The intensive flow of pollutants into ecosystems leads to their structural and functional changes. In such anthropogenically transformed ecosystems, the mechanisms of balanced functioning are disrupted, which leads to a loss of ecological sustainability. The paper examines the issue of the established response of the biotic component of the ecosystem to the impact of anthropogenic pollutants. It is proved that the biotic component of ecosystems is a reliable indicator of their sustainability. It is noted that the study of the levels of reactions of living organisms in ecosystems and their thresholds to the harmful effects of anthropogenic pollutants allows developing the approach for assessing the level of their environmental sustainability. The authors have proposed the approach for assessing the sustainability of ecosystems based on studies of the viability of their biotic component. The results of the research have shown that the biotic component of ecosystems allows to reliably reflect the level of their sustainability as an informative indicator of their ecological reliability. The paper demonstrates that the assessing ecological sustainability of anthropogenically loaded ecosystems is a highly informative indicator of determining the level of their ecological reliability and can be successfully applied for managing ecological reliability of such anthropogenically loaded ecosystems.