C6–C9 aromatic hydrocarbons (benzene, toluene, ethylbenzene, xylene, cumene) in freshwater and marine water

​​Toxicant default guideline values for protecting aquatic ecosystems

October 2000

Description of chemical

Uses

Benzene, toluene, ethylbenzene and xylenes are the simplest C6-C9 aromatic hydrocarbons. They are important and common aromatic solvents used for adhesives, resins, fibres, pesticides and ink, and in the rubber industry, as industrial cleaners and degreasers and as thinners for paints and lacquers (Nielsen & Howe 1991, Nielsen et al. 1991). They are common intermediates for many industrial chemicals including benzoic acid, phenol, styrene, explosives, dyes and detergent alkalenes. Benzene and toluene have been used as fuel additives and xylenes are used in aviation fuel and in polyester manufacture (Crookes et al. 1993). Ethylbenzene is a constituent of asphalt and naphtha. They are constituents of crude oil and are products of oil refining. In 1976, benzene emissions from stationary and mobile sources in the USA were calculated to be 650,000 tonnes (HSDB 1996). This group of chemicals, collectively known as BTEX, is commonly associated with contaminated petroleum sites in soils and groundwater. In the context of BTEX, users should note that additivity of toxic effects (i.e. mixture toxicity) always needs to be considered (Section 8.3.5.18 of the ANZECC & ARMCANZ 2000 guidelines).

Isopropylbenzene (cumene) is used in the production of phenol, acetone, and other industrial chemicals. Almost 2 million tonnes are produced in Western Europe alone (Nielsen et al. 1994). It is soluble in water to 50 mg/L, compared to 1800 mg/L for benzene and 515 mg/L for toluene. The log K_ow for cumene is 3.66. The current analytical PQL for benzene and xylenes is 1 µg/L (NSW EPA 2000).

Fate in the environment

The high volatility and relatively low water solubility of these chemicals indicates that they would be rapidly lost to atmosphere from a water body, with half-lives for evaporation £5 hours at 20°C (HSDB 1996). Biodegradation is also very rapid. The half-life of benzene was 16 days in an aerobic river test (Vaishnav & Babeu 1987) but degradation is much faster in systems contaminated by oil (HSDB 1996). Photodegradation is similarly rapid. Benzene and toluene are not expected to adsorb strongly to sediments but can occur at high concentrations adjacent to some contaminated sites.

None of these compounds are expected to bioaccumulate and this is reflected by low bioconcentration factor (BF) values for fish and clams (HSDB 1996). The log K_ow values for xylenes were 3.1–3.2, and the calculated log BCF values for fish were 2.14–2.20 (HSDB 1996) but the measured log BCF for eels was only 1.3 (Ogata & Miyaka 1978).

Aquatic toxicology

The para-isomer (4-xylene) is slightly more toxic than 2- or 3-xylene (Crookes et al. 1993). Short-term acute toxicity data are listed in table 8.3.14. Chronic invertebrate and fish toxicity NOEC data are as follows.

Benzene

Freshwater fish: one species, Pimephales promelas, 7-d growth and mortality of 10,200 µg/L to give ACR of 2.4. The lowest acute figure (Oncorhynchus mykiss) is given as 4.6 mg/L but the geometric mean of this species is 20 mg/L. The lowest geometric mean is 6.8 mg/L for O. nerka.

Marine invertebrate: one species, Cancer magister, 40-d mortality of 180-1200 µg/L (different life stages) (geometric mean of 460 µg/L). Acute LC50 figures were 8.4-108 mg/L for this species.

Marine diatom: one species, Skeletonema costatum, 3-10-d growth and mortality of 10,000-35,000 µg/L.

The default acute-to-chronic ratio (ACR) of 10 was used, instead of the experimental overall ACR of 1.97, to calculate freshwater and marine TVs for benzene. This was to provide adequate protection to sensitive species: for freshwater, the most sensitive life-stage of pink salmon O. gorbuscha and for marine systems, chronic toxicity to the crab, C. magister. For marine only, the 99% protection level for slightly to moderately disturbed systems was also recommended for protection of the crab.

Toluene

Marine fish: one species, Cyprinodon variegatus, 28-d mortality of 3200 µg/L.

Alternative low reliability trigger values for toluene (QSAR-derived) at different protection levels were 99% 110 µg/L, 95% 180 µg/L, 90% 230 µg/L and 80% 330 µg/L.

Ethylbenzene

Freshwater algae and blue–green algae: two species, 8-d growth of 1000 to 17,000 µg/L.

Alternative low reliability trigger values for ethylbenzene (QSAR-derived) were 99% 50 µg/L, 95% 80 µg/L, 90% 110 µg/L and 80% 160 µg/L.

The meta and para isomers of xylene can not currently be distinguished analytically. It is assumed that the mode of action is the same and that the toxicity of the isomers is additive.

Alternative low reliability trigger values for m-xylene (QSAR-derived) were 99% 50 µg/L, 95% 75 µg/L, 90% 100 µg/L and 80% 150 µg/L. The ortho and para isomers are listed in Table 3.4.1 in the ANZECC & ARMCANZ 2000 guidelines. Analogous values for i-propylbenzene are 20 µg/L, 30 µg/L, 40 µg/L and 70 µg/L.

Australian and New Zealand toxicity data

The only toxicity data available from Australia and New Zealand for these chemicals were from short-term bacteria tests.

References

ANZECC & ARMCANZ 2000. Australian and New Zealand Guidelines for Fresh and Marine Water Quality, Australian and New Zealand Environment and Conservation Council and Agriculture and Resource Management Council of Australia and New Zealand, Canberra.

Crookes MJ, Dobson S & Howe PD 1993. Environmental hazard assessment: Xylenes. TSD12. Department of Environment, Building Research Establishment, Garston, UK.

HSDB (Hazardous Substances Data Bank) 1996. Micromedex Inc. 31 July 1996.

Nielsen IR & Howe P 1991. Environmental hazard assessment: Toluene TSD 1. Building Research Establishment, Department of Environment, Garston, UK.
Nielsen IR, Diment J & Dobson S 1994. Environmental hazard assessment: Cumene, TSD20, Toxic Substances Division, Department of Environment, Garston, UK.

Nielsen IR, Read JD & Howe PD 1991. Environmental hazard assessment: Benzene TSD 4. Building Research Establishment, Department of Environment, Garston, UK.

NSW EPA 2000. Analytical Chemistry Section, Table of Trigger Values 20 March 2000, LD33/11, Lidcombe, NSW.

Ogata M & Miyaka Y 1978. Disappearance of aromatic hydrocarbons and organic sulfur compounds from fish flesh reared in crude oil suspension. Water Research 12, 1041-1044.

Vaishnav DD & Babeu L 1987. Comparison of occurrence and rates of chemical biodegradation in natural waters. Bulletin of Environmental Contamination and Toxicology 39, 237-44.