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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.
Tests on freshwater and marine
organisms have shown that o-, m-, and p-cresol can exert toxic effects
to aquatic organisms. Comparing results of freshwater and marine
studies, cresols tend to be more toxic to marine organisms.
The lowest LC50 values found in
short-term toxicity tests on freshwater fish species range between 4.4
mg/L (p-cresol) and 7.6 mg/L (m-cresol).
Also in studies on short-term toxicity
to aquatic invertebrates toxic effects of cresols could be observed.
EC50 values of 9.6 mg/L and 7.7 mg/L were found on the freshwater
species Daphnia pulex and Daphnia magna for o-cresol and
p-cresol. In contrast, m-cresol seems to be less toxic to aquatic
invertebrates. For m-cresol an EC50 of > 99.5 mg/L was determined on Daphnia
pulicaria. The lower toxicity of m-cresol to aquatic invertebrates
is supported by findings of marine studies. A critical EC50 of 5 mg/L
was found for p-cresol on the marine sea urchin Strongylocentrotus
droebachiensis, while testing with m-cresol resulted in a higher
EC50 of 30 mg/L.
Reliable results on short-term toxicity
of cresols to algae or cyanobacteria are not available.
Comparing short-term results on fish
and aquatic invertebrates the most sensitive LC50 was found to be 4.4
mg/L on the fish species Salmo trutta, determined for p-cresol.
In general L(E)C50 values on fish and aquatic invertebrates are similar.
In a non-guideline study (comparable to
OECD 212) long-term toxic effects of o-, m-, and p-cresol to eggs and
larvae of the marine fish species Gadus morrhua were tested.
p-Cresol was found to be more toxic than o-cresol and m-cresol. NOEC
values of 3 mg/L were determined for o- and m-cresol, while the most
critical NOEC of 0.3 mg/L was found on p-cresol. The long-term toxic
effect of p-cresol also was tested on the freshwater fish species Pimephales
promelas in a study similar to OECD 210. After an exposure period of
32 d a NOEC of 1.35 mg/L was found.
Long-term toxicity to aquatic
invertebrates was tested with p-cresol. In
a study according to a guideline proposal of the German Umweltbundesamt
a NOEC of 1 mg/L was determined on Daphnia magna.
Toxicity of cresols to aquatic algae
and cyanobacteria was studied by Bringmann and Kuehn (1975, 1976, 1978,
1990). NOEC values of 6.8 mg/L and 13 mg/L were determined for o-cresol
and m-cresol on the cyanobacteria Microcystis aeruginosa.
p-Cresol was tested on the green algae Desmodesmus subspicatus and
resulted in an EC10 of 4.6 mg/L.
Comparing the three trophic levels the
most sensitive NOEC-freshwater was found to be 1 mg/L on Daphnia
magna and the most sensitive NOEC-marine was found to be 0.3 mg/L on Gadus
morrhua. Both results were determined on p-cresol.
Toxicity to microorganisms
Numerous studies examining the toxicity
of o-, m-, and p-cresol to microorganisms are available.
The sensitivity of activated sludge to
m-cresol and p-cresol was determined by respiration inhibition tests
according to OECD 209. IC50 values of 462 mg/L and 440 mg/L were found
for m-cresol and p-cresol.
Nitrification inhibition of m-cresol
and p-cresol was measured in tests comparable to ISO/DIS 9509 resulting
in an EC75 of 11.4 mg/L for m-cresol and an EC50 of 27 mg/L for
p-cresol. In non-guideline studies on inhibition of nitrification an
EC75 of 16.5 mg/L was found for p-cresol and an EC75 of 12.8 mg/L was
found for o-cresol.
Cell multiplication inhibition tests on
the bacteria Pseudomonas putida and the protozoa Entosiphon
sulcatum resulted in the following NOEC values:
NOEC = 33 mg/L
NOEC = 53 mg/L
NOEC = 17 mg/L
NOEC = 31 mg/L
Testing growth inhibition of p-cresol
on Tetrahymena pyriformis an EC50 of 157 mg/L was found.
Comparing all data on toxicity to
microorganisms, tests on nitrification inhibition resulted to be the
most sensitive one. The lowest EC75 of 11.4 mg/L, determined for
m-cresol, was used for PNEC calculation.
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