1) Ethylene glycol is a colorless, odorless, sweet-tasting chemical found in many household products, including antifreeze, deicing products, detergents, paints, and cosmetics.
2) I am not aware of any use with pesticides.
3) The first symptom of ethylene glycol ingestion is similar to the feeling caused by drinking alcohol (ethanol). Within a few hours, more toxic effects become apparent. Symptoms may include nausea, vomiting, convulsions, stupor, or even coma. An overdose of ethylene glycol can damage the brain, lungs, liver, kidneys, and lungs. The poisoning causes disturbances in the body's chemistry, including metabolic acidosis. The disturbances may be severe enough to cause profound shock, organ failure, and death.
4) It has been used in the past as a sweetener for certain wines with serious consequences for their consumers.

1) Ethylene glycol is a colourless, odourless, relatively non-volatile liquid.
It is widely used as an anti-freeze and deicing agent. It is also used as an
ingredient in inks found in ink pads and ballpoint pens. It is used as solvent
in the paint and plastics industry, and is used to produce polyester fibres. It
is an intermediate in the manufacture of polyethylene terephthalate (PET). It
has been used is some cosmetics but this was a very minor use.

2) Ethylene glycol has been approved for use in the US as an 'Antifreeze,
deactivator for all pesticides used before crop emerges from soil and in
herbicides before or after crop emerges'. As it is not an active ingredient it
has not been reviewed by JMPR. I do not know of its use elsewhere in pesticides.
I know of no use such as suggested, i.e. to make the pesticide visible when it
is used.

3) As with all chemicals, the risks associated with its use depend on the
exposure level. Ethylene glycol is of low acute toxicity. The effects of
exposure to large amounts of ethylene glycol are mostly a consequence of its
metabolism to acidic products, including oxalic acid. Intoxication with ethylene
glycol results first in effects on the brain (central nervous system), with
feelings of tiredness, seizures and unconsciousness, metabolic acidosis with
disturbances of acid-base balance, followed by effects on the heart and lungs
(increased heart rate, high blood pressure, tissue damage), and finally renal
damage, due to crystallisation of the metabolite calcium oxalate in the urine,
leading to renal failure. Repeated exposure to high doses, below those causing
acute intoxication as above, can lead to renal damage and renal failure. Less
severe effects in the liver may also be seen at these doses. Low doses, even on
repeated exposure do not cause any harm. There is minimal risk from use of the
chemical as recommended, or from exposure to products that contain ethylene
glycol, unless there is intentional or accidental intoxication. There is no
additional risk from mixing ethylene glycol with pesticides, as long as the
formulation is used as recommended.

4) The closely related compound, diethylene glycol, has been added illegally on
occasion to wine, to increase its 'body' and sweetness. Although this is
potentially toxic, the WHO International Programme on Chemical Safety estimated
that to be harmful 28 bottles of wine per day would need be consumed for two
weeks. There is no evidence that ethylene glycol has been used in this way, but
given that it has similar characteristics to diethylene glycol, including a
sweet taste, such misuse is a possibility.