Yes, while Moutain Rose Herbs has a great selection of organic herbs, that only takes into account the actions of the farmer himself. That does not include actions of those around him and other environmental factors.
Chemical contamination certainly is a concern and should be considered. Lead and other heavy metals can and do accumulate in our bodies. They are not easy to expel.
Fortunately, there are many good online vendors to choose from. You need to decide what level of risk you are willing to take and proceed accordingly.
Patrick and I are trying to learn how to grow what we need personally and also for our business. Sure gives a better warm fuzzy about the plants.