After further research, I found the email to be a hoax.
The folks at Johns Hopkins sat down with Dr. Rolf Haden, assistant professor at Department of Environmental Health Sciences and the Center for Water and Health at the Johns Hopkins Bloomberg School of Public Health.
Dr. Haden dispelled the myth saying "This is an urban legend. There are no dioxins in plastics. In addition, freezing actually works against the release of chemicals."
The bottom line is that there is no cancer risk in drinking water from frozen water bottles.