Among the typical examples of foreign matter in herbal raw ingredients, there are parts of a plant not named in the specification and description, such as when parts of a stem are detected in an ingredient specified for its leaves. According to the guidance, this type of foreign matter should not exceed 5% by weight of raw ingredient.
Another example is an organism or product of an organism that’s not part of the specified plant, for example grass clippings in mint leaves. This type of foreign matter may not exceed 2% by weight.
Finally, some traces of minerals may also be present in raw material, such as soil, stones, metal, sand, and dust.
"Botanical ingredients are grown in nature where they are exposed to an array of foreign matter," said AHPA Chief Science Officer Dr. Maged Sharaf. "This document recognizes this fact and helps the industry set acceptable limits for various types of foreign matter."
The association noted that official pharmacopeias around the world may recognize different limits of foreign matter for the same herbal material.
“Although not specific to foreign matter as defined [by AHPA], the U.S. Food and Drug Administration (FDA) establishes maximum levels of natural or unavoidable defects in foods that present no health hazards for humans,” according to the association.
The guidance can be found here.