Environmental hormesis, a fundamental non-monotonic biological phenomenon with implications in ecotoxicology and environmental safety

The biological response of individual organisms or groups of organisms to stress is crucial in several scientific disciplines, and hormesis is the most appropriate concept for studying dose-response relationships. The concept of hormesis supports that the response to low-level doses of an agent opposes the response to high-level doses and is characterized by a J or U shape outstretched in the Euclidean space. Hormesis has been widely known for chemical compounds and radiation; however, whether hormesis appears upon a variety of environmental factors remains underexplored. Here I provide evidence for the occurrence of environmental hormesis which opens Pandora's "pithos" for a wide variety of scientific disciplines. I demonstrate that plant response to environmental factors is often well described by hormetic model suggesting that dose responses should be evaluated based on a wide range of dose levels, taking into account potential effects at both low and high levels. I anticipate this study to serve as a starting point for more sophisticated experiments. The concept of environmental hormesis provides critical quantitative information for biological plasticity; is relevant to ecological and evolutionary theory; and may have long-term ecological implications within the context of global change. The concept of environmental hormesis can also be utilized for the benefit of human welfare and biosphere sustainability. However, to understand the underpinning biological or physiological mechanisms of environmental hormesis, trans-disciplinary research is needed. Environmental hormesis should be considered when developing science-based Environmental Quality Criteria (EQC).