Quantum dots (QDs) are semiconducting nanocrystals with unique optical properties. When coated with shell/capping, QDs are not deleterious to cells and organisms. However, when QDs are retained in the cellular environment for a certain period of time, their coatings may be degraded, yielding "naked" QDs. Although some studies have documented the acute effects of cadmium telluride (CdTe) QDs in various cell lines, however, to our knowledge, there are no published studies on the chronic effects of CdTe QDs in normal lung cells. In this study, we therefore sought to study the effects of CdTe QDs of various particle sizes on their cytotoxicity and carcinogenicity in normal human bronchial epithelial cells (BEAS-2B). A total of three particle sizes of CdTe QD with emission maximum at 520, 580, and 730 nm were employed (abbreviated as 520Q 580Q and 730Q respectively). Our results indicated that acute exposure to 520Q (similar to 2.04 nm in diameter) and 580Q (similar to 3.24 nm in diameter) elicited dose-dependent cytotoxicity; while acute exposure to 730Q (similar to 5.40 nm in diameter) elicited negligible cytotoxicity in BEAS-2B cells. Notably, chronic exposure to CdTe QD of all three tested particle sizes induced BEAS-2B cell transformation as evidenced by enhanced cell migration and anchorage-independent growth on soft agar. Taken together, our findings suggest that CdTe QDs are potent human lung carcinogens. (C) 2017 Elsevier Inc. All rights reserved.