The obvious place to begin is by defining “hazard” and “risk” in the context of chemicals. Outside of this context, the common dictionary definition for hazard uses these terms as if they were synonymous and interchangeable. But when discussing chemical toxicity – particularly in relation to chemicals management and regulation – there are important distinctions between hazard and risk.
Within this framework, hazard refers to a substance’s potential to cause adverse health or environmental effects. Hazard is thus an inherent or intrinsic characteristic of that substance. That a substance is hazardous means the chemical has characteristics that can cause adverse effects but says nothing specific about how likely that harm is to occur.
On the other hand, risk cannot exist without hazard and in the context of chemicals management, risk is defined as a function of hazard and exposure. Determining the risk a chemical poses means assessing the likelihood that harm will be caused by exposure to a hazardous substance. And exposure can vary in different ways: by amount (the level, concentration, or dose); by duration; by timing – exposure at a critical or vulnerable point in development or biological process; by route or pathway (was a substance inhaled, ingested or touched, for example); and by combination with exposure to other stressors, chemical or other, that may be affecting human or environmental health.
The confusion of hazard and risk is amply evident in the response to the recent International Agency for Research on Cancer (IARC) classification of glyphosate – the active ingredient in the herbicide sold in numerous weed-killing products, including Roundup – as a “probable human carcinogen.” The IARC assessments are hazard assessments not risk assessments. To arrive at their conclusions about whether or not a substance is potentially carcinogenic, IARC committees review existing scientific literature on a substance’s health effects and toxicity: animal studies, cell culture studies, and human epidemiological studies. The classifications reflect IARC’s judgment – based on this evidence – that a substance has the potential to cause cancer. They do not, however, specify the circumstances under which cancer might occur or its statistical likelihood of occurring; that would be a risk assessment.
Risk assessments must include studies that evaluate a substance’s toxicity or inherent hazards but a risk assessment can conclude that it is acceptable or otherwise okay to be exposed to a certain amount of a hazardous substance under certain circumstances without denying that substance’s toxicity. In other words, deciding that a limited exposure to a hazardous substance is acceptable does not mean that the substance itself is “safe” or non-toxic.
However, in responding to the IARC glyphosate classification, the chemical’s manufacturers and trade associations representing agricultural chemical producers and users have focused on risk. The European and US government agency assessments these groups have cited as evidence of the chemical’s safety are risk assessments: evaluations designed to determine how likely it is that exposure will result in cancer or other adverse health effects.
We have air quality and drinking water standards based on risk assessments for scores of hazardous substances that may be present in ambient air and household water supplies. And when it comes to manufactured products, companies and governments constantly generate risk assessments for chemicals in finished products. The current debate over formaldehyde regulation in wood and other building materials, flame retardants in upholstery foams, and highly fluorinated chemicals in consumer products are but several examples.
Hazard elimination is also fundamental to the principles of green chemistry. These principles maintain that the best way of preventing toxic exposures and harmful pollution is by not creating substances that are inherently toxic – whether to human health or the environment – and do not result in toxic by-products or waste. This idea has been extended to product design as manufacturers seek to create products (and manufacturing processes) that are free from hazardous substances, and thus eliminate or reduce risk of harm to the environment or human health throughout the product’s life cycle.