Toxicology of Parathion


at the point where the acetylcholine is formed, and acetic acid
and choline are formed immediately. As soon as the acetyl-
choline is destroyed the muscle stops its contraction. If cholines-
terase is not present acetylcholine accumulates and this causes
a continuous twitching of the muscle. Muscular twitching is a
symptom of parathion or other phosphatic insecticide poisoning.
Thus, the loss of cholinesterase due to the absorption of a phos-
phatic insecticide results in an accumulation of acetylcholine.
 Not only are acetylcholine and cholinesterase necessary
for the proper functioning of muscles, they are also necessary
and are present at nerve endings in glands and in the vital organs
of the body such as the liver, the pancreas, the stomach, the
brain, etc. The presence of cholinesterase is necessary in all
tissues of the body. When a phosphatic insecticide has been
absorbed into the body the end result is the destruction of or a
reduction in the amount of cholinesterase present. A person may
be able to tolerate temporarily a fairly large cholinesterase re-
duction, but if too much is destroyed, symptoms result.
 Phosphatic insecticide poisoning may occur as the result of
a very large dose of the insecticide. However, in most cases
under field conditions poisoning is the end product of prolonged
exposures to small amounts of parathion or other similar insecti-
cides. There is good evidence to show that parathion is not
stored in the organs of the body (4, 13) and thus it is not cumu-
lative in the sense that lead or arsenic poisoning is cumulative.
In lead poisoning, for example, quantities of lead actually ac-
cumulate in the tissues of the body. In the case of parathion the
action may be cumulative. If it be assumed that the body is
capable of producing 50 units of cholinesterase per day and the
parathion exposure is such that only 45 units are destroyed per
day the body is capable of replacing cholinesterase as rapidly as
it is destroyed. Thus, there will be no lowering of the cholines-
terase levels in the tissues of the body and no symptoms of
poisoning will occur. However, if the exposure to parathion
results in the destruction of 60 units of cholinesterase per day,
this represents a loss of 10 units per day and at the end of each
day there will be 10 less units of cholinesterase in the body than
when the day started. If this process be continued, ultimately
the individual will have such a severe lowering of his cholines-
terase reserves that symptoms of poisoning will appear and he
may be seriously ill.
 A complicating factor in the cumulative effect of parathion