Table 2.
aeAyoan ee
bw
PNR
He 8] ie ha ot
Activity
‘residue
ue.fem.
30 days)
LONG-LIVED a-ACTIVITIES IX DRINKING WATERS AND IN
THEIR RESIDUES
Type of water
No, of
samples
Spa
9
pf
pp
GAO e
wwoeng
Ke
Cet
rw
=
were
st!
NO
FPREOorR
063-0
ee
Se
046
0-37
mean
14:6
12
O11
O-34
32
0-6
15
0-8
0-02
0:18)
13-1
0-4
3-2
1
2
St. Ives
Penzance
Camborne
Penzance
Cambome
2
3
1
1
2
2
3
198:0
8-4
6-8
81:3
ws-4
37
a-ACTIVITIES IN “yc./LITRE
Short-lived
a-activity due
to radium-224|
(Th XY) and
daughters
at time of
sampling
Bath Spa
Bristol
2:2
14
min,
1:7
11
Helston
Helston
9-4
2-9
in gpe./gm.
max.
36:4
32
St. Ives
Sop wan
48-5
mean|
23°1
Borehole (in
chalk)
Surface
chalk}
Llandrindod Spa
Wore censh
|
min.
1°8
10
9
Specimen
| TH] Eee rsworsts | | eerscorsrocens |
Od! 6044s ea
Sdoor rower
in zuc./litre
max.
Cornish
Borehole (not
Table 3.
1 |
Activity of water | Activity of residuc
Long-lived
a-activity
after 30 days
a-Activity due
to radon-222
and daughters
at time of
sampling
30-0
26°32
77
2:9
37-0
1°8
1,000-2,000
600-700
0:7
Us)
0°3
0-3
Q-2
1-0
0-9
0-6
1-0
0-5
9,000-10,000
500-600
4,000-5,000
100-200
4,000-5,600
21-0
2:8
2-4
9-4
2:2
4:1
200-300
9,000-10,000
100-200
~ 600
found for surface waters or waters derived from
boreholes.
The Cornish specimens, although having a mean
level of activity lower than the spa waters by a
factor of 12, are still approximately ten times higher
in activity than the mean values of chalk borehole
or surface waters.
The mineral contents of the
Cornish waters are relatively low; but the mineral
matter has specific activitic s ranging up to 92 wue./gm.,
doubtless associated with the known deposits of
uranium and radium in parts of that county.
Next in descending order of long-lived «-activity
come the drinking waters derived from boreholes in
geological strata other than chalk. The mean activity
of this group is only slightly lower than that found
for the Cornish waters, and this would appear to be
due to their higher mean contents of mineral matter,
400 parts per million compared with 90 for the
Cornish samples.
Waters derived from boreholes in chalk have still
lower activities with a mean level down by a factor
of 4 below those derived from boreholes in other
strata. It is interesting to note that the mean value
found for the a-activities of their mineral residues
(1-5 uue./gm.) is very close to that reported previously
by us!? for the a-activity of chalk specimens.
The least-active group .- waters observed by us
are surface waters from rivers, lakes and reservoirs,
even though a number are derived from areas of
Pre-Cambrian or granitic rock formations.
Their
mean mineral content is 100 parts per million and
their mean long-lived «-activity is lower by a factor
of 12 than the Cornish waters.
There was, of course, the possibility that a substantial fraction of the observed long-lived a-activity
was due to uranium-238.
However, measurements
of uranium contents of a number of waters in Great
Britain have been reported by Smith and Chandler™,
who found values of less than 1 ugm. (0-34 uwyuec.) per
litre in 124 out of a total of 162 specimens examined.
Waters with values higher than this figure were, with
one exception, not drinking waters.
Our own
observations on the growth of a-activity of the
residues during the 30 days following evaporation
leave little doubt that also in our series of waters the
content of radium-226 is several times higher than
the activity due to uranium-238.
Moreover, investigations of the uranium contents
of North American river waters by Rona and Urry"
show a ratio of radium-226 to uranium-238 of
approximately 4:1.’ In another study of the
activities of ground waters in the United States,
Scott and Barker? also observed levels of radium-226
in excess of those due to uranium-238.
These results are borne out by the chemical
estimations made by us of the uranium-238 contents
of a number of our more active residues. These con-
firm the presence of uranium at levels of activity
which represent only a small fraction of the total
long-lived a-activity in each case. It is to be noted
that even if the radium/uranium ratio is as low as
4:1, then the «-activity due to radium-226 and its
daughters will still comprise 90 per cent of the total
long-lived activity contributed by members of the
uranium series.
In respect of the thorium series, Stehney”? found no
evidence of long-lived members such as thorium-228
in his studies of American potable waters, while Rona
and Urry!! assessed the ratio of thorium-230 (ionium230) to uranium-238 in North American river waters
as being a very small fraction of unity. The very low
levels of long-lived’ «-activity due ‘to the thorium
series found by us in the present investigation agree
with the findings of these observers.
In the absence, therefore, of either uranium-238 or
thorium-228 at levels of activity comparable with
those due to radium-226, the long-lived «-activities
listed in Table 1 may be regarded as due to radium226 and its «-emitting daughters, radon-222, polonium-218 and polonium-214, existing in radioactive
equilibrium. The radium-226 content of any particular specimen is therefore taken as one quarter of
the long-lived activity given in column 2 of Table 1.
It
will be
seen,
therefore,
that
the
contents
of
radium-226 observed in this series of waters cover a
range of 2,400-1, namely, from 0-005 uuc./litre to
12-1 wye./litre.
If we exclude the spa waters and assume a daily
intake of 2-5 litres per head of the population of
Britain!*, then the daily intakes of radium-226 from
water alone cover a range of almost 500-1, namely,
from 0-013 pyc. to 5-9 puc. In terms of long-lived
a-activity the intakes from water range from 0:05 to
approximately 24 uuc. per head per day.
So far we have considered only the long-lived
a-activity due to the presence of radium-226 andits
daughters.
It will, however, be seen from Table 1
that a number of the waters possess relai'vely very
high contents of radon-222 and its daughters at the
tune of sampling. This is especially the case in the
Cornish specimens where the «-activities due to
radon-222 and its daughters, polonitum-218 and
polonium-214, range up to 10,000 wuc./litre. On the
basis of a daily intake of 2-5 litres the ingested
x-activity can therefore be as high as 25,000 uuc. a
day, that is, approximately 8,000 uuc. of radon and
of each of ita two short-lived «-emitting daughters.
In any attempt to assess the possible significance of
these materials we are faced with an almost complete
lack of data concerning their metabolism in the
human body. Meyer!’ in a elassical series of experimonts in the late 1920's came to the conclusion that