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EC number: 284-892-9
CAS number: 84989-04-8
The fraction of tar acid rich in 3- and 4-methylphenol, recovered by distillation of low-temperature coal tar crude tar acids.
The lowest valid result, which leads to the most critical PNEC, was found in m-cresol:EC75 (4 h) = 11.4 mg/L on activated sludge of predominantly domestic sewage (inhibition of nitrification, similar to ISO/DIS 9509)
No standard tests
concerning the respiration inhibition on microorganisms in sewage
treatment systems are available. However, several tests are available to
evaluate the toxicity of o-cresol to microorganisms.
described the influence of o-cresol on the nitrification process in
domestic wastewater. A purified activated sludge was incubated for 2 to
4 hours to the wastewater (BSB5 = 250 mg/L, 50 to 80 mg NH4-N/L)
fortified with different concentrations of o-cresol. The effect on the
inhibition of the nitrification was determined by photometric analysis
of nitrite and nitrate. An EC75 -value of 12.8 mg/L was given for the
inhibition of the reaction step of ammonia to nitrite.
The toxicity of
o-cresol to Pseudomonas putida was assessed in a cell
multiplication inhibition test according to Bringmann (1976). Bacteria
were exposed for 16 hours at a temperature of 25 °C to the test
substance. A toxicity threshold concentration of 33 mg/L was determined
after 16 hours exposure. This result is equivalent to an EC3 or
a NOEC. The endpoint biomass is measured by turbidity determination with
a photometric detector.
In another test by
Bringmann (1978), the protozoa Entosiphon sulcatum was exposed to
o-cresol for 72 hours using the cell multiplication inhibition test
method. A toxicity threshold of 17 mg/L was obtained which is equivalent
to a NOEC or an EC3.
The sensitivity of
activated sludge to m-cresol was determined by a respiration inhibition
test according to OECD Guideline 209.The 3 h-IC50 was 462 mg/L (Klecka
and Landi 1985). In a non-guideline study the effect of m-cresol on
activated sludge was determined by a respiration inhibition test. A 49
h-IC50 of 440 mg/L was obtained (Blum and Speece 1991). Nitrification
inhibition by m-cresol was measured by a method similar to ISO/DIS 9509
yielding an EC75 of 11.4 mg/L during a 2-4 h incubation period
(Tomlinson, Boon, and Trotman, 1966). In a cell multiplication
inhibition test conducted with Entosiphon sulcatum a 72 h-NOEC of
31 mg/L was determined (Bringmann, 1978). For Pseudomonas putida a
NOEC of 53 mg/L was obtained in a cell multiplication inhibition test
during 16 hours of exposure (Bringmann, 1976).
The sensitivity of
activated sludge to p-cresol was determined by a respiration inhibition
test according to OECD Guideline 209. The 2 h-IC50 for respiration
inhibition of microorganisms was 440 mg/L (Chan et al. 1999). The effect
of p-cresol on activity of Nitrosomonas was measured by a nitrification
inhibition method comparable to ISO/DIS 9509. The 24 h-IC50 was 27 mg/L
(Blum and Speece 1991). Inhibition of respiration was measured in a test
comparable to ISO 8192. A 49 h-IC50 of 260 mg/L was found for
respiration rate. Nitrification inhibition by p-cresol was also measured
by a similar method yielding an EC75 of 16.5 mg/L during a 2-4 h
incubation period (Tomlinson, Boon, and Trotman, 1966). Testing growth
inhibition of Tetrahymena pyriformis an EC50 of 157 mg/L was
found after a testing period of 48 h (Schultz, 1996).
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