Toxicity Profiles
Toxicity Summary for STRONTIUM-90
NOTE:
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- EXECUTIVE SUMMARY
- 1. INTRODUCTION
- 2. METABOLISM AND DISPOSITION
- 3. NONCARCINOGENIC HEALTH EFFECTS
- 3.1 ORAL EXPOSURES
3.2 INHALATION EXPOSURES
3.3 OTHER ROUTES OF EXPOSURE
3.4 TARGET ORGANS/CRITICAL EFFECTS
- 4. CARCINOGENICITY
- 4.1 ORAL EXPOSURES
4.2 INHALATION EXPOSURES
4.3 OTHER ROUTES OF EXPOSURE
4.4 EPA WEIGHT-OF-EVIDENCE
4.5 CARCINOGENICITY SLOPE FACTORS
- 5. REFERENCES
DECEMBER 1994
Prepared by: Sylvia S. Talmage, Ph.D., D.A.B.T., Chemical Hazard Evaluation Group, Biomedical and
Environmental Information Analysis Section, Health Sciences Research Division, Oak Ridge National
Laboratory*, Oak Ridge, Tennessee.
Prepared for: Oak Ridge Reservation Environmental Restoration Program.
*Managed by Martin Marietta Energy Systems, Inc., for the U.S. Department of Energy under
Contract No. DE-AC05-84OR21400.
EXECUTIVE SUMMARY
Strontium-90 is a radioactive isotope of strontium that is produced in nuclear fission. It is a low energy
emitter with a physical half-life of approximately 28 years. In the environment, it is accompanied by its
decay product, yttrium-90, also a emitter (NCRP, 1991).
Metabolically, strontium is an analog of calcium. Strontium-90 is rapidly absorbed from the
gastrointestinal tract or the lung into the bloodstream and is subsequently deposited in bone (Hobbs and
McClellan, 1986). Retention in the bone is long-term, with yearly loss of the existing burden in adults of
7.5% from cortical bone and 30% from trabecular bone (Papworth and Vennart, 1984).
Oral intake at high levels of activity results in irradiation of target organs and nearby tissues. At
high exposures, death results from radiation-induced hemorrhagic syndrome; at lower exposures, death
results from destruction of the bone marrow. As survival times increase at lower administered activities,
these effects are accompanied by neoplasms. Oral administration to miniature swine at 115 x 106 Bq/day
resulted in radiation-induced hemorrhagic syndrome and death within 4 months. Lower intakes, 4.62 x
106 to 0.037 x 106 Bq/day induced effects on the hematopoietic system ranging from pancytopenia to
neutropenia. Mean survival times were decreased in all exposure groups (NCRP, 1991). Subchronic
exposures (5.6 x 104 to 133 x 104 Bq/day) also resulted in cytopenias in beagle dogs (NCRP, 1991).
Median survival times were reduced, particularly at the two highest exposures. Doses in the latter study
were estimated at 22.5 to 107 Gy. In a three-generation study of miniature swine, no effects were noted
on litter size, the percentage of stillborn, or birth weight when dams received life-shortening exposures
(Clarke et al., 1972). The EPA has not calculated subchronic or chronic oral reference doses (RfD) for
radionuclides.
Inhalation of soluble forms of strontium-90 at high activity levels resulted in early death of beagle dogs
from bone marrow hypoplasia, panleukocytopenia, terminal hemorrhage, and bacterial infection (Gillett
et al., 1987; NCRP, 1991). Long-term bone burdens of 17 x 106 to 41 x 106 Bq were calculated. Acute
pulmonary effects observed in mice exposed to high activity levels of insoluble strontium-90 were radiation
pneumonitis and pulmonary fibrosis (Scott et al., 1987). The dose lethal to 50% of animals was 370 Gy.
The EPA has not calculated subchronic or chronic inhalation reference concentrations (RfC) for
radionuclides.
The primary effect in animals surviving acute effects of strontium-90 exposure is neoplasia of bone
and bone-related tissues. Soft tissue carcinomas in tissues near the bone were also observed above control
levels. Chronic ingestion in beagle dogs and miniature swine also produced a high incidence of
myeloproliferative disease, including frank leukemia (Hobbs and McClellan, 1986). Orally administered
activity levels of 0.1 x 104 to 133 x 104 Bq/day to beagle dogs, beginning in utero and continuing to 540
days of age induced primary bone sarcomas and myeloproliferative disorders at activity levels of >5.6 x
104 Bq/day (Pool et al., 1973; NCRP, 1991). Bone sarcomas and hematopoietic neoplasms were induced
in F1 and F2 generations of miniature swine that chronically ingested 4.62 x 106 Bq/day or 23.1 x 106
Bq/day (Clarke et al., 1972; NCRP, 1991). These generations were exposed in utero and gradually raised
to the treatment level by 6 months of age. At higher exposure activities, mean survival time was drastically
reduced (to less than tumor induction time); at lower exposure activities, 0.037 x 106 to 0.925 x 106
Bq/day, no bone sarcomas were observed, and survival times were increased to approximately that of
controls.
The primary effect in adult beagle dogs administered strontium-90 in a single inhalation exposure and
surviving more than 2 years was an excess of bone tumors (McClellan et al., 1973; NCRP, 1991). This
effect was induced in dogs with long-term retained bone burdens of >1.0 x 106 Bq/kg.
Bone tumors were induced in 2 of 7 adult monkeys administered strontium-90 by gavage (NCRP,
1991), in adult beagle dogs administered strontium-90 by intravenous injection (Mays and Finkel, 1980),
and in mice administered strontium-90 by intraperitoneal injection (Nilsson and Ronnback, 1973). Soft
tissue sarcomas in tissues near the bone were observed in the beagle dogs (Mays and Finkel, 1980). No
tumors were observed over a 20-year period in young and adult Rhesus monkeys administered a single
injection at activity levels of 0.13 x 106 to 6.21 x 106 Bq (NCRP, 1991).
The EPA has classified all radionuclides as Group A carcinogens based on their property of emitting
ionizing radiation and on the weight of evidence provided by epidemiological studies of radiation-induced
tumors in humans (EPA, 1994). A slope factor of 8.9E-10 (risk/Bq) was calculated for oral ingestion. The
combined oral slope factor for strontium-90 and yttrium-90 is 9.7E-10 (risk/Bq). For inhalation exposure,
the slope factor for strontium-90 is 1.5E-09 (risk/Bq); the combined inhalation slope factor for strontium-90
plus yttrium-90 is 1.7E-09 (risk/Bq). Because of their low penetration ability, external exposures (risk/yr
per Bq/g soil) for strontium-90 and strontium-90 plus yttrium-90 are both 0.0E+00.
1. INTRODUCTION
Strontium-90 (CAS Reg. No. 10098-97-2) is one of 11 radioisotopes of strontium that are produced
in nuclear fission. Strontium-90 is a low-energy beta () emitter (0.02 MeV) that decays to its radioactive
daughter, yttrium-90, with a relatively long physical half-life of approximately 28 years. Yttrium-90 has
a shorter half-life (2.7 days) and a higher energy beta emission (maximum, 2.3 MeV) than strontium-90
(NCRP, 1991). Because of radioactive decay, yttrium-90 is always present in the environment with
strontium-90. Strontium-90 may be released to the environment from normal operation of nuclear power
plants and reactors, nuclear plant accidents, past nuclear weapons testing, and leakage from radioactive
waste sites (NCRP, 1991).
Strontium is an alkaline earth metal belonging to Group IIA of the periodic table. No information on
the physical and chemical properties of strontium-90 was located, but the chemical behavior of a
radionuclide is essentially the same as that of the stable element (stable strontium or strontium-88) and is
similar to that of other elements in the same chemical group such as calcium.
Radionuclide uptake is expressed in units of activity [Curies (Ci) or Bequerels (Bq)] rather than mass.(1)
Absorbed dose is expressed in terms of rads or Grays (Gy); dose equivalent (the relative biological
effectiveness of the type of radiation) is expressed in terms of rems or Sieverts (Sv).(2) Many of the studies
discussed in this profile were reviewed and summarized with activity units converted from Ci to Bq by the
National Council on Radiation Protection and Measurements (NCRP, 1991).
2. METABOLISM AND DISPOSITION
The gastrointestinal tract absorption factor for strontium-90 is 30% (EPA, 1994); the lung clearance
classification recommended by the International Commission on Radiological Protection is defined in terms
of days, indicating minimal retention in the lung (EPA, 1994). Ingested and soluble inhaled forms of
strontium-90 such as 90SrCl2, are rapidly absorbed into the bloodstream and translocated primarily to the
skeleton where retention is longterm (McClellan et al., 1972; Hobbs and McClellan, 1986). Strontium-90
delivered to the lung within an insoluble fused aluminosilicate particle matrix has a long retention period
in the lung (Scott et al., 1987).
In biological systems, the behavior of stable and radioactive strontium is similar to and partially
governed by that of calcium (NCRP, 1991). However, living organisms generally discriminate against
strontium in favor of calcium. Following absorption, strontium is (1) distributed in an exchangeable pool
consisting of the plasma, soft tissues, and exchangeable bone, (2) deposited in the bone, and (3) removed
from the body by urinary and fecal excretion. Deposition and turnover of calcium (and strontium) in the
bone is dynamic and long-term deposition depends on the age of the exposed individual. Because of de
novo formation of bone in the young compared to the adult, ingestion of the same amount of strontium-90
on a body weight basis will result in a greater deposition of strontium in the bone of the young. Analyses
of human bones for strontium-90 between the years 1956 and 1970 showed peak values of strontium-90
in children aged 1 to 2 years (Bryant et al., 1964; Papworth and Vennart, 1984).
Radioautographs of the femurs of five week old rats injected intraperitoneally with strontium-90
showed even deposition of strontium throughout the mineral part of the bone and deposition in the
calcifying trabeculae beneath the epiphyseal plate (Hamilton, 1947).
Based on the concentrations of strontium-90 in human bone and human diet in the United Kingdom,
Papworth and Vennart (1984) estimated uptake and turnover in the skeleton. In adults, approximately
7.5% of the existing burden of strontium-90 is lost each year from cortical bone; the rate of loss from
trabecular bone is 30%. Approximately 4.5% of the dietary intake of strontium-90 reaches the skeleton,
half going to cortical bone and half to trabecular bone.
The retention of strontium-90 following ingestion of food contaminated as a result of radioactive fallout
was studied in a human volunteer (Hardy et al., 1965). The daily intake level over a 7-day period,
measured above background levels, was 640 pCi/day (24 Bq/day). Most of the strontium-90 was
unabsorbed. Almost 50% of the dose was excreted in the feces by 10 days after the ingestion period,
whereas only 2.5% was eliminated in the urine. Both fecal and urinary excretion fell sharply by 10 days
after the ingestion period and dropped to pretreatment levels by 180 days. The retention curve was best
represented by a series of exponentials that leveled off after 140 days and approached a value of 25%.
3. NONCARCINOGENIC HEALTH EFFECTS
3.1. ORAL EXPOSURES
3.1.1. Acute Toxicity
In general, acute toxicity of radionuclides is of less concern than for nonradioactive chemicals because
the levels required to cause adverse effects are extremely large and are not commonly encountered in the
environment. Chronic exposure to low levels of radioactive contaminants is the most common exposure
situation (EPA, 1989).
3.1.1.1. Human
Information on the acute oral toxicity of strontium-90 in humans was not available. Stable strontium
is considered relatively nontoxic to humans (EPA, 1988).
3.1.1.2 Animal
Information on the acute oral toxicity of strontium-90 in animals was not available. Soluble stable
strontium compounds are of a low order of acute toxicity with LD50 values for several species ranging from
1826 mg/kg [Sr(NO3)2, mouse] to 7500 mg/kg (SrCl2, rabbit) (EPA, 1988).
Miniature swine administered strontium-90 at a level of 115 x 106 Bq/day in the diet beginning at 9
months of age died of radiation-induced hemorrhagic syndrome within 4 months (NCRP, 1991).
3.1.2. Subchronic Toxicity
3.1.2.1. Human
Information on the subchronic oral toxicity of strontium-90 in humans was not available.
3.1.2.2. Animal
Subchronic exposures to high levels of strontium-90 result in irradiation of the bone marrow producing
effects on the hematopoietic system and subsequent death. There was an increased incidence (statistical
data not given) of myelolymphoproliferative syndrome (bone marrow dyscrasias ranging from aplastic
anemia to myeloid leukemia) in beagle dogs ingesting strontium-90 (90SrCl2) at levels of 1.5, 3, 12, or 36
Ci/day (5.6 x 104, 11.1 x 104, 44.4 x 104, or 133 x 104 Bq/day). Exposures lasted from the onset of fetal
calcification in utero to the end of the growth period at 540 days of age. Average doses to the bone were
estimated at 22.5, 50.4, 80.2, and 107 Gy (Pool et al., 1973; Raabe et al., 1981; data summarized in
NCRP, 1991). A distinction between cytopenias and leukemia was not made.
3.1.3. Chronic Toxicity
3.1.3.1. Human
Information on the chronic oral toxicity of strontium-90 in humans was not available.
3.1.3.2. Animal
Strontium-90 ingestion in female miniature swine, beginning at 9 months of age, resulted in effects on
the hematopoietic system (neutropenia, lymphopenia, thrombocytopenia, and myeloproliferative disorders
with myeloid and histiocyte infiltration of tissues of the kidney, heart, testes, and lung) (Clarke et al., 1972;
NCRP, 1991). At a feeding level of 115 x 106 Bq/day, all animals died of radiation-induced hemorrhagic
syndrome within 4 months. Females fed 23.1 x 106 Bq/day survived to produce a second generation, but
the second generation, exposed in utero and gradually raised to the treatment level by 6 months of age, had
a mean life span of 3 months; observed effects in the young were pancytopenia-hemorrhagic crisis and
myeloid metaplasia (bone marrow aplasia). At 4.62 x 106 Bq/day, neoplasms accompanied by
pancytopenia were induced; the lifespan was shortened to 3.5 years for the combined F1 and F2
generations. At lower exposure activities, 0.925 x 106, 0.185 x 106, and 0.037 x 106 Bq/day, neutropenia,
with some neoplastic effects at the 0.925 dose level, was the primary observed effect. At these latter
activities, mean survival times of 10-11 years were close to the mean survival time of 11 years in a control
group. Doses to the bone were not calculated.
3.1.4. Developmental and Reproductive Toxicity
3.1.4.1. Human
Information on the developmental and reproductive toxicity of strontium-90 in humans was not
available.
3.1.4.2. Animal
In a summary of their studies on the effects of strontium-90 in three generations of miniature swine,
Clarke et al. (1972) noted no significant differences in the litter size, the percentage of stillborn, or in birth
weight between control animals and animals ingesting up to 625 Ci/day (23.1 x 106 Bq/day). Sows
ingesting 3100 Ci/day (115 x 106 Bq/day) did not survive the gestation period.
3.1.5. Reference Dose
The EPA (1994) has not calculated subchronic or chronic oral reference doses (RfD) for radionuclides.
3.2. INHALATION EXPOSURES
3.2.1. Acute Toxicity
3.2.1.1. Human
Information on the acute toxicity of strontium-90 in humans following inhalation exposure were not
available.
3.2.1.2. Animal
The D50 (LD50) for the rat from inhalation of strontium-90 in fused aluminosilicate particles
corresponds to 1200 kBq/g lung or a 900 day dose of 370 Gy (37,000 rad) (Scott et al., 1987). The cause
of death was radiation pneumonitis.
Administration of strontium-90 (90SrCl2) to beagle dogs by a single inhalation exposure resulted in early
deaths (6 of 66 dogs within 32 days) which were attributed to acute bone marrow destruction manifest by
a profound pancytopenia (Gillett et al., 1987; NCRP, 1991). Septicemia, secondary to leukopenia, was
the immediate cause of death; hemorrhaging was a contributing factor. The authors calculated "long-term
body burdens" of 17 x 106 to 41 x 106 Bq (1.7 x 106 to 4.1 x 106 Bq/kg body weight).
3.2.2. Subchronic Toxicity
Information on the subchronic toxicity of strontium-90 in humans or animals following inhalation
exposure was not available.
3.2.3. Chronic Toxicity
3.2.3.1. Human
Information on the chronic toxicity of strontium-90 in humans or animals following inhalation exposure
was not available.
3.2.3.2. Animal
In a study of the early effects of inhaled radionuclides, a total of 280 male and female F344/CRL rats
were exposed by inhalation to strontium-90 in equilibrium with its daughter radionuclide, yttrium-90 (Scott
et al., 1987). The radionuclides were delivered within an insoluble fused aluminosilicate particle matrix
that has a long retention period in the lung. There were three exposure groups (low, medium, and high)
and one control group; initial lung burdens ranged from 0 to 3000 kBq/g of lung. Subgroups within each
group were monitored 1.5 years postexposure for body weight, mortality (40 animals/treatment group),
hematological measurements (10 animals/treatment group), and pulmonary function (20 animals/treatment
group). Reductions in weight gain did not occur in groups where a majority of animals survived. The
major cause of death was radiation pneumonitis and pulmonary fibrosis with a peak in the distribution of
deaths between 140 and 180 days after exposure. The dose lethal to 50% of animals succumbing to
radiation pneumonitis was 370 Gy. Total lymphocyte counts were reduced in exposed animals (data not
given). Nonlethal doses as low as 65% of the median lethal dose of 370 Gy caused impaired pulmonary
function observable as late as 1.5 years after exposure.
3.2.4. Developmental and Reproductive Toxicity
Information on the developmental and reproductive toxicity of strontium-90 in humans or animals
following inhalation exposure was not available.
3.2.5. Reference Concentration
The EPA (1994) has not calculated subchronic or chronic inhalation reference concentrations (RfC)
for radionuclides.
3.3. OTHER ROUTES OF EXPOSURE
No data on noncarcinogenic effects following administration by other routes of exposure were
available.
3.4. TARGET ORGANS/CRITICAL EFFECTS
Noncarcinogenic effects were noted on target organs following administration of life-shortening doses.
3.4.1. Oral Exposures
GI tract: Oral administration at high doses resulted in death from radiation-induced hemorrhagic
syndrome in miniature swine.
Bone: Translocation to the bone leads to damage to the hematopoietic system (from chronic
irradiation of the bone) resulting in early deaths (at high doses) from bone marrow hypoplasia (aplastic
anemia) among other bone marrow dyscrasias.
3.4.2 Inhalation Exposures
Lung: Administration of insoluble strontium-90 compounds to rats by the inhalation route results in
radiation pneumonitis and lung fibrosis.
Bone: Translocation to the bone leads to destruction of the marrow cellular elements.
4. CARCINOGENICITY
The carcinogenicity of strontium-90 has been studied in mice, rats, beagle dogs, miniature swine, and
monkeys. Single oral, inhalation, or intravenous administration results in high incidences of neoplasia of
bone and bone-related tissues. The most frequently observed neoplasms have been osteosarcomas,
hemangiosarcomas, fibrosarcomas, and epidermoid carcinomas. Chronic ingestion in beagle dogs and
miniature swine produced a high incidence of myeloproliferative disease, including frank leukemia (Hobbs
and McClellan, 1986). Target organs for strontium-90 are the red bone marrow because of its relevance
to the induction of leukemia and the endosteal bone surfaces because of their relevance to the induction of
bone cancer.
In some of the following studies, doses were not calculated from exposure activities. For humans,
estimates of the average risk of fatal cancer from low linear energy transfer radiation range from
approximately 0.007 to 0.07 fatal cancers/Sv (EPA, 1989). Doses above 1 Sv are not normally associated
with radioactive contamination in the environment.
4.1. ORAL EXPOSURES
Primary bone sarcomas and myelolymphoproliferative syndrome developed in beagle dogs that were
administered strontium-90 in the diet from the onset of fetal calcification in utero to the end of the growth
period at 540 days of age (Pool et al., 1973; updated summary data in NCRP, 1991). Average daily intake
activities were 0.0, 0.03, 0.08, 0.5, 1.5, 3, 12, or 36 Ci/day (0.0, 0.1 x 104, 0.3 x 104, 1.9 x 104, 5.6
x 104, 11.1 x 104, 44.4 x 104, or 133 x 104 Bq/day). Average doses to the bone were estimated at 0, 0.38,
1.15, 6.70, 22.5, 50.4, 80.2, and 107 Gy, respectively. Deaths occurred in tumor-bearing animals at 1.5-3
years of age in the highest dose group and at 6-8 years in the groups administered 44.4 x 104 and 11.1 x
104 Bq/day (compared with 14.6 yr in the control group). Incidences of tumors in the control to highest
dose groups were 2.5% (2 of 80 dogs), 0.0% (0 of 75 dogs), 2.5% (1 of 40 dogs), 0.0% (0 of 66 dogs),
5.7% (4 of 69 dogs), 15.9% (10 of 63 dogs), 27% (17 of 63 dogs), and 53% (10 of 19 dogs), respectively.
Irradiation of the bone marrow following ingestion of 5.6 x 104 to 133 x 104 Bq/day produced effects on
the hematopoietic system, including myeloproliferative disorders; soft tissue carcinomas in tissues near the
bone were also observed above control levels in these groups. Statistical analyses were not performed.
Chronic strontium-90 ingestion in miniature swine resulted in effects on the hematopoietic system
(Clarke et al., 1972; NCRP, 1991). Experiments involving the ingestion of 0, 1, 5, 25, 125, 625, or 3100
Ci per day (0.0, 0.037 x 106, 0.185 x 106, 0.925 x 106, 4.62 x 106, 23.1 x 106, or 115 x 106 Bq/day) by
773 female miniature swine extending over three generations were conducted. Treatment for the P1
generation was initiated at 9 months of age, but treatment in the second and third generations began in
utero. Female offspring in the F1 and F2 generations were gradually raised to the treatment level of
respective dams by 6 months of age. As noted in Subsect. 3.1.3.2, the parental generation and their
offspring administered 115 x 106 Bq/day did not survive to tumor induction time. Bone sarcomas,
primarily in the skull, occurred in the groups receiving 23.1 x 106 Bq/day and 4.62 x 106 Bq/day of the
combined F1 and F2 generations but not in groups administered lower doses. The incidence in the group
fed 4.62 x 106 Bq/day was 25%, but the incidence in the group fed 23.1 x 106 Bq/day was unclear due to
deaths and discontinued feeding regimes. There appeared to be a slight increase in soft-tissue carcinomas
in groups fed <4.62 x 106 Bq/day, but statistical analyses were not performed. The primary effects from
administration of 4.62 x 106 Bq/day were pancytopenia, hematopoietic neoplasms and bone tumors; the
mean survival time was 3.5 years. Administration of 0.037 x 106 Bq/day to 0.925 x 106 Bq/day resulted
in a mean survival time of 10-11 years compared to 11 years in the control group; the primary effect was
neutropenia.
4.2. INHALATION EXPOSURES
At 12 to 14 months of age, 66 beagle dogs (weight 10 kg) of both sexes were administered a single
exposure of a 90SrCl2 aerosol and observed over their lifespan (McClellan et al., 1973; data summarized
in NCRP, 1991). Initial body burdens ranged from 3.59 x 104 to 703 x 104 Bq/kg and long-term retained
burdens (bone burdens) ranged from 1 to 120 Ci/kg (0.036 x 106 to 4.4 x 106 Bq/kg). The primary effect
among long-term survivors was an excess of bone tumors, occurring in 30 surviving dogs that received a
long-term retained burden of approximately 1.0 x 106 Bq/kg or greater. Survival times in dogs with bone
tumors ranged from 2.2 to 9.5 years post exposure, whereas those in the 0. 0.037, 0.125, and 0.185 Bq/kg
dose groups survived 11 years (mean survival of the controls was estimated by the authors at >12 yr).
Two myelomonocytic leukemias and three malignancies of tissues in the oral cavity and nasopharynx were
also observed at long-term retained burdens of <1.3 x 106 Bq/kg.
4.3. OTHER ROUTES OF EXPOSURE
Forty male and female Rhesus monkeys aged 2 to 12 years and weighing 2.6 to 9.4 kg were
administered a single injection of strontium-90 (form not given) at a level of 0.13 x 106 to 6.21 x 106 Bq
(0.018 x 106 to 0.14 x 106 Bq/kg) (NCRP, 1991). Strontium retention was followed over a 20-year period.
No biological effects attributable to strontium-90 administration were observed. No further details were
available.
Seven adult monkeys were administered 1.85 x 106 or 3.7 x 106 of strontium-90 (form not given) by
gavage in a single exposure (NCRP, 1991). Two monkeys developed bone sarcoma, one occurring at
36 months (chondrosarcoma) and one occurring at 45 months (osteosarcoma) after administration. For the
animal dying at 45 months with osteosarcoma, the skeletal dose at the start of tumor growth was calculated
to be 25 Gy, and the skeletal dose at death was calculated to be 34 Gy.
Eighty-seven young adult beagle dogs, in groups of 12-14 animals, were administered a single
intravenous injection of strontium-90 at activity levels of 0, 2.11 x 104, 6.36 x 104, 12.8 x 104, 40.0 x 104,
121 x 104, 235 x 104, or 362 x 104 Bq/kg (Mays and Finkel, 1980; revised dosimetry in NCRP, 1991).
The control population consisted of 125 beagles of which 57 were sham injected. The most prominent
effect in the treated animals was bone sarcoma (neoplasia of the soft tissues near bone in the
oronasopharynx and paranasal sinuses). Bone marrow dysplasia was observed at lower but significant
incidences (p<0.05). Bone sarcomas were not observed in animals receiving doses of 12.8 x 104 Bq or
lower (average skeletal dose one year before death of 6 Gy or lower). Incidences in the 40.0 x 104, 121
x 104, 235 x 104, and 365 x 104 dose groups were 8.3, 16.7, 66.7, and 57.1%, respectively; absorbed
doses were estimated by the authors to be 21.7, 60.2, 71.4, and 85.2 Gy, respectively. Blood dysplasia
was observed in 5 dogs in the four highest dose groups; malignant soft tissue tumors were observed in the
three highest dose groups. Soft-tissue neoplasia was observed at lower doses. Average times to death were
shortened in the three highest dose groups, 10, 5.8, and 3.4 years, respectively, compared with an average
life span in the control group of 11.5 years. The average times to death in the four lower dose groups
ranged from 11 to 13 years.
Groups of male and female CBA mice were administered a single intraperitoneal injection of 0.8 Ci
(3 x 104 Bq) (males) or 0.4 Ci (1.5 x 104 Bq) (females) strontium-90 in the form of 90Sr(NO3)2 (Nilsson
and Ronnback, 1973). Bone tumors were recorded but not classified histologically. Among male mice
that survived to development of the first tumor, there was a mean number of 2.3 bone tumors per mouse
with a mean induction time of 316 days. Tumor incidence in males was 88% (99/113 animals). Among
female mice that survived to the development of the first tumor, there was a mean number of 2.0 bone
tumors per mouse with a mean induction time of 379 days. Tumor incidence in females was 80% (75/94
animals). Treatment with estrogenic hormones increased the incidence of bone tumors in both male and
female mice. No tumors were present in mice treated with only estrogen.
4.4. EPA WEIGHT-OF-EVIDENCE
The EPA classifies all radionuclides as Group A carcinogens based on their property of emitting
ionizing radiation and on the weight of evidence provided by epidemiological studies of radiation-induced
tumors in humans (EPA, 1994).
The EPA has set the National Interim Primary Drinking Water Regulations for radioactivity due to beta
particle and photon emitters in community water systems at 4 mrem/year (56FR 33050; July 18, 1991).
4.5. CARCINOGENICITY SLOPE FACTORS
The EPA (1994) has calculated slope factors for strontium-90 for lifetime excess total cancer risk per
unit intake of exposure for ingestion, inhalation, and external exposure:
Ingestion (risk/Bq): 8.9E-10
Inhalation (risk/Bq): 1.5E-09
External exposure (risk/yr per Bq/g soil): 0.0E+00
The combined slope factors (risk) from strontium-90 plus its decay product, yttrium-90, have also been
calculated:
Ingestion (risk/Bq): 9.7E-10
Inhalation (risk/Bq): 1.7E-09
External exposure (risk/yr per Bq/g soil): 0.0E+00
5. REFERENCES
Bryant, F.J. and J.F. Loutit. 1964. The entry of strontium-90 into human bone. Proc. Royal Soc.
London, Ser. B 159:449-465.
Clarke, W.J., R.H. Busch, P.L. Hackett, et al. 1972. Strontium-90 effects in swine: A summary to date.
In: Biomedical Implications of Radiostrontium Exposure, M. Goldman and L.K. Bustad, eds. CONF-710201; National Technical Information Service, Springfield, Virginia. pp. 242-258.
Gillett, N.A., B.A. Muggenburg, B.B. Boecker, et al. 1987. Single inhalation exposure to 90SrCl2 in the
beagle dog: Hematological effects. Radiat. Res. 110:267-288.
Hamilton, J.G. 1947. The metabolism of fission products and heaviest elements. Radiology 49:325-343.
Hardy, E.P., Jr., J. Rivera and R.A. Conrad. 1965. Cesium-137 and strontium-90 retention following
an acute ingestion of Rongelap food. In: Radioactive Fallout from Nuclear Weapons Tests, AEC
Symposium Series 5, A.W. Klement, Ed. CONF-765; National Technical Information Service,
Springfield, Virginia, pp. 743-757.
Hobbs, C.H. and R.O. McClellan. 1986. Chapter 21: Toxic effects of radiation and radioactive materials.
In: Casarett and Doull's Toxicology: The Basic Science of Poisons, C.D. Klaassen et al., eds.
Macmillan Publishing Co., Inc., New York. pp. 669-705.
ICRP. 1979. International Commission on Radiological Protection. Limits for Intakes of Radionuclides
by Workers, ICRP Publication 30. Pergamon Press, Oxford.
Mays, C.W. and M.P. Finkel. 1980. RBE of alpha particles vs. beta particles in bone sarcoma induction.
Fifth International Congress of the IRPA, Vol. II. (Cited in NCRP, 1991).
McClellan, R.O., B.B. Boecker, R.K. Jones, et al. 1972. Toxicity of inhaled radiostrontium in
experimental animals. In: Biomedical Implications of Radiostrontium Exposure, M. Goldman and L.K.
Bustad, eds. CONF-710201; National Technical Information Service, Springfield, Virginia. p. 149-167.
McClellan, R.O., S.A. Benjamin, B.B. Boecker, et al. 1973. Neoplasms in dogs that inhaled 90SrCl2.
In: Radionuclide Carcinogenesis, C.L. Sanders et al., eds. CONF-720505; National Technical
Information Service, Springfield, Virginia. pp. 215-232.
NCRP. 1991. National Council on Radiation Protection and Measurements. Some Aspects of Strontium
Radiobiology. NCRP, Bethesda, Maryland.
Nilsson, A. and C. Ronnback. 1973. Carcinogenic effect in bone of radiostrontium and estrogenic
hormones. In: Radionuclide Carcinogenesis, C.L. Sanders et al., eds. CONF-720505; National
Technical Information Service, Springfield, Virginia. pp. 154-158.
Papworth, D.G. and J. Vennart. 1984. The uptake and turnover of 90Sr in the human skeleton. Phys.
Med. Biol. 29:1045-1061.
Pool, R.R., J.R. Williams, M. Goldman and L. Rosenblatt. 1972. Comparison of bone-tumor sites in
beagles continually fed 90Sr or injected with 226Ra as a means of scaling risk to humans. In:
Radionuclide Carcinogenesis, C.L. Sanders et al., eds. CONF-720505; National Technical
Information Service, Springfield, Virginia. pp. 475-487.
Raabe, O.G., S.A. Book, N.J. Parks, C.E. Chrisp, and M. Goldman. 1981. Lifetime studies of 226Ra and
90Sr toxicity in beagles - A status report. Radiat. Res. 86:515-528.
Scott, B.R., F.F. Hahn, G.J. Newton, et al. 1987. Experimental Studies of the Early Effects of Inhaled
Beta-Emitting Radionuclides for Nuclear Accident Assessment. NUREG/CR-5025, U.S. Nuclear
Regulatory Commission, Washington, DC.
U. S. Environmental Protection Agency (EPA). 1988. Drinking Water Criteria Document for Stable
Strontium. ECAO-CIN-DO11, Environmental Criteria and Assessment Office, Cincinnati, OH.
U. S. Environmental Protection Agency (EPA). 1989. Risk Assessment Guidance for Superfund: Human
Health Evaluation Manual: Part A. Office of Emergency and Remedial Response, Washington, DC.
U. S. Environmental Protection Agency (EPA). 1994. Health Effects Assessment Summary Tables.
Annual FY-1994. Prepared by the Office of Health and Environmental Assessment, Environmental
Criteria and Assessment Office, Cincinnati, OH, for the Office of Emergency and Remedial Response,
Washington, DC.
1. A Curie is defined as 3.7 x 1010 nuclear disintegrations per second; 1 Ci = 3.7 x 1010 Bq. A Bequerel
is defined as one nuclear disintegration per second; 1 Bq = 2.7 x 10-11 Ci or 27 pCi.
2. A radiation absorbed dose of one Gray = 100 rad; a dose equivalent of one Sievert = 100 rem.
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