INTRODUCTION
The general concensus from the
open literature is that » poten
tially, the most
biologically hazardous Mater
ials known to man are radi oOnuc
lides belonging to
the actinide series.
The transuranics (neptuniun
lu tonium, americium, and
curium) may represent the most
sipnificant hazards in
of their increasing production
in reactor operations a
lives (McKay, 1961),
However, few data have been
publi
transuranics in terrestrial
environments and these are
Plutonium.
The Purpose of this presentati
on is not to
literature on laboratory studi
es of transuranics which
nium studies, but to assemble
the published data releva
native small vertebrates inhab
iting somewhat natural te rrest
rial environments,
CHEMICAL PROPERTIES OF BIOLO
GICAL IMPORTANCE
radi foe mide Series, there
is a gradual contraction in atomi
c and lonic
eae rom thorium to lawrencium
.
In addition, the ionic radius
is smaller
iC ae er yavence states of
each element.
These size variations are impor
(clewie TBrelative compl
tant
ex-forming tendencies and ion-e
xchange properties
i solute
DIn general, this decrease may
be accompained by an increase
re Sobel ¥
oxide, in the stability of chela
tes, and a decrease in basic
importane ne detec
it
States of many of the actinides
are especially
h
™
etermining complex-forming tende
nci
es.
These
catio
ns
polymericpretestological PH
giving rise to insoluble, collo
idal, and probably.
:
ess readily hydrated cations
ma y exist as compl
wmach aré more soluble and more
monomeric, hence more transporta
ble inlivin
erences:
In addition, isotopes of high
Specific activity (low mass)
are nore
re sole rransported indicating
mass is related to the formation
of colloidal
ymeric material. Atomic size
and valence 8 tate,
f£
then
absorption, tranportation, and
excretion of actinides in living
ever Th
most coho aes state is
dominant for americium and highe
r actinides
th
stable oxidation states for
transuranics ne Ptunium and
plutonium
and moot eet tvely (ICRP, 1972).
°
Durbin (1975) reported that tetra
valent Pu
xidation state {n biological
system
s,
is
th
to polymerize forming vadiocollo
,
ids under Physiological condi
tions. Fara”
thorough review of chemistry of actini
land (1967), and Taylor (1973).
nides, see Katz and Seaborg (1957), Cleve~
386
LABORATORY STUDIES
The biology of transuranics was the subject of several symposia (Hanford,
1962, 1972; IAEA, San Francisco, 1975).
A good review of the metabolism of
some actinides can be found in ICRP (1972) and Durbin (1973).
Whereas actinides
have a number of valence states and tend to hydrolyze to insoluble complexes
in physiological systems, it has been demonstrated that if they enter the bady
as stable compounds with a chelating agent, their biological behavior may be
considerably modified.
It should be emphasized that introduction into biclogical systems during experimentation has been highly variable as to mode of
introduction, chemical form, and dosage, and the results often do not readily
lend themselves to interpretation or generalization.
The generai consensus,
however, is that it is extremely unlikely that uncomplexed transuranic ions
can exist to any significant extent in vertebrate systems.
The physiclogical behavior of the transuranics appears to be related to mode
of uptake and is valence dependent.
Durbin (1962, 1975} and Nenot et al.
(1972) discussed transuranics in mammalian tissues in relation to chemical
properties and route of uptake. A decrease in ionic radius was negatively
correlated with skeleton burden and positively correlated with liver burden,
Schubert et al. (1961) and Lindenbaum and Rosenthal (1972) have pointed out
that colloidal solutions are taken up preferentially by organs containing
reticuloendothelial cells, primarily liver, but also spleen and bone marrow.
More monomeric solutions are largely retained in the skeleton. Taylor (1972)
discussed interactions of transuranium elements and the components of cells
and tissues. He emphasized the importance of proteins as complexing molecules
and the lysosomal association of some transuranics in cellular metabolism.
Of these transuranics, plutonium has received the most attention and has been
studied intensively in laboratory animals. Whereas much fewer data are available for other transuranics, the available data suggest that generalizations
about the behavior of plutonium may be carefully extended to these other
transuranics.
From the results of numerous studies summarized in Wick (1967), ICRP (1972),
Hodge et al. (1973}, and several symposia (Hanford, 1962, 1972; LASL, 1974),
the metabolic distribution of plutonium is determined by the chemical form,
route of uptake, age, sex, physiological condition, and species of animal.
The natural modes of entry include absorption from the gastrointestinal (GI)
tract, from the intact or damaged skin, and inhalation.
The results of many laboratory studies indicate that actinides are not absorbed
from the digestive tract in significant quantities. This was expected because
the high pH in the duodenum of mammals favors hydrolysis and the formation of
colloidal and polymeric material. Hamilton (1947, 1948) reported that less
than 0.05% of some lanthanides and actinides were absorbed Erom the GI tract |
of rats.
in later studies with rats, Katz et al. (1955) and Weeks et al.
(1956) estimated that from 0.002 to 0.05% Pu was absorbed from the GI tract.
In their study, skeletal deposition was approximately 90% of absorbed dose and
387