The Hormetic Effect: Is a Little Bit of Pollution a Good Thing? Should We Care?

The Hormetic Effect: Is a Little Bit of Pollution a Good Thing? Should We Care?

When it comes to environmental contamination and its effect on living things, there is a tendency to see the relationship as fairly black and white. Typically, as environmental scientists we view any level of contamination as bad. However, some scientists have argued that the relationship might not be that simple.

The Hormetic Effect or “hormesis” occurs when a living thing has a two-phase response to a contaminant. In certain doses the response to the stressor is positive (beneficial) and in other doses it is negative. For example, a very small dose of zinc can boost your immune system, but high doses can poison you.

This process is typically thought to be an adaptive response to stress (in this case the contamination)—the “low dose contaminant stress” triggers overzealous cellular repair and maintenance. This overcompensation of the cell in turn produces a low-dose beneficial effect. Similar to how frequently performing maintenance on your car—like changing oil and rotating your tires would be beneficial. However, the most interesting instances of hormesis occur when low doses of harmful environmental toxins are shown to be beneficial.

Image provided by P.D. Mangan, Rouge Health and Fitness

For decades toxicologists have studied and confirmed the linear trend of mid-to-high dose response to environmental contaminants (E.g. Mercury is bad for you, more mercury is even worse). This is generally referred to as the linear, no threshold (LNT) dose response. It assumes that a contaminant proven to be dangerous at high concentrations—will be dangerous at any concentration. However, a movement of toxicologists have argued that hormetic response curves (see figure above) exist in the relationships between hundreds of environmental contaminants and living things.

For example, low doses of heavy metals have been shown to potentially show some benefit to stream ecosystems.[1] Low doses of dioxin have been shown to reduce tumor risk in rats.[2] Some crop growth was stimulated by low concentrations of hexavalent chromium [3]. Low concentrations of crude oil have been shown to potentially benefit certain plant growth.[4] And more recently hormesis was cited in the Trump Administration’s arguments to lower the regulatory guidance values for various contaminants including—radiation.[5]

So, what does this mean? Could hormetic dose response change the way we view environmental contamination? Should regulations change—cleanup standards be reduced? Should all citizens demand 5 ppb chromium be included in their drinking water? In short, definitely no.

Although a fascinating scientific phenomenon, most toxicologists argue that the “benefits” of hormesis are not worth the risks that a regulatory reworking could have on public health. In fact, the majority of environmental experts have criticized recent hormesis support by the Trump Administration, citing it as a flimsy pretext to weaken environmental regulations of well-known toxic substances.[6]

The truth is, hormesis is often based on a small sample size and individual responses to specific chemicals, i.e. what is beneficial for some—could still potentially adversely affect others. Furthermore, many hormesis studies examine these dose relationships in a lab setting. In real-world conditions, toxins regularly mix and interact, which can vastly alter their effect on the population. The unpredictable and often unreproducible nature of hormesis in real-world conditions means that responsible regulation should mandate that a conservative approach be applied to contaminant thresholds and guidance values. One that is inclusive of all people.

Above all, hormesis demonstrates that environmental science is never as simple as it may seem. As we environmental scientists and engineers investigate and remediate sites—it is important to remember that this field is ever evolving. At Fleming-Lee Shue, Inc. we are first and foremost scientists, and we keep our staff on the cutting edge of environmental science to help assist our clients.

[1] Lefcort, Hugh, Freedman, Zachary. “Hormetic Effects of Heavy Metals in Aquatic Snails: Is a Little Bit of Pollution Good?” Ecohealth, 2008.

[2] Calabrese, Edward. “Paradigm Lost, Paradigm Found: The Re-emergence of Hormesis as a Fundamental Dose Response Model in the Toxicological Sciences.” Environmental Pollution, 2005.

[3] Patnaik, Anita, Achary V. Mohan. “Chromium (VI)-induced Hormesiss and Genotoxicity are Mediated Through Oxidative Stress in Root Cells of Allium cepa L.” Plant Growth Regulation, 2013.

[4] Carr, R. “Vegetative Frowth in Soils Containing Crude Petroleum.” Soil Scienices. 1919.

[5] Malone, Patrick. “Radiation Is Good for You? The Heretical View Gains Ground Under Trump.” Center for Public Integrity, 27 February 2019.

[6] Rust, Susanne. “Scientist Says Some Pollution is Good for You—a Disputed Claim Trump’s EPA Has Embraced.” Los Angeles Times, 19 February 2019.