Strontium hydrogen phosphate

Endpoint summary

Description of key information

Two publications are available on feeding studies which address a broad range of parameters: Kroes et al (1977; SrCl2.6H2O) and Kshirsagar (1975; Sr3(PO4)2). Several publications are available on effects of repeated Sr exposure via feed or drinking water (SrCl2 or Sr as unspecified salt) specifically on bone parameters. All studies were performed with rats. The rationale for the use of data from substance analogues is included in section 13.

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

Study period:

1976

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

study well documented, meets generally accepted scientific principles, acceptable for assessment

Remarks:

Study performed with the substance analogue Strontium chloride hexahydrate. The study was not performed according to OECD guidelines, or GLP Principles. It is however a well-documented study and fulfills the data requirements of OECD guideline 408 with regard to the most important parameters.

Qualifier:

no guideline followed

Principles of method if other than guideline:

Rats received SrCl2 hexahydrate in a diet at dose levels of 0, 75, 300, 1200, and 4800 ppm for 90 days. Growth, food intake, behaviour and mortality were measured, extensive haematology and clinical biochemistry were carried out, organ weight was determined and complete histopathological examination was performed. In addition, X-ray photographs of the bones were taken and the Sr content of blood, bone and muscles was determined in additional groups of rats.

GLP compliance:

no

Remarks:

Study performed before GLP guidelines were in place.

Limit test:

no

Species:

rat

Strain:

Wistar

Sex:

male/female

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: National Institute of Public Health
- Housing: wire cages, two in a cage according to sex
- Weight at study initiation: 40-60g (males and females; 90-day experiment; )130-170g (males and females; range-finding experiment)
- Diet: semi-purified diet (Muracon SSP-tox, Trouw Ltd., Putten, The Netherlands), ad libitum
- Water: tap water, ad libitum

ENVIRONMENTAL CONDITIONS
- conventional conditions

Route of administration:

oral: feed

Analytical verification of doses or concentrations:

not specified

Duration of treatment / exposure:

90 days

Frequency of treatment:

Continuous exposure through diet

Remarks:

Doses / Concentrations:
0, 75, 300, 1200 or 4800 ppm
Basis:
nominal in diet

No. of animals per sex per dose:

10

Control animals:

yes, plain diet

Details on study design:

- Dose selection rationale:
The dosing was determined based on a range-finding experiment with 0, 3, 30, 300 and 3000 ppm in the diet.

Positive control:

No

Observations and examinations performed and frequency:

CAGE SIDE OBSERVATIONS: Yes
- Time schedule: daily

BODY WEIGHT: Yes
- Time schedule for examinations: weekly

FOOD CONSUMPTION AND COMPOUND INTAKE (if feeding study):
- Food consumption was measured in week 2, 5, 9 and 12.

FOOD EFFICIENCY:
- Body weight gain in kg/food consumption in kg per unit time X 100 calculated as time-weighted averages from the consumption and body weight gain data: Yes

HAEMATOLOGY:Yes
- Time schedule for collection of blood: after 90 days (all animals); after 6 and 12 weeks (5 males/ group)
- Anaesthetic used for blood collection: No data
- Animals fasted: No data
- How many animals: 10 females and 10 males of each group
- Parameters examined: Hb, Ht, erythrocute count, leucocyte count, MCV, MCHC and MCH


CLINICAL CHEMISTRY: Yes
- Time schedule for collection of blood: after 4 and 12 weeks (5 males/ group)
- Anaesthetic used for blood collection: No data
- Animals fasted: No data
- How many animals: 10 females and 10 males of each group
- Parameters examined: ALT, Alkaline phosphatase, glycogen and urea content in the serum
- Microsomal liver enzymes (AH and APDM; 5 males/ dose in weeks 4 and 12), glycogen content in the liver (5 males at 8 weeks and 6/sex in week 12)

URINALYSIS: Yes
- Time schedule for collection of urine: after 12 weeks
- Animals fasted: No data
- How many animals: 10 female and 10 male rats
- Parameters examined: protein, blood, bilirubin and ketones, and pH (using Bililabstix® (Ames Cy.))

OTHER:
Strontium content was determined in bone, muscle and blood by X-ray spectrometry with a limit of detection of 1 mg/kg. Magnesium and calcium concentrations in the serum were determined by atomic absorption spectrometry. This was done in 5 controls in the beginning of the experiment and in 5 males per group after 4, 8 and 12 weeks. In weeks 9 and 12 analysis of the bones were performed of 2/sex of the controls and 5/dex at 4800ppm.

Sacrifice and pathology:

GROSS PATHOLOGY: Yes
- Weight of brain, pituitary gland, heart, thyroid, liver, kidneys, spleen, adrenals, ovaries or testes, uterus or prostate was determined
HISTOPATHOLOGY: Yes
- Organs above, and also lungs, thymus, pancreas, mesenterial lymph nodes, stomach, duodenum, ileum, jejunum, coecum, colon, rectum, urinary bladder, nervus ischiadicus, musculus quadriceps and femur

Statistics:

Student's t-test was used to compare seperate treatment groups and corresponding controls.

Clinical signs:

no effects observed

Mortality:

no mortality observed

Body weight and weight changes:

no effects observed

Food consumption and compound intake (if feeding study):

no effects observed

Food efficiency:

no effects observed

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

not examined

Ophthalmological findings:

not examined

Haematological findings:

no effects observed

Clinical biochemistry findings:

effects observed, treatment-related

Urinalysis findings:

no effects observed

Behaviour (functional findings):

not examined

Organ weight findings including organ / body weight ratios:

effects observed, treatment-related

Gross pathological findings:

not specified

Histopathological findings: non-neoplastic:

effects observed, treatment-related

Histopathological findings: neoplastic:

not examined

Details on results:

CLINICAL SIGNS AND MORTALITY
After more than 11 weeks one control animal died during bleeding procedure.

BODY WEIGHT AND WEIGHT GAIN
No effects observed.

FOOD CONSUMPTION AND COMPOUND INTAKE (if feeding study)
No effects observed.

FOOD EFFICIENCY
No effects observed.

HAEMATOLOGY
A lower leucocyte count was found in males at 300 ppm, in absence of a dose-response this is considered not to be substance related.

CLINICAL CHEMISTRY
No significant changes in alkaline phosphatase activity, ALT and urea in serum were observed. The levels of Ca, Mg, and P in the blood were not changed at any dose level, and the Ca/P ratio remained constant. No significant changes in microsomal liver enzyme activities were detected. The glycogen concentration in the liver after 12 weeks showed a dose-related decrease, only significant in females at the highest dose level.

URINALYSIS
No significant changes detected.

ORGAN WEIGHTS
A significant increase of the relative thyroid weights was found for the males at the two highest dose levels. Relative pituitary weights of the females at 300 ppm and 4800 ppm were statistically significantly decreased. The relative prostate weights were statistically significantly decreased at 75 and 1200 ppm. In the absence of a dose-relationship, the effects on organ weights were considered not toxicologically relevant.

HISTOPATHOLOGY: NON-NEOPLASTIC
Histopathological examination revealed slight changes in the liver and thyroid. The changes consisted of a loss of glycogen in the liver and a slightly increased activity of the thyroid of the males in the highest dose group.

OTHER FINDINGS
Neither after 9 nor after 12 weeks changes could be noticed in the X-ray photographs of the animals.
Detectable amounts of Sr in blood and muscle were only noticed at the highest dose level: approx. 3 µg/ g wet tissue after 4 and 8 weeks, approx. 2 µg/ g wet tissue after 12 weeks in blood; approx. 2 µg/ g wet tissue in muscle at all examined time points compared to below detection limit in controls. Sr concentration in bone was elevated at all dose levels (at 4, 8 and 12 weeks (30, 68, 160 and 660 times control at 75, 300, 1200 and 4800 ppm resp. after 12 weeks). Concentrations did not increase over time (results are included in table).

Dose descriptor:

NOAEL

Effect level:

> 1 200 ppm

Based on:

test mat.

Sex:

female

Basis for effect level:

other: Based on decreased glycogen content in the liver at 4800 ppm. Based on an average weight of 250g and a daily intake of 21.7 g food, the NOAEL of 1200 ppm correlates with 104 mg test material/kg bw/day.

Critical effects observed:

not specified

Results range-finding experiment:

Behaviour, growth, food intake and food efficiency were not affected in the range-finding experiment. Haematological investigation revealed only a slight elevation of the total number of erythrocytes in males and females and a slight increase of the white cell count in the males at the highest dose level. No differences were found in liver and kidney weights and histopathological examination revealed no abnormalities. Sr in blood and muscle were only noted at the highest dose level (3000 ppm): appr. 2 and 1 µg/ g wet tissue for resp. blood and muscle in females and appr. 2 and 4 µg/ g wet tissue for resp. blood and muscle in males. In the bone, Sr concentrations were raised at 300 and 3000 ppm to resp. 266 and 1451 µg/ g wet tissue in females and 232 and 1711 µg/ g wet tissue in males (approximate values) versus 43 and 28 µg/ g wet tissue in resp control females and males.

Strontium-content in µg/ g bone tissue in 5 male rats per group after 0, 4, 8 and 12 weeks:

	start	4 weeks	8 weeks	12 weeks
0	35 ± 2	20 ± 17	10 ± 4	9 ± 4
75 ppm		276 ± 30	240 ± 19	273 ± 49
300 ppm		619 ± 64	463 ± 76	523 ± 87
1200 ppm		1473 ± 107	1237 ± 103	1430 ± 100
4800 ppm		6088 ± 267	5259 ± 486	5941 ± 783

Conclusions:

A feeding study was conducted for 90 days with strontium chloride hexahydrate, with doses of 0, 75, 300, 1200 and 4800 ppm with male and female rats. If the increased concentrations of strontium in the bone can be considered a non-adverse effect, a NOAEL of 1200 ppm SrCl2.6H2O can be derived from this study, based on decreased glycogen content in the liver at 4800 ppm.

Executive summary:

A feeding study was conducted for 90 days with strontium chloride hexahydrate, with doses of 0, 75, 300, 1200 and 4800 ppm with male and female rats (10/ sex/ dose). No substance related mortality occurred, no clinical signs were noted. No effects were seen on body weight gain, food consumption and haematological parameters. The glycogen concentration in the liver after 12 weeks showed a dose-related decrease, only significant in females at the highest dose level. Detectable amounts of Strontium in blood and muscle were only noticed at the highest dose level (both sexes). Strontium concentration in bone was elevated at all dose levels in both sexes, the concentrations did not increase over time. A NOAEL of 1200 ppm strontium chloride hexahydrate can be derived from this study

(if the increased concentrations of strontium in the bone can be considered a non-adverse effect), based on decreased glycogen concentration in the liver at 4800 ppm. Based on an average weight of 250 g and a daily intake of 21.7 g food, the NOAEL of 1200 ppm correlates with 104 mg test material/kg bw/day.

Endpoint conclusion

Endpoint conclusion:

adverse effect observed

Dose descriptor:

NOAEL

104 mg/kg bw/day

Study duration:

subchronic

Species:

rat

Quality of whole database:

Several publications with Klimisch reliability 2 are available on SrCl2. One publication is available on effects of Strontium phosphate (Klimisch 2). Three publications on Strontium are available with Klimisch score 2, without further data on the Strontium salt used. All studies were perfomed with rats. The hypothesis for the analogue approach is attached in section 13.

Repeated dose toxicity: inhalation - systemic effects

Endpoint conclusion

Endpoint conclusion:

no study available

Repeated dose toxicity: inhalation - local effects

Endpoint conclusion

Endpoint conclusion:

no study available

Repeated dose toxicity: dermal - systemic effects

Endpoint conclusion

Endpoint conclusion:

no study available

Repeated dose toxicity: dermal - local effects

Endpoint conclusion

Endpoint conclusion:

no study available

Additional information

Two publications are available in which general parameters were addressed:

Kroes et al (1976), key study:

A feeding study was conducted for 90 days with strontium chloride hexahydrate, with doses of 0, 75, 300, 1200 and 4800 ppm with male and female rats (10/ sex/ dose). No substance related mortality occurred, no clinical signs were noted. No effects were seen on body weight gain, food consumption and haematological parameters. The glycogen concentration in the liver after 12 weeks showed a dose-related decrease, only significant in females at the highest dose level. Detectable amounts of Strontium in blood and muscle were only noticed at the highest dose level (both sexes). Strontium concentration in bone was elevated at all dose levels in both sexes, the concentrations did not increase over time. A NOAEL of 1200 ppm strontium chloride hexahydrate can be derived from this study (if the increased concentrations of strontium in the bone can be considered a non-adverse effect), based on decreased glycogen concentration in the liver at 4800 ppm. Based on an average weight of 250g and a daily intake of 21.7 g food, the NOAEL of 1200 ppm correlates with 104 mg test material/kg bw/day.

Kshirsagar (1975), supporting study:

A feeding study was performed in which young male rats were exposed to approximately 0, 500, 1000 or 2000 mg/kg bw/day for 2, 4 or 6 weeks (control and 2000 mg/kg bw/day groups) or 6 weeks (500 and 1000 mg/kg bw/day groups). Mortality up to 30% was recorded in rats of the 2000 mg/kg bw/ day group (exposed for 4-6 weeks). No mortality was reported in other groups. Reduction in body weight gain were seen in rats exposed to 1000 mg/kg bw/d or more. No clinical signs or pathological findings were noticed in rats in the 500 and 1000 mg/kg bw/d groups. Widening of the epiphyseal cartilage plate were seen in rats exposed to 2000 mg/kg bw/d for 4 to 6 weeks, this effect reverted after a recovery of 2 weeks. In parallel, strontium was found to accumulate in liver, kidney and intestinal tissue, this was found to be reversible and is not regarded as an adverse effect. Based on the severe reduction in body weight gain at 1000 mg/kg bw/ day, the NOAEL was found to be 500 mg/kg bw/day.

Furthermore, several publications on repeated dose studies (either via feed or via drinking water) are available on the substance analogues SrCl2, or Sr (nature of salt not given) with strong focus on effects on bones. Effects on body weight gain are described in Banks (1951; LOAEL SrCl2 = 14.5 g/kg bw/ day) and Johnson (1968, LOAEL Sr (unknown salt) = 405 mg/kg bw/ day). Effects on bone parameters were published by Marie (1985; NOAEL SrCl2 = 524.6 mg/kg bw/day, defective bone mineralization at higher doses), Marie (1986; LOAEL SrCl2 = 630 mg/kg bw/day, distinct early effects on bone formation and resorption) and Johnson (1972, LOAEL Sr (unknown salt) = 365 mg/ kg bw/ day, affected bone parameters). Grynpas et al (1996) do not describe adverse effects ( NOAEL Sr (unknown salt) = 168 mg/kg bw. The reported LOAEL values for effects on morphology and/or calcification of teeth or bones in these supporting studies are well above the NOAEL found in the key study by Kroes et al (1977). It can be concluded that the accumulation of strontium in bone is clearly a dose-dependent process. Although the effects of strontium on bone mineralisation are demonstrated in various studies, the effects on bone strength and functioning were not addressed. None of the studies report effects that could be related to decreased bone strength (such as high incidence of fractures, or impairment in movement in the exposed groups). Based on the lack of severe effects in the studies with strontium, it is concluded that there are no indications that the accumulation found at the NOAEL in the key study can be regarded as an adverse effect. This conclusion is further supported by the findings of Grynpas et al (1996; supporting study), who report beneficial effects on bone at a level of 168 mg/kg bw/ day.

Justification for selection of repeated dose toxicity via oral route - systemic effects endpoint:
Study performed with substance analogue strontium chloride hexahydrate. It is a well-documented study and fulfills the data requirements of OECD guideline 408 for the most important parameters, but the study was not performed according to OECD guidelines, or GLP requirements. In this study the lowest NOAEL for a substance analogue was described.

Justification for classification or non-classification

No significant toxicity was described following Strontium exposure at dosage levels triggering classification. Based on these data, strontium hydrogen phosphate is not classified for specific target organ toxicity after repeated exposure according to Regulation (EC) No 1272/2008 on classification, labelling and packaging (CLP) of substances and mixtures.