Some Thoughts on Exposure Assessment and Chemical Hazard v. Chemical Risk

Authors: Peter B. Harnett, MS, MPH, CIH and Mary E. Greenhalgh, MPH, CIH

Exposure assessment is defined as a process to provide answers to questions about who was exposed, exposure routes (inhalation, dermal, ingestion), frequency, length, level and duration of exposure to the chemical. Ideally, actual levels of the chemical in the exposure media are measured. Frequently, claims of exposure are made without any examination of whether exposure was possible. For example, many chemistry laboratories have sodium cyanide salt in the laboratory. An approximate fatal dose to humans is between 2 and 3-grams. A container of sodium cyanide in the laboratory is likely to be 50-grams or more. However, the simple presence of sodium cyanide in a container in the laboratory does not demonstrate any exposure to this highly toxic chemical. Although sodium cyanide is a hazard, it does not pose a chemical risk concern in the absence of an exposure.

A client of ours faced workers’ compensation payouts to employees with vague complaints, i.e., respiratory irritation, headache, pain, nausea due to alleged exposure to an alkaline aerosol. We collected approximately 500-air measurements with the majority showing “non-detectable” amounts of this irritating compound. At the work locations for the “affected” employees within the 50+ facilities visited, no levels above 10% of the only published occupational exposure limit for a workday and short-term (15-minute exposure) period were measured. It is highly improbable that such de minimus airborne concentrations could be causing health effects from inhalation or any other route of exposure. At a loss for identifying the cause of these alleged symptoms, several non-occupational physicians indicated our client’s chemical, which had just been introduced to the plant, was the cause of the person’s health complaints. The extensive air sampling data, which would not support such health claims, were of limited value in eliminating the workers’ compensation claims. The reasoning of these physicians was no more complicated than new allegations of health complaints must be associated with the “new” chemical in the plant. Again the chemical is hazardous, yet does not pose a chemical risk concern in the absence of an exposure.

In our chemophobic society, school children are often told that they should avoid exposure to chemicals. On face value, this is reasonable advice. However, there is no attempt to communicate to students that the amount of exposure to the chemical determines whether toxic effects will likely result. Many of these students continue through high school lacking any fundamental understanding of chemical risk and the role of sufficient exposure to result in health effects. The personal concerns regarding health effects due to chemical exposure are further exacerbated by better analytical techniques capable of detecting successively lower concentrations of chemicals in our environment.

We need to develop training programs to better educate science teachers on chemical hazard v. chemical risk. Namely, a chemical may be hazardous, but in the absence of an exposure, the chemical does not pose a risk to someone’s health or well-being. As more nuanced education about chemical hazard and chemical risk are provided as the student matures, we will have more adults capable of properly assessing chemical situations and with the capability to better examine news media claims regarding allegations of chemical risk. These chemical “savvy” adults will be in a position to better influence policy-makers and some of them may play roles in better scientific communication of chemical concerns through public media.