In the aquatic ecosystem, trace metal contamination is ubiquitous. Since post-industrialization, trace metals have been an immanent factor that exists in many environmental quarters and is known to be toxic to several groups of organisms. Invertebrates are one such group that are remarkable eco-indicators of trace metal toxicity due to their participation in various processes of the ecosystem. Although trace metal stress on bioindicator organisms like invertebrates has been reported in previous studies, few questions are still pertinent and relevant concerning the effects of trace metals. For example, do trace metals pose toxic effects at all times, if yes, at what concentration are they toxic, how are organisms affected by the toxicity, and what are the dynamics and fate of trace metals in the entire ecosystem. This chapter delves into understanding the above-mentioned crucial concepts on trace metal toxicity and its effects on organisms, exemplified through invertebrates, an eminent group of bioindicators. To address such issues, firstly, a comprehensive review of the general properties of trace metals focussing on their chemical properties, sources, toxic effects, and knowledge gaps of mainly the priority pollutants (antimony, arsenic, beryllium, cadmium, chromium, copper, lead, mercury, nickel, selenium, silver, thallium, and zinc) was documented. Consequently, an outline of the emergence of trace metals showing diverse sources such as the agricultural, anthropogenic, geogenic, and groundwater, along with the pathway encompassing different environmental compartments, was provided. To decipher the effects of trace metal toxicity, this chapter explores the diverse factors that determine the effects and highlights the significance of studying invertebrates, which are at the forefront of chemical stresses being omnipresent in diverse environmental compartments. In this chapter, the main factors influencing trace metal toxicity are reported as exposure time and concentration, route of exposure, and chemical forms of exposed trace metals, including the life stages and physiological status of the exposed invertebrates. Furthermore, regarding toxicity, a broader impact of trace metals was documented on the environmental risks and hazards, underscoring the need for revised policy instruments, integrated management, environmental monitoring, and impact assessments.