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The Science of Nature -     

Enhanced growth and reproduction of Caenorhabditis elegans (Nematoda) in the presence of 4-nonylphenol

The nematode Caenorhabditis elegans was exposed over a whole fife-cycle (72 h) to several concentrations of 4-nonylphenol (NP; nominal concentrations: 0-350 microg/l). Growth and reproduction of C. elegans were enhanced at NP concentrations of 66 and 40 microg/l, respectively, with effects showing dose-response relationships. These stimulatory effects might be of ecological relevance in benthic habitats, where organisms can be exposed to high concentrations of NP.     

Empirical Bayes calculations of concordance between endpoints in environmental toxicity experiments

Hierarchical models are considered for estimating the probability of agreement between two outcomes or endpoints from an environmental toxicity experiment. Emphasis is placed on generalized regression models, under which the prior mean is related to a linear combination of explanatory variables via a monotone function. This function defines the scale over which the systematic effects are modelled as additive. Specific illustration is provided for the logistic link function. The hierarchical model employs a conjugate beta prior that leads to parametric empirical Bayes estimators of the individual agreement parameters. An example from environmental carcinogenesis illustrates the methods, with motivation derived from estimation of the concordance between two species carcinogenicity outcomes. Based on a large database of carcinogenicity studies, the inter-species concordance is seen to be reasonably informative, i.e. in the range 67–84%. Stratification into pertinent potency-related sub-groups via the logistic model is seen to improve concordance estimation: for environmental stimuli at the extremes of the potency spectrum, concordance can reach well above 90%.