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Description of key information

When tested in oral repeated dose toxicity studies in rats, melamine caused formation of urinary calculi in the bladder and hyperplasia in the bladder epithelium of both sexes. The effects were dose-related, with the male rats being more sensitive than females to the effects in the bladder.
Mice were also investigated: The incidence of bladder stones was dose related as in rats, being greater in males than in females, but starting at much higher doses than in rats.
In a newer subchronic study with monkeys the kidney was also the primary target organ. A NOAEL of 60 mg/kg/d was obtained, much the same as in the rat study, but it should be considered that the study is of poor reliability.

Key value for chemical safety assessment

Repeated dose toxicity: via oral route - systemic effects

Link to relevant study records
Reference
Endpoint:
sub-chronic toxicity: oral
Type of information:
experimental study
Adequacy of study:
key study
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: NTP studies are considered as high quality studies, even if GLP was formally not stated and some standard methods were not applied. The studies are peer reviewed. The test substance was analysed extensively.
Reason / purpose:
reference to same study
Reason / purpose:
reference to other study
Qualifier:
according to
Guideline:
other: NTP standards
Deviations:
yes
Remarks:
No haematology and clinical chemistry investigations were performed. No statistical analysis was reported or performed.
Principles of method if other than guideline:
Three 13 weeks toxicity studies were performed:
In the first 13-week study, diets containing 0, 6000, 9000, 12000, 15000, or 18000 ppm melamine were fed to groups of 12 male and 12 female rats and to groups of 10 male and 10 female mice for 13 weeks.

Two additional 13-week studies were conducted to find a no-effect level for urinary bladder stone formation and to determine the effect of ammonium chloride in the drinking water on stone formation.
In the second 13-week study, groups of 10 rats of either sex were fed diets containing 0, 750, 1500, 3000, 6000, or 12000 ppm melamine for 13 weeks; At day 65, five rats of either sex fed 750 ppm melamine and two control rats of each sex were placed in metabolism cages and fasted overnight. Urine samples collected from each cage were centrifuged and the sediment fractions were examined microscopically.

In a third 13-week study, groups of 10 rats of either sex were fed diets containing 0, 10000, or 18000 ppm melamine in the presence and absence of 1 % ammonium chloride in the drinking water.
GLP compliance:
not specified
Limit test:
no
Species:
rat
Strain:
Fischer 344
Sex:
male/female
Details on test animals and environmental conditions:
TEST ANIMALS
- Source: Frederick Cancer Research Center, Frederick, MD
- Age at study initiation: 5 - 6 weeks.
- Housing: Rats were housed four 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:
First and second studies: Tap water (acidified with hydrochloric acid to pH 2.5).
Third study: ± 1 % ammonium chloride in drinking water.
Test diets, control diets, and tap water were available ad libitum.
- Bedding: Absorb-Dri heat-treated hardwood chips, changed twice per week.
- Acclimation: 2 weeks
- Randomization: Animals assigned to cages by species and sex such that the cage weighs were approximately the same.

ENVIRONMENTAL CONDITIONS
- Temperature, humidity: The temperature in the animal rooms was 22 °- 26 °C and the relative humidity was 30 %-70 %.
Route of administration:
oral: feed
Vehicle:
unchanged (no vehicle)
Details on oral 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 at 4 °C for no longer than 2 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.
Duration of treatment / exposure:
13 weeks
Frequency of treatment:
continuously
Remarks:
First study: 0, 6000, 9000, 12000, 15000 or 18000 ppm melamine in the diet for rats of bothe sexes. Basis: nominal in diet. The estimated melamine consumption in mg/ kg/ day for each animal was: 0, 560, 850, 1100, 1400, or 1700 for male rats; 0, 560, 880, 1200, 1400 or 1600 for female rats; according to Table 1 of NTP 1983.

Remarks:
Second study: 0, 750, 1500, 3000, 6000 or 12000 ppm for bothe sexes. Basis: nominal in diet
The estimated melamine consumption in mg/ kg/ day for each animal was: 0, 72, 150, 300, 590, or 1300 for male rats and 0, 84, 150, 300, 600, or 1300 for female rats, according to Table 1 of NTP 1983.
Remarks:
Third study: 0, 10000 or 18000 ppm. Basis: nominal in diet.
No. of animals per sex per dose:
FIRST STUDY
- 12 males/12 females
SECOND STUDY
- 10 males/10 females
THIRD STUDY
- 10 males/10 females
Control animals:
yes, concurrent no treatment
Details on study design:
Post-exposure period: none
Observations and examinations performed and frequency:
CAGE SIDE OBSERVATIONS: Yes
- Time schedule: daily for mortality and signs of morbidity.

DETAILED CLINICAL OBSERVATIONS: No

BODY WEIGHT: Yes
- Time schedule for examinations: weekly.

FOOD CONSUMPTION AND COMPOUND INTAKE (if feeding study):
- Time schedule for examinations: weekly.

WATER CONSUMPTION AND COMPOUND INTAKE (if drinking water study): No

OPHTHALMOSCOPIC EXAMINATION: No

URINALYSIS: Yes (only study No. 2)
-control animals: 1 male, 2 females.
- low dosed animals (750 ppm): all animals.

HAEMATOLOGY: No

CLINICAL CHEMISTRY: No

URINALYSIS: No

NEUROBEHAVIOURAL EXAMINATION: No


Sacrifice and pathology:
GROSS PATHOLOGY (study No. 1 - 3): Yes (all animals)

HISTOPATHOLOGY (study No. 1): Yes (all animals control group (0 ppm) and highest dosed group (18000 ppm).
-gross lesions, tissue masses
-abnormal lymph nodes
-skin
-mandibular lymph nodes
-mammary glands
-salivary gland
-thigh muscle
-sciatic nerve
-bone marrow
-costochondral junction (rib)
-thymus
-larynx
-trachea
-lungs and bronchi
-heart
-thyroid
-parathyroid
-oesophagus
-stomach
-duodenum
-jejunum
-colon
-mesenteric lymph nodes
-liver
-pancreas
-spleen
-kidneys
-adrenals
-urinary bladder
-seminal vesicles
-prostate
-testes
-ovaries
-uterus
-nasal cavity
-brain
-pituitary

all animals low dose (6000 ppm) group:
-kidney
-urinary bladder

HISTOPATHOLOGY (study No. 2): Yes (all animals)
-kidney
-urinary bladder

HISTOPATHOLOGY (study No. 3): No
Statistics:
not reported.
Clinical signs:
not specified
Mortality:
mortality observed, treatment-related
Description (incidence):
Study 1: One male rat receiving 18,000 ppm and two males receiving 6,000 ppm died.
Study 2: None of the rats died.
Body weight and weight changes:
effects observed, treatment-related
Description (incidence and severity):
Study 1: Mean body weight gain in males and females receiving 12000 ppm or more was depressed by more than 8% when compared with controls.
Study 2: Mean body weight gain was depressed by more than 10% when compared with controls for male rats receiving 6,000 and 12,000 ppm, but no depression was observed in any group of dosed females.
Food consumption and compound intake (if feeding study):
effects observed, treatment-related
Description (incidence and severity):
Study 1: Feed consumption by rats receiving 18000 ppm was approximately 80%-90% that of controls.
Study 2: Feed consumption was not affected by incorporation of melamine in the feed.
Food efficiency:
not specified
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:
no effects observed
Description (incidence and severity):
Study 2: There were no differences in the urine samples that could be attributed to the presence of melamine in the feed. Microscopic examination of the urine did not provide any evidence of melamine crystalluria.
Behaviour (functional findings):
not specified
Immunological findings:
not specified
Organ weight findings including organ / body weight ratios:
not specified
Gross pathological findings:
effects observed, treatment-related
Description (incidence and severity):
Study 1: Stones were found in the urinary bladders of most dosed male rats, and the incidence was dose related. Twenty-five percent (3/ 12) or more females in the two highest dosed groups had stones.
Study 2: Other than stones in the bladder of dosed male rats, no compound-related effects were observed at necropsy. The incidence of stones in the urinary bladder of male rats was dose related.
Neuropathological findings:
not specified
Histopathological findings: non-neoplastic:
effects observed, treatment-related
Description (incidence and severity):
Study 1: Histopathologic evaluations were performed on 10 animals of either sex from the high-dose (18,000 ppm), low-dose (6,000 ppm), and control groups. Diffuse epithelial hyperplasia of the urinary bladder was found in 8/ 10 males and 2/ 10 females receiving 18,000 ppm melamine, while in animals receiving 6,000 ppm melamine, focal epithelial hyperplasia was observed in only 1 / 10 males and in none of the females. The urinary bladders of animals from other dosed groups were not examined microscopically. No other compound-related histopathologic effects were observed.
Study 2: Stones were present even in the male group receiving 750 ppm. Hyperplasia of the transitional epithelium of the bladder was present in 1/10 male rats receiving 3,000 ppm, in 3/10 receiving 6,000 ppm, and in 919 receiving 12,000 ppm melamine. The hyperplastic epithelial changes, which were found only in male rats that had bladder stones, were accompanied by prominent capillaries and occasional edema and scattered mast cells in the submucosa. Kidney changes in male rats were minimal. There was no evidence of urinary bladder stones or hyperplasia of the bladder epithelium in any groups of dosed female rats, but dose-related calcareous deposits were observed in the straight segments of the proximal tubules in female rats (2/10 controls, 3/ 10 receiving 750 ppm, 4/ 10 receiving 1,500 ppm, 10/ 10 receiving 3,000 ppm, 8/ 10 receiving 6,000 ppm, and 10/ 10 receiving 12,000 ppm melamine).
Histopathological findings: neoplastic:
no effects observed
Other effects:
not specified
Details on results:
STUDY No. 1:
CLINICAL SIGNS AND MORTALITY
One male rat receiving 18,000 ppm and two males receiving 6,000 ppm died .
(See Table 4)
BODY WEIGHT AND WEIGHT GAIN
Mean body weight gain in males and females receiving 12,000 ppm or more was depressed by more than 8% when compared with controls.
(See Table 4)
FOOD CONSUMPTION AND COMPOUND INTAKE (if feeding study)
Feed consumption by rats receiving 18,000 ppm was approximately 80%-90% that of controls.
GROSS PATHOLOGY
Stones were found in the urinary bladders of most dosed male rats, and the incidence was dose related. Twenty-five percent (3/ 12) or more females in the two highest dosed groups had stones.
HISTOPATHOLOGY: NON-NEOPLASTIC
Histopathologic evaluations were performed on 10 animals of either sex from the high-dose (18,000 ppm), low-dose (6,000 ppm), and control groups. Diffuse epithelial hyperplasia of the urinary bladder was found in 8/ 10 males and 2/ 10 females receiving 18,000 ppm melamine, while in animals receiving 6,000 ppm melamine, focal epithelial hyperplasia was observed in only 1 / 10 males and in none of the females. The urinary bladders of animals from other dosed groups were not examined microscopically. No other compound-related histopathologic effects were observed.

STUDY No. 2:
CLINICAL SIGNS AND MORTALITY
None of the rats died.
BODY WEIGHT AND WEIGHT GAIN
Mean body weight gain was depressed by more than 10% when compared with controls for male rats receiving 6,000 and 12,000 ppm, but no depression was observed in any group of dosed females.
FOOD CONSUMPTION AND COMPOUND INTAKE (if feeding study)
Feed consumption was not affected by incorporation of melamine in the feed.
URINALYSIS
There were no differences in the urine samples that could be attributed to the presence of melamine in the feed. Microscopic examination of the urine did not provide any evidence of melamine crystalluria.
GROSS PATHOLOGY
Other than stones in the bladder of dosed male rats, no compound-related effects were observed at necropsy. The incidence of stones in the urinary bladder of male rats was dose related.
HISTOPATHOLOGY: NON-NEOPLASTIC
Stones were present even in the male group receiving 750 ppm. Hyperplasia of the transitional epithelium of the bladder was present in 1/10 male rats receiving 3,000 ppm, in 3/10 receiving 6,000 ppm, and in 919 receiving 12,000 ppm melamine. The hyperplastic epithelial changes, which were found only in male rats that had bladder stones, were accompanied by prominent capillaries and occasional edema and scattered mast cells in the submucosa. Kidney changes in male rats were minimal. There was no evidence of urinary bladder stones or hyperplasia of the bladder epithelium in any groups of dosed female rats, but dose-related calcareous deposits were observed in the straight segments of the proximal tubules in female rats (2/10 controls, 3/ 10 receiving 750 ppm, 4/ 10 receiving 1,500 ppm, 10/ 10 receiving 3,000 ppm, 8/ 10 receiving 6,000 ppm, and 10/ 10 receiving 12,000 ppm melamine).

STUDY No. 3:
CLINICAL SIGNS AND MORTALITY
None of the rats died.
BODY WEIGHT AND WEIGHT GAIN
Rats fed diets containing 18,000 ppm melamine plus 1% ammonium chloride in the drinking water had decreased weight gains relative to groups receiving drinking water acidified with hydrochloric acid.
FOOD CONSUMPTION AND COMPOUND INTAKE (if feeding study)
There were no effects.
GROSS PATHOLOGY
The addition of ammonium chloride in the drinking water had no apparent effect on the incidence of urinary bladder stones in male or female rats. Urinary bladder stones were seen in 8/8 males and 3/9 females in the group that received 18,000 ppm melamine in feed plus 1% ammonium chloride in drinking water, compared with 10/ 10 males and 3/10 females in the groups administered 18,000 ppm melamine in feed without 1% ammonium chloride in the water. No other compound-related effects were observed at necropsy.

Key result
Dose descriptor:
NOAEL
Effect level:
750 ppm
Based on:
test mat.
Sex:
male
Basis for effect level:
gross pathology
other: 2 urinary bladder stones were detected compared to 1 in the control group. Statistically, 750 ppm is the NOAEL.
Dose descriptor:
NOAEL
Effect level:
72 mg/kg bw/day (nominal)
Based on:
test mat.
Sex:
male
Basis for effect level:
other: 2 urinary bladder stones were detected compared to 1 in the control group. Statistically, 750 ppm is the NOAEL.
Key result
Dose descriptor:
NOAEL
Effect level:
6 000 ppm
Based on:
test mat.
Sex:
female
Basis for effect level:
body weight and weight gain
other: body weight
Dose descriptor:
NOAEL
Effect level:
600 mg/kg bw/day (nominal)
Sex:
female
Basis for effect level:
other: body weight
Key result
Critical effects observed:
yes
Lowest effective dose / conc.:
1 500 ppm
System:
urinary
Organ:
bladder
Treatment related:
yes
Dose response relationship:
yes
Relevant for humans:
yes

The relevant results in the tables of the study are assembled in the attachment.

Conclusions:
Most noticeable was the development of uroliths (urinary bladder stones) at 750 ppm and higher doses, mainly in males.
Executive summary:

Melamine (2,4,6-triamino-s-triazine) was administered in the diet to F344 rats or B6C3F1 mice for 13 weeks (subchronic) to determine its toxicologic profile. The dose levels of melamine in the subchronic studies ranged from 750 to 18000 ppm for rats, and 6000 to 18000 ppm for mice. In these studies, compound-related lesions were observed in the urinary tract. Most noticeable was the development of uroliths (urinary bladder stones), which occurred at a greater frequency in males than females of either species. Increased incidences of urinary bladder stones and hyperplasia of the bladder epithelium were observed at 13 weeks in male rats fed diets containing melamine.

Endpoint conclusion
Endpoint conclusion:
adverse effect observed
Dose descriptor:
NOAEL
72 mg/kg bw/day
Study duration:
subchronic
Species:
rat
Quality of whole database:
Klimisch 1.
System:
urinary
Organ:
bladder
kidney

Repeated dose toxicity: inhalation - systemic effects

Link to relevant study records
Reference
Endpoint:
sub-chronic toxicity: inhalation
Data waiving:
study scientifically not necessary / other information available
Justification for data waiving:
other:
Critical effects observed:
not specified

Repeated dose toxicity: inhalation - local effects

Link to relevant study records
Reference
Endpoint:
sub-chronic toxicity: inhalation
Data waiving:
study scientifically not necessary / other information available
Justification for data waiving:
other:
Critical effects observed:
not specified

Repeated dose toxicity: dermal - systemic effects

Link to relevant study records
Reference
Endpoint:
sub-chronic toxicity: dermal
Data waiving:
study scientifically not necessary / other information available
Justification for data waiving:
other:
Critical effects observed:
not specified

Repeated dose toxicity: dermal - local effects

Link to relevant study records
Reference
Endpoint:
sub-chronic toxicity: dermal
Data waiving:
study scientifically not necessary / other information available
Justification for data waiving:
other:
Critical effects observed:
not specified

Mode of Action Analysis / Human Relevance Framework

The relevant trigger for the toxicity of melamine is the production of urinary tract crystals and calculi at sufficiently high doses, because of the precipitation of melamine in the urine above the solubility limit. Other toxicities observed are considered sequels of the crystals or uroliths. The main toxic effects of melamine are urinary bladder stones and hyperplasia of the transitional epithelium of the bladder in rats, in case uroliths were present. Other effects (lower body weight gain, kidney lesions) were observed at higher doses.

The relevance for humans is low, 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.

Additional information

With one unreliable exception, only oral studies are available. Most of them with rats or mice, ranging from 14-day to chronic studies.

Subchronic studies, rats:

The second NTP 1983 13-weeks study with rats is selected as the key repeated dose toxicity studies, as NTP-studies are generally considered to be of high reliability. In this case there are few doubts on the high reliability, as there is an unexpected result for the crucial finding, i.e. urinary bladder stones: There was 1/10 stone in the control group, which is suspicious, as urinary bladder stones in rats are seldom. The results of the chronic study of Reno 1983 (NOAEL = 1000 ppm) and subacute study of Tyl 1982 (NOAEL = 2000 ppm) are considered to be more appropriate as key studies, but the NTP 13-weeks study with rats was up to now preferred as the worst case study by the health authorities EFSA, WHO, US FDA.

The NTP-studies confirmed that the main effects of melamine are urinary bladder stones. Hyperplasia of the transitional epithelium of the bladder is detected, in case uroliths were present. These effects occurred in male rats, becoming significant at 1500 ppm in feed (equivalent to 150 mg/kg bw/day), in a dose dependent way. 1/10 stone in the control group and 2/10 stones in the lowest dose of 750 ppm (72 mg/kg/d) were observed. The difference between control and lowest dose is not statistically significant. Other effects (lower body weight gain, kidney lesions) were observed only at ca. 10 times higher doses and above. The NOAEL13weeks, reported by NTP, is 72 mg/kg bw/day, based on urinary stones in male rats. (The US FDA has calculated from the same results of the NTP-study a NOELrat,13w,oral of 63 mg/kg bw/day. No data as to how FDA arrived to the result are available.) Hard et al. 2009 re-evaluated the histological specimen of the kidneys and detected additional lesions, but only at the highest dose level.

Chronic studies, rats:

A long-term NOAEL of 2250 ppm, corresponding to ca. 126 mg melamine/kg bw/day, was derived from the NTP 1983 2-years study for male rats, see section 7.7. Interestingly enough, the 5 bladder stones detected in 10 animals in the 13-weeks study at 1500 ppm were not anymore detected at the even higher dose of 2250 ppm at the end of the 2-years study, as only 1 rat out of 50 dosed rats had a bladder stone. A regression of bladder stones occurs with time, even at ongoing dosing. Hard et al. 2009 re-evaluated the histological specimen of the kidneys and detected retrograde nephropathy in 7 out of 50 rats in the low dose group (2250 ppm), turning the NOAEL of 2250 ppm into a LOAEL. Based on the steep dose-response relation, a NOAEL of 2250/3 = 750 ppm, equivalent to 126/3 = 42 mg/kg bw/d is derived.

A chronic study with rats and with doses at the lower end of the NTP-study was performed by Reno 1985. The NOAEL was 1000 ppm for male and 2000 ppm for female rats.

Subacute studies, rats:

- The NOAEL of the NTP 14-days study with rats is 417 mg/kg bw/d.

- The study of Tyl 1982 investigated the formation of stones in weanling rats, dosed for 4 weeks. The NOEL was obtained to 2000 mg/kg feed (ca. 240 mg/kg bw/day). There was a strong correlation between hyperplasia of bladder epithelium and contained stones. No indication for a higher sensibility of young rats was obtained. Uroliths were composed primarily of melamine and protein, with traces of phosphate, oxalate und uric acid. (Another publication, Ogasawara 1995, reported that the calculi were composed of melamine and uric acid in an equimolar ratio, see Section 7.7. Calculi from Chinese patients were composed of uric acid and melamine in a molar ratio of 1.2:1 to 2.1:1, WHO 2009.).

- A study (El Rabey 2014) reported several lesions in different organs of rats at an oral dosing of 30 000 ppm in the feed for 28 days (ca. 2000 mg/kg/d). This was the only (too high) dose level investigated.

- A NOAEL of 140 mg/kg/d for a 14d toxicity study with rats was recently published (Early 2013a). In the next higher dose of 700 mg/kg/d the kidney lesions were prominent, but some lesions to thymus and spleen were detected too. There were no compound-related findings in the high-dose recovery animals, pointing to a regression of the lesions. The large factor of 5 between the low and mid doses doesn't make the study a first choice for the determination of a NOAEL.

 

NOAELs in relation to the exposure duration for rats are:

     14 days: 417 mg/kg bw/day

     28 days: 240 mg/kg bw/day

     13 weeks: 72 mg/kg bw/day

     2 years: 42 mg/kg bw/day

 

Mice: Mice were also investigated by NTP: The incidence of bladder stones was dose related as in rats, being greater in males than in females, starting at much higher doses of 12000 mg/kg feed.

 

Dogs: Only a very old study (Shaffer 1955) with 3 high dosed (30000 mg/kg feed) dogs is reported. Crystalluria, and in 1 animal chronic cystitis and a stone were reported as the only lesions.

 

Monkey: In a subchronic study with monkeys (Early 2013), the kidneys were again the primary target organ. A NOAEL of 60 mg/kg/d was derived, much the same as in the rat study. The study has a poor reliability.

 

Pigs: Pigs were orally dosed at 200 mg/kg/d for 28 days (Stine 2011). Investigations concentrated on calculi formation in the urinary tract. The NOAEL was 200 mg/kg/d.

 

Dermal route:

No study with the dermal route was performed. Based on the estimated low dermal absorption of melamine (see Chapter 7.1.2) and the toxicokinetics behaviour (rapid oral absorption, no metabolism), it can be estimated that the toxicity of melamine by the dermal route will be much lower than by the oral route. No study with the dermal route is therefore required, see Chapter 7.5.3.

 

Inhalation route:

One study (Ubaydullayev 1993) was performed with inhalation exposure to male rats. This study is considered to be unreliable and some reasons are:

1) It is not clear from the report, if a dust or an aerosol from a solution was applied.

2) The systemic lesions detected in a range of organs in the mid and high dose groups, were "basic hematopoietic disorder and dystrophic alterations in the internal organs (brain, lungs, liver, spleen and testicles)". Lesions in the urinary bladder were not detected. This creates some further doubts on the reliability of the study, as the findings are not in agreement with that observed in the available oral studies. In the oral repeated dose studies, the dominant lesion at the lowest doses was that of the urinary bladder. Lesions of the haematopoietic system, brain, lungs and liver were not detected in the oral studies even at high doses and even in long-term studies.

3) From toxicokinetic studies in rats it is known that melamine is rapidly and completely absorbed after oral dosing and that it remains unchanged in the organism. No first pass effect is observed. Complete absorption as a worst case and no metabolism can also be assumed for the inhalation route. Therefore the kinetic behaviour of melamine should not be the cause of major qualitative and quantitative differences at the oral and the inhalation route (except for possible local effects).

4) The NOAELoral,rat,13w is 63 mg/kg bw/d, see NTP 1983. Using the default respiratory volume for rats of 0.8 L/min/kg bw = 1.15 m3/kg bw/d, see Guidance Document on Information requirement and CSA, Table R.8-2, a NOAEC of 54.8 mg/m3 is estimated. This is quite in contrast to the 5000 times lower NOAEC of 0.01 mg/m3, derived by Ubaydullayev 1993.

 

The performance of a new inhalation study is not justified because:

- A rapid and complete absorption was found after the oral route (see Chapter 7.1.1.). The same can be assumed as a worst case for the inhalation route. The absorbed doses can be calculated according to the Guidance Document on Information requirement and CSA, Table R.8.

- Melamine is not irritant to eyes and skin, and it can be expected therefore that no local but mainly systemic toxic effects would occur (if any).

- There is apparently no metabolism of melamine in the organism (see Chapter 7.1.1) and by this no first pass effect. It is therefore justified to estimate the possible toxic effects after inhalation exposure, based on the outcome of the oral experiments.

- The NOAELinhalation can be estimated from the NOAELoral taking into account the respiratory volume. This is sufficient for a risk assessment, and does not justify an own inhalation animal experiment.

 

Justification for selection of repeated dose toxicity via oral route - systemic effects endpoint: See above.
Repeated dose toxicity: via oral route - systemic effects (target organ): urogenital: kidneys

Justification for classification or non-classification

The LOAELrat,oral,13weeks of 150 mg/kg bw/d of the key study is higher than the guidance value for a serious toxic effect in a subchronic study of <100 mg/kg bw/day, which is stated in the CLP. No classification as to "specific target organ toxicity - repeated exposure" is therefore required.