Melamine

Carcinogenicity

Description of key information

Two-year carcinogenicity studies were performed in rat and mouse by the US National Toxicology Program (NTP). Statistically significant increases in the incidence of transitional-cell carcinoma and combined incidences of transitional-cell carcinoma and papilloma in the urinary bladder were observed in male rats exposed to 4500 ppm melamine (ca. 263 mg/kg bw/day), but not when exposed to 2250 ppm melamine. With one exception, urinary bladder stones were observed in male rats that had transitional-cell carcinomas. Female rats did not develop tumours even when exposed up to 9000 ppm.

No neoplastic findings related to treatment were observed in male or female mice.

A further 2-years carcinogenicity study (Reno 1983) was performed at lower doses and after the NTP study. It did not reveal carcinogenicity in male rats (and also not in female rats) up to the highest used doses of 1000 ppm in male and 2000 ppm in female rats.

Key value for chemical safety assessment

Carcinogenicity: via oral route

Link to relevant study records

Reference

Reference 1

Endpoint:

carcinogenicity: oral

Type of information:

experimental study

Adequacy of study:

key study

Study period:

1978 to 1981

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

other: NTP studies are considered as top quality studies, even if GLP was formally not stated. The studies are peer reviewed.

Reason / purpose for cross-reference:

reference to same study

Reason / purpose for cross-reference:

reference to other study

Qualifier:

according to guideline

Guideline:

other: NTP standards

Deviations:

not specified

Principles of method if other than guideline:

A carcinogenesis bioassay of melamine was conducted by feeding diets containing melamine in two concentrations to groups of rats of each sex for 103 weeks. Groups of rats served as controls.
An overview of the methods of the NTP-studies, from acute toxicity to carcinogenicity, is presented in the method Table, see the attachment.

GLP compliance:

not specified

Species:

rat

Strain:

other: F344/N

Sex:

male/female

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: Charles River Breeding Laboratories, Portage, MI
- Age at study initiation: 4 weeks.
- Housing: Rats were housed five per cage in polycarbonate cages covered with nonwoven polyester filter sheets. Racks and filters were changed once every 2 weeks. Cages, bedding, and glass water bottles (equipped with stainless steel sipper tubes) were replaced twice per week.
- Diet: Purina Laboratory Chow. Ralston Purina Co. Stainless steel feed containers were changed once per week.
- Water: Tap water (acidified with hydrochloric acid to pH 2.5).
Test diets, control diets, and tap water were available ad libitum.
- Bedding: Absorb-Dri hardwood chips.
- Acclimation: 2 weeks
- Randomization: Animals were assigned to individual cages according to a table of random numbers. The cages were then distributed to control and dosed groups according to another table of random numbers.
ENVIRONMENTAL CONDITIONS
- Temperature, humidity: The temperature in the animal rooms was 22 °- 26 °C and the relative humidity was 30 %-70 %.
- Air changes (per hr): Room air was changed 12-15 times per hour. The air was prefiltered with DRICO air filters and then filtered with HEP A filters.
- Photoperiod: Fluorescent lighting provided illumination 12 hours per day.

Route of administration:

oral: feed

Vehicle:

unchanged (no vehicle)

Details on exposure:

DIET PREPARATION
- Mixing appropriate amounts with: Test diets were prepared by first mixing a small amount of Purina B Lab Chow and the required amount of melamine with a mortar and pestle and then adding this premix to the required amount of animal meal and mixing for 10 to 30 minutes in a Patterson-Kelly@ twinshell blender equipped with an intensifier bar.
- Storage temperature of food: Test diets were stored in the freezer for no longer than 3 weeks.

Analytical verification of doses or concentrations:

yes

Details on analytical verification of doses or concentrations:

- Prepared diets containing 100 000 ppm melamine were analyzed and were found to be stable for 2 weeks at temperatures up to 45 °C.
Control animals were fed Purina Lab Chow.
Dosed feed samples from the chronic studies were analyzed periodically by ultraviolet spectroscopy. The results obtained indicate that only one of the formulations analyzed was slightly (+ 10.6 %) out of specifications (>± 10 %).
Results from three separate referee analyses verified the accuracy of the formulations.

Duration of treatment / exposure:

103 weeks.

Frequency of treatment:

/

Post exposure period:

No.

Remarks:

0 - 2 250 - 4 500 ppm melamine per kg feed to 50 male rats. Basis: nominal conc.
Conversion to mg/kg bw/d according to Table H1 of NTP 1983: 0 - 126 - 263 mg/kg bw/d.

Remarks:

0 - 4 500 - 9 000 ppm melamine per kg feed to female rats. Basis: nominal concentration.
Conversion to mg/kg bw/d according to Table H1 of NTP 1983: 0 - 269 - 542 mg/kg bw/d.

No. of animals per sex per dose:

50 female and 50 male rats per dose group and control group. One control male rat was discarded at week 13, when a sexing error was discovered.

Control animals:

yes, concurrent no treatment

Details on study design:

- Dose selection rationale: Doses were selected according to 14-days and 13-weeks studies.

Positive control:

No.

Observations and examinations performed and frequency:

CAGE SIDE OBSERVATIONS: Yes
- Time schedule: All animals were observed twice daily for morbidity or mortality.
DETAILED CLINICAL OBSERVATIONS: Yes
- Time schedule: Clinical signs were recorded monthly.

BODY WEIGHT: Yes
- Time schedule for examinations: Body weights by cage were recorded once per week for the first 13 weeks, monthly until week 91, and then every 2 weeks. The mean body weight of each group was calculated by dividing the total weight of all surviving animals in the group by the number of surviving animals in the group.

FOOD CONSUMPTION AND COMPOUND INTAKE (if feeding study): Feed consumption by cage was recorded once per week for the first 13 weeks, monthly until week 91, and then every 2 weeks. The average feed consumption per animal was calculated by dividing the total feed consumption measured for all cages in a group by the number of surviving animals in the group.

WATER CONSUMPTION AND COMPOUND INTAKE (if drinking water study): No.
OPHTHALMOSCOPIC EXAMINATION: No.
HAEMATOLOGY: No.
CLINICAL CHEMISTRY: No.
URINALYSIS: No.
NEUROBEHAVIOURAL EXAMINATION: No.

Sacrifice and pathology:

GROSS PATHOLOGY: Yes
HISTOPATHOLOGY: Yes
- Moribund animals and animals that survived to the end of the bioassay were killed with carbon dioxide and immediately necropsied.
- Examinations for grossly visible lesions were performed on major tissues or organs.
- Tissues were preserved in 10 % neutral buffered formalin embedded in paraffin, sectioned, and stained with hematoxylin and eosin.
- The following were examined microscopically: gross lesions, skin with mammary gland, mandibular lymph node, salivary gland, sternum with bone marrow, larynx or anterior trachea, esophagus, thyroid, parathyroid, lungs with mainstem bronchi, heart, stomach (glandular and nonglandular), duodenum, large intestine, liver, gallbladder (mice), pancreas, spleen, kidneys, adrenal glands, urinary bladder, entire gonads, prostate or uterus, brain, and pituitary gland.
- Necropsies were performed on all animals found dead and on those killed at the end of the study, unless precluded in whole or in part by autolysis or cannibalization. Thus, the number of animals from which particular organs or tissues were examined microscopically varies and is not necessarily equal to the number of animals that were placed on study in each group.
- The pathology report and selected slides were evaluated by the NTP Pathology Working Group. The classification of neoplastic nodules was done according to the recommendations of Squire and Levitt (1975) and the National Academy of Sciences (1980). The diagnoses represent a consensus of contracting pathologists and the NTP Pathology Working Group.

Statistics:

Data on this experiment were recorded in the Carcinogenesis Bioassay Data System. The data elements include descriptive information on the chemicals, animals, experimental design, clinical observations, survival, body weight, and individual pathologic results, as recommended by the International Union Against Cancer.
Probabilities of survival were estimated by the product-limit procedure of Kaplan and Meier (1958) and are presented in the form of graphs. Animals were statistically censored as of the time that they died of other than natural causes or were found to be missing; animals dying from natural causes were not statistically censored. Statistical analyses for a possible dose-related effect on survival used the method of Cox (1972) for testing two groups for equality and Tarone's (1975) extensions of Cox's methods for testing for a dose-related trend. All reported P values for the survival analyses are two-sided.
The incidence of neoplastic or nonneoplastic lesions has been given as the ratio of the number of animals bearing such lesions at a specific anatomic site to the number of animals in which that site was examined. In most instances, the denominators included only those animals for which that site was examined histologically.
However, when macroscopic examination was required to detect lesions (e.g., skin or mammary tumors) prior to histologic sampling, or when lesions could have appeared at multiple sites (e.g., lymphomas), the denominators consist of the numbers of animals necropsied.
For the continued description of the statistical methods, see under "Any other information on material and methods" (due to maximum number of letters available in this field).

Clinical signs:

no effects observed

Mortality:

no mortality observed

Body weight and weight changes:

effects observed, treatment-related

Food consumption and compound intake (if feeding study):

no effects observed

Food efficiency:

not examined

Water consumption and compound intake (if drinking water study):

not examined

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 examined

Gross pathological findings:

effects observed, treatment-related

Histopathological findings: non-neoplastic:

effects observed, treatment-related

Histopathological findings: neoplastic:

effects observed, treatment-related

Details on results:

CLINICAL SIGNS: No compound-related clinical signs were observed.
BODY WEIGHT AND WEIGHT GAIN: After week 20, mean body weights of dosed rats of each sex were lower than those of the controls. See also attached Table.
FOOD CONSUMPTION: The average daily feed consumption per rat by low- and high-dose rats was 97 % and 99 % that of the controls for males and 99 % and 99 % for females. See also attached Table.
SURVIVAL: Estimates of the probabilities of survival of male and female rats fed diets containing melamine at the concentrations of this bioassay, together with those of the control group, are shown by the Kaplan and Meier curves, see also the attached Figures. One control rat in the male group was mis-sexed and removed from the study. The survival of the high-dose group of male rats was significantly reduced when compared with that of the controls (P=0.03). No significant differences were observed between any other groups of either sex.
In male rats, 30/49 (61 %) of the controls, 30/50 (60 %) of the low-dose, and 19/50 (38 %) of the high-dose group lived to the termination period of the study at 105 weeks; 30/50 (60%) of the high-dose group of male rats survived 92 weeks of the study. In female rats, 34/50 (68 %) of the controls, 30/50 (60 %) of the low-dose, and 27/50 (54 %) of the high-dose group lived to the termination period of the study at 105 weeks. The survival data include one low-dose and one high-dose male rat that died during the termination period of the study. For statistical purposes, these animals are considered to have been killed at the end of the study.

PATHOLOGY:
Histopathologic findings on neoplasms in rats and findings on nonneoplastic lesions are summarized in the Tables in the attachment.
Incidences of urinary bladder and kidney lesions are presented also in Tables there. Other Tables contain the statistical analyses of those primary tumors that occurred with an incidence of at least 5 % in one of the three groups.

Urinary Bladder:
Transitional-cell carcinomas in the urinary bladder of male rats occurred with a statistically significant (P ≤ 0.002) positive trend (controls, 0/45; low-dose, 0/50; high-dose, 8/49, 16 %) and the incidence in the high-dose group was significantly higher (P ≤ 0 .016) than that in the controls.
The combined incidence of transitional cell carcinomas and papillomas showed a statistically significant (P < 0.001) positive trend (controls, 0/45; low-dose, 0/50; high-dose, 9/49, 18 %) and the incidence in high-dose rats was significantly higher (P ≤ 0.008) than that in the controls.
These tumors were not observed in statistically significant proportions in female rats (0/49, 1/49, 1/47).

The transitional-cell carcinomas were visualized grossly as 1- to 1.5-cm masses attached to the mucosal surface of the urinary bladder. Seven of the eight high-dose male rats with transitional-cell carcinomas also had bladder stones (calculi). Microscopically, most of the carcinomas had transitional-like cells that formed protrusions into the bladder lumens. Some had papillary areas. The carcinomas had moderate numbers of mitoses and some nuclear pleomorphism. Discrete invasions through the bladder wall occurred in one male rat, but no metastases were evident in the lungs or other tissues.

Kidney:
Chronic inflammation was observed in significantly (P ≤ 0.01) increased incidence in dosed female rats. The dose relationship and intensity of the increased interstitial lymphoplasmocytic infiltrates and cortical fibrosis clearly set these changes apart from the minor inflammatory component that may accompany the progressive nephropathy normally encountered in aging F344/N rats. The changes in the high-dose females were often observed grossly as pitted or roughened renal cortical surfaces. Chronic inflammation of the kidney was not significant in dosed male rats. In those animals in which this lesion was observed, there was no correlation with urinary bladder stones.

Pancreas:
Pancreatic islet-cell carcinomas in male rats occurred with a statistically significant (P =0.034) negative trend (control, 3/44, 7%; low-dose, 0/48; high-dose, 0/45) by the Cochran-Armitage test. The incidences were not significant in pairwise comparisons between the dosed groups and the controls, and these tumors were not observed in female rats. Total pancreatic islet-cell tumors (adenomas or carcinomas) were not significantly different for either sex of rats.

Thyroid:
C-cell carcinoma in the thyroid was observed in female rats with a statistically significant (P ≤ 0.038) positive trend (controls, 0/50; low-dose, 0/49; high-dose, 3/ 50, 6%). Neither the pairwise comparisons of the high-dose group with the controls nor the combination of C-cell adenomas or carcinomas was statistically significant in any of the tests. These tumors were not observed in statistically significant proportions in male rats.

Uterus:
Endometrial stromal polyps were observed in statistically significant (P ≤ 0.017) negative trend (controls, 11/5O, 22 %; low-dose, 7/50, 14 %; high-dose, 2/50, 4 %) and in decreased incidence (P ≤ 0.022) in the high-dose group in a pairwise comparison with the controls. The combined incidence of endometrial stromal polyps and sarcomas was statistically significant (P ≤ 0.017) in the negative direction (controls, 14/50, 28 %; low-dose, 7/50, 14 %; high-dose, 4/50, 8 %). A significantly lower (P ≤ 0.029) incidence in the high-dose group was observed in the pairwise comparisons with the controls. The combined incidence of endometrial stromal polyps and sarcomas in the high-dose group was not significantly different from the historical rate of this tumor in untreated female F344/N rats at the same laboratory (117/759, 15.4 %).

Dose descriptor:

NOAEL

Effect level:

2 250 mg/kg diet

Sex:

male

Basis for effect level:

other: Transitional-cell carcinomas in the urinary bladder.

Remarks on result:

other: Effect type: carcinogenicity (migrated information)

Dose descriptor:

NOAEL

Effect level:

2 250 mg/kg diet

Sex:

male

Basis for effect level:

other: Urinary bladder stones; kidney, chronic inflammation

Remarks on result:

other: Effect type: toxicity (migrated information)

Dose descriptor:

NOAEL

Effect level:

< 4 500 mg/kg diet

Sex:

female

Basis for effect level:

other: Chronic inflammation, kidney.

Remarks on result:

other: Effect type: toxicity (migrated information)

Dose descriptor:

NOAEL

Effect level:

126 mg/kg bw/day (nominal)

Based on:

test mat.

Sex:

male

Basis for effect level:

gross pathology

histopathology: neoplastic

histopathology: non-neoplastic

For Tables and Figures of the NTP carcinogenicity study see the attached documents "NTP carcinogenicity rats - Tables and Figures.doc" and "NTP carcinogenicity rats - feed consumption.doc".

Conclusions:

Under the conditions of this bioassay, melamine was carcinogenic for male rats, causing transitional-cell carcinomas in the urinary bladder. With one exception, urinary bladder stones were observed in male rats that had transitional-cell carcinomas.
Melamine was not carcinogenic for female rats.

Executive summary:

A carcinogenesis bioassay of melamine (>95 % pure) was conducted by feeding diets containing 2250 or 4500 ppm melamine to groups of 50 male F344/N rats for 103 weeks. Groups of 50 female rats were fed diets containing 4500 or 9000 ppm melamine. Groups of 49 male rats and 50 female rats served as controls.

Mean body weights of dosed rats of each sex were lower than those of the controls after week 20. Survival of high-dose male rats was significantly lower (P<0.05) than that of the controls. Survival of all other dosed rat groups was comparable with that of the respective controls.

Transitional-cell carcinomas in the urinary bladder of male rats occurred with a statistically significant positive trend (P ≤ 0.002; controls, 0/45; low-dose, 0/50; high-dose, 8/49, 16 %) and the incidence in the high-dose group was significantly higher (P ≤ 0.016) than that in the controls. A transitional-cell papilloma was observed in the urinary bladder of an additional high-dose male rat. These tumors were not observed in statistically significant proportions in female rats.

Seven of the eight high-dose male rats with the transitional-cell carcinomas also had bladder stones. An association (P ≤ 0.001) was found between bladder stones and bladder tumors in male rats. 

Chronic inflammation, distinguishable from the nephropathy observed in aging F344/N rats, was significantly increased (P ≤ 0.01) in the kidney of dosed female rats (controls, 4/50, 8 %; low-dose, 17/50, 34 %; high-dose, 41/50, 82 %) and is attributed to the administration of melamine.

 

The mean body weight of high-dose male mice was lower than that of controls after week 50 of the study. The mean body weights of dosed and control female mice were comparable throughout the study.

Survival of high-dose male mice was significantly less (P < 0.02) than that of the controls. Survival of all other dosed groups was similar to that of the respective controls.

 

Under the conditions of this bioassay, melamine was carcinogenic for male F344/N rats, causing transitional-cell carcinomas in the urinary bladder. With one exception, urinary bladder stones were observed in male rats that had transitional-cell carcinomas.

Melamine was not carcinogenic for female F344/N rats.

Reference 2

Endpoint:

carcinogenicity: oral

Type of information:

experimental study

Adequacy of study:

key study

Study period:

1978 to 1981

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

other: NTP studies are considered as top quality studies, even if GLP was formally not stated. The studies are peer reviewed.

Reason / purpose for cross-reference:

reference to same study

Qualifier:

according to guideline

Guideline:

other: NTP standards

Deviations:

not specified

Principles of method if other than guideline:

A carcinogenesis bioassay of melamine was conducted by feeding diets containing melamine in two concentrations to
groups of mice of each sex for 103 weeks. Groups of mice served as controls.

GLP compliance:

not specified

Species:

mouse

Strain:

B6C3F1

Sex:

male/female

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: Charles River Breeding Laboratories, Portage, MI
- Age at study initiation: 4 weeks.
- Housing: Mice were housed five per cage in polycarbonate cages covered with nonwoven polyester filter sheets. Racks and filters were changed once every 2 weeks. Cages, bedding, and glass water bottles (equipped with stainless steel sipper tubes) were replaced twice per week.
- Diet: Purina Laboratory Chow. Ralston Purina Co. Stainless steel feed containers were changed once per week.
- Water: Tap water (acidified with hydrochloric acid to pH 2.5).
Test diets, control diets, and tap water were available ad libitum.
- Bedding: Absorb-Dri hardwood chips.
- Acclimation: 2 weeks
- Randomization: Animals were assigned to individual cages according to a table of random numbers. The cages were then distributed to control and dosed groups according to another table of random numbers.
- Quality control: A quality control skin grafting program to monitor genetic integrity of inbred mice used to produce the hybrid B6C3F1 test animal has been in effect since early 1978. In mid-1981 data were obtained showing incompatibility between the NIH C3H reference colony and the C3H colony from a Bioassay Program supplier. In August, 1981, inbred parental lines of mice were further tested for genetic homogeneity via isozyme and protein electropherograms that demonstrate phenotypic expressions of known genetic loci.
The C57BL/6 mice were homogeneous at all loci tested. Eighty-five percent of C3H mice monitored were variant at one to three loci, indicating some heterogeneity in the C3H line from this supplier. Nevertheless, the genome of this line is more homogeneous than that of random bred stocks.
Male mice from the C3H colony and female mice from the C57BL/6 colony were used as parents for the hybrid B6C3F1 mice used in this bioassay. The influence of the potential genetic non-uniformity in the hybrid mice on the bioassay results is not known. However, the bioassay is valid since matched, concurrent controls were included in the study.

ENVIRONMENTAL CONDITIONS
- Temperature, humidity: The temperature in the animal rooms was 22 °- 26 °C and the relative humidity was 30 %-70 %.
- Air changes (per hr): Room air was changed 12-15 times per hour. The air was prefiltered with DRICO air filters and then filtered with HEP A filters.
- Photoperiod: Fluorescent lighting provided illumination 12 hours per day.

Route of administration:

oral: feed

Vehicle:

unchanged (no vehicle)

Details on exposure:

DIET PREPARATION
- Mixing appropriate amounts with: Test diets were prepared by first mixing a small amount of Purina B Lab Chow and the required amount of melamine with a mortar and pestle and then adding this premix to the required amount of animal meal and mixing for 10 to 30 minutes in a Patterson-Kelly@ twinshell blender equipped with an intensifier bar.
- Storage temperature of food: Test diets were stored in the freezer for no longer than 3 weeks.

Analytical verification of doses or concentrations:

yes

Details on analytical verification of doses or concentrations:

- Prepared diets containing 100 000 ppm melamine were analyzed and were found to be stable for 2 weeks at temperatures up to 45 °C.
Control animals were fed Purina Lab Chow.
Dosed feed samples from the chronic studies were analyzed periodically by ultraviolet spectroscopy. The results obtained indicate that only one of the formulations analyzed was slightly (+ 10.6 %) out of specifications (>± 10 %).
Results from three separate referee analyses verified the accuracy of the formulations.

Duration of treatment / exposure:

103 weeks.

Frequency of treatment:

/

Post exposure period:

No.

Remarks:

Doses / Concentrations:
Diets containing 0 - 2 250 - 4 500 ppm melamine were fed to mice of both sexes.
Basis:
nominal conc.

Remarks:

Male mice:
Conversion to mg/kg bw/d according to Table H2 of NTP 1983: 0 - 327 - 688 mg/kg bw/d.

Remarks:

Female mice:
Conversion to mg/kg bw/d according to Table H2 of NTP 1983: 0 - 523 - 1065 mg/kg bw/d.

No. of animals per sex per dose:

50 female and 50 male mice per dose group and control group. One control male mice was discarded at week 13, when a sexing error was discovered.

Control animals:

yes, concurrent no treatment

Details on study design:

- Dose selection rationale: Doses were selected according to 14-days and 13-weeks studies.

Positive control:

No.

Observations and examinations performed and frequency:

CAGE SIDE OBSERVATIONS: Yes
- Time schedule: All animals were observed twice daily for morbidity or mortality.
DETAILED CLINICAL OBSERVATIONS: Yes
- Time schedule: Clinical signs were recorded monthly.

BODY WEIGHT: Yes
- Time schedule for examinations: Body weights by cage were recorded once per week for the first 13 weeks, monthly until week 91, and then every 2 weeks. The mean body weight of each group was calculated by dividing the total weight of all surviving animals in the group by the number of surviving animals in the group.

FOOD CONSUMPTION AND COMPOUND INTAKE: Feed consumption by cage was recorded once per week for the first 13 weeks, monthly until week 91, and then every 2 weeks. The average feed consumption per animal was calculated by dividing the total feed consumption measured for all cages in a group by the number of surviving animals in the group.

WATER CONSUMPTION AND COMPOUND INTAKE (if drinking water study): No.
OPHTHALMOSCOPIC EXAMINATION: No.
HAEMATOLOGY: No.
CLINICAL CHEMISTRY: No.
URINALYSIS: No.
NEUROBEHAVIOURAL EXAMINATION: No.

Sacrifice and pathology:

GROSS PATHOLOGY: Yes
HISTOPATHOLOGY: Yes
- Moribund animals and animals that survived to the end of the bioassay were killed with carbon dioxide and immediately necropsied.
- Examinations for grossly visible lesions were performed on major tissues or organs.
- Tissues were preserved in 10 % neutral buffered formalin embedded in paraffin, sectioned, and stained with hematoxylin and eosin.
- The following were examined microscopically: gross lesions, skin with mammary gland, mandibular lymph node, salivary gland, sternum with bone marrow, larynx or anterior trachea, esophagus, thyroid, parathyroid, lungs with mainstem bronchi, heart, stomach (glandular and nonglandular), duodenum, large intestine, liver, gallbladder (mice), pancreas, spleen, kidneys, adrenal glands, urinary bladder, entire gonads, prostate or uterus, brain, and pituitary gland.
- Necropsies were performed on all animals found dead and on those killed at the end of the study, unless precluded in whole or in part by autolysis or cannibalization. Thus, the number of animals from which particular organs or tissues were examined microscopically varies and is not necessarily equal to the number of animals that were placed on study in each group.
- The pathology report and selected slides were evaluated by the NTP Pathology Working Group. The classification of neoplastic nodules was done according to the recommendations of Squire and Levitt (1975) and the National Academy of Sciences (1980). The diagnoses represent a consensus of contracting pathologists and the NTP Pathology Working Group.

Statistics:

Data on this experiment were recorded in the Carcinogenesis Bioassay Data System. The data elements include descriptive information on the chemicals, animals, experimental design, clinical observations, survival, body weight, and individual pathologic results, as recommended by the International Union Against Cancer.
Probabilities of survival were estimated by the product-limit procedure of Kaplan and Meier (1958) and are presented in the form of graphs. Animals were statistically censored as of the time that they died of other than natural causes or were found to be missing; animals dying from natural causes were not statistically censored. Statistical analyses for a possible dose-related effect on survival used the method of Cox (1972) for testing two groups for equality and Tarone's (1975) extensions of Cox's methods for testing for a dose-related trend. All reported P values for the survival analyses are two-sided.
The incidence of neoplastic or nonneoplastic lesions has been given as the ratio of the number of animals bearing such lesions at a specific anatomic site to the number of animals in which that site was examined. In most instances, the denominators included only those animals for which that site was examined histologically.
However, when macroscopic examination was required to detect lesions (e.g., skin or mammary tumors) prior to histologic sampling, or when lesions could have appeared at multiple sites (e.g., lymphomas), the denominators consist of the numbers of animals necropsied.
For the continued description of the statistical methods, see under "Any other information on material and methods" (due to maximum number of letters available in this field).

Clinical signs:

no effects observed

Mortality:

no mortality observed

Body weight and weight changes:

effects observed, treatment-related

Food consumption and compound intake (if feeding study):

effects observed, treatment-related

Food efficiency:

not examined

Water consumption and compound intake (if drinking water study):

not examined

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 examined

Gross pathological findings:

effects observed, treatment-related

Histopathological findings: non-neoplastic:

effects observed, treatment-related

Histopathological findings: neoplastic:

no effects observed

Details on results:

CLINICAL SIGNS: No other compound-related clinical signs were observed.

BODY WEIGHT: Mean body weights of high-dose male mice were slightly lower than those of the controls after week 50 of the study; mean body weights of dosed and control female mice were comparable throughout the study, see the attached Tables.

FOOD CONSUMPTION AND COMPOUND INTAKE: The average daily feed consumption per mouse by low- and high-dose mice was 93 % and 95 % that of the controls for males and 88 % and 87 % for females, see the attached Table.

SURVIVAL
Estimates of the probabilities of survival of male and female mice fed diets containing melamine at the concentrations of this bioassay, together with those of the control group, are shown by the Kaplan and Meier curves, see the attached Figures. One control mouse in the male group was mis-sexed and removed from the study. The survival of the high-dose group of male mice was significantly reduced when compared with that of the controls (P = 0.013). No other significant differences in survival were observed between any groups of either sex.
In male mice, 39/49 (80 %) of the controls, 36/50 (72 %) of the low-dose, and 28/50 (56 %) of the high-dose group lived to the termination period of the study at 105 weeks. In female mice, 37/50 (74 %) of the controls, 43/50 (86 %) of the low-dose, and 41/50 (82 %) of the high-dose group lived to the termination period of the study at 105 weeks. The survival data include one control and one low-dose female mouse that died during the termination period of the study.
For statistical purposes, these animals are considered to have been killed at the end of the study.

PATHOLOGY
Histopathologic findings on neoplasms and on nonneoplastic lesions occurring in mice are summarized, see the attached Tables. The statistical analyses of those primary tumors that occurred with an incidence of at least 5 % in one of the three groups is found in the attached Tables.

Urinary Bladder: The incidences of stones (calculi) and inflammatory and hyperplastic changes in the urinary bladder are presented in the attached Table. The incidences of stones were obtained from gross examination of the urinary bladder, while the incidences were also obtained from microscopic examination. Most of the stones were green and multiple. Although epithelial hyperplasia occurred at higher incidences in males and females fed diets containing melamine, there was no evidence, either in histopathologic features or incidence of neoplasia in the bladder, to suggest that this change was preneoplastic. Hyperplasia was generally very mild.

Lung: The lungs of three high-dose female mice were diffusely infiltrated with structures morphologically compatible with the protozoan organism Pneumocystis carinii. Similar involvement was not present in other groups of mice. P. carinii can occur as a latent, inapparent infection in laboratory rodents. Under conditions of stress (e.g., immunosuppression), the organism is capable of being pathogenic. Two of the affected mice killed at the end of the study (104 weeks) had a neoplasm (chromophobe adenoma or malignant lymphoma). The other mouse died with no evidence of generalized systemic disease. Other than the presence of generalized neoplasia in two of the affected mice, there was no direct morphologic evidence of systemic immunosuppression in these animals.
Alveolar/bronchiolar adenomas in female mice were observed in decreased (P < 0.025) incidence in the low-dose group compared with that of the controls (controls, 5/44, 11 %; low-dose, 0/48). The incidence in the high-dose group (2/50, 4 %) was not significantly different from that in the controls, and the combined incidence of alveolar/ bronchiolar adenomas and carcinomas was not significantly different between any groups of either sex of mice. In addition, the low-dose incidence of alveolar/ bronchiolar adenomas is not significantly different from the historical rate of this tumor in untreated female B6C3F1 mice at the same laboratory (25/502, 5.0 %).

Dose descriptor:

NOAEL

Effect level:

< 2 250 mg/kg diet

Sex:

male

Basis for effect level:

other: Acute and chronic inflammation and epithelial hyperplasia of the urinary bladder. Bladder calculi.

Remarks on result:

other: Effect type: toxicity (migrated information)

Dose descriptor:

NOAEL

Effect level:

2 250 mg/kg diet

Sex:

female

Basis for effect level:

other: Acute and chronic inflammation and epithelial hyperplasia of the urinary bladder. Bladder calculi.

Remarks on result:

other: Effect type: toxicity (migrated information)

For Tables and Figures of the NTP carcinogenicity study see the attached documents "NTP carcinogenicity mice - Tables and Figures.doc".

Conclusions:

Melamine was not carcinogenic for B6C3F1 mice of either sex.

Executive summary:

A carcinogenesis bioassay of melamine was conducted by feeding diets containing 2250 or 4500 ppm melamine to groups of 50 mice of each sex for 103 weeks. Groups of 49 male mice and 50 female mice served as controls.

The mean body weight of high-dose male mice was lower than that of controls after week 50 of the study. The mean body weights of dosed and control female mice were comparable throughout the study. Survival of high-dose male mice was significantly less than that of the controls.

Survival of all other dosed groups was similar to that of the respective controls.

Acute and chronic inflammation and epithelial hyperplasia of the urinary bladder were found in increased incidence in dosed male mice. The incidence of bladder stones in dosed male mice was increased relative to controls; however, there was no evidence of bladder tumor development in this species. Also, four high-dose female mice had bladder stones without any tumors.

Melamine was not carcinogenic for mice of either sex.

Reference 3

Endpoint:

carcinogenicity: oral

Type of information:

experimental study

Adequacy of study:

weight of evidence

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

other: An extensive carcinogenicity study, with GLP.

Principles of method if other than guideline:

The study was conducted in order to clarify effects observed in the NTP Carcinogenesis study in rats (NTP 1983). An extensive carcinogenicity study was performed with lower doses.

GLP compliance:

yes

Species:

rat

Strain:

Fischer 344

Sex:

male/female

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: Charles River Breeding Lab.
- Age at study initiation: weanling
- Housing: individual
- Diet (e.g. ad libitum): yes
- Water, partially demineralized by reverse osmosis and sterilized by ultraviolet light, was provided ad libitum throughout the study from an automatic watering system.
- Acclimation period: 13 d
ENVIRONMENTAL CONDITIONS
- Temperature (°F): 72 +- 3
- Humidity (%): 50 +- 20

Route of administration:

oral: feed

Vehicle:

unchanged (no vehicle)

Details on exposure:

Four test diets containing 100, 500, 1000, and 2000 ppm Melamine and a negative control diet (0 ppm) were prepared and offered each week. A
1 % premix was prepared and used in the mixing of the test diets. Prepared diets were stored in airtight plastic containers.

Analytical verification of doses or concentrations:

yes

Details on analytical verification of doses or concentrations:

Prior to study initiation samples of the 100, 1000, and 2000 ppm diets were prepared and analyzed for homogeneity and stability of the test compound in the basal diet. Each of these test diets were assayed for homogeneity of the mixture by sampling four different locations in the mixing bowl (top, two opposing sides, and the bottom). The remaining portions of these diets were stored at ambient temperature and assayed at 9, 14, 22, and 29 days after mixing to determine stability. The mean value of the homogeneity assays for each diet was used as the initial value for the stability study.
During Weeks 1-131, two 100-g samples of each test diet were taken. One of the samples was analyzed for Melamine content during each of the first 4 weeks of the study. Beginning at Week 5, one test diet was selected at random and analyzed for Melamine content. Remaining samples from each diet are being retained frozen until acceptance of the fina1 report.

Duration of treatment / exposure:

Ca. 28 to 30 months.
All animals received their test diets throughout the entire study period from 16 days post-weaning (6 weeks of age) to study termination (123 weeks on test for the male Groups 1-4 and the high dosed female Group 8, and 131 weeks on test for female Groups 5-7) , except those that were scheduled for the interim sacrifice, sacrificed in a moribund condition, or died on test.

Frequency of treatment:

continuously

Post exposure period:

none.

Remarks:

Doses / Concentrations:
male: 0 - 100 - 500 - 1000 ppm (ca. 6.5 - 65 mg/kg bw/d)
Basis:
nominal in diet

Remarks:

Doses / Concentrations:
female: 0 -100 - 1000 - 2000 ppm (ca. 6.5 - 130 mg/kg bw/d)
Basis:
nominal in diet

No. of animals per sex per dose:

65, plus additional animals for baseline clinical data and quality control.

Control animals:

yes, concurrent no treatment

Positive control:

no

Observations and examinations performed and frequency:

Observations
All animals were observed in their cages for mortality or moribundity twice daily 7 days a week.

Growth Data
The body weight of each animal was recorded prior to administration of the test material, and then weekly through 13 weeks and monthly beginning on Week 16 and continuing through Week 130.
Individual feed consumptions were measured weekly for Weeks 1-13 and then during those weeks when body weights were recorded beginning at Week 16 and continuing through Week 130.

Ophthalmic Examinations
A slit-lamp ophthalmic examination was conducted on all surviving animals during Week 77 and again during Week 121 prior to termination.

Clinical Pathology
Prior to the initiation of the study, 10 males and 10 females were selected at random, fasted overnight, and bled for baseline hematology and serum chemistry tests. During the 18th month on test, an additional 10 animals were selected at random from the survivors of each group and had blood and urine collected and analyzed. Prior to the termination of each group, 10 animals were selected at random from the remaining survivors in the group; urine and blood samples were collected from these animals and analyzed.

Sacrifice and pathology:

A complete necropsy was done on all animals sacrificed at 18 months and at termination of the study and on those animals that were sacrificed in a moribund condition or that died on test.
Organ Weight Data
At the 18-month and terminal necropsies.

Microscopic Pathology
All tissues collected from animals in the control and high dose groups at 18 months and at termination and from animals that died on test or that were sacrificed in a moribund condition were examined microscopically. From the animals in the low and mid dose groups, only tissues with gross lesions were examined microscopically following scheduled sacrifices.

Statistics:

Statistica1 eva1uation of equa1ity of group means was made by one-way analysis of variance techniques, followed by a multiple comparison procedure, if needed, for body weights, feed consumptions, hematology, blood chemistry and urina1ysis data, and for absolute and re1ative organ weights. Where significant differences among the means were indicated, Dunnett's -test was used to determine which means were significant1y different from those of the control group.

Details on results:

Males treated with 0, 100, 500, and 1000 ppm Melamine in the diet for up to 124 weeks on test did not have any biologically significant effects on in-life clinical observations, body weights, feed consumptions, hematologic values, serum chemistries, or urine values throughout the study.

Females treated with 0, 100, and 1000 ppm Melamine in the diet for up to 131 weeks and with 2000 ppm Melamine for up to 124 weeks on test did not have any biologically significant effects on in-life clinical observations, body weights, feed consumptions, hematologic values, serum chemistries, or urine values throughout the study.

Although there were statistical indications that Melamine may affect the incidence of MNL in spleens of treated females, the data were inconclusive. All spleens were not examined microscopically in the low and middle dose groups.
In females, the total incidences of dilated glands in glandular gastric mucosa and inflammation in nonglandular gastric mucosa occurred with a statistically significant positive trend with dose. In most animals the mucosal glands were only mildly dilated and were not accompanied by other gastric lesions. Inflammation of the nonglandular mucosa was of ten associated with mucosal erosion and/or ulceration in the same animal.

Four primary tumors of the urinary bladder were identified in this study and no group contained more than one tumor. Transitional cell papillomas were found in the urinary bladder of one 0-ppm male and one l000-ppm male sacrificed at the 29-/31-month sacrifice. The remaining tumors occurred in DOT or moribund rats and included one transitional cell papilloma in a 0-ppm female and one anaplastic transitional cell carcinoma in a 500-ppm female. The primary tumors were not accompanied by other lesions of the urinary bladder wall or cystic calculi.

Key result

Dose descriptor:

NOAEL

Effect level:

1 000 mg/kg diet

Sex:

male

Basis for effect level:

other: 1000 ppm is the highest dose used.

Remarks on result:

other: Effect type: chronic toxicity and carcinogenicity.

Key result

Dose descriptor:

NOAEL

Effect level:

2 000 mg/kg diet

Sex:

female

Basis for effect level:

other: 2000 ppm is the highest dose used.

Remarks on result:

other: Effect type: chronic toxicity and carcinogenicity.

Critical effects observed:

no

Males treated with 0, 100, 500, and 1000 ppm Melamine in the diet for up to 124 weeks on test did not have any biologically significant effects on in-life clinical observations, body weights, feed consumptions, hematologic values, serum chemistries, or urine values throughout the study.

Females treated with 0, 100, and 1000 ppm Melamine in the diet for up to 131 weeks and with 2000 ppm Melamine for up to 124 weeks on test did not have any biologically significant effects on in-life clinical observations, body weights, feed consumptions, hematologic values, serum chemistries, or urine values throughout the study.

Not relevant or not significant findings:

The mean thyroid weights were increased in the 1000-ppm male group at the l8-month sacrifice and were decreased in the 1000-ppm and 2000-ppm female groups at the 29-/3l-month sacrifice. However, the microscopic findings in this study indicate that Melamine had no effect upon the incidence of neoplastic or non-neoplastic thyroid lesions in either sex.

At the l8-month sacrifice, the mean gonad weight was lower in the l00-ppm males when compared with that of the 0-ppm males. Interstitial cell tumors of male gonads were found frequently in all male groups at the l8-month sacrifice, and the variation in size of these tumors was probably responsible for the difference in male gonad weights. The total incidence of interstitial cell tumors was high in all groups regardless of the time of death or sacrifice, but the incidence was not treatment-related.

The mean adrenal weight of the 500-ppm males was increased at sacrifice because two rats had unilateral pheochromocytomas. Total incidence of primary adrenal tumors was not affected by the 29-/3l-month. However, the total incidence of primary adrenal tumors was not affected by treatment.

At the 29-/3l-month sacrifice, several rats in the l00-ppm female group had splenomegaly secondary to MNL, which caused the mean splenic weight of the group to be significantly greater than that of the 0-ppm female group.

Although the total incidence of pituitary adenomas in l00-ppm male, was 2-fold greater than that of 0-ppm males, there were no statistical differences between the two groups. For the l8-month, 29- to 30-month, and died on test and moribund sacrifices, there were no significant differences between the incidences of pituitary adenomas in treated and control male groups. As expected, angiectasis was found frequently in the pituitaries of results that had pituitary adenomas. In conclusion, the results of this study indicated that Melamine did not affect the incidence of microscopic lesions in pituitary glands of Fischer 344 rats.

Because of similar morphologic appearances, no attempt was made to differentiate lymphoid tumors from other mononuclear cell neoplasms of the hemic/lymphatic system; all were classified as MNL. The total incidence of MNL was high in all groups but there was no indication that the incidence was affected by treatment. Although there were statistical indications that Melamine may affect the incidence of MNL in spleens of treated females, the data were inconclusive. All spleens were not examined microscopically in the low and middle dose groups.

In females, the total incidences of dilated glands in glandular gastric mucosa and inflammation in nonglandular gastric mucosa occurred with a statistically significant positive trend with dose. In most animals the mucosal glands were only mildly dilated and were not accompanied by other gastric lesions. Inflammation of the nonglandular mucosa was often associated with mucosal erosion and/or ulceration in the same animal.

Four primary tumors of the urinary bladder were identified in this study and no group contained more than one tumor. Transitional cell papillomas were found in the urinary bladder of one 0-ppm male and one l000-ppm male sacrificed at the 29-/3l-month sacrifice. The remaining tumors occurred in died on test (DOT) or moribund rats and included one transitional cell papilloma in a 0-ppm female and one anaplastic transitional cell carcinoma in a 500-ppm female. The primary tumors were not accompanied by other lesions of the urinary bladder wall or cystic calculi.

Conclusions:

The carcinogenic effects in the urinary bladders, seen in the NTP-carcinogenicity study, which was performed at doses of 2250 and 4500 ppm melamine in the diet for male rats and 4500 and 9000 ppm for female rats, were not observed at lower doses (up to 1000 ppm in male and up to 2000 ppm in female rats) in the present study.

Executive summary:

The study was conducted in order to clarify effects observed in the NTP Carcinogenesis study in rats (NTP 1983). An extensive carcinogenicity study was performed with lower doses.

Haematological, clinical investigations and urinalysis failed to show any difference between treated and controls except a dose-related trend for dilated glands in glandular gastric mucosa and  inflammation in non glandular gastric mucosa. 

Urinary bladder calculi formation was not observed in this study. A total of 4 tumors of the urinary bladder were observed (two in controls, one in 1000 ppm male, one in 500 ppm female). The tumors were not accompanied by other lesions of the urinary bladder wall or cystic calculi. 

Endpoint conclusion

Endpoint conclusion:

adverse effect observed

Dose descriptor:

LOAEL

126 mg/kg bw/day

Study duration:

chronic

Species:

rat

Quality of whole database:

NTP studies are recognised as high standard investigations.

System:

urinary

Organ:

bladder

Carcinogenicity: via inhalation route

Endpoint conclusion

Endpoint conclusion:

no study available

Carcinogenicity: via dermal route

Endpoint conclusion

Endpoint conclusion:

no study available

Mode of Action Analysis / Human Relevance Framework

Several studies to evaluate the mechanism of bladder neoplasms were performed. Experimental data show that melamine is not genotoxic, confirmed in many studies using different methods.

The relevant trigger for the toxicity of melamine are the urinary tract calculi at sufficiently high doses, because of the precipitation of melamine in the urine above the solubility limit. The calculi in the urinary bladder are leading to chronic irritation, hyperplasia and finally to tumours. This mechanism is also known for implanted foreign inert bodies but also for low toxic substances such as thymine, uracil, silicates, sodium ascorbate, etc. (Okumura 1992, Ogasawara 1995, IARC 1999, McGregor 2010). For IARC 1999 and McGregor 2010 see Section 13. No tumour formation is to be expected when the urinary levels of melamine are maintained below the threshold level of precipitation.

Additional dosing of NaCl, which causes a higher water intake, and a dilution in the urine, suppresses the calculus formation and hyperplasia of the papilla in the kidney (Ogasawara 1995).

The mode of action is not relevant for humans, as no high enough doses has ever been observed to occur in humans to produce bladder calculi, except for the past cases of fraudulent tainting infant formulas in China. No such high exposures are also anticipated in the future. Recently, Cohen SM stated: "The risk assessment for such chemicals as melamine is not related to its carcinogenicity in the animal model, but to the actual toxicity of the formation of calculi, which can occur in humans. Thus, if urinary solids formation is the mode of action concluded for a particular chemical, the risk assessment is related to the toxicity of urinary solid formation, not to carcinogenicity." [Cohen SM. Screening for human urinary bladder carcinogens: two-year bioassay is unnecessary. Toxicol. Res., 2018, 7, 565].

In the next publication, SM Cohen stated: "The mode of action analysis shows that the key events are ingestion of high doses of the test material leading to formation of the urinary tract crystals or calculi producing urothelial toxicity and consequent urothelial proliferation. Tumors occur in rodents if this persists for a long period of time.

The question is whether these tumorigenic effects occur in all species, whether rodents, pets, or humans. It turns out that the urothelial tumors secondary to urinary crystals or calculi do not predict to tumors in other species such as cats, dogs, nonhuman primates, and humans" [Cohen SM.Crystalluria and Chronic Kidney Disease. Toxicol Pathol. 2018 Dec;46(8):949-955]. The main point is that in humans,calculi are present for short periods of time and tumors do not develop. ...There are a few unusual circumstances where calculi can be present in the urinary bladder of humans for long periods oftime, such as bladder diverticuli or neurogenic bladder secondary to paraplegia. ... Consequently, most regulatory authorities consider urinary tract crystals and calculi not to be relevant to human carcinogenesis.

 

Justification for classification or non-classification

The IARC evaluated and stated in 1999:

"In making its overall evaluation, the Working Group noted that the non-DNA-reactive mechanism by which melamine produced urinary bladder tumours in male rats occurred only under conditions in which calculi were produced. Melamine is not classifiable as to its carcinogenicity to humans (Group 3)." Because melamine caused tumours only at high doses in one sex and species, and the mode of action is not relevant to humans, a classification is not needed.

 

The publication by McGregor D. et al. 2010 on "Guidance for the classification of carcinogens under the Globally Harmonised System of Classification and Labelling of Chemicals (GHS)", see Section 13, evaluated, inter alia, the carcinogenicity of melamine in male rats and the relevance of the findings for human. It was suggested that rats may have a higher susceptibility for the development of calculus-induced bladder tumours in comparison with humans. Melamine was considered to have a low carcinogenic potency. Taking into account the intended uses of melamine, the proposed mode of action of melamine in rats is considered not to be relevant for humans.

 

The IARC evaluation of 2017:

Mid 2017, IARC has re-assessed the carcinogen grouping for melamine (IARC 2017, see Section 13) and announced to group melamine as “possibly carcinogenic to humans”(Group 2B). The monograph on it, explaining and justifying this decision, is still awaited (March 2019). Two facts have changed or were added compared to the evaluation of melamine by IARC in 1999:

1) From the abuse of melamine being added to milk products for infants in China it is known that urinary tract stones can occur at high doses in humans. The Chinese incidence is the only case where humans have been intoxicated by melamine. The incidence cannot be regarded as a reasonably expected use, and therefore is not relevant for classification according to CLP. Published data on the toxicity of melamine, which are based on the Chinese incidence, has therefore not to be taken into account for classification of melamine, as they cannot be regarded a reasonably expected use under the applicable legislation of the EU.

2) A paper of insufficient reliability was published by Cremonezzi et al. 2001, reporting a non-defined lesion 'dysplasia and carcinoma in situ' in mice, not even reporting the affected sex.

 

SM Cohen, an independent expert in urinary tract lesions, came to the conclusion in his publication Crystalluria and Chronic Kidney Disease, see section 13:"The mode of action analysis shows that the key events are ingestion of high doses of the test material leading to formation of the urinary tract crystals or calculi producing urothelial toxicity and consequent urothelial proliferation. Tumors occur in rodents if this persists for a long period of time.

The question is whether these tumorigenic effects occur in all species, whether rodents, pets, or humans. It turns out that the urothelial tumors secondary to urinary crystals or calculi do not predict to tumors in other species such as cats, dogs, nonhuman primates, and humans".

 

Justification for non-classification

The considered mode of action of tumour formation is the formation of urinary bladder stones as the first step if a threshold exposure level is exceeded and in a next step, the bladder stones trigger the development of bladder tumours if the exposure and the irritation of the urinary bladder persists. This mode of action is theoretically possible in humans. Only if it would be assumed that infants growing to be children and then to adults are consuming tainted infant formula as the only diet for many years (and not considering that these individuals would seek relief from their stones by stopping consumption of infant formulas or by medical assistance) a situation could be construed that could possibly result in tumours. This scenario has not to be considered in the classification process. It is not realistic and the experience in China is not based on a reasonably expected use. Therefore, and confirmed by the Guidance on CLP, and authors cited above, the mode of action by which melamine induces bladder tumours in male rats is considered to be not relevant to humans.

 

Difference between CLP and IARC criteria:

The already announced classification of melamine as a carcinogen by the IARC is no reason for classifying melamine as a carcinogen as well under CLP. Both bodies have relevant differences in their classification criteria, e.g.:

- Substances in CLP versus 'agents' in IARC

- Restriction to intrinsic properties only in CLP

- 'Urinary bladder tumours due to crystals in the bladder' specifically exempted from classification, according to the CLP Guidance.

- Abuse restrictions only in CLP

 

It is therefore concluded that melamine has not to be classified as a carcinogenic substance according to CLP.

 

Additional information

Carcinogenicity: via oral route (target organ): urogenital: urinary bladder