Ranking Biotoxins on a Toxic Scale

A basic concept in toxicology is that “only the dose makes the poison”. Everyday harmless substances like water have the potential to be lethal when consumed in large enough concentrations. Measuring a lethal dosage is very difficult.

First, living things are complex: factors like size, diet, biochemistry, and genetics vary across species. This makes it difficult to qualify toxicity in a universal way.

Second, individual factors like age or sex can also affect how deadly a substance is. This is why children have different doses for medications than adults.

Third, how a poison is taken into the body (orally, intravenously, dermally, etc.) can also impact its deadliness.

As a result, there are many ways to measure and rank toxicity, depending on what substance or organism is under investigation. Median lethal dose (LD50) is one common way for measuring toxicity. LD50 is the dose of a substance that kills 50% of a test population of animals. It is commonly reported as mass of substance per unit of body weight (mg/kg or g/kg). In the graphic above, we curate LD50 data of some select biotoxins found in nature and present them on a scale of logarithmic LD50 values.