43
14 to 17 support the values of “background” concentrations chosen in these calculations. Measurements
are in progress to estimate further the *°*Ra content
and also to assess the emanation rate of the ***Rn
daughter from the wood, which determines the fraction
of the “28Ra forming 7!°Pb in the wood.
since these results indicate that the circulation of
Aiba
“ame?
(AYO wéhyi9d) Gdoiz
lend in heartwood is small after a certain time, if any
‘significant portion of the lead was derived either from
direct atmospheric uptake or from increased concentrition in the soil from atmospheric fallout, the wood
might show the effects of changes in exposure over the
years, Some measurements of the stable Pb concentra-
| tion in these trees made by Dr. Ter Haar are shown in
{ Ol
Figure 38.4) Although environmental lead may be increasing, the few points available indicate a lower con-
+ centration of stable lead in trees in more recent times.
ee
| This effect may be caused by the weighting of the data
hoo
which because of metabolic activity may be unrepre} sentative of the remainder of the wood. Also, as the
tree ages and roots become deeper, the availability to
'b specific
wer curve
by the low values in the outer rings (near ¢ = Q),
the trees of stable lead may decrease relative to that of
219P}, Thus, mereased lead in the atmosphere and soil
4% ™Pb/g' over the years may notbe available to the wood, and
so the effects are not seen in this type of measurement.
Both the ?*6Ra and stable lead data are consistent
with those of the 72°Pb (7*°Po) in that the concentrations In the hickory are much higher than in the other
woods by factors of 2 to 10. The reasons for these vari-
, ations are unknown, but they could be caused by basic
metabolic differences, the higher ash content of the
hickory, or to differing environmental levels to which
| our particular specimens were exposed. The latter case
/ secms unlikely since one would not expect all three
materials to merease simultaneously.
In summary, the decrease of the 21°Pb concentration
with a 21.4-year half-life shows there is little circula-
tion of lead in hickory heartwood more than 20 years
oll, while in oak thereis little circulation even in wood
less than 5 years old (but with less certainty). The
uncertamties in these conclusions are caused by the
low concentration of 71°Pb and the presence of *°*Ra
in the oaks. The 74°Po does not appear to circulate,
either. Decreased, rather than increased, concentration
of stable lead in recent times is evidenced by these
data. However, more detailed measurements are neces-
sary to check this point.
REFERENCES
1. Crozaz, G. and Langway, C. C., Jr. Dating Greenland
Firn-Ice Cores with Pb-210. Harth and Planetary Science
Letters 1, 194-196 (1966).
2. Keisch, B., Feller, R. L., Levine, A. 8., and Edwards, R.
R. Dating and Authenticating Works of Art by Measurement of Natural Alpha Emitters. Science 165, 1238-1241
(1967).
,
3. Keisch, B. Dating Works of Art through the Natural
Radioactivity: Improvements and Applications. Science
160, 413-414 (1968).
4, Ter Haar, G. L., Holtzman, R. B., and Lucas, H. F., Jr.
Lead and Lead-210 in Rainwater. Nature 216, 353-355
(1967).
5. Murozumi, H., Chow, T. J., and Patterson, C. Concentrations of Common Lead in Greenland Snows. U.8. Atomic
Energy Commission Report NYO-3450-1 (1966), pp.
213-215.
6. Jaworowski, Z. Stable Lead in Fossil Bones. Nature 217,
152-153 (1968).
7. Ault, W. U., Senechal, R. G., and Erlebach, W. E. Isotopic
Composition as a Natural Tracer of Lead in Man’s
Environment. Paper presented at American Chemical
Society Meeting, Minneapolis, Minnesota, April 16,
1969.
8. Stewart, C. M. Excretion and Heartwood Formation in
Living Trees. Science 153, 1008-1074 (1966).
9. Adams, W. H., Christenson, C. W., and Fowler, E. B.
Relationship of Soil, Plant and Radionuclide. Radiocactive Fallout, Soils, Planis, Foods, Man, Ed. Eric. B.
Fowler.
Elsevier Publishing Company,
1965, pp. 46-49.
Amsterdam,
10. Holtzman, R. B. Measurement of the Natural Contents
of RalD (Pb29) and RaF (Po?) in Human Bone—Estimates of Whole-Body Burdens. Health Phys. 9, 385-400
(1963).
11. Assoc. of Official Agricultural Chemists. Official Methods of
Analysis of the Association of Official Agricultural Chemists.
Washington, D. C., 1965, pp. 369-370.
12. Ter Haar, G. L., The Ethyl Corporation. Personal communication.
THE CONCENTRATION OF LEAD IN HUMAN BONE
R. B. Holteman, H. F. Lucas, Jr., and F. H. Ilcewicz
The concentration of lead in bone from humans whose ages
minged from newborn to 85 years was found to increase with
wer ut a rate of 0.6 4g (g ash)? yr? and to be 8.7 ug (g ash)*
1" Lirth. These results corroborate previous reports of increases
ead in °
"P to age 30, and they show a continuing and similar increase
nN the group over 35 years of age. This rate represents an in-
"tase in skeletal content of dbout 4 »g/day, which is about 1%
of the daily intake. The biological half-life of lead implied
from the data from this study ranges from 70 to 90 years and
is longer than previously reported. The concentrations of lead
in the group over 30 apparently consisted of two normallydistributed populations, which mayreflect differences in the
cigarette smoking habits of the subjects. Further studies are
required to more accurately evaluate the effects of smoking