3.0 Basics of Toxicology and Risk Assessment

3.0 Basics of Toxicology and Risk Assessment


Video length: 5 min 30

Greenfacts.org. (Nov 24, 2014). Hazard, Risk & Safety – Understanding Risk Assessment, Management and Perception. available from: YouTube.

3.1 Toxicological Hazard and Risk


Hazard is the ability a xenobiotic has to cause harm. The term ‘hazard’ is commonly confused with the term ‘risk.’ In toxicological terms, a hazard does not pose a risk unless an organism is exposed to enough of the hazard to result in harm. An example of hazard classifications are the IARC carcinogen classifications.

Risk is the probability that an adverse outcome will occur following exposure to a xenobiotic. Simply because a particular xenobiotic is particularly hazardous, does not necessarily mean that it is high risk. Risk is entirely dependent on exposure and dose.

In simplistic terms:

Compound Interest. (2015). A rough guide to the IARC’s carcinogen classifications. Compound Chem.

3.2 Graham’s Hierarchy of Disagreement

Many areas of human health risk assessment and toxicology are politically and socially charged. Accordingly, they attract a range of reactions and comments from relevant stakeholders.

A very useful way of working through arguments and feedback to determine their relevance to a risk assessment is to use the Hierarchy of Disagreement developed by computer scientist Paul Graham. Graham’s Hierarchy can be represented as a pyramid with the most convincing form of disagreement at the top, and the weakest form of disagreement at the bottom.

Commentary on a human health risk assessment that falls into the categories at the bottom of the hierarchy can be safely judged to have no scientific relevance (many political statements fall into these categories). However, comments that fall into the upper categories potentially have validity and their scientific validity should be checked.

Animation adapted from RocketOOO. (2008). Graham Hierarchy of Disagreement. https://en.wikipedia.org/wiki/File:Graham%27s_Hierarchy_of_Disagreement.svg.

Listen to some of the claims discussed in the video below and think about how you would form an argument to disagree with those claims if they were presented to you


Video length: 5 min 30

CBC News. (Dec 2 2017). Fact checking fake health and medical news on the internet (The Investigators with Diana Swain). Available from: YouTube.