Improved empirical models describing hormesis

Abstract

During the past two decades, the phenomenon of hormesis has gained increased recognition. To promote research in hormesis, a sound statistical quantification of important parameters, such as the level and significance of the increase in response and the range of concentration where it occurs, is strongly needed. Here, we present an improved statistical model to describe hormetic dose-response curves and test for the presence of hormesis. Using the delta method and freely available software, any percentage effect dose or concentration can be derived with its associated standard errors. Likewise, the maximal response can be extracted and the growth stimulation calculated. The new model was tested on macrophyte data from multiple-species experiments and on laboratory data of Lemna minor. For the 51 curves tested, significant hormesis was detected in 18 curves, and for another 17 curves, the hormesis model described that data better than the logistic model did. The increase in response ranged from 5 to 109%. The growth stimulation occurred at an average dose somewhere between zero and concentrations corresponding to approximately 20 to 25% of the median effective concentration (EC50). Testing the same data with the hormesis model proposed by Brain and Cousens in 1989, we found no significant hormesis. Consequently, the new model is shown to be far more robust than previous models, both in terms of variation in data and in terms of describing hormetic effects ranging from small effects of a 10% increase in response up to effects of an almost 100% increase in response.

Hormesis: Biphasic Dose-Responses to Fungicides in Plant Pathogens and Their Potential Threat to Agriculture

“…According to Cedergreen et al (99), a deficiency of the Brain and Cousens model is that if the slope at the EC50 (β) is smaller than 1 then the model will not yield a curve; therefore they proposed a model that circumvents this drawback. Cedergreen et al (99) provide a robust detection method but it does not estimate the EC50, NOAEL or MSD. In general, a combination of methods may be used to detect hormesis, determine its magnitude and estimate the EC50, NOAEL and MSD, depending on the type of data that is being analyzed and on the behavior of the dose-response curve.…”

Exposure to Nanoparticles and Hormesis

“…To investigate the hazard of titanium dioxide Exposure to lower doses of nanoparticles caused a slight increase of root length whereas, root growth was clearly restricted with increasing concentration Lin and Xing (2007) To evaluate the effects of rare earth oxide nanoparticles on root elongation of plants Cerium, lanthanum, gadolinium and ytterbium oxide nanoparticles Rape 0.2 -2000 mg/L At low concentrations (< 0.8 mg/L) lanthanum and ytterbium nanoparticles had positive effects on root elongation but negative effects at higher concentrations Ma et al (2010) using a three parameter log logistic curve fitting with a hormesis parameter added as described by Brain and Cousens (1989) and with a lack of fit model as described by Cedergreen et al (2005), revealed, for the larger nanoparticles (30 nm), a biphasic relationship with a statistically significant stimulation of the algal growth rate at lower concentrations and an inhibition at higher doses. Recently, a study by Mortimer et al (2010), conducted on the ciliated protozoa Tetrahymena thermophila exposed to 31.25, 62.5, 125, 250 and 500 mg/L of copper nanoparticles (Cu-NPs) and to 1.…”

Low Doses of Fenoxaprop-P-Ethyl Cause Hormesis in Littleseed Canarygrass and Wild Oat

“…Growth stimulation due to low doses of different herbicides has been shown in several crop species both in controlled and in the field conditions (Davies et al, 2003;Duke et al, 2006;Cedergreen et al, 2007;Velini et al, 2008). The literature revealed that herbicides at low doses cause on average 20-30% of growth stimulation under controlled conditions (Cedergreen et al, 2007) and 10-25% under uncontrolled field conditions (Cedergreen et al, 2005(Cedergreen et al, , 2009). However, depending on the crop species, type of herbicide and other factors, this average stimulation increased up to 200% (Calabrese, 2008;Velini et al, 2008).…”