I loved drinking tea, but I recently stopped when I found out that green and black tea have a large amount of Fluoride, highly toxic to the human body. I drink just hot water, or one tea bag split between a whole tea pot, or coffee.
Edited: Fluoride is NOT a heavy metal. and spelling
Apparently tea can have up to ~10x as high a Fluoride concentration as municipal drinking water.
Also, there seems to be a case of a woman who developed bone fluorosis after consuming several gallons of double strength instant tea a day for a considerable time.
So potentially it could be a concern but in practical terms it's unlikely to be a problem. If you're concerned I'd study which teas have the highest Fluoride levels (it's dependent on region and type of tea), determine whether your municipal tap water is also Fluoridated, and crunch some numbers to make sure you're nowhere near unsafe Fluoride consumption levels.
Edited: Fluoride is NOT a heavy metal. and spelling