Lead (and other heavy metals) in tea, and what to do about them

With the recent flurry of concern about lead in drinking water following the disaster in Flint, Michigan, I was curious to look into the question of lead and other heavy metals in tea leaves, and how much ends up in the tea we drink, and how much of that ends up absorbed into our bodies.

The answer to this question is complicated by the enormous differences in soil, growing conditions, environmental contamination, age of leaf and type of processing of the leaf that teas represent. Furthermore, different teas available in different countries appear to have very different levels of heavy metals.

However, here are some generalizations: 

• soils at lower pH lead to a greater uptake of heavy metals by the plant;
• location in proximity to sources of contamination increase plant contamination, both in the leaf and on the leaf's surface;
• younger leaves harvested in the spring have less contamination than leaves harvested in the fall, which have less than leaves harvested in the summer;
• leaves that are treated with steam have less contamination than leaves treated in other ways, such as pan-firing, so that a Japanese green tea has very little if any contamination.

Fukamushicha — very long-steamed Japanese green tea. 

Image from Wikipedia.

What you can do about the presence of heavy metals in your tea leaves:

• quickly rinse your tea leaves with the hot water you are going to use for brewing: this removes surface contamination from air pollution;
• brew for as short a time as possible, as longer brewing times increase the chances of heavy metals being leached out of the leaf; you may also want to avoid multiple steeping unless they are very short; nevertheless, the greatest amount of metals is leached out within the first five minutes of steeping, so it may not be possible to avoid this step;
• avoid lowering the pH of the tea, for example by adding lemon juice: heavy metals in tea leaves and in brewed tea are complexed with the flavonols, catechols,  and polyphenols in the tea; as long as  they remain in these complexes, they are generally less available for absorption into the body; lowering the pH of the tea releases the heavy metals from these complexes.

In their exhaustive review of studies of the analysis of metals in teas published in 2012, Anna Szymczycha-Madeja and her colleagues stated:

"...these studies are valuable, but the approaches used in these works do not retrieve information about existing species that are present in tea and crucial to assess the bio-availability of elements through habitual tea drinking. Thus, still more effort is required to understand the speciation of elements in tea and their impact on the human health." **

This review was a call to action. I'm now seeing more and more papers published concerning the implications of heavy metal contamination for human health. The problem is that each of these papers concerns one particular tea, grown in one particular spot, at one particular time, and prepared for one specific market, in one particular way. It's certainly not possible to make any sweeping statements such as ones I've seen in the popular press lately.

Nevertheless, the generalizations I've listed above hold true, as do the basic recommendations. 

==>>  There is one more generalization that is important to make: so far there is no evidence that consumption of Camellia sinensis or assamica tea in moderation causes any adverse health problems due to heavy metal contamination. 

** 

Anna Szymczycha-Madeja, 

Maja Welna, 

Pawel Pohl. 

Elemental analysis of teas and their infusions by spectrometric methods. TrAC Trends in Analytical Chemistry Volume 35, May 2012, Pages 165–181.