Toxic decisions: How safe substances become dangerous

The risk a substance poses depends on its inherent capacity to cause harm and one’s exposure to it, but some seem unable to grasp this concept, writes Henry I Miller

Since the development of the science of toxicology in the 16th century, its guiding principle has been that “the dose makes the poison”. It is a rule that applies to the medicines used by patients worldwide many billions of times a day. The right dose of aspirin can be a therapeutic godsend, but consuming too much can be lethal. The principle even applies to foods: Large amounts of nutmeg or liquorice are notoriously toxic.

The risk that a substance poses broadly depends on two factors: its inherent capacity to cause harm and one’s exposure to it. It is a simple idea, but even some presumptive professionals seem unable to grasp it — as evidenced by the decision by the International Agency for Research on Cancer (IARC), a component of the World Health Organisation, to classify the commonly used herbicide 2,4-D as “possibly carcinogenic to humans”.