Sources of Contamination
January 1999

While contamination of dietary supplements is extremely rare, it is helpful to be aware of possible causes so that outbreaks are prevented. 

Contamination can occur anywhere in the production cycle. Pesticide residues and heavy metal pollutants can be introduced to botanicals by growers, or they can seep in from a neighbor's field or the groundwater. Soil can be contaminated from previous uses. Bacteria, which have filled every conceivable ecological niche, can infiltrate crops.

Minerals can be contaminated by the chemical processes used to extract them from rocks and ores. Raw materials might be stored in places that previously held chemicals or other undesirable substances. The manufacturing process itself could expose a product to whatever herbs or other materials were previously run through a particular machine.

Manufacturers establish and follow procedures for ensuring that contaminants do not enter the plant in the form of raw materials and are not introduced during processing. Practices such as testing of materials, regular cleaning of machinery, and tracking of materials by lot number are used to ensure purity. Standardized good manufacturing practices (GMPs) also include guidelines for ensuring cleanliness.

The exemplary safety record of dietary supplement products shows that manufacturers have done an excellent job of ensuring that dietary supplements remain uncontaminated.