Dolomite (CaMg(CO3)2), calcined

Toxicity to reproduction

Administrative data

Endpoint:

fertility, other

Remarks:

based on test type (migrated information)

Type of information:

migrated information: read-across from supporting substance (structural analogue or surrogate)

Adequacy of study:

supporting study

Study period:

no data available

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: see 'Remark'

Remarks:

Very well-documented publication. Under physiological conditions, the hydroxyl- and carbonate ions released from calcined dolomite following oral adminstration have been neutralised in the GI tract or have been released as CO2 and are therefore not relevant for consideration of systemic/reproductive toxicity. Therefore for assessment of any systemic effects of lime following administration via the oral route including toxicity to reproduction, the magnesium ion Mg2+ is the chemical species of interest. In the current study, magnesium was administered in the form of magnesium sulphate, the sulphate ion being a ubiquitious component of mammalian mineral supply via the diet, and involved in many biochemical reactions, and therefore of limited toxicologically relevance at the doses administered. The objective of the study was the evaluation of any effects of magnesium. In view of the the limited relevance of the anionic counter-ions discussed here, magnesium released both from calcium magnesium carbonate oxide and magnesium sulphate can be considered as analogous substances, and the results of the study can be used by read-across.

Data source

Reference

Reference Type:

publication

Title:

Effect of magnesium deficiency on reproduction in the white rat

Author:

Andrieux-Domont, C.; Le Van Hung, L.V.

Year:

1973

Bibliographic source:

Br. J. Nutr. 29, 203-210

Materials and methods

Test guideline

Qualifier:

no guideline available

GLP compliance:

no

Limit test:

yes

Test material

Test material information

Constituent 1

Reference substance name:

Magnesium sulfate

IUPAC Name:

Magnesium sulfate

Constituent 2

Reference substance name:

Magnesium sulphate

EC Number:

231-298-2

EC Name:

Magnesium sulphate

Cas Number:

7487-88-9

IUPAC Name:

231-298-2

Details on test material:

- Name of test material (as cited in study report): Magnesium sulfate
- Physical state: solid
No further details are given.

Test animals

Species:

rat

Strain:

Wistar

Sex:

male/female

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source:
- Age at study initiation: (P) 3 months
- Diet: ad libitum
- Water: ad libitum; demineralised water

No further details are given.

Administration / exposure

Route of administration:

oral: feed

Vehicle:

unchanged (no vehicle)

Details on exposure:

DIET PREPARATION
Two different diets were prepared: The control was complete and balanced with a Mg content of 460 mg/kg; the second diet was deficient in Mg, its Mg content being only 30 mg/kg.
No further details are given.

Details on mating procedure:

- M/F ratio per cage: 25 control females were mated with control males, and the other 20 control females were mated with males on the Mg-deficient diet. 20 females on the Mg-deficient diet were mated with control males and the remaining 20 MG-deficient females were mated with males on the Mg-deficient diet. Four groups of animals were thus obtained. During the mating period, each mating couple was maintained on the Mg-deficient diet where one animal in the couple was maintained on the Mg-deficient diet before mating.
- Length of cohabitation: After 5 days of mating, males were separated from females and each group of females was further divided into two sub-groupss: One half were given the Mg-deficient diet and the other half were given the control diet for the remainder of the gestation period.
- Proof of pregnancy: sperm in vaginal smear referred to as day 0 of pregnancy
- After successful mating each pregnant female was caged: The females were isolated in individual cages 8 days before the end of pregnancy.

Analytical verification of doses or concentrations:

not specified

Details on analytical verification of doses or concentrations:

No details are given.

Duration of treatment / exposure:

Control group: Rats were maintained on the control diet from weaning until the age of 3 months.
Deficient-diet group: Rats were maintained on the diet for 42 days.

Frequency of treatment:

Continuously

Details on study schedule:

No further details are given.

Doses / concentrations

Doses / concentrations 1

Remarks:

Doses / Concentrations:
30 mg magnesium/kg
Basis:
nominal in diet
magnesium deficient diet

Doses / concentrations 2

Remarks:

Doses / Concentrations:
460 mg magnesium/kg
Basis:
nominal in diet
magnesium balanced diet (control)

No. of animals per sex per dose:

Control group: 45 females and 10 males
Deficient-diet group: 40 females and 10 males

Control animals:

yes

Details on study design:

No further details are given.

Positive control:

No positive control substance was used.

Examinations

Parental animals: Observations and examinations:

CAGE SIDE OBSERVATIONS: No data

DETAILED CLINICAL OBSERVATIONS: No data

BODY WEIGHT: No data

FOOD AND WATER CONSUMPTION AND COMPOUND INTAKE: No data

OTHER:
- some females were killed during gestation to study the foetuses
- magnesium concentrations in organs like kidneys and liver were determined
- number of abortions

No further details are given.

Oestrous cyclicity (parental animals):

no data available

Sperm parameters (parental animals):

no data available

Litter observations:

PARAMETERS EXAMINED
The following parameters were examined in [F1] offspring:
- number and sex of pups
- body weight gain of the litter until weaning
- 5 days after birth, the amount of magnesium in the livers and kidneys of some rats was determined by flame spectrometry.

No further details are given.

Postmortem examinations (parental animals):

SACRIFICE
- Maternal animals: All surviving animals, after the litter was weaned. Because of the large number of abortions and reduced size of the litters from Mg-deficient females mated with normal males or with males given Mg-deficient diet, it was decided to kill several additional females to study the contents of the uterus.

No further details are given.

Postmortem examinations (offspring):

SACRIFICE
- The F1 offspring were sacrificed at 5 days of age.

No further details are given.

Statistics:

No data available

Reproductive indices:

No data available

Offspring viability indices:

No data available

Results and discussion

Results: P0 (first parental generation)

General toxicity (P0)

Clinical signs:

effects observed, treatment-related

Body weight and weight changes:

not specified

Food consumption and compound intake (if feeding study):

not specified

Organ weight findings including organ / body weight ratios:

not specified

Histopathological findings: non-neoplastic:

not specified

Other effects:

not specified

Reproductive function / performance (P0)

Reproductive function: oestrous cycle:

not specified

Reproductive function: sperm measures:

not specified

Reproductive performance:

effects observed, treatment-related

Details on results (P0)

CLINICAL SIGNS AND MORTALITY (PARENTAL ANIMALS)
It was observed that the duration of Mg-deficiency had a considerable effect on fertility. After 3 months of Mg-deficiency male and female rats were so weakened - with signs such as intense keratinisation of vagina, oedema of limbs and cataract blindness - that reproduction was impossible.
However, very few clinical signs were present after 6 weeks of Mg-deficiency before mating, and reproduction was possible.

REPRODUCTIVE PERFORMANCE (PARENTAL ANIMALS)
MATING OF NORMAL FEMALE RATS WITH NORMAL MALES OR WITH MALES GIVEN Mg-DEFICIENT DIET:
Verification of impregnation by vaginal smear analysis showed that for males from the control group a pregnancy rate of 70% was obtained; this was similar to the accepted statistical averages. Mating with Mg-deficient males produced a pregnancy rate of only 60%.
The females that were given the control diet during gestation gave birth to viable young; but those that were mated with Mg-deficient males produced smaller litters (4 to 5 young instead of 8 or more). When these same females were given the Mg-deficient diet during lactation they either died at the end of this period, or killed their offspring without devouring them.
When females were given the Mg-deficient diet during gestation, the percentage of live births remained the same, but about 50% of the litter was either abandoned or devoured by the mother, and when the Mg-deficient diet was continued, the female rats died during or at the end of lactation.

MATING OF Mg-DEFICIENT FEMALE RATS WITH NORMAL MALES OR WITH MALES GIVEN Mg-DEFICIENT DIET:
Vaginal smear analysis showed that there was a 60-70% mating rate, but the pregnancies reached full term only when the Mg-deficient diet was withdrawn immediately after separation of the males and the females. Nevertheless, litters were smaller (4 to 5 young rats) and 20% of the litters were devoured by the mother. On the other hand, when Mg-deficient females were maintained on the Mg-deficient diet after mating, numerous abortions were observed and all the newborn rats either were abandoned by their mother and died, or were devoured by her.

Because of the large number of abortions and reduced size of the litters, it was decided to kill several additional females to study the contents of the uterus. It was observed that gestation began normally at the opening of the uterus and the number of implantations was similar to the normal figure obtained with rats on the control diet. Towards the end of pregnancy the number of foetuses was reduced, although the number of implantation sites remained the same. The condition of the foetuses showed considerable variation: some were fully developed, but others had stopped developing or were already partly resorbed.

EFFECTS OF Mg-DEFICIENCY ON LACTATION:
The females given the Mg-deficient diet before and during gestation devoured their young; the females given the Mg-deficient diet before mating and then placed on normal diet during gestation had a normal though smaller litter, and they suckled their young until weaning.
When females in the latter group were placed again on the Mg-deficient diet at the beginning of lactation, two of them died at the beginning of this period and all died before weaning. By then, they weighed much less than normal females. At autopsy their kidneys were seen to be injured, appearing nephritic; the Mg concentration in the kidneys - about 16µg/g fresh tissue in the rats given the control diet - reached 18µg/g. This increase in concentration of Mg in the kidneys is one of the characteristics of Mg deficiency in the adult rat (Andrieux-Domont & Le Van Hung, 1969). In contrast, the magnesium concentration of the liver in females given the Mg-deficient diet decreased.

When the females in the control group were given the Mg-deficient diet during pregnancy and lactation, they died before the pups were weaned; but females which were placed on the control diet after giving birth produced milk normally and the gain in body weight of the litters was satisfactory.

Results: F1 generation

General toxicity (F1)

Clinical signs:

not specified

Mortality / viability:

mortality observed, treatment-related

Body weight and weight changes:

no effects observed

Sexual maturation:

not examined

Organ weight findings including organ / body weight ratios:

not specified

Gross pathological findings:

effects observed, treatment-related

Histopathological findings:

not specified

Details on results (F1)

MATING OF NORMAL FEMALE RATS WITH NORMAL MALES OR WITH MALES GIVEN Mg-DEFICIENT DIET: The concentration of magnesium in livers of young rats (5 days old) was slightly lower in those born to mothers who were given the Mg-deficient diet during gestation.

MATING OF Mg-DEFICIENT FEMALE RATS WITH NORMAL MALES OR WITH MALES GIVEN Mg-DEFICIENT DIET: The weights of the newborn rats were normal, but the magnesium concentration in their livers was slightly lower than those born in the control group (200 µg/g fresh liver compared to 220 µg/g for the controls).

Overall reproductive toxicity

Reproductive effects observed:

not specified

Applicant's summary and conclusion

Conclusions:

The results substantiate the importance of Magnesium for proper reproductive function and foetal development and the detrimental effects of Magnesium deficiency during gestation and lactation. The highest dose MgSO4 (460 mg/kg bw/d, corresponding to 92.87 mg Mg/kg bw/d) did not elicit any negative effects on reproductive parameters. Therefore, a NOAEL could not be identified.