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