The American Herbal Products Association (AHPA) has published new industry guidance titled Limits of Foreign Matter in Herbal Ingredients, which outlines maximum quantitative limits on foreign matter in various herbal raw materials.
 
The guidance recommends plant parts of the same herbal raw material species, other than those named in specifications, should not exceed 5% (by weight), and all other foreign matter should not exceed 2% (by weight).
 
It is natural for herbal raw materials to contain some foreign matter which may consist of:
 

• Plant parts of the herbal raw material other than those named in its specification and description, for example the European Pharmacopeia Hawthorn Leaf with Flower monograph limits lignified branches with a diameter > 2.5mm to not more than 8%;
• Any organism, part or product of an organism, other than those named in the specification and description of the herbal raw material, for example grass clippings in mint leaves;
• Mineral admixtures present in the herbal raw material, for example soil, stones, metal, sand and dust.
• Official pharmacopeias worldwide recognize quantitative limits of foreign matter as part of monograph specifications for herbal raw materials. Limits of foreign matter for the same herbal material may differ in various pharmacopeias. Although not specific to foreign matter as defined here, 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.

 
“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 guidance offers an overview of standard industry practices for the detection and mitigation of foreign matter and recommends good agriculture and collection practices, such as those outlined in the AHPA Guidance for Good Agricultural and Collection Practices and Good Manufacturing Practices for Botanical Materials, to minimize foreign matter in raw herbal materials.
 
The guidance can be found here.