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Carcinogenicity

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Description of key information

There is no carcinogenicity bioassay or other chronic study available to assess the carcinogenic potential of p-cresol. 
However, for read across purposes, the recently published studies on carcinogenicity with m/p-cresol mixture (60:40; US Department of Health and Human services 2007) is considered.

Key value for chemical safety assessment

Carcinogenicity: via oral route

Link to relevant study records
Reference
Endpoint:
carcinogenicity: oral
Type of information:
migrated information: read-across from supporting substance (structural analogue or surrogate)
Adequacy of study:
key study
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: only male rats in test
Qualifier:
equivalent or similar to
Guideline:
OECD Guideline 451 (Carcinogenicity Studies)
Principles of method if other than guideline:
Groups of 50 male rats were fed diets containing 0, 1,500, 5,000 or 15,000 ppm m-/p-cresol (equivalent to average daily doses of approximately 70, 230, or 720 mg cresols/kg body weight) for 105 weeks. All animals were observed twice daily. Body weights were recorded at the beginning of the study, weekly for the first 13 weeks, at 4-week intervals thereafter, and at study termination. Clinical findings were recorded during week 5 of the study, at 4-week intervals thereafter, and at study termination.
Complete necropsies and microscopic examinations were performed on all rats. At necropsy, all organs and tissues were examined for grossly visible lesions, and all major tissues were fixed and preserved in 10% neutral buffered formalin (eyes were first placed in Davidson’s solution), processed and trimmed, embedded in paraffin, sectioned to a thickness of 4 to 6 μm, and stained with hematoxylin and eosin for microscopic examination. For all paired organs (e.g., adrenal gland, kidney, ovary), samples from each organ were examined. For extended evaluation of renal proliferation lesions, additional sections of both kidneys from the residual formalin-fixed wet tissues were obtained for each male rat, imbedded in separate paraffin blocks, and step sectioned at 1 mm intervals. Three (left kidney) or four (right kidney) sections were examined for each rat.
GLP compliance:
yes
Species:
rat
Strain:
other: Fisher 344/N
Sex:
male
Details on test animals and environmental conditions:
TEST ANIMALS
- Source: Taconic Laboratory Animals and Sevices, Germantown, NY
- Age at study initiation: 6 weeks
- Housing: 2-3 rats/cage
- Diet: ad libitum
- Water: ad libitum):
- Acclimation period: 11 days


ENVIRONMENTAL CONDITIONS
- Temperature (°F): 72
- Humidity (%): 50
- Air changes (per hr): 10
- Photoperiod (hrs dark / hrs light): 12/12
Route of administration:
oral: feed
Vehicle:
unchanged (no vehicle)
Details on exposure:

DIET PREPARATION
- Rate of preparation of diet (frequency): monthly
- Mixing appropriate amounts with NTP-2000 food
- Storage temperature of food: at 25 °C in the dark

Analytical verification of doses or concentrations:
yes
Details on analytical verification of doses or concentrations:
Periodic analyses of the dose formulations were conducted by the study laboratory usinng GC. The dose formulations were analyzed
approximately every 3 months.All of the dose formulations analyzed for rats were within 10 % of the target concentration.
Duration of treatment / exposure:
105 weeks
Frequency of treatment:
daily
Post exposure period:
no
Remarks:
Doses / Concentrations:
0, 1500, 5000 or 15000 ppm = equivalent to average daily doses of approx. 0, 720, 230, or 720 mg/kg bw/day
Basis:
nominal in diet
No. of animals per sex per dose:
50 male rats per dose
Control animals:
yes, plain diet
Details on study design:
- Dose selection rationale: the highest exposure concentrations was based on the minimal toxicity observed at this level
in the 13 week study with m/p-cresol mixture
Positive control:
no
Observations and examinations performed and frequency:
CAGE SIDE OBSERVATIONS: Yes
- Time schedule: twice daily

DETAILED CLINICAL OBSERVATIONS: yes
- Time schedule:
Clinical findings were recorded during week 5 of the study, at 4 week intervallsthereafter and at terminiation

BODY WEIGHT: Yes
- Time schedule for examinations:
at the beginning of the study weekly for the first 13 weeks, at 4 week intervals thereafter and at study termination

FOOD CONSUMPTION AND COMPOUND INTAKE (if feeding study):
- Food consumption for each animal determined Yes
at the beginning of the study weekly for the first 13 weeks, at 4 week intervals thereafter:
Food consumption calculated as mean g/day
Compound consumption calculated as mean mg/kg bw/day

OPHTHALMOSCOPIC EXAMINATION: No
HAEMATOLOGY: No
CLINICAL CHEMISTRY: No
URINALYSIS: No
NEUROBEHAVIOURAL EXAMINATION: No
Sacrifice and pathology:
GROSS PATHOLOGY: Yes
was performed on all rats
HISTOPATHOLOGY: Yes
complete histopathology was performed on all rats. In additon to gross sesions and tissue masses , the following tissues were
examined:
adrenal gland, none with marrow, brain, esophagus, eye, hardrian gland, heart and aorta, large intestine, small intestin kidney,
liver, lung, mainstem bronchi, lymph nodes (mandibular and mesenteric), mammary gland, nose, pancreas, parathyroid gland,
pituitary gland, preputial gland, prostate gland, salivary gland, skin, spleen, stomach (forestomach and glandular), testis with
epididymis and seminal vesicle, thymus, thyroid gland, trachea and urinary bladder

For all paired organs samples from each organ were examined

For extended evaulation of renal proliferation lesions, additional sections of both kidneys from the residual formalin-fixed
wet tissues were obtained for each male rat. 3 sections of the left kidney and 4 sections of the right kidney were examined for
each rat
Other examinations:
no
Statistics:
Kaplan Meier, Cox-method, Tarone's life-table test, Poly-k-test,
Clinical signs:
effects observed, treatment-related
Mortality:
mortality observed, treatment-related
Body weight and weight changes:
effects observed, treatment-related
Food consumption and compound intake (if feeding study):
effects observed, treatment-related
Food efficiency:
not specified
Water consumption and compound intake (if drinking water study):
no effects observed
Ophthalmological findings:
not examined
Haematological findings:
not examined
Clinical biochemistry findings:
not examined
Urinalysis findings:
not examined
Behaviour (functional findings):
not examined
Organ weight findings including organ / body weight ratios:
not specified
Gross pathological findings:
effects observed, treatment-related
Histopathological findings: non-neoplastic:
effects observed, treatment-related
Histopathological findings: neoplastic:
effects observed, treatment-related
Description (incidence and severity):
at 15000 ppm in 4/50 rats renal tubular adenomas ; increase not significant but exceeding historical controls of the laboratory [1/297 [feed studies])
Details on results:
see section "remarks on results"
mean body weights of the 15000 ppm group wee less than those of the controls throughout the study and decreased
to 15 % less than that of the controls by the end of the study
There were no clinical findings related to exposure to cresols.
Equivocal finding :
The incidence of renal tubule adenomas was increased in the 15000 ppm group and the incidence exceeded
the historical range for controls in feed studies (0-2 %)
Dose descriptor:
LOAEL
Effect level:
720 mg/kg diet
Based on:
test mat.
Sex:
male
Basis for effect level:
other: Under the conditions of these 2-year studies, there was equivocal evidence of carcinogenic activity of 60:40 m-/p-cresol in male F344/N rats based on the marginally increased incidence of renal tubule adenoma
Remarks on result:
other: Effect type: carcinogenicity (migrated information)
Dose descriptor:
NOAEL
Effect level:
230 mg/kg diet
Based on:
test mat.
Sex:
male/female
Remarks on result:
other: Effect type: carcinogenicity (migrated information)

Concentration in feed

0, 1,500, 10,000 or 15,000 ppm

equivalent to average daily doses of approximately 0, 70, 230, 720 mg/kg bw/day

Body weights

15,000 ppm group: less than the control group

Survival rates : 33/50, 34/50, 33/50, 31/50

Nonneoplastic effects

----Kidney

pelvis, transitional epithelium, hyperplasia (0/50, 0/50, 2/50, 8/50);

severity of nephropathy (1.4, 1.4, 1.7, 2.1)

----Nose:

goblet cell, hyperplasia (23/50, 40/50, 42/50, 47/50);

respiratory epithelium, hyperplasia (3/50, 17/50, 31/50, 47/50)

respiratory epithelium, metaplasia, squamous (0/50, 1/50, 8/50, 40/50);

inflammation (17/50, 19/50, 19/50, 28/50)

----Liver:

eosinophilic focus (14/50, 14/50, 13/50, 23/50)

Neoplastic effects

-----None

Equivocal findings:

---- Kidney:

renal tubule adenoma

--standard evaluation - 0/50, 0/50, 0/50, 3/50;

--standard and extended evaluations combined - 0/50, 0/50, 0/50, 4/50(8%)

Level of evidence of carcinogenic activity : equivocal evidence

Executive summary:

Under the conditions of these 2-year studies (oral feed, 0, 1500, 5000 or 15000 ppm = equivalent to average daily doses of approx. 0, 720, 230, or 720 mg/kg bw/day), there was equivocal evidence of carcinogenetic activity of 60:40 m/p-cresol in male F344/N rats based on the marginally increased incidence of renal tubule adenoma. The LOAEL(male rats) is therefore 720 mg/kg bw/day.

Endpoint conclusion
Endpoint conclusion:
adverse effect observed
Dose descriptor:
NOAEL
230 mg/kg bw/day
Study duration:
chronic
Species:
rat
Quality of whole database:
The materials/methods and results are described in detail und are sufficient for evaluation.

Carcinogenicity: via inhalation route

Endpoint conclusion
Endpoint conclusion:
no study available

Carcinogenicity: via dermal route

Endpoint conclusion
Endpoint conclusion:
no study available

Additional information

There is no carcinogenicity bioassay or other chronic study available to assess the carcinogenic potential of p-cresol.

However, for read across purposes, the recently published studies on carcinogenicity with m/p-cresol mixture (60:40; US Department of Health and Human services 2007) will be considered.

In 2007, US Health and Human Services published a Toxicity and Carcinogenicity Study in which only male rats or only female mice were fed m/p-cresol mixture over a period of two years without interim kill. Neither absolute/relative organ weights nor blood biochemistry data were reported so far. The report contains only histopathological data.

Rat study

Male F344/N rats received in feed 0, 1500, 5000, or 15000 ppm (= equivalent to daily doses of approx. 0, 70, 230 or 720 mg/kg bw/day) for 105 weeks. Under the condition of these 2-year studies, there was equivocal evidence of carcinogenic activity on m/p-cresol based on the 4/50 male rats with renal tubular adenomas. The incidence of these neoplasms was not significant but exceeded the historical control data of the laboratory (1/297[feed studies]).

Mouse study

Female B6C3F1 mice received in feed 0, 1000, 3000, 10000 ppm (= equivalent to dailydoses of approx. 0, 100, 300 or 1040 mg(kg bw/day) for 104-105 weeks. Under the conditions of these 2-year studies there was some evidence of carcinogenic activity of m/p-cresol mixture based on the increased incidence of forestomach squamous cell papillomas. However, there is no human counterpart for the rodent forestomach (Proctor et al., Toxicol Sci 98, 313 -326, 2007). Therefore, the forestomach squamous cell paplillomas are of minor significance for the human situation. In addition, due to the corrosive property of the test substance, chronic irritation is expected to be the mode of action.


Justification for selection of carcinogenicity via oral route endpoint:
A NTP technical report on the toxicology and carcinogenesis studies of cresols (CAS no. 1319-77-3) in male F344/N rats and female B6C3F1 mice (feed studies). The most reliable study concernig effects relevant for humans is used as key value and for classification.

Carcinogenicity: via oral route (target organ): urogenital: kidneys

Justification for classification or non-classification

No classification is required