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Creosote oil, acenaphthene fraction (wash oil) is a liquid UVCB substance mainly consisting of 2- and 3-ring polycyclic aromatic compounds. Major constituents are (typical concentration): naphthalene (ca 11 - 13 %), 2-methylnaphthalene (ca. 17 - 20 %), 1-methylnaphthalene (ca. 7 - 9 %), and acenaphthene (ca. 13 - 15 %). Fluorene is present at a typical concentration of ca. 5 %. Maximum percentage of acenaphthene can be up to 40 %. These substances comprise some 50 % (typical concentration) of total wash oil.

When comparing the environmental toxicity of individual wash oil constituents, acenaphthene is one of the most toxic substances. The other major components (methylnaphthalenes, naphthalene) are environmentally less toxic (compare to ref. EU (2008): EU RAR Coal-tar pitch, high temperature). In addition, physical-chemical and distribution properties of acenaphthene are close to average values for wash oil (see Chapters 1.3. and 4.).

Fluorene is of similar aquatic toxicity (same order of magnitude) as acenaphthene being slightly more toxic for some aqueous organisms (fish, invertebrates, chronic effects, see data below). However, physical-chemical and distribution properties are not as close to the average for wash oil as are the properties of acenaphthene. In addition, concentration of fluorene in wash oil is only about 5 % compared to 40 % of acenaphthene used in the environmental assessment of wash oil, far overcompensating for its somewhat higher toxicity to fish and aquatic invertebrates.

Taking into account these facts, acenaphthene is considered to represent best the environmental toxicity of wash oil. For these reasons, acenaphthene is selected as marker substance for the environmental assessment of wash oil. In case data for wash oil is lacking, data for acenaphthene will be used in the first place. Data for other wash oil constituents may also be reported in order to draw parallels.

Aquatic toxicity of wash oil itself was only tested in short-term but not in long-term studies. Short-term tests have been conducted with fish, with aquatic invertebrates (daphnia), and with algae. Additional short-term tests have been performed using the wash oil component acenaphthene (marker substance).

Long-term aquatic toxicity data are only present for the wash oil components acenaphthene and fluorene. Species tested were fish and daphnia.

Sediment toxicity has been tested in Rhepoxynius abronius, a freeburrowing, marine infaunal amphipod with acenaphthene as test substance.

Aqueous short-term toxicity

Due to the complex composition and variable solubility of its components, water solubility of wash oil is not clearly defined. Depending on the quantity used, concentration of material dissolved in saturated water samples is variable. Therefore, water accommodated fractions (WAFs) have been used in acute aquatic toxicity tests with wash oil. Thus, results of short-term tests with wash oil are given as loadings (LL/EL50, NOELR).

Acute aquatic toxicity of wash oil has been examined in fish, daphnia and alga, in daphnia under static sealed/closed and largely open conditions, while for fish (semi-static) and alga (static) the test conditions were open. All tests were performed according to respective OECD/EU test guidelines.

The lowest acute toxicity value was obtained under closed test conditions of a daphnia study: EL50(48 h) = 2.7 mg/L. Under open conditions, the corresponding value in daphnia was more than 20 times higher: EL50(48 h) = 69 mg/L. These findings indicate that volatility of wash-oil components is substantial and that volatile components contribute most to acute intoxication under experimental conditions. This is further supported by the fact that the dissolved fraction of about 1.5 mg TOC/L under closed condition produced the same acute toxicity as about 9 - 10 mg TOC/L under open condition. It may be assumed that narcosis is the main underlying mechanism for the high intoxication by the volatile fraction.

All other toxicity data with wash oil are significantly above 10 mg/L (based on loading, open conditions). Under open conditions, the algae proved to be the most sensitive species:

Fish: LL50(96 h) = 79 mg/L

Daphnia: EL50(48 h) = 69 mg/L

Algae: ELr50= 25 mg/L.

For comparison with total wash oil, the short term aquatic toxicity of the marker substance acenaphthene is reported. Acenaphthene produced acute toxicity in freshwater and marine fish within its water solubility. 96h fresh water LC50ranged from 0.58 to 1.72 mg/L depending on fish species tested. Short-term toxicity to marine fish was less pronounced compared to freshwater fish.

Fish, freshwater: LC50(96 h) = 0.58 mg/L (measured)

Fish, saltwater: LC50(96 h) = 3.1 mg/L (measured)

Aqueous long-term toxicity

No data is available for wash oil itself. But long-term aquatic toxicity tests have been performed apart from other wash oil constituents also for the marker substance acenaphthene and the basic wash oil constituent fluorene. Long-term data are available for fish (fresh- and saltwater), aquatic invertebrates (daphnia), and algae. Test substances produced chronic toxicity in freshwater and marine organisms within their water solubility: The lowest NOEC/EC10 values were observed in algae (38 µg/L, analytical, acenaphthene) and in daphnia (25 µg/L, analytical, fluorene).

Sensitivity of aqueous species is different for acenaphthene and fluorene, respectively. For acenaphthene, NOEC/EC10are different by a factor of about 10 between algae and fish with daphnia EC10close to algae (see data below). Algae is the most sensitive organism. This is consistent with sensitivities observed in short-term tests using total wash oil as test substance (most sensitive species algae). Fluorene toxicity did not differ much between the three species tested (range of NOEC/EC10between 25 and 82 µg/L). Most sensitive species is daphnia.

The lowest NOEC/EC10for acenaphthene (algae) and fluorene (daphnia) are similar (38 µg/L and 25 µg/L, respectively). As the concentration of acenaphthene in wash oil is substantially higher than the concentration of fluorene, it can be assumed that the average ecotoxicological characteristics of wash oil are mainly and sufficiently accurately determined by the properties of acenaphthene. In addition, environmental fate properties of acenaphthene are closer to the average characteristics of wash oil compared to fluorene. Therefore, acenaphthene is selected as marker substance for the environmental assessment of wash oil (see above). For the derivation of PNECs, the lowest EC10of acenaphthene (38 µg/L) will be used.


Fish, freshwater: NOEC(34 d) = 332 µg/L (larval development) (Cairns et al., 1982)

Fish, salt water: NOEC(28 d) = 520 µg/L (mortality) (Ward et al., 1981)

Daphnia: EC10(7 d) = 42 µg/L (mortality and reproduction) (Bisson et al., 2000)

Alga: EC10(72 h) = 38 µg/L (growth) (Bisson et al., 2000)


Fish (freshwater): NOEC(30 d) = 47 µg/L (growth rate) (Finger et al., 1985)

Daphnia: EC10(7 d) = 25 µg/L (mortality and reproduction) (Bisson et al., 2000)

Alga: EC10(72 h) = 82 µg/L (growth) (Bisson et al., 2000)

Inhibitory effect to micro-organisms:

A structure-related tar-oil (creosote) is taken as supporting substance to characterise the toxic effects of wash oil on microorganisms. Creosote caused no substantial inhibition to a mixed microbial population (activated sludge from a municipal STP) but at high nominal concentrations (3h-EL50= 670 mg/L, OECD TG 209). 3h-EL0was ca. 36 mg/L (below lowest dose tested - 125 mg/L).

Sediment toxicity

Toxicity of the marker substance acenaphthene to sediment organisms has been determined in a long-term (10d) static sediment toxicity test using Rhepoxynius abronius, a freeburrowing, marine infaunal amphipod. 10d-LC50and LC10values were-originally produced in sediment containing 3% organic carbon. The indicated LC50and LC10data have been "normalised" by recalculating them to a standard carbon content of 10%.

Amphipod (marine): LC10= 156 mg/kg sediment dw (measured, normalised for standard carbon content of 10%).