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S KOMMISSION OER EURQPAlSCHEN GEMEINSCHAFTEN
COMMISSION DE3 c o mmu n a u t Es e u r o p Ee n n e s
UNITED STATES ENVIRONMENTAL PROTECTION A6ENCV
INTERNATIONAL SYMPOSIUM
Environmental health aspects of lead
Die gesundheitlichen Aspekte der Umweltverschmutzung durch Blei
Les problfemes sanitaires poses par le plomb prdsent dans I'environnement
METABOLISM AND DISTRIBUTION OF RADIO ACTIVE AND STABLE LEAD IN MAN
E. DI FERRANTE and P. BOURDEAU
UnitS Scientifique "Nuisances", D.G.Ill Commission of the European Communities BRUSSELS, BELGIQUE
Amsterdam, October 2 - 6, 1972
N40715
Abstract
The literature concerning the metabolism tod the* distribution of radio active and stable lead in animal and human organisms was reviewed# The available data have been summarised in tables sd that a comparison bet ween results obtained using either radioisotopes of lead or stable lead could be made# The purpose of such comparison was to ascertain whether the information obtained with radiolead could clarify the metabolic pro cesses of stable lead in man* The usefulness of the experiments performed with radioactive tracers seems unquestionable; the results of studies on the retention and excretion of radiolead in animals and in humans are, in general, ponfirmad by direct observations male on the behaviour of stable lead in man* Some inconsistencies might be due to differences in the experimental conditions# However, the critical examination of the literature on both radioactive and stable lead reveals that the mecha nism of lead absorption in man is not completely known# Precise infor mation, for instance, on transfer coefficients of lead through the re spiratory and gastro-intestinal tracts is not reported in the liters^ ture# The analysis of the various studies on lead metabolism has shown where additional research is required# Some specific points to be cla rified, also through experiments with radiolead, are suggested#
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*In an attempt to evaluate the hazards resulting from exposure to at*" mospherie lead from automobile exhaustst the Commission of the European Communities has organized a Seminar on "Human lead metabolism"t held at Xjuxembourg, 25-27 April 1972* One of the points reviewed* was to ascertain whether radioactive and stable lead behave similarly so that the experiments performed with radioisotopes of lead in animals and humans may provide useful infor mation on the metabolism of stable lead in inan#
Data from the literature on lead distribution in the human body and on the retention and excretion of the element in animal organisms and in man, are shown in Tables I and IX# It seems evident, in general, that the results of experiments performed with radioactive tracers are confirmed by those on the behaviour of stable lead in man# However, metabolic differences may occur for carrierfree radiolead and for stable lead introduced into the organism at nor mal or abnormal levels#
Despite the relative abundance of data found in the literature, trans fer coefficients of lead through the respiratory and gastrointestinal tracts are not known with a sufficient degree of precision# Data on storage of lead in the different compartments of the organism are also far from being consistent# The absorption and retention* values given by some authors have always a range of variation, sometimes rather large f they do not provide, therefore, a completely satisfactory basis for the establishment of permissible levels of exposure# Many important questions, therefore, concerning the toxicological aspects of environmental contamination due to lead are still without satisfactory answer# Experiments with lead radioisotopes Which in the past were performed with the aim of estimating the degree of exposure to radiolead for the establishment of radioprotection rules, might be usefully pursued to fill in the subsisting gaps concerning stable lead#
* A detailed text of this review, published elsewhere, is available on request#
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The choice of the radioisotope and the experimental conditions should he, of course, carefully studied in order to obtain results and con-* elusions which give a valid- contribution to the elucidation of "the toxicity mechanism of lead* The analysis of the various studies on lead metabolism has shown where additional research is required# The following list includes the main subjects to be further studied also with the use of radiolead s 1) Form of Pb circulating in plasma (in vivo studies not performed)#
Mature of binding to plasma constituents# 2) Relationship between Fb in blood and in soft tissues and between Pb
in blood and in total exchangeable Pb pool Factors influencing the relation of Fb in blood to Pb in soft tissues e#g# age, sex, blood type, etc### 3) Mechanism of Fb transportation across the intestinal mucosa into systemic circulation# 4) Mechanism of deposition of Pb in bone or metabolic factors modifying the interaction of Fb with bone# 5) Effects of interruption of Pb absorption on reduction of Fb body burden# Factors influencing mobilization of Fb in the body# 6) Fate of inhaled Pb# Absorption rates for particles of less than 1 p. (radioisotopes of lead could be particularly useful)# 7) Effects of lead on enzymatic systems#
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References
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nium and Radioiead" Sutton, U.K. 30-April-l May 1970.
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TABLE I Distribution of radioactive and stable lead in man
Tissue v
% of body burden
210Pb
Stable Pb
O
N reference
(see list)
JM
V
Bone
Liver
Spleen
Muscle
Soft tisaues(all) ' Blood
63.0 58.0 80.0 79.0 80.O
1.7 2.8
1,5
' 2.2
0,14
17.0 13.0
4.4
30.0
2.0 1,6
83*0
70.0 90.0 91.0 95.0
3.1
5.1 0,2
4.6 7.7 30,0
2,4
2*3 5 5 (other authors) .13 13 (other author) 3 (ICBP) 12 (other author) 23 27
2j j 5 (other author) 5 (other author) 13 5 (ICRP)
5 5 (ICBP)
2 5 (other authors) 13 2 5 (ICBP)
5 5 (ICBP)
5
13 5 (ICBP)
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I ISABLE
R etention and e x c re tio n .o f ra d io a ctive and stable
lung d e p o sitio n * in h a la tio n minus e xh a la tio n , as s p e c ifie d by authors
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