A toxic effect at molecular level can be expressed at community level: A case study on toxic hierarchy

This study demonstrated hierarchical toxicity and addressed the relevance and differences of toxic effects at the molecular, individual, population, and community levels. Superoxide dismutase (SOD) activity, photosynthetic oxygen production, filtration rate, life span and densities of Platymonas helgolandica var. tsingtaoensis, Isochrysis galbana, and Brachionus plicatilis in single-species tests and customized community tests were examined in response to a concentration gradient of aniline ranging from 0 to 50.0 mg L^-1. The SOD activity was the most sensitive endpoint with the fastest response to aniline according to the calculated no-detection of toxic effect concentration (NDEC) and the EC₅₀. The individual- and population-level endpoints, showing a lower response to aniline, could be constructed from the SOD activity in a stepwise manner. A multi-scale hierarchical model with endpoints at 4 levels was used to characterize toxic effects, at the scales of time and size. Linkage of SOD activity to toxic effects at a community level was established level by level to express the change in the customized community with the concentration of aniline. The calculated threshold concentration of aniline for the customized community was nearly equal to the minimum NDEC, demonstrating as great an impact on interactions by the toxic effect at subpopulation-level as that at the community level. However, we identified a trend of higher sensitivities of measured endpoints at sub-population level, decreasing sensitivity at higher levels but a great variety of sensitivities at community level. Although the characteristics of toxic effects are different at different levels, the structure and process of endpoints at adjacent levels are related to and interact with each other. The resulted indirect effects, together with direct effect, determine the toxic effect at every levels of biological complexity. The toxic effects at adjacent levels should be studied at the same time to better understand the ecological risk of contaminants.