https://phys.org/news/2018-05-hormesis-paradoxical-effects-exposure-formaldehyde.html

However, in recent years, there has been growing recognition that the nonmonotonic responses of living organisms can occur quite often when the direction of the organism's reaction changes with increasing strength of the acting factor. These include hormesis and paradoxical effects. In case of hormesis, low doses of pollutants have a positive effect on the state of the living organism, while high doses cause a negative effect. Paradoxical effects include complex dose-effect relationships, when an increased dose of a toxicant results in a decrease in its damaging effect and, conversely, the damaging effect increases with a decrease in the toxicant dose.

Nonmonotonic changes in plant indicators used to determine the quality of the environment can result in an incorrect assessment of the pollution level. Therefore, it is important to know how often hormesis and paradoxical effects occur when plants are exposed to various pollutants.