Search

The nature of the dose-response relationship in the low dose zone and how this concept may be used by regulatory agencies for science-based policy guidance and risk assessment practices are addressed here by using the effects of surface ozone (O3) on plants as a key example for dynamic ecosystems sustainability. This paper evaluates the current use of the linear non-threshold (LNT) dose-response model for O3. The LNT model has been typically applied in limited field studies which measured damage from high exposures, and used to estimate responses to lower concentrations. This risk assessment strategy ignores the possibility of biological acclimation to low doses of stressor agents. The upregulation of adaptive responses by low O3 concentrations typically yields pleiotropic responses, with some induced endpoints displaying hormetic-like biphasic dose-response relationships. Such observations recognize the need for risk assessment flexibility depending upon the endpoints measured, background responses, as well as possible dose-time compensatory responses. Regulatory modeling strategies would be significantly improved by the adoption of the hormetic dose response as a formal/routine risk assessment option based on its substantial support within the literature, capacity to describe the entire dose-response continuum, documented explanatory dose-dependent mechanisms, and flexibility to default to a threshold feature when background responses preclude application of biphasic dose responses. Capsule: The processes of ozone hazard and risk assessment can be enhanced by incorporating hormesis into their principles and practices. © 2018 Elsevier B.V.

The United States Environmental Protection Agency (US EPA) has recently proposed changes to strengthen the transparency of its pivotal regulatory science policy and procedures. In this context, the US EPA aims to enhance the transparency of dose-response data and models, proposing to consider for the first time non-linear biphasic dose-response models. While the proposed changes have the potential to lead to markedly improved ecological risk assessment compared to past and current approaches, we believe there remain open issues for improving the quality of ecological risk assessment, such as the consideration of adaptive, dynamic and interactive effects. Improved risk assessment including adaptive and dynamic non-linear models (beyond classic threshold models) can enhance the quality of regulatory decisions and the protection of ecological health. We suggest that other countries consider adopting a similar scientific-regulatory posture with respect to dose-response modeling via the inclusion of non-linear biphasic models, that incorporate the dynamic potential of biological systems to adapt (i.e., enhancing positive biological endpoints) or maladapt to low levels of stressor agents.

Documented biphasic dose-responses date some 150 years back; however, massive evaluations of the occurrence of pollutant-induced hormesis, its quantitative characteristics, and the underlying mechanisms have been performed only in the recent years. One of the reasons why hormesis is not included in the ecological risk assessment may be its poorly explored relevance to levels of biological organization beyond the individual. Here, we summarize the highly reproducible occurrence of hormesis induced by various individual and combined chemicals in microorganisms, the hormetic response of bioluminescence, and the hormesis-based drug resistance. We also summarize key underlying mechanisms and discuss the relevance of hormesis in microorganisms-regulated organismic interactions, biological communication, and communities of microorganisms. Our exposition indicates the need for enhanced studies directed to reveal the implications of hormesis to levels of biological organization beyond the individual and that hormesis is considered in the ecological risk assessment.

Ozone (O3) is a natural component of the atmosphere. It occurs in the stratosphere, where it protects biota against ultraviolet radiation, but also in the lower troposphere, where it can directly harm biota. Because of its (i) high toxicological potential for biota, (ii) high reactivity and molecular instability, and (iii) difficult differentiation from other reactive oxygen species, O3 challenges scientists in a continuing effort to develop methods for its monitoring. We present here the operation principles of the most used techniques, along with some new technological developments for atmospheric O3 monitoring, with emphasis upon near surface. Huge amounts of scientific data have been produced thanks to progresses in O3 monitoring technologies. However, it remains a challenge to further develop reliable methods with rapid response and high sensitivity to ambient O3, which will also be free from the disadvantages of the current technologies.

Massive additional quantities of disinfectants have been applied during the COVID-19 pandemic as infection preventive and control measures. While the application of disinfectants plays a key role in preventing the spread of SARS-CoV-2 infection, the effects of disinfectants applied during the ongoing pandemic on non-target organisms remain unknown. Here we collated evidence from multiple studies showing that chemicals used for major disinfectant products can induce hormesis in various organisms, such as plants, animal cells, and microorganisms, when applied singly or in mixtures, suggesting potential ecological risks at sub-threshold doses that are normally considered safe. Among other effects, sub-threshold doses of disinfectant chemicals can enhance the proliferation and pathogenicity of pathogenic microbes, enhancing the development and spread of drug resistance. We opine that hormesis should be considered when evaluating the effects and risks of such disinfectants, especially since the linear-no-threshold (LNT) and threshold dose-response models cannot identify or predict their effects., This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors. E.A. acknowledges multi-year support from The Startup Foundation for Introducing Talent of Nanjing University of Information Science & Technology (NUIST), Nanjing, China (Grant No. 003080). E.J.C. acknowledges longtime support from the US Air Force (Grant No. AFOSR FA9550-13-1-0047) and ExxonMobil Foundation (Grant No. S18200000000256). The views and conclusions contained herein are those of the authors and should not be interpreted as necessarily representing policies or endorsement, either expressed or implied. Sponsors had no involvement in study design, collection, analysis, interpretation, writing and decision to and where to submit for publication consideration.

A great number of dose–response studies indicate that hormesis is a common phenomenon, occurring in numerous organisms exposed to singular or combined environmental stressors, such as pharmaceuticals, heavy metals, micro/nanoplastics, organic flame retardants, pesticides, and rare earths. (1−6) While biological responses to low exposure levels are often beneficial, exposure to doses below the no-observed-adverse-effect-level (NOAEL; hereafter subthreshold doses) does not always translate to beneficial responses. (2,4) For example, subthreshold contaminant doses can enhance the virulence of phytopathogenic microbes and promote the resistance of crop pests with significant implications for crop production. (2,7,8) Subthreshold contaminant exposures can also stimulate infectious animal/human pathogens and promote their resistance to antibiotics and other drugs, threatening long-term sustainability. Importantly, the hormetic function of common pathways that regulate cancer progress indicate that current regulatory standards may not protect adequately against cancer risks. (9−11), We are grateful to Dr. Patrick H. Brown, Distinguished Professor of Plant Science at the University of California, Davis, U.S.A., and Dr. Adrian Covaci, Professor of Environmental Toxicology and Chemistry at the University of Antwerp, Belgium, for comments and suggestions on an early draft of the paper. This study did not receive a specific grant from funding agencies in the public, commercial, or not-for-profit sectors. E.A. acknowledges support from the National Natural Science Foundation of China (No. 4210070867), The Startup Foundation for Introducing Talent of Nanjing University of Information Science & Technology (NUIST), Nanjing, China (No. 003080), and the Jiangsu Distinguished Professor program of the People’s Government of Jiangsu Province. E.J.C. acknowledges longtime support from the U.S. Air Force (AFOSR FA9550-13-1-0047) and ExxonMobil Foundation (S18200000000256). The sponsors were not involved in the study design; the collection, analysis or interpretation of the data; the preparation of the manuscript or the decision where to submit the manuscript for publication. All authors hold senior editorial positions in various scientific journals. The views presented herein are those of the authors and do not represent views of journals’ editorial board as a unit, journals’ editorial office, journals themselves or their publishers, authors’ institutions, or scientific societies where authors hold senior positions.

Microplastics have become predominant contaminants, attracting much political and scientific attention. Despite the massively-increasing research on microplastics effects on organisms, the debate of whether environmental concentrations pose hazard and risk continues. This study critically reviews published literatures of microplastics effects on organisms within the context of "dose". It provides substantial evidence of the common occurrence of threshold and hormesis dose responses of numerous aquatic and terrestrial organisms to microplastics. This finding along with accumulated evidence indicating the capacity of organisms for recovery suggests that the linear-no-threshold model is biologically irrelevant and should not serve as a default model for assessing the microplastics risks. The published literature does not provide sufficient evidence supporting the general conclusion that environmental doses of microplastics cause adverse effects on individual organisms. Instead, doses that are smaller than the dose of toxicological threshold and more likely to occur in the environment may even induce positive effects, although the ecological implications of these responses remain unknown. This study also shows that low doses of microplastics can reduce whereas high doses can increase the negative effects of other pollutants. The mechanisms explaining these findings are discussed, providing a novel perspective for evaluating the risks of microplastics in the environment., This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors. E.A. acknowledges multi-year support from The Startup Foundation for Introducing Talent of Nanjing University of Information Science & Technology (NUIST), Nanjing, China (No. 003080 to E.A.). E.J.C. acknowledges longtime support from the US Air Force (AFOSR FA9550-13-1-0047) and ExxonMobil Foundation (S18200000000256). The sponsors were not involved in the study design; the collection, analysis or interpretation of the data; the preparation of the manuscript or the decision where to submit the manuscript for publication.

Microplastics pollution is predicted to increase in the coming decades, raising concerns about its effects on living organisms. Although the effects of microplastics on individual organisms have been extensively studied, the effects on communities, biological diversity, and ecosystems remain underexplored. This paper reviews the published literature concerning how microplastics affect communities, biological diversity, and ecosystem processes. Microplastics increase the abundance of some taxa but decrease the abundance of some other taxa, indicating trade-offs among taxa and altered microbial community composition in both the natural environment and animals’ gut. The alteration of community composition by microplastics is highly conserved across taxonomic ranks, while the alpha diversity of microbiota is often reduced or increased, depending on the microplastics dose and environmental conditions, suggesting potential threats to biodiversity. Biogeochemical cycles, greenhouse gas fluxes, and atmospheric chemistry, can also be altered by microplastics pollution. These findings suggest that microplastics may impact the U.N. Sustainability Development Goals (SDGs) to improve atmospheric, soil, and water quality and sustaining biodiversity., E.A. acknowledges support from The Startup Foundation for Introducing Talent of Nanjing University of Information Science & Technology (NUIST), Nanjing, China (No. 003080). E.J.C. acknowledges longtime support from the US Air Force (AFOSR FA9550-13-1-0047) and ExxonMobil Foundation (S18200000000256). The sponsors were not involved in the study design; the collection, analysis or interpretation of the data; the preparation of the manuscript or the decision where to submit the manuscript for publication.

Elevated levels of ground-level ozone threaten terrestrial ecosystems and biodiversity., Elevated tropospheric ozone concentrations induce adverse effects in plants. We reviewed how ozone affects (i) the composition and diversity of plant communities by affecting key physiological traits; (ii) foliar chemistry and the emission of volatiles, thereby affecting plant-plant competition, plant-insect interactions, and the composition of insect communities; and (iii) plant-soil-microbe interactions and the composition of soil communities by disrupting plant litterfall and altering root exudation, soil enzymatic activities, decomposition, and nutrient cycling. The community composition of soil microbes is consequently changed, and alpha diversity is often reduced. The effects depend on the environment and vary across space and time. We suggest that Atlantic islands in the Northern Hemisphere, the Mediterranean Basin, equatorial Africa, Ethiopia, the Indian coastline, the Himalayan region, southern Asia, and Japan have high endemic richness at high ozone risk by 2100.

Ground-level ozone (O3) pollution can adversely affect human health and vegetation, thus being an important environmental issue nowadays. Ozone biological monitoring (biomonitoring) is a method of O3 monitoring by observing quantitative changes in living organisms physically present in a specific environment. Here, we provide a concise view of the field of O3 biomonitoring, along with recent advances that are expected to advance this field in the future. We also recommend that O3 biomonitoring is included in citizen science initiatives as well as in worldwide curricula of educational institutions. Policy-makers and the general public may not understand biomonitoring data; hence, a major challenge is how to communicate the information to the audience in a way that permits the best comprehension.

The need to protect plants against environmental challenges, abiotic and biotic, leads to the application of nanomaterials and pesticides in the environment. Recently, nanopesticides have been developed to replace classic pesticides. Their wide application in the agricultural practice leads to deposition of nanomaterials (and potential residuals) in the natural environment. The use of nanopesticides is a great challenge for biodiversity; however, not as originally envisioned. We discuss how nanopesticides may pose risks for biodiversity at far lower concentrations/doses than currently thought.

The environmental contamination of antibiotics caused by their over or inappropriate use is a major issue for environmental and human health since it can adversely impact the ecosystems and promote the antimicrobial resistance. Indeed, considering that in the environmental matrices these drugs are present at low levels, the possibility that bacteria exhibit a hormetic response to increase their resilience when exposed to antibiotic subinhibitory concentrations might represent a serious threat. Information reported in this review showed that exposure to different types of antibiotics, either administered individually or in mixtures, is capable of exerting hormetic effects on bacteria at environmentally relevant concentrations. These responses have been reported regardless of the type of bacterium or antibiotic, thus suggesting that hormesis would be a generalized adaptive mechanism implemented by bacteria to strengthen their resistance to antibiotics. Hormetic effects included growth, bioluminescence and motility of bacteria, their ability to produce biofilm, but also the frequency of mutation and plasmid conjugative transfer. The evaluation of quantitative features of antibiotic-induced hormesis showed that these responses have both maximum stimulation and dose width characteristics similar to those already reported in the literature for other stressors. Notably, mixtures comprising individual antibiotic inducing stimulatory responses might have distinct combined effects based on antagonistic, synergistic or additive interactions between components. Regarding the molecular mechanisms of action underlying the aforementioned effects, we put forward the hypothesis that the adoption of adaptive/defensive responses would be driven by the ability of antibiotic low doses to modulate the transcriptional activity of bacteria. Overall, our findings suggest that hormesis plays a pivotal role in affecting the bacterial behavior in order to acquire a survival advantage. Therefore, a proactive and effective risk assessment should necessarily take due account of the hormesis concept to adequately evaluate the risks to ecosystems and human health posed by antibiotic environmental contamination.

Evaluations of ozone effects on vegetation across the globe over the last seven decades have mostly incorporated exposure levels that were multi-fold the preindustrial concentrations. As such, global risk assessments and derivation of critical levels for protecting plants and food supplies were based on extrapolation from high to low exposure levels. These were developed in an era when it was thought that stress biology is framed around a linear dose-response. However, it has recently emerged that stress biology commonly displays non-linear, hormetic processes. The current biological understanding highlights that the strategy of extrapolating from high to low exposure levels may lead to biased estimates. Here, we analyzed a diverse sample of published empirical data of approximately 500 stimulatory, hormetic-like dose-responses induced by ozone in plants. The median value of the maximum stimulatory responses induced by elevated ozone was 124%, and commonly

The rapid progress in nanotechnology has dramatically promoted the application of engineered nanomaterials in numerous sectors. The wide application of nanomaterials and the potential accumulation in the environment sparked interest in studying the effects of nanomaterials on algae and plants. Hormesis is a dose response phenomenon characterized by a biphasic dose response with a low dose stimulation and a high dose inhibition. This paper quantifies for the first time nanomaterial-induced hormesis in algae and plants. Five hundred hormetic concentration-response relationships were mined from the published literature. The median maximum stimulatory response (MAX) was 123%, and commonly below 200%, of control response. It was also lower in algae than in plants, and occurred commonly at concentrations