Since many radioisotopes accumulate in hair, this tropism was investigated by comparing the radioactivity of shaved with plucked hair collected from rats at various time intervals up to 24 hrs after intravenous injection of the ecologically important radioisotopes, iodine-131, manganese-54, strontium-85, and zinc-65. The plucked hair includes the hair follicles where biochemical transformations are taking place. The data indicate a slight surge of each radioisotpe into the hair immediately after injection, a variation of content of each radionuclide in the hair, and a greater accumulation of radioactivity in plucked than in shaved hair. These results have application not only to hair as a measure of exposure to radioisotopes, but also to tissue damage and repair at the hair follicle

Flynn, A.

Fratianne, R. B.

Pories, W. J.

Strain, W. H.

English

NASA Technical Reports Server

HAIR RADIOACTIVITY AS A MEASURE OF EXPOSURE TO RADIOISOTOPES
W. H. STRAIN, W. J. PORIES, R. B. FPJ_TIANNE AND A. FLYNN
Cleveland Metropolitan General Hospital
and
Case Western Reserve University
/
AB ST RACT
Measurement of hair radioactivity appears to be a suitable method
for monitoring systemic exposure to radioisotopes and certain types of
manmade radiation. This concept has developed from a suggestion we
made in 1963 that the strontium-90 content of hair affords a nondestruc-
tive method of estimating the body burden of this radionuclide. Since
many radioisotopes accumulate in hair, this tropism has been investi-
gated by comparing the radioactivity of shaved with plucked hair col-
lected from rats at various time intervals up to 24 hrs. after intraven-
ous injection of ca 5 uCi of the ecologically important radioisotopes,
iodine-131, manganese-54, strontium-85, and zinc-65. The plucked hair
includes the hair follicles where important biochemical transformations
are taking place. The data indicate a slight surge of each radioisotope
into the hair immediately after injection, a variation of content of
each radionuclide in the hair, and a greater accumulation of radioactiv-
ity in plucked than in shaved hair. These results have application not
only to hair as a measure of exposure to radioisotopes, but also to tis-
sue damage and repair at the hair follicle.
In 1963, we (ref. l) suggested that the stron-
tium-90 content of hair provided a nondestructive
method of estimating the body burden of this ra-
dioactive fission product. Sternberg (ref. 2),
had previously noted that strontium-90 injected
in pregnant guinea pigs was distributed to hair
as well as to the embryos. Our results from stud-
ies on rats were quickly confirmed by Della Rosa
et al. (ref. 3), who investigated beagles. Their
data indicated that the strontium-90 content of
beagle hair could be used to estimate directly the
radionuclide concentration of the diet and plasma,
982
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andindirectly the remodelinglabeledportionof
the skeletons. Latein 1964,Moelleret al. (ref.
4) reportedthat the strontium-gOcontentof hu-
manhair seemedto correlatewith the levelsof
the radionuclidein thediet. Thisinitial report
wasexpandedbyMagnoet al. (ref. 5), whoshowed
that thereweresomeirregularities betweenthe
meanlevelsof strontium-90in thediet, andin
thehair collectedfromchildrenliving in five
installations participatingin U.S.PublicHealth
ServiceInstitutional DietSamplingProgram.
Theaccumulationof otherradioisotopesin the
hair of severalspecieshasbeenstudiedby vari-
ousinvestigators. Cesium-137(ref. 6) hasbeen
shownto bepresentin AlaskanEskimohair asa
result of fallout, but correlationwith bodybur-
denhasnotbeendefinitely established.Iron-59
(ref. 7), sulphur-35(ref. 8), andzinc-65(ref.
9) havealsobeenshownto accumulatein human
hair. Amongthe first radioisotopesto bestudied
in this way,wereselenium-75in doghair (ref.
I0), andiodine-131(ref. ll,12) in rat hair. Oth-
er radioisotopesinvestigatedin rat hair include
cobalt-58(ref. 13),vanadium-48(ref. 14), and
zinc-65(ref. 15,16).
Themechanismsbywhichradioisotopes,espec-
ially of traceelements,accumulatein hair and
othertissuesare importanto us. Weareinves-
tigating themetabolismof traceelementswith
radioisotopesto developnewdiagnosticprocedures,
to evaluatetissuedamagefromtoxic excesses,to
developnewtherapiesfor burnandwoundhealing,
andto studyparticulatepollutants. Accordingly,
wehaveexplicatedthetropismof variousradio-
nuclidesfor rat hair by comparingtheradioactiv-
ity of clippedwith pluckedhair at varioustime
intervals after intravenousinjection of ecologi-
cally importantradioisotopes.Thepluckedhair
includesthehair follicle whereimportantbio-
chemicaltransformationsare takingplace. The
radionuclidesemployedwereiodine-131(T/2, 8D),
manganese-54(T/2, 300D),strontium-85(T/2, 64D),
andzinc-65(T/2, 2_5D).
METHODSANDRESULTS
Theprocedureusedfor measuringthe accumula-
tion of radioisotopesin rat hair wasanelabor-
ation of apreviouslydescribedmethod(ref. 17).
Theradionuclidestudiedincludedsodiumiodide-
1-131,manganous-Mn-54chloride,strontium-Sr-85
chloride,andzinc-Zn-65chloride. Commercial
preparationsof theseradioisotopeswith high
specific activity weredilutedwith normalsaline
sothat l.O ml of eachsolutioncontainedca5
uCi. Both young adult and old retired breeder
male Sprague-Dawley rats were used, so that age
effects could be investigated. Eight rats were
injected in a tail vein with l.O ml of each radio-
isotope, and then divided into two groups of four
animals each so that adequate quantities of hair
could be harvested. Samples of hair ranging in
weight from 0.20 to 0.50 mg were plucked with
tweezers or shaved with animal clippers from the
back of each rat at intervals of 1,2,4,6,12, or 24
hrs. These hair samples were weighed to l mgm,
counted in a deep-well gamma scintillation count-
er, and the specific activity calculated. Between
intervals of sample collection, the rats were
housed individually in stainless steel cages pro-
vided with food and water ad lib. A l.O ml ali-
quot of each radioisotope solution was diluted to
lO0 ml, and l.O ml of this diluted solution was
counted simultaneously with the hair samples to
983
provideastandardthat wascorrectedfor decayto
calculateretentionof injecteddosepergramof
hair.
Theresultsareshowngraphicallyin figures
I-5, in whichthemeanvaluesandrangeof the
percentretentionof eachradioisotopepergramof
hair areplottedagainsttimeonsemilogarithmic
paper. Asis evidentfromthesegraphicrepre-
sentations,thepatternsof accumulationaresim-
ilar for all radionuclides.Thepluckedhair with
follicle alwaysretaineda higherpercentof ra-
dioisotopepergramof hair thanthe shavedhair.
Theeffect of ageis to reduceslightly therate
of accumulationof eachradioisotopein hair, as
is illustrated bythe comparisonof dataonthe
accumulationof strontium-85in shavedhair of
youngadult andold breedermalerats, in figure
5. Standarderrorsandanalysesof significance
havenotbeenincludedbecausethesevaluesprob-
ablycannotbeappliedto thehair samples,and
wouldmaskcertainpeculiarities if theywererou-
tinely used.
1311 ACCUMULATION IN HAIR
x
" l
e{ ;
m
#
i
:
/
HOURS AFTER INJECTION
Ftgu_ 1. Comparison of todtne-)31 retent$on in plucked and shaved rat
hair following intravenous injection of ca 5 .uCi of sodt_m
iodide-I-131 in nomal saline. The la_e differences between
the radioactivity of plucked and shaved hair suggest that
radtoiodtne accumulates rapidly In the hair follicleo and en-
ters the hair shaft slowly from the follicle.
54Mn ACCUMULATION IN. HAIR
I00--
t_
o_
X
e
'_lO-
¢,J
ae
HOURS AFTER INJECTION
Figure 2. Accumulation of manganese-54 in plucked vs. shaved hair, fol-
lowing intravenous injection of ca 5 jJCi of manganous-Mn-54
chloride, shows an initial slight surge of the radioisotope
into both kinds of hair.
85Sr ACCUMULATION IN HAIR
I/ISHAVE
IZ * 6 2"4
HOURS AFTER INJECTION
Figure 3. After intravenous injection of ca 5 )JCi of strontium-Sr-85
chloride into rats, plucked hair shows a surge of the radio-
isotope, but shaved hatr does not. This suggests that the
radionucllde accumulates rapidly in the hair fo111cle, and
passes slowly into the hair shaft from the follicle.
984
65ZnACCUMULATIONN HAIR
DISCUSSION
Figure 4.
IOO 1
 ,lrt..
124s 2"4
HOURS AFTER INJECTION
The accumulation of radioactivity in rat hair after intra-
venous injection of ca 5 _uCi of zinc-Zn-65 chloride is slow-
er than of the other radioisotopes, and the difference in ra-
dioactivity of plucked and shaved hair is small. Although
the rate of accumulation of zinc-65 is slow initially, hair
and hone become, and remain, the tissues with the highest
specific activity after eight days.
The curves showing the large ranges and mean
values for the accumulation of the four radionu-
clides in plucked and shaved hair bring out simi-
larities and differences. The large ranges proba-
bly relate to the mixture of hair in growing, tran-
sitional, and resting stages which are obtained by
the sampling procedure. Iodine-131, manganese-54,
and strontium-85, but not zinc-65, show a surge of
radioactivity into the hair immediately after in-
jection. This surge is followed by an ebbing out
from the hair tissue which suggests that the hair
levels reflect both the rise and fall in blood lev-
els and something about the biochemistry of the
hair follicle. There are significant differences
in the retention patterns of manganese-54 (figure
2) and strontium-85 (figure 3) between plucked and
shaved hair which indicate that the rate of uptake
is much greater for strontium-85 than for mangan-
ese-54. As shown by the differences in the curves
85Sr ACCUMULATION IN HAIR (PLUCKED)
IOO--
O
x
L
_m
G.
IO.
YOUNG MALES
HOURS AFTER INJECTION
Figure 5. Comparison of uptake of strontiom-85 in plucked hair from
young adults and old retired male breeder rats indicates a
faster rate of accumulation of radioisotope in the hair by
the younger animals.
for the radioactivity of plucked and shaved hair
in figure l, iodine-131 seems to accumulate rapid-
ly in the hair follicle and is then slowly trans-
ferred to the hair shaft. Zinc-65, in contrast,
enters the hair follicle less rapidly than the oth-
er radioisotopes, and, apparently, is transferred
rapidly to the hair itself, as shown in figure 4.
The absence of a surge and ebb response may be re-
lated to the information of stable ligands of zinc
with the sulfhydryl groups which are abundant in
hair.
The effect of age on the uptake of radioiso-
topes is brought out in figure 5 which shows a
comparison of uptake of strontium-85 by the hair
of younger adult with that of old retired breeder
male rats. Strontium-85 is particularly suitable
985
for this comparison since it is the only radionu-
clide of the four which seems to be transferred
easily from hair follicle to hair shaft. As is
evident from the two curves, the accumulation of
strontium-85 is much less in the hair of the older
than of the younger animals.
Hair growth proceeds through three stages des-
ignated as anagenesis, catagenesis, and telogene-
sis (ref. i_ T, _n_gen_is there is active
growth of hair from the follicle, but there is
little information on the biomechanisms for pro-
ducing keratin, the protein of hair which has such
a high sulfur content. Keratin synthesis presuma-
bly takes place in the hair follicle, and incorpor-
ation of labeled sulfur amino acids, such as cys-
tine-S-35, in hair is so prompt that injection of
small amounts of this radiolabeled amino acid into
an animal provides a way of measuring hair growth
(ref. 19). The incorporation of most inorganic
elements in hair is usually explained as an excre-
tion, but there is no real information on possible
mechanisms of the excretion. Presumably, the ex-
cretion takes place in the hair follicle, where
some of these elements from ligands with sulfhydryl
and other chelating groupings of keratin. The
iodine content of hair, however, is the highest of
any body tissue other than thyroid, and, apparent-
ly, the iodine is present entirely as inorganic
iodide (ref. ll,12).
Determi nation of hair radi oacti vi ty has poten-
tial as a method of diagnosing inadvertent exposure
to radioisotopes or radiation which produces radio-
isotopes in the body (ref. 20,21). Additional
investigations are needed to establish the best
methods of sampling and handling hair and related
tissues, and of developing statistical relation-
ship. Statistical analysis does not seem appro-
priate for the present studies because of the short
cycle of hair growth in the rat of about 28 days.
It is difficult to distinquish the stage of a
cycle without a biopsy of the skin which would
invalidate further work. Since the hair cycle is
very much longer in man, as much as three years,
and some head hairs persist for many years, hair
analysis seems much more appropriate for man.
Exposure to high levels of radionuclides usu-
ally produces burns and traumatic injuries. The
specialized tissues of the hair follicle and seba-
ceous glands are stimulated by injury to form
migrating epithelium which will cover the injured
surface (ref. 22). Since we (ref. 23) and others
(ref. 24,25) have found that oral zinc therapy
promotes healing of burns and wounds in man, there
is need for an understanding of the biochemistry
of hair follicles and hair formation. According-
ly, investigations on the accumulation of stable
and radioactive forms Of the elements in hair may
provide additional information for the repair of
burns, trauma, and critical injuries. These stud-
ies are sorely needed because of the lack of pro-
grams to furnish such basic information.
986
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988


Hair radioactivity as a measure of exposure to radioisotopes

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