of the sheepshead minnow, with 7.7 mg l-1
causing a significant decrease in hatching. The
maximum acceptable toxicant concentration was calculated
as > 3.2 mg l-1 (Ward and Parrish
No data could be located for sediment-dwelling
Jones and Zabel (1996) concluded that bioaccumulation
in marine organisms appeared to be low. The highest
BCF of 13.2 has been reported for eel flesh based
on wet weight. Also, the rate of depuration, when
organisms are returned to uncontaminated water,
is reported to be rapid.
Potential effects on interest
features of European marine sites
Potential effects include:
- toxicity of toluene to invertebrates and fish
at concentrations above the EQS of 40 µg
l-1 (annual average) and 400 µg
l-1 (maximum allowable concentration)
in the water column.