Herbal Supplements Often Have Contaminants, Study Finds - NYTimes.com
The level of lead in the supplements tested was low, but if a person takes a number of different supplements, the lead could add up in the body. Many had pesticides, as well.
Apparently (via Dr Edell) nearly all supplements are now manufactured in China and there is absolutely no oversight or testing. All the vitamin C is from China. If I was a big supplement-taker, I would recommend brands that were tested by Consumerlabs.com and found to be free of contaminants and actually contain the listed amount of ingredient.