Chemicals & Human Health

Toxicology Problem Set

Problem 1: Natural and human-made chemicals

For help to answer the question:

Which statement is the most correct?
A. Chemicals manufactured by humans are more dangerous to human health than naturally occurring chemicals.
B. Both natural and human-made chemicals are potentially toxic to humans.
C. Naturally occurring chemicals are more poisonous to humans than synthetic chemicals.


Natural and synthetic chemicals

Both natural and human-made chemicals have the potential to harm humans. Toxic chemicals can occur naturally. For example, rattlesnake poison and botulin are both naturally occurring chemicals that harm humans. Botulin is the toxin which causes food poisoning and is produced by bacteria. Another example of a naturally occuring chemical that is dangerous to humans is radon. Radon is a naturally occurring radioactive gas that enters homes and buildings from the rocks and soil beneath them. Toxic chemicals can also be created by humans, for example, lead-based paints or pesticides such as DDT.

Photos courtesy of Bayou Bob

The dose makes the difference

Whether a chemical is harmful or beneficial depends largely on the dose. Paracelsus, a Swiss physician, wrote in 1567 that:

All substances are poisonous.

There is nothing which isn't poisonous.

The right dose differentiates a poison from a remedy.

This means that ALL chemicals, natural or synthetic, have the potential to be hazardous substances to humans, BUT the level of harm depends on the dose.

Toxicology Problem Set Chemicals & Human Health

The Southwest Environmental Health Sciences Center
The Biology Project
The University of Arizona
Tuesday, September 16, 1997
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