What does “toxic” mean?

Frequently we hear claims about how certain chemicals are “toxic”, or how certain products contain only “non-toxic” ingredients. Just what do these claims mean, and are they accurate?

In my opinion “toxic” is a highly misused word, particularly in the media. Common usage implies that certain chemicals are always toxic, while other chemicals are “safe”. In reality, essentially every chemical is toxic at some point; even drinking too much water has been associated with kidney damage. Toxicity is dependent not just on the chemical, but on how much a person is exposed to (or, more specifically, how much reaches the part of the body where it has its effects). If you’re going to classify chemicals as being either “toxic” or “non-toxic” then you have to consider whether the dose that someone could be exposed to is actually high enough to produce a toxic effect.

It’s common for environmental groups to make claims about how we’re exposed to “toxins”. For example, Environmental Defence tested blood and urine from several people, then talked about how these people had a “cocktail of harmful chemicals“. However, there was absolutely no evaluation of whether the levels detected were high enough to produce any effects, and in fact many of the chemicals included in the analysis were naturally occurring (as I discussed in a previous entry, natural substances are just as likely to be “toxic” as synthetic chemicals) – all they looked at was whether a chemical was detected, and automatically assumed that it was therefore harmful. I consider studies like this to be pure political fear-mongering, with virtually no scientific substance or value.

There are also specific regulatory definitions of “toxic” that are tailored to legal needs. The Canadian Environmental Protection Act has a very specific definition of a “toxic” chemical:

1. have or may have an immediate or long-term harmful effect on the environment or its biological diversity;
2. constitute or may constitute a danger to the environment on which life depends; or
3. constitute or may constitute a danger in Canada to human life or health.

In this case only one of the three ways a substance can be declared toxic relates to actual toxicity to humans; a second relates to toxicity to other organisms. Part ‘b’ of the definition has nothing to do with toxicity, but satisfies a regulatory need for being able to manage substances that have environmental effects other than toxicity (this is the part of the definition used to classify substances like greenhouse gases as “toxic”). The process for determining whether a substance meets part ‘a’ or part ‘c’ basically involves collecting data (or estimating) on concentrations of the chemical in various environmental media, estimating exposures to ‘typical’ humans and ecological receptors, and comparing these exposures to toxicity-based benchmarks. The assessment is based on exposures to the general population or Canada as a whole, as opposed to at a specific location.

As a general rule, when the media or an advocacy group talks about “toxins” or otherwise uses the word “toxic”, take it with a grain of salt; in most cases I suspect there hasn’t been any critical evaluation of whether toxicity is actually present. If a regulatory agency classifies something as “toxic”, then it is important to see how the agency defines toxic and their process for making this decision in order to understand what this classification actually means.