Lead contamination is a legitimate concern. Recognized sources of lead contamination includes:
* air pollution (mainly caused by automobiles and mainly affect plantations near urban areas)
* soil pollution (deposition from automobiles and mainly affect plantations by the road side)
* harvest method (bud and younger leaves are more free of contamination)
* processing - lead contamination from equipment. This is supposed to be the easiest to avoid but unfortunately happens sometimes. According to a study published in a Chinese journal, among the 18 factories whose tea products are sampled, the factories focusing on higher grade teas have the lowest lead contents, and the lead content is less after processing compared with before processing. The factories focusing on lower grade teas have the highest lead contents. I think that's consistent with common sense, as people tend to deal with high grade tea more carefully. Besides, the equipment of manually processed tea is more likely traditional and natural.
According to a Chinese article about lead standard, the Chinese tea inspection standard is 2mg/kg. Japanese standard is 25mg/kg. EU is 5mg/kg. Australia and Canada's is 10mg/kg. I don't know how accurate it is about other countries' standards and if there have been any changes since the article is from 2008. Besides, not all tea products are inspected. So it seems to me "high grade tea" and "young leaves" are the most visible standards to consumers.