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Introduction
As long ago as the Sixteenth Century the German physician Paracelsus pointed out
that "all things are poisons, only the dose decides when a substance has no poisonous
action", yet four hundred years later our society uses some ten thousand or more
chemical compounds despite the fact that we have little detailed knowledge concerning
the toxic actions of more than a few hundred of these substances. This is the case in
the radiation curing industry where a multiplicity of chemicals is used, most of these
are injurious to human health if significant amounts enter the human body, by
inhalation, ingestion or absorption through the skin, yet their toxicity is as yet
incompletely understood.
The problem facing the toxicologist is to decide what is the minimum amount of a
particular chemical compound which is likely to produce an unacceptable risk of
serious damage to the health of an individual. For many years the primary concern was
to determine exposure levels which would not acutely damage the workers health
following relatively short exposures, however today we are often much more
concerned with effects, especially cancer and hereditary effects in children which may
arise only many years after exposure to very small amounts of a substance. Attempts to
define minimum toxic levels for humans is frequently hampered by: the fact that the
information which we need is generally incomplete and almost always comes from
studies in animal experiments carried out in species which are not ideal models for
homo sapiens. Nevertheless, despite the lack of the detailed knowledge which would
be desirable, our modern understanding of at least some of the molecular mechanisms
of toxicity is beginning to allow the prediction of the likely toxicity of many
compounds and to propose exposure limits which will adequately protect the worker
and which are economically achievable by good plant design and good industrial
hygiene.
In radiation curing there are three broad classes of compound in use, namely esters
of acrylic acid, esters of phthalic acid and epoxycompounds. All these compounds
potentially are harmfiul, but, fortunately, they do not belong to the most toxic classes of
industrial chemicals. Table I compares the toxicity of some typical aciylate, phthalate
or epoxycompounds with that of cyanide or. ionic lead. The toxicities are expressed as
the , the dose required to kill 50% of treated rats within 30 days, and the values
are given in mMoles per kg body weight in order to permit easy comparison on a
molecular basis
