J. exp. Biol. (1981). 9*. 333-335 333
Mith 1 figure
nted
in Great Britain
SHORT COMMUNICATIONS
FERROMAGNETIC CRYSTALS (MAGNETITE?)
IN HUMAN TISSUE
BY
JOSEPH L. KIRSCHVINK
Department of Geological and Geophysical Sciences, Princeton University
{Received 15 August 1980)
In recent years, a variety of animals have been found which are able to synthesize
the ferromagnetic mineral magnetite (Fe
3
O
4
). Lowenstam (1962) originally recognized
biogenic magnetite in the radular teeth of a primitive marine mollusc, the chiton
(Polyplacophora),
and since then it has been identified as a precipitate in several
magnetically sensitive organisms, including honey bees (Gould, Kirschvink &
Deffeyes, 1978), homing pigeons (Walcott, Gould
&
Kirschvink, 1979) and in magneto-
tactic bacteria (Frankel, Blakemore & Wolfe, 1979). Zoeger, Dunn & Fuller (1980)
also report a localized concentration of magnetite in dolphin heads, although magneto-
sensory behavioural experiments have not as yet been done on them.
Magnetite is biologically unique because it is both ferromagnetic and conducts
electricity like a metal; consequently it interacts strongly with magnetic and electric
fields. Due to the numerous industrial and research environments which expose
people to artificially intense electromagnetic conditions, it is of importance to know
whether or not this material might exist in human tissue. Kirschvink & Gould (1980)
have argued that there are probably one or more non-sensory metabolic functions for
magnetite from which specialized magnetoreceptors could have evolved; consequently
one might expect to find small amounts of magnetite in all animals, including humans.
In an attempt to partially answer this question,
I
searched for magnetic remanence in
four intact human adrenal glands which had been removed during autopsy and were
frozen quickly in non-magnetic containers. Results of this analysis are shown on
Fig. 1. Indeed, there is a measurable amount of high-coercivity ferromagnetic material
present which appears to be finely disseminated throughout the tissue. Between
1
and
10 million single-domain magnetite crystals per gram would be necessary to account
for the observed magnetic remanence. Although these measurements do not uniquely
identify the crystal phase as magnetite, no other ferromagnetic minerals have ever
been observed as biologic precipitates. Positive identification, of course, awaits the
development of magnetic separation techniques capable of isolating and purifying
these submicroscopic crystals. Barnothy & Sumegi (1969) have shown that mouse
adrenals are particularly prone to degeneration in moderately strong magnetic fields;
this effect might be due to the presence of magnetite.
The presence of ferromagnetic material in human adrenal tissue suggests that it
•jght be found in other organs as well. Indirect evidence for this comes from Presti
^Pettigrew's (1980) work on the neck muscles of birds and a similar study on the
334
J. L.
KIRSCHVINK
400 i-
300
X
8
C
§
200
100
0
IRM 10
20 30
40
50 60
Peak alternating
field
(mT)
Fig.
i. Ferromagnetic remanence in human adrenal glands. The 29 g sample of adrer^al
tissue was frozen to about
—
20
°C and briefly exposed to a 0'3 tesla magnetic field. The
resulting saturation Isothermal Remanent Moment (sIRM) measured in the zero-field
environment of a super-conducting rock magnetometer was 3-4 x
10"*
joule/tesla (N.B.:
1
joule/tesla =10* emu) which could be produced by 74 x
io~*
g of single-domain magnetite
26 ppb by weight, or roughly 1-10 million single-domain crystals per
gram).
Demagnetization
of the sIRM produced an exponential decrease in remanence with the peak alternating field
which is consistent with the ferromagnetic material being dispersed single-domain magnetite
of size similar to that found in pigeons, bacteria or chitons. Non-human control tissues
(pigeon brain and kidney) dissected and measured at the same time and in the same fashion had
no detectable remanence (e.g. less than io~
n
joule/tesla), suggesting that the ferromagnetic
material was present in the tissues before the magnetic analysis. Surgical contamination
during autopsy was unlikely as the gland was removed intact and the tissue for analysis
dissected from the interior with non-magnetic tools. Three other human adrenal glands
gave similar results (3-6, 4-5 and 80 nano-joules/tesla).
magnetic remanence distributed between and throughout the midbrain and corpus
callosum of Rhesus monkeys (Kirschvink, in the Press). Unfortunately, it is currently
far easier to detect the presence of magnetite than it is to determine what, if anything,
it does. The biological function of this material needs to be understood in order to
evaluate the merits of proposed human exposure guidelines to strong electromagnetic
fields (recently reviewed by Salles-Chuna, Battocletti & Sances, 1980).
I thank C. Denham and V. Schmidt for use of their palaeomagnetic laboratories,
and J. L. Gould, A. G. Fischer and M. E. Purucker for helpful comments on the
manuscript. This work was supported by NSF grant SP 179-14845.
Ferromagnetic
crystals (magnetite?) in human tissue 335
REFERENCES
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R. B.,
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