International Journal of Applied Radiation and Isotopes, 1975, VoL 26, pp. 595-599. Pergamon Press. Printed in Northern Ireland

Uptake of Trace Elements in Human Hair by Anion Exchange E. S T E I N N E S Institutt for Atomenergi, Isotope Laboratories, Kjeller, Norway (P~cdved 24 March 1975)

The 8orption of some trace elements to human hair is studied by means of radioactive tracen. Experiments with SSFe, e~Cu, aZn, V2Ga and USCd in HCI media show a great similarity between human hair and Dowex 1- × 10, indicating that the hair acts as a strongly basic anion exchanger. A corresponding similarity with strong cation exchangers is not found. Specific sorption of trace elements seems to be of little use in hair identification studies. INTRODUCTION

Dtremo the last decade considerable attention has been paid to the study of trace element concentrations in h u m a n hair because of the potential use of such data as evidence in crime detection. Since the rather optimistic report of JERws et al. tl) indicating that trace element distribution patterns in human hair determined by instrumental neutron activation analysis might be used for identification of individuals, a great n u m b e r of investigations have been carried out in this field, some of which have been quite extensive. (~'s) Most of these investigations were concentrated on trace element determinations and interpretation of analytical data, with less regard to the study of the different processes by which trace elements m a y be incorporated in hair. Clearly the use of trace element data to identify individuals might have a greater chance of success if only trace elements supplied from the body could be measured. In order to achieve this, it would be necessary to find a cleaning procedure that was capable of removing efficiently the fraction of trace elements introduced through the surface of the hair, without altering the fraction taken up through the root. A variety of washing procedures have been proposed in the literature, but very few systematic studies of human hair regarding the adsorption and desorption of trace elements have appeared. In a work by VAN DEN BERO et al. (4) the sorption behaviour of some trace elements with regard to human hair was studied. It was shown that certain elements (Cu, Zn) could be taken

up in high concentrations from fairly dilute solutions, whereas the uptake of other elements (Na, Cr, Mn, As) was less extensive. Moreover the mobility of different ions in the hair showed appreciable differences. O n the basis of that work the authors suggested that hair might be considered as a kind of ion exchanger, but they did not try to identify the actual mechanism involved. Furthermore, they raised the question whether an identification of hair might be based on individual differences in maximum absorption capacity of different ions instead of the concentrations of these ions present in the hair. In the work reported in the present paper, radiotracer experiments were performed in order to see what the possible ion exchange processes occurring in the hair might be. A limited number of experiments concerning the uptake of trace elements to hair from different persons were also carried out, in order to test the feasibility of hair identification based on individual differences in absorption properties. EXPERIMENTAL

PROCEDURE

Hair samples of 5-10 mg were used for the sorption experiments. Before use the hair was cleaned by contacting for a few minutes at room temperature with respectively distilled w a t e r methanol/aceton(l : 1)-distilled water, and subsequently drying with tissue paper. The hair sample was then placed in contact for a preset length of time with 20 ml of sorption solution containing radioactive tracer of the element under investigation. The amount of tracer added was so adjusted that the element

595

E. S ~ . s

596

concentration in the solution amounted to about 50 ppm. After the sorption period, the hair was dried with tissue paper, and the gammaactivity of the radioisotope in question was measured by means of a 3 × 3 in. NaI(TI) crystal connected to a y-spectrometer. After the activity measurement the hair was weighed after drying for 10 rain at 110°C. The following radiotracers were used in the experiments: 65Zn, " F e , ~=Ga, 11~Cd, e4Cu, Z~°La.

behaviour include Cd, Zn, Fe, Ga and Cu. Distribution coefficients in the system Dowex 1- × 10/HC1 have been published by KRAUS and NSLSON.(5) The maximum value of the distribution coefficient and the HCI concentration at which this maximum occurs, is somewhat different for the five elements in question. Similar distribution curves for human hair were obtained by placing hair samples from one person in contact with radiotracers of the five elements in solutions of varying HCI concentraION EXCHANGE P R O P E R T I E S tion. A contact time of 20 hr was used. The OF HAIR results of this experiment, expressed in terms of The study of possible ion exchange properties adsorbed activity/mg hair, are shown in Fig. 1. of human hair was carried out by comparison The curves obtained are very similar to those with a strongly basic anion exchanger and a reported for Dowex 1 - × 10. 6sZn and zxsCd strongly acidic cation exchanger respectively. show a steep rise in adsorption at HC1 concenElements showing very characteristic sorption trations below 1 M, as observed for these elements properties with the synthetic resin in a particular in the case of the anion exchanger. The curves solution system were tested with hair samples for Ga and Fe exhibit the same trend as those of in the same system, and the distribution curves Dowex I - × I0 for Fe(III) and Ga, showing an thus obtained were compared with those of the increase of more than two orders of magnitude in the region 1-9 M HCI. 64Cu shows an insynthetic resin. crease in the same concentration region, but Anion exchange much less pronounced than in the case of Fe(III) Some of the most characteristic distribution and Ga, which again corresponds well to the curves with strong anion exchangers are ob- trend evident from the Dowex 1 - × I0 curves. tained in chioridc solutions, where a number of T h e large increase in adsorption with increasing metal cations m a y show very high distribution HC1 concentration was verified by similar excoefficients with the resin duc to the formation periments with hair from other persons. T h e results indicate that anions are adsorbed of negatively charged chloride complexes. For some of these elements the distribution coeffi- to hair by a mechanism similar to that governing the exchange process on a strongly basic anion cient shows a drop of several orders of magnitude as the chloride concentration is reduced by a exchange resin such as Dowex-1. Probably the relativcly small factor. Elements showing this anion exchange capability of hair is somehow

6~Cu

10

72C~

59~

11~Cd

65Zn

/ ~ ~.~

~ ~ty

~ I of He;

~ ~ -~

Fro. 1. Distribution of Cu(II), Ga(III), Fe(III), Zn(II) and Cd(II) between human hair and HCI solutions of variable concentration, studied by means of radiotracers.

Uptake of trace elementsin human hair by anion exchange

597

associated with amino groups present in the hair matrix.

T ~ u z 1. Adsorption of SSZn to hair from different individuals from 3 M HC.d. Contact time: 1 hr

Cation exd~age T h e search for cation exchange properties of hair was done by looking for similarity with a strongly acidic cation exchanger, using a4°La tracer. Lanthanium is strongly adsorbed to a cation exchange resin of this type from solutions of low and moderate acidity. O n Dowex 50- × 8, for example, a distribution coefficient of > 1 0 s is observed for La s+ at 0.I M HCI, decreasing to 10.4 at 4.0 M HC1 (6). Sorption experiments were carried out for 20 hr with solutions of the following HC1 molarities: 0, 0"1, 0.2, 0.5, 1.0, 2-0, 4.0, 8.0. T h e amount of 14°La tracer adsorbed per mg of hair was found to bc very low compared to the total amount added, and no significant differences were found with increasing hydrogen ion concentration. From this experiment it seemed probable that human hair has a very limited cation exchange capacity, and the experiments along this line were discontinued.

Initial run New run Activity Person SexAge Hair counts/ Relative Relative No. colour nag hair activity activity

H A I R I N D I V I D U A L I Z A T I O N BY ADSORPTION PROPERTIES

O n the basis of the experience gained in the study on anion exchange properties, it seemed to be a logical continuation to investigate if different types of hair show different anion exchange capacity for a given element. I f so, this might be used as a tool for hair identification, following the line of thought put forth by VAN DEN BERG et a/. {4}

Such an investigation was initiated using Zn as a test dement. Sorption experiments were carried out in 3 M HCI solution. At this HCI concentration, Zn has reached its maximum "distribution coefficient" value (Fig. 1). In an initial run, duplicate samples of hair from eight different persons were placed in contact with 65Zn tracer in 3 M HCA for I hr. T h e results are given in Table 1. T h e experiment was repeated after six months with freshly cut hair from four of the same persons, and relative absorption values from the new run are given in Table 1 for comparison. As seen from the Table, the uptake of 65Zn was different in hair of different persons, while the reproducibility of samples taken simultane-

1

M 30 Brown

256 250 310 295 982 953

2

F

25 Blond

3

F

20 Dark blond

4

F 48 Brown/ 1060 grey 762

5

M

6

1-02 1.00

1"00

1.24 1.18 3.9 3.8

4.2

791 889

3.0 3.2 3.6

F 26 Blond

497

2'0

7

M

26 Dark

626 241

2.5 0.96

blond

243

0.97

1"14

8

F

30 Blond

1016 1009

4.1 4-0

5.8

2 Fair

1.32

* Hair samples taken 6 months later. ously from the same head was good in most cases. T h e relative adsorption values observed in the run taken after six months are somewhat different from the initial ones, but the disagreement is not sufficiently large to exclude the possibility of using adsorption capacity for hair identification at this stage. T h e results do not indicate any specific connection between the amount adsorbed and factors such as sex, age and hair colour. T h e question arose whether the observed differences were due to real differences in anion exchange capacity, or simply related to different migration rates of tracer into the hair. In order to clarify this point, hair from 3 persons was exposed to sorption solutions for different periods of time, ranging from 15 rain to 50 hr. The tracers used were " C u , " Z n and n t " C d , and 6 M HC1 was used instead of 3 M HC1 in order to obtain an increased adsorption of Cu. Results of these experiments are given in Fig. 2. For all three dements the adsorption increases up to about 10 hr, at which time saturation seems to have been reached. After 40-50 hr decreased adsorption is observed, perhaps indicating incipient degradation of the hair matrix. The

598

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TABLE 2. Adsorption of ~Zn to hair from different individuals from 3 M HCI. Contact time: 20 h r

.>

IF.

8

o

I

I

Person No. Sex Age

° ~

•

o

Hair colour

1

1 I I IIIII

I

I

I I IIIII

~Cu

I

I

M

30

Brown

o

526 468 411 422 413

448

488

d e

489 482 482 491 497

a

b c d

I I

x •

Activity Sample CountJ/ site* mg hair Mean

e

H,

4

F

48

Brown/ grey

a

b c

i

i',

~

S6Zn

I,*,i[

,

o[ •

,

,

l,,,d

,

,

i I

8

F

30

Blond

a b c d e

532 514 502 510 501

510

9

M

52

Blond] grey

a b c d e

447 432 442 427 403

430

10

F

58

Grey

a b c d

541 514 531 486 515

517

81•

I 0.t

t

10 EXPOSURE TIME (HOURS)

Fro. 2. Sorption of Cu(II), Zn(II) and Cd(II) from 6 M HC1 into human hair from 3 individuals, as a function of time. shape of the curves for a given element during the first few hours is somewhat different for hair from different individuals. For example hair from subject no. 8 adsorbs Zn at a considerably higher rate than hair from subjects 1 and 7, which show an approximately equal adsorption rate. This is in agreement with the trend indicated in T a b l e 1, where hair from subject No. 8 showed about 4 times higher uptake after 1 hr in 3 M HCI than was the case with subjects 1 and 7. At this point it seemed reasonable to assume that the anion exchange capacity of hair from different persons is similar, once a saturation level has been reached. Support for this hypothesis was obtained from a new experiment with hair from 5 different persons and 6~Zn tracer, employing 3 M H C I and 20 hr' contact time. H a i r from five different locations on each head was used, and the results are given in T a b l e 2. T h e activity per m g of hair is very similar for all five subjects.

e

* a: Back of the head, b: Above right Above left ear, d: Crown, e: Forehead.

~r,

c:

O n the basis of the experience gained from the study described above, it seemed reasonable to assume that different sorption is not a property that can be used with any high degree of confidence for the purpose or hair identification. H a i r from different individuals m a y show significantly different sorption of one or more elements at relatively short exposure times, but this fact probably relates to the surface rather than the matrix of the hair. REFERENCES 1. ,JERws R. E., PERXONSA. K., MAC,mTOSH W. D. and K~RR M. F. Proc. int. conf. Modern Trends in Activation Ana~s/s, p. 107, College Station, Texas (1961).

Uptake of trace elements in human hair by anion exchange 2. PSREONSA. K. and JExvxs R. E. Pro¢. Int. Conf. Modern Trends in Activation Ana/y.r/s, p. 295, College Station, Texas (1965). 3. COLemAN R. F., Csmvs F. H., SVOL~ONA. and SCOT'r H. D. Report AWRE 0-86]66 (1967). 4. VAN DEN BERG A. J., DE BRUINM. and HotrrMAN

599

.J.P. W . Modern Trends in Activa~n Arises/s,p. 661

I.A.E.A., Vienna (1967). 5. KRAUSK. A. and NEZ.SO~F. Proc. Int. Conf. Peaceful Uses of Atomic Enersy , Geneva Vol. 7, p. 113

U N E S C O (1956). 6. STmZLOW F. W. E. Aria/yr.C/,.on.32, 1185 (1960).