Hmm.. what a fascinating discussion you have here.

To me, it really boils down to 2 things: how young is the tea shoots?
Does your tea taste good?

As Dogma pointed out, tea plants accumulate minerals. When drinking
white tea and green tea, the best guarantee is to drink from the
youngest tea shoots - the first 10 days or so in Spring. They usually
make the highest grade. They also contain the least environmental
contaminants.

The best tea garden tends to use little pesticides. They just don't
need it. These tend to be tea gardens situated at high altitude at
sloping lands. The entire region tends to be prosperous tea growers
(in China consisted of small tea gardens), situated away from
factories and road traffics.

Their teas tend to be wholesaled at very high prices and not so
commonly available in the West. I came across a few tea gardens and
they hardly bother about organic labelling - Chinese market doesn't
care that much when it comes to these very sought-after teas.

Organic labelling per se doesn't mean much.

Use of chemicals is not a viable long term strategy for the best tea
gardens. If your tea tastes good, chances are it comes from a fertile
tea garden with the right conditions that make overuse of chemicals
unlikely.

Julian