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Iron and Cobait in Ecology
Sufficient
organisms in the sea.
aml F resent
s of arsenic, copper, selenium, molybdenum,
prount
y lead have been Supplied to marine water during
ar ogical history to have resulted in a poisoned
<vlne environment had they not been scavenged
tii the water (Mason, 1958).
The chemical characteristics of iron and co-
walt which influence their distribution in the
‘;thosphere and hydrosphere are also important in
their utilization by organisms,
[ron and cobalt
are transition elements and exhibit the characteristics of variable valence, easy oxidation and
reduction, and a strong tendency to form complexes
with organic material.
Thus, they are potentially useful in physio—
logical processes in both animals and plants, in
which these chemical characteristics are required,
Although the amount of tron required by
plants is low, it is nevertheless essential for
growth. It is a constituent of several enzymes
and carriers which operate in the cell respiratory
pechanisms of which catalase, peroxidase, cyto-
chromes, and cytochrome oxidase are exagples
(Miller, 1957),
It is physiologically active in
the ferrous state and when taken in as the ferric
jon, is rapidly reduced in the cells. It ts one
of the most immobile of all elements in plants
(Biddulph, 1951; Meyer et al., 1960), and often
cannot be absorbed from the soil although it may
be plentiful. With low pH and low internal phosphate, iron is readily absorbed by roots or leaves
and rapidly becomes distributed in the plant.
However, at neutrality and high levels of phosphate,
iron, applied to leaves, is precipitated in the
veins of the leaves (Rediske and Biddulph, 1953).
Iron is toxic to plants only in the case of low
soil pH, lack of aeration, or combinations of these
conditions (Meyer et al, 1960).
Cobalt has not been proven to be essential
for higher plants although it is required by lower
plants such as algae and fungi (Miller, 1957),
Cobalt does aid in the accumulation of chlorophyll
in the leaves of some higher plants, It decreases
the decomposition of chlorophyll in the dark
(Solovera and Makorova, 1961}, and activates some
plant enzymes including carboxylases and peptidases
(Meyer et al., 1960).
In animals, iron can be ingested only in the
ferrous state.
It is an active component of
hemoglobin and myoglobin and is associated with
the activity of cytochromes, cytochrome oxidases,
and catalase,
Thus,
it is important in animals
in oxidative processes, transport of oxygen,
Storage of oxygen in muscle, and in intermediate
cell metabolism.
It is usually strongly bound in
the animal body and, therefore, has a low turnover rate (Underwood, 1956),
Cobalt in animals is active in vitamin Bigs
Neither higher plants nor animals can synthe8ize the vitamin which is formed primarily by
bacteria and actinomycetes (Sherman, 19575, Cobalt
18 poorly retained by most animal tissues and is
rapidly eliminated by many animal species (Under-
Wood,
1956).
Thus the functions of iron and cobait in
Plants and animals are at least partly known and
the geochemical characteristics of these elements
have been determined,
However, these types of
t ervations
do not necessarily provide the inwhee tion required to determine the mechanisms
ich control the uptake of these elements by
Organisms from their environments, Even if the
‘mounts of iron and cobalt were measured in re-
‘resentative samples of the organisms and their
tye trouments , only the static condition at the
ime of sampling would be determined,
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Page 563
The biological factors which control the
levels of iron and cobalt in various trophic
levels are incompletely known and experimental
data are needed on the movements of these elements
through given ecosystems. Some of these factors
include: (a) population sizes, (b) population
biomasses, (c) ratios of population surface areas
to biomasses,
(d) chemical characteristics of sur-
face areas of different species, (e) average movements of populations, (f) movements of individuals, (g) feeding habits, (h) physiological selectivity, (1) turnover rates, (j) reproductive
rates, (x) growth rates, and (1) average life
spans,
The characteristics of the biota ina given
environment are usually complex and subject to
continued changes in balance. The interactions
of the great number of variables upon each other
result in an over-all problem of such complexity
that the solution probably cannot be achieved by
the determination of the variables and applying
them to mathematical models,
A simplified approach to the complex problem
of iron and cobalt metabolism in a given ecosystem is that of producing a perturbation in the
system and Studying the resulting fluctuation
through the system, The introduction of one or
more radioisotopes of the element into the system
at one or more trophic levels will simultaneously
produce the perturbation and the marker by which
the fluctuation may be followed, An approximation of mass transfer within the system may aiso
be achieved if the amount of isotope dilution in
samples from all trophic levels is determined
with increased time after the introduction of
the radionuclide,
The interrelationships of the environment
and the various trophic levels may be more accurately determined, however, if tracer experiments in an ecosystem are correlated with selected investigations in the laboratory to determine
accurately some of the above mentioned characteristics of the organisms,
The use of radionuclides
as tracers depends
on the premises that: (a) the chemical properties of all isotopes of a given element are
identical and that the introduced radicelement is
in the same chemical and physical form as the
naturally occurring element, (b) the added radionuclide does not result in sufficient radiation
damage to alter the viability of the organisms,
and, (c)} the added radionuclide does not significantly increase the total amount of the element
under consideration.
Most of the observations on the cycling of
radionuclides have been made in areas of fallout
from nuclear weapons tests, at sites contaminated
by reactor incidents, in areas receiving cooling
water from large reactors, or downstream and
downwind from installations in which radioactive
materials are processed,
In the cooling waters from reactors several
neutron-induced radionuclides have been identi_ fied, including iron-59, Cobalt-58, and cobalt60 (Heath, 1956; Moeller, 1957; Conley, 1954;
Foster and Rostenbach, 1954; Rebeck et al., 1954).
In fallout from nuclear tests the nuclides
iron-55, iron-59, cobalt-57, cobalt 58 and
cobalt-60, have been reported (Kawabata, 1954;
South and Lowman, 1955; Rinehart et al., 1955;
Yamada et al,, 1955; Saiki et al., 1955; Mori
and Saiki, 1956; Yoshii, 1956; Nagasawa et al.,
1956; Seymour et al., 1957; Lowman, et al., 1957;
Lowman, 1958; Palumbo and Lowman, 1958; Welander,
1958; Lowman, 1960),
Only a limited number of observations have
<)