By Chris Kirkham and Aishwarya Venugopal (Reuters) -Sales of Juul e-cigarettes were blocked by the U.S. Food and Drug Administration on Thursday, in a major blow to the once high-flying firm whose products have been tied to a surge in teenage vaping. The agency said the applications “lacked sufficient evidence” to show that sale of the products would be appropriate for public health, following a nearly two-year-long review of data provided by the company. Some of the findings raised concerns due to insufficient and conflicting data, including whether potentially harmful chemicals could leach o…