 China burns about half of the world's coal, spewing heavy metals such as mercury led into the atmosphere, and affecting the development of neighboring children. But what if you don't live in China, or eat anything produced in China? Well, you could still be exposed to mercury that settles in the oceans, if you eat fish and seafood, but some people drink something from China. Tea. China is one of the biggest exporters, but their rapid industrialization has raised concerns about lead contamination. Lead is a toxin that can affect almost every organ in the body. And the more lead in the soil, the more that ends up in the tea leaves. And the closer the tea is grown to the highway, the higher the level, suggesting leaded gas, which wasn't banned in China until the year 2000, may also be playing a role. And just like larger, longer-living fish accumulate more mercury, longer-living leaves accumulate more lead. Young tea leaves appear to have two to six times less lead than mature tea leaves. So not only do the young leaves that are used to make green tea and white tea have significantly less lead than the older leaves used to make black and oolong tea, the lead in black and oolong tea appears to be released much more readily into the tea water when brewed. And so the health risk from lead may be 100 times lower for green tea compared to oolong and black. Since certain fungicides may have heavy metal impurities, one might assume organic teas would be less contaminated, but in a study of 30 common teas off North American store shelves, there did not seem to be less toxic element contamination than regular tea, though presumably organic tea would have much less pesticide contamination. In terms of lead, the source of the tea, the country of origin, appears to be the most important. So, bottom line, how much tea is safe to drink? Based on the most stringent safety limits in the world, like California's Prop 65 parameters, and the largest studies of tea-laid contamination from around the world, this is what I was able to come up with. If you're not pregnant and you're just drinking green tea, it doesn't matter where you get your tea from. You can drink as much as you want. You can drink one cup of tea a day. You can drink 15 cups a day. But given the average levels of lead in Chinese black tea samples, more than three cups a day would exceed the daily safety limit for lead, or at least could exceed it. Now that's if you're drinking tea, throwing the tea leaves or tea bag away. If you're eating the leaves, like drinking matcha tea, which is powdered green tea, or throwing tea leaves into your smoothie like I like to do, I wouldn't add more than two or three heaping teaspoons, unless you're using Japanese green tea, which is so low in lead that you can safely eat 15 spoonfuls a day. The only reason I would caution more than eight is that would could exceed the daily recommended limit for caffeine for adults. What about children? If you're a 70-pound 10-year-old, lead still isn't a problem drinking green tea, but the safe caffeine intake for children is probably down around 3 milligrams per kilogram, which would limit you to about four cups a day, though I wouldn't add more than two spoonfuls of Japanese green tea to a child's smoothie for caffeine reasons, and more than one of Chinese green tea for lead reasons. Similarly, I wouldn't like to see children drinking more than one cup of black tea a day and wouldn't want them eating the leaves at all. What about pregnant women? Pregnant women should be able to drink a cup a day of green tea throughout pregnancy, regardless of the source, based on average tea lead levels, and the limit for Japanese tea is really just the caffeine limit above four cups a day. I wouldn't recommend drinking black tea during pregnancy, though, or eating any kind of tea leaves, unless you know you're getting tea from a low-lead source.