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Toxicity to microorganisms

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Description of key information

Data for petro pitch are not available. Results from an activated sludge respiratory inhibition test with the supporting substance creosote is used to characterise toxicity of petro pitch to microorganisms. An EL0 of 36 mg/L is determined by extrapolation based on the dose-response curve.

Key value for chemical safety assessment

EC50 for microorganisms:
670 mg/L
EC10 or NOEC for microorganisms:
36 mg/L

Additional information

No experimental data is available for the substance pitch, petroleum, arom. (petro pitch) itself, but data have been identified for pitch, coal tar, high temp. (CTPht) and the tar oil creosote. These are used as supporting substances. Both substances consist of PAH. CTPht is closely structure related to petro pitch and comprises also an inert matrix of highly ring condensed polycyclic aromatic hydrocarbons. PAH constituents of the tar oil creosote are better bioavailable compared to the two pitches. Therefore, exposure to creosote is a worst-case situation.

Toxicity to microorganism was tested with CTPht in a Pseudomonas putida cell multiplication inhibition test (Hillmann E. 1991). No inhibition was detected up to a loading of 10,000 mg/L (EL0 = 10,000 mg/L).

In an activated sludge respiratory inhibition test according to OECD TG 209 (Lebertz H. 2002), an EL50 (effective loading) of 670 mg/L was determined. From the dose-response curve, a non-inhibitory loading (EL0) of ca. 36 mg/L could be extrapolated. This value is used to characterise the toxicity of petro pitch to microorganisms.