Bioindicators serve as vital proxies for detecting pollutants and assessing potentially toxic element (PTE) concentrations, contributing to biomonitoring programs that inform environmental policies and conservation efforts by revealing disturbances from anthropogenic activities. Due to their sensitivity to various toxic elements, such as heavy metals and gases, bioindicators reflect the overall health of terrestrial and aquatic environments. A variety of organisms, including animals, plants, and microbes, have been classified as biological indicators. By functioning as proxies, their use enables non-invasive, real-time, and cost-effective pollution monitoring, providing a valuable early warning system to detect ecosystems at risk. Bioindicators are also important in the development of ecological management strategies. To better understand the role of bioindicators as proxies for toxic elements, this review focuses on scenarios that prove how effectively they are used for detecting pollution and assessing environmental health, highlighting case studies, methodological approaches, as well as species-specific sensitivities across the ecosystems.