Hormesis: the new approach in risk assessment?

Cadmium toxicity to and accumulation in a soil collembolan (Folsomia candida): major factors and prediction using a back-propagation neural network model

Accurate prediction of cadmium (Cd) ecotoxicity to and accumulation in soil biota is important in soil health. However, very limited information on Cd ecotoxicity on naturally contaminated soils. Herein, we investigated soil Cd ecotoxicity using Folsomia candida, a standard single-species test animal, in 28 naturally Cd-contaminated soils, and the back-propagation neural network (BPNN) model was used to predict Cd ecotoxicity to and accumulation in F. candida. Soil total Cd and pH were the primary soil properties affecting Cd toxicity. However, soil pH was the main factor when the total Cd concentration was < 3 mg kg-1. Interestingly, correlation analysis and the K-spiked test confirmed nutrient potassium (K) was essential for Cd accumulation, highlighting the significance of studying K in Cd accumulation. The BPNN model showed greater prediction accuracy of collembolan survival rate (R2 = 0.797), reproduction inhibitory rate (R2 = 0.827), body Cd concentration (R2 = 0.961), and Cd bioaccumulation factor (R2 = 0.964) than multiple linear regression models. Then the developed BPNN model was used to predict Cd ecological risks in 57 soils in southern China. Compared to multiple linear regression models, the BPNN models can better identify high-risk regions. This study highlights the potential of BPNN as a novel and rapid tool for the evaluation and monitoring of Cd ecotoxicity in naturally contaminated soils.

A critique of the use of hormesis in risk assessment

There are severe problems and limitations with the use of hormesis as the principal dose-response default assumption in risk assessment. These problems and limitations include: (a) unknown prevalence of hormetic doseresponse curves; (b) random chance occurrence of hormesis and the shortage of data on the repeatability of hormesis; (c) unknown degree of generalizability of hormesis; (d) there are dose-response curves that are not hormetic, therefore hormesis cannot be universally generalized; (e) problems of post hoc rather than a priori hypothesis testing; (f) a possible large problem of ‘false positive’ hormetic data sets which have not been extensively replicated; (g) the ‘mechanism of hormesis’ is not understood at a rigorous scientific level; (h) in some cases hormesis may merely be the overall sum of many different mechanisms and many different dose-response curves - some beneficial and some toxic. For all of these reasons, hormesis should not now be used as the principal dose-response default assumption in risk assessment. At this point, it appears that hormesis is a long way away from common scientific acceptance and wide utility in biomedicine and use as the principal default assumption in a risk assessment process charged with ensuring public health protection.

Effects of electromagnetic fields on parthenogenic eggs of Daphnia magna Straus

Developing parthenogenetic eggs of Daphnia magna were used as a test-system to evaluate the effect of a number of low-frequency electromagnetic fields (EMF) of 75microT density. Two blocks of EMF acting frequencies were found in the studied series-45, 110, and 175Hz, and 435 and 500Hz. Developing parthenogenetic eggs of D. magna exposed to EMF with indicated parameters have shown accelerated rates of embryonic development. Females that developed from exposed eggs have shown deteriorated production characteristics in their first brood. Used test-system may be successfully utilized to detect weak effects directly during embryogenesis. However, results obtained only during daphnids' early developmental stages are incomplete without observations on their further development.

Hormetic Effects of Hormones, Antihormones, and Antidepressants on Cancer Cell Growth in Culture: In Vivo Correlates

Evidence is presented that the ability of hormones and antihormones to cause biphasic (hormetic) proliferative responses in cancer cells in vitro correlates with a similar effect of these substances in humans with cancer. Certain antidepressants also produce biphasic growth responses of cancer cells in vitro and stimulate cancer growth in rodents, correlating with an increased risk of breast and other cancers in some, but not all, epidemiological studies assessing early and/or late cancer incidence in patients on antidepressant drugs. The observation that certain drugs with biphasic effects on cancer cell growth in vitro may also produce an "up-down" effect on cancer growth in humans supports Calabrese's suggestion that the concept of the hormetic dose response must be taken seriously by toxicologists and regulators.