-12 -
that of any other food stuff although other foods may have a higher
Sr-90 to Ca ratio.
As a matter of fact, cow's milk contains less
strontium per gram of calcium than do the vegetables which comprise the balance of our calcium inteke.
This is because, as
noted by other speakers, biological processes in general tend to
discriminate against strontium.
Milk contains less strontium
per grem of calcium because the calcium has passed through two
biological processes.
The strontiim has passed through the
vegetable and then through the cow.
Thus the Sr-90 has been
selectively eliminated by two stages in the case of milk and
only one stage in the case of a vegetable.
Nevertheless, milk
seems to be the best possible index to human exposure to Sr-90
because it is the source of60-902df the calcium in the skeletons
of American adults.
Moreover, it is a material which is relatively
easy to sample and the samples represent the pooling of milk from
large geographical areas.
Monthly enalyses of milk samples are availeble from six major
milk sheds in the United States, for periods ranging from one to
four years.
The sampling procedures have been designed to follow
the exposure level of the human populetion at the location rather
than to follow an individuel ferm or even en individual processing plant.
The determination of Sr-90 in milk is e relatively simple
procedure, since the cow discriminates sharply against other
fission products.
The main analytical problem is the seperation
of Sr-90 from the large amount of calciim present.
bPFARCH
6)