US researchers who investigated the increased risk of lung cancer in workers exposed to chromium VI found that those most at risk, with over three times the risk of dying from the disease, were those who had worked longer in the plants. The authors said this was probably due to their higher cumulative exposure. Because of this, they suggested exposure limits were insufficiently protective, as they didn’t take account of this cumulative effect, noting “these results suggest a potential excess risk of death from lung cancer among US workers exposed to the current permissible exposure limit (PEL) for hexavalent chromium.”
ER Braver and others. An analysis of lung cancer risk from exposure to hexavalent chromium, Teratogenesis, carcinogenesis and metagenesis, volume 5, issue 5, pages 365-378, 1985.