‘Risk’ and ‘hazard.’
These two words are often used interchangeably, but they have distinct meanings in the context of chemical safety assessment. When we say a particular chemical is ‘hazardous,’ we are noting its mere potential to cause negative health or environmental effects. On the other hand, ‘risk’ describes the probability that these negative effects will actually occur under specific circumstances. In order to generate a measurable risk, some exposure to the hazard in question must occur.
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If you have followed my last several posts, you’ve probably caught on to the idea that attempting to declare a chemical ‘safe’ or ‘unsafe’ is an exercise in futility. To comprehensively determine risk, we must know not only the detailed structure and function of a chemical, but also understand the intricacies of its interactions with the environment and the human body. Current chemical regulation in the United States operates within a risk-based framework. We establish standards and criteria for acceptable levels of hazardous compounds in products, in the environment and in our bodies; we enact bans and restrictions on chemicals in order to limit our exposures. These regulations are the product of risk assessments, which report not only the hazardous properties of chemicals but also the likelihood of human exposure.
My recent post on BPA illustrates the complexity of risk assessment. Though BPA has demonstrated hazardous potential, the levels to which humans are exposed to the compound, and therefore the actual risks of its use, are uncertain. Exposure may seem like a simple factor to evaluate, but our understanding of exposure is continually evolving, particularly with consideration for the special vulnerability of developing babies and children. The ban on BPA in baby bottles reflects this emerging awareness of long-term effects of chemical exposures. However, the replacement of BPA with BPS illustrates the shortcomings of an approach that controls risk by limiting exposure to specific high-profile hazardous compounds.
The replacement of BPA, a known hazard, with BPS – an untested and unregulated compound with a nearly identical structure – may be considered an example of what scientists and regulators refer to as “regrettable substitution.” Regrettable substitution occurs when we eliminate one hazardous chemical from consumer products, only to replace it with a similar or even more hazardous alternative. Our risk-based chemical regulation enables us to remove demonstrably dangerous chemicals from consumer products, but also leaves profound loopholes for new chemicals, untested and unregulated, to enter the market in their stead, as long as risk assessments have not proven them dangerous. In a 2010 post on his Environmental Defense Fund blog, Dr. Richard Denison refers to this process as playing “whack-a-mole” with chemicals. No sooner have we knocked one hazardous chemical back into its hole, than a replacement rears its likely-hazardous head…until we generate evidence of its actual risk and seek to replace it with another unknown quantity.
Is this game of “whack-a-chemical” inevitable, or do more precautionary approaches exist? In Europe, regulators are striving for a balance between risk assessment and the more protective approach of hazard classification. While risk assessment relies on scientific studies to determine the risks of chemicals under different exposure scenarios, hazard classification groups chemicals based on their inherent hazard potential. It is this potential to cause harm that guides regulation, not demonstrated adverse effects. A hazard classification regulatory scheme might have prevented BPS from entering the market, since its structural similarities to BPA make it a likely health hazard.
Hazard classification is essentially a more precautionary approach to chemical regulations. And when we operate in a framework of precaution rather than risk, the regulatory question itself changes. “A precautionary approach asks how much harm can be avoided rather than asking how much is acceptable,” write Dr. Ted Schettler and coauthors in a 2002 essay on the role of the Precautionary Principle in regulation and policymaking.
How can we better incorporate the Precautionary Principle into the chemical regulation process in the US? This question has been at the epicenter of the debate on reforming the Toxic Substances Control Act (TSCA), which I will cover next time on Backyard Talk.