When I wildcraft, I usually try to avoid areas 25 feet from a roadway, but truth is, that is often the disturbed land where the herbs grow best. If the herb I need is growing there and there isn't any other around, I may use it anyway. I won't use it for my daily infusions however, because a steady diet of plants grown near roadways where lead pollution from old gasoline may have fallen, isn't good. Manufactured herbs have problems too. Schultz's article describes workers pulling herb out of bags with one label to put into capsules with an entirely different one- cayenne capsules filled with red beet powder for instance.
Quality control is necessary, especially with discount, mass-marketed brands.
Many tincture manufacturers used high ratios of alcohol to herb, insuring that little medicinal action would get through. And there are small manufacturers who use techniques which may or may not be warranted for a specific herb- insufficient alcohol in the usnea, too much in the reishi tincture and glycerites, which are often poor extractors, playing upon the fear of alcohol of many health seekers. Proper preparation of the herbs makes the necessary compounds bioavailable. Herbal cancer researcher Ingrid Naiman found that a syrup preparation of Harry Hoxey's trifolium compound worked for her clients while the same herbs in a tincture or capsule did not. As the herbal medicine field becomes flooded with recently graduated amateurs, or scientists who lack clinical herbalist training, quality can become a wider problem.