Tea is a beverage brewed by steeping leaves of a type of camellia bush (or sometimes ‘tree’). White tea uses only the newest growth (and has the least caffeine); green, black, and pu-erh (fermented) have progressively more caffeine and use older foliage. A teasan (or herbal tea) is a beverage brewed by steeping other types of plant material; naturally decaffeinated.
Concerns with heavy metal contamination due to industrial pollution and/or to past inorganic practices such as spraying with an arsenic-based pesticide.
Concerns with chemical commonly used in tea bags.
Survey of good and bad teas chemically speaking