That will depend on the type of contaminant.
Potential for lead poisoning
It would be unusual to get lead poisoning from touching a door knob. In theory, if the door knob had been painted with a paint that contains lead, and if the paint was now flaking off and gets onto your hand, and if you fail to wash your hands before eating, and you get flakes of lead based paint into your food and eat it, then yes, you could get lead poisoning.
Because cans seems are or where sealed by lead. The lead, after a time, contaminated the contents. This caused food poisoning.
There is some evidence that ancient, prehistoric peoples who smelted lead and tin suffered from lead poisoning.
Due to the fact that most pencil lead is graphite, you can't get lead poisoning. :)
Lead poisoning is caused by breathing in lead dust or ingesting lead in some way. Today little children can get lead poisoning if they put something coated with lead, say a toy colored with led paint, in their mouths. They sometimes eat lead chips of brightly colored paint. Adults can get lead poisoning by working with lead in some capacity, such as a person making stained glass, or by eating canned food that was packed in a lead lined can. (Although banned in the United States, lead lined cans for food are allowed in other parts of the world.) As for the relevancy of lead poisoning to ancient Rome, yes, the ancient Romans had the opportunities to contract lead poisoning big time. The pipes leading from the aqueducts to private homes and public fountains were made of lead. (the pipes in the aqueducts themselves were of more durable ceramic) The Romans also literally ate lead. They used lead as a sweetener, especially in wine. Many cosmetics were lead based as were the brightly colored glazes used in their ceramic dinnerware.
In the food you eat, if it smells it has food poisoning in it
To avoid food poisoning - which could lead to diarrhea, vomiting and fever, or even death if severe enough.
Bacteria contamination and growth which can lead to food poisoning can be eliminated (or reduced)by cooking at the proper temperature for that food.
yes
When a person ingests or breathes in too much lead for their body to naturally process, they are at risk for lead poisoning.
When a person ingests or breathes in too much lead for their body to naturally process, they are at risk for lead poisoning.