why is egg white used as an antidote for Pb or Hg poisoning?

Answer 1

Albumen/albumin, or egg white is 54% ovalbumin.
Medicinal characteristics of ovalbumin.
In cases where poisoning by heavy metals is suspected, ovalbumin should be administered on direction from emergency personnel. Ovalbumin chelates to heavy metals and traps the metal ions within the matrix of the protein. After the poison has been absorbed, one may be instructed to induce vomiting to purge the metal–protein mixture. Iron poisoning is the second leading cause of death among toddlers in the United States and it is recommended that parents always keep eggs around the house and lock up all vitamins and supplements out of the reach of children.

Answer 2

It is because egge white contains albimin which reacts with heavy metal. This prevents the intestinal cells from being afected by lead and mercury because they are made up of proteni. In that way the metals pass through the alementary canal without being absorbed more and more. In this way the small amount that has entered the blood system is converted by the liver.

Answer 3

Lancenigo di Villorba (TV), Italy

Egg's white containts many biological compounds among these are present proteins disposed by thiolic functional groups
(e.g. -S-H). The latters are very able to specific interactions with lead and mercury's ions whom are main responsible for most common heavy metal's poisoning.
In effect, biological molecules of our living organism behave in analogous interactions, thus egg's white "blocks" heavy metal's ions before they kill the host organism.

I hope this helps you.