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 atmospheric deposition.

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 water.

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 respectively.

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.

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)

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 unreliable.

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 of toxicity.

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 1981).

No data could be located for sediment-dwelling organisms.

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 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.

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