Tumors arising adjacent to bone have been noted in several species treat!
with 90Sr.
In mice, squamous cel] carcinomas were reported to originate in
the hard palate and sebaceous gland of the external auditory meatus (Nilsson,
1972).
Squamous cell carcinomas were also reported in the maxillary sinus in
rats (Moskalev et al., 1972) and in the lining of fnternal and external ear in
rabbits (Vaughan and Williamson, 1969).
Squamous cel] carcinomas of the
gingiva have been found to be fmportant Jater-occurring effects in beagles
exposed to 905, (by ingestion) from prior to birth untfl 18 months of age
and observed for life (Parks et a}., 1980).
For the dogs, the gingiva! tumors
probably reflect the results of continual frradiation from 90sr in teeth
that is maintained at a high level, since teeth show a slower turnover of
90Sr than does the rest of the skeleton (Della Rosa et al., 1964).
Fortunately, too few humans have been exposed to radiostrontium at high
enough levels for the risk of neoplasia to be estimated.
Based dn radium dial
painter risks, however, Mays and Lloyd (1972) estimated risks from 99Sr.
Their best estimates for the 50 yr risk to an individual for bone sarcoma fron
one rad were (1 x3) x 30-8, using a linear model, and (4 + 4) x 10-10,
using a dose-squared model.
The current ICRP (1977) estimate of risk for
90Sr-tike radiation ts 5 x 10-6 per ren.
These numbers can be canpared
with a natural incidence of about 5 x 1074,