Technology-critical elements (TCEs), essential in emerging technologies, are increasingly finding their way into our environment, raising concerns about their sparsely studied behavior and toxicity. To contribute insights into the toxicological aspects, we employed in vitro bioassays to investigate the possible cytotoxic effects in four representative cell lines (AR-EcoScreen GR-KO-M1, DR-EcoScreen, MCF7AREc32, VM7Luc4E2) and the potential to induce oxidative stress via the nuclear factor erythroid 2-related factor 2 (Nrf2) pathway for a number of these elements. Nine TCEs, three rare-earth elements (REEs: Gd, Nd, Yb) and six less-studied TCEs (LSTCEs: Ga, Ge, In, Ta, Te, Tl), were selected for this study, along with three well-studied traditional metal contaminants (TMCs: As, Cd, Pb) for comparison. Among the 12 studied elements, nine showed signs of inducing cytotoxicity: As, Cd, Ga, Nd, and Te in three out of the four studied cell lines and Gd, Ta, Tl, and Yb in one to two cell lines. Tellurium repeatedly exhibited the highest potency. The TCEs Ga and In, similar to As and Cd, also demonstrated the potential to induce oxidative stress. The results of this study suggest that some TCEs may potentially cause adverse health effects similar to As and Cd, thus prompting further investigations.