Læknablaðið - 01.06.1973, Side 47

LÆKNABLAÐIÐ
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patient as in pulmonary tuberculosis or
puerperal streptococcal infection. But it
may also be necessary to intensify case
finding as in gonorrhoea which is certain-
ly not under control. You have been able
to halt the increase, but we have not.
Primary preventive medicine has been
concerned hitherto mainly with the con-
trol of communicable human infections
and the removal of known toxic substances
from the human environment. Secondary
preventive medicine is concerned rather
with the early detection of treatable
human disease or disability and there is
a tertiary field of preventive medicine in
the limitation of disability.
There are dangers to human health
other than human infections as we all
know. Gross examples of poisons in the
environment, particularly the working en-
vironment, have been known for a very
long time. Measures to limit exposure to
toxic doses of lead in industry or through
the effect of acid waters dissolving lead
in domestic water-pipes were known long
ago. Essentially such occurrences were
episodes associated with circumstances
which could be removed and avoided in
future, but there has recently been con-
cern about insidious increases in the
amounts of lead and other heavy metals
in the environment and we are far from
being certain whether or to what extent
this is harmful. The auestion is not so
much one of detectable symptom-producing
frank poisoning as of the part that traces
of some chemicals in small excess can
play in long-term health changes. The
incident at Minimata in Japan some years
ago when mercury used in industrial pro-
cesses and discharged, as supposedly in-
solub'le residues, into an enclosed bay, was
found to be slowly rendered soluble by
bacterial action, absorbed by diatoms and
so entering the fcod chain of fish and then
of man at levels which producsd serious,
even fatal poisoning in those whose diet
was substantially of fish from this source.
Two years ago there was a report of the
adverse eífect of cobalt used as a foaming
agent in beer, in verv small concentration,
contributing to cardiovascular disease. The
known relationship of cadmium or carbon
bisulphide to hypertension and cardiovas-
cular disease leads to suspicion that
amounts sometimes found as environ-
mental pollutants could be damaging to
health. The evidence obtained in Britain
i and elsewhere that cardiovascular disease
mortality is higher in areas supplied with
soft water for drinking purposes than
those supplied with hard water raises the
question whether calcium, magnesium or
some trace substance in the hard water
may promote health or prevent harm from
some contaminant otherwise present in
coft water. We have had examples of harm
from excess mercury in children who de-
veloped Pink disease after being repeated-
ly given a traditionally used teething
powder which contained mercury. We are
only at the beginning of the investigation
of the effects of small quantities of sub-
stances either added to our environment
or naturally occurring in it.
Nitrates and nitrites have been widely
used in the curing of rneat. Nitrates have
been used as fertilisers and especially
where artificial irrigation of land takes
place, they find their way in excessive
amounts into rivers and other water sup-
plies. Using new and highly sensitive ana-
lytical techniques, minute quantities of
nitrosamines, known to be carcinogenic to
animals in much larger doses, have been
found in a varietv of cured and cooked
fcods. Various additives propcsed for food
have been found on occasion to be damag-
ing in large doses to experimental animals
and have had to be excluded. The arti-
ficial sweeteners, cyclamates, were found
two years ago to be capable in very large
doses of producing malignant bladder
tumours in rats. It was believed that this
was the result of conversion to cyclo-
hexylamine in metabolism by the rat and
that such a change did not occur in man;
but it is now known to occur in a pro-
portion of humans. There is evidence that
some of the monoenoic acids, particularly
erucic acid, in large doses may have ad-
verse effects on the cardiovascular system
in experimental animals and erucic acid
is a constituent of some rape-seed oil which
may be used in margarine or other edible
fats.