Extraction of copper and zinc from rubber and silicone stoppers

Drugs and other chemicals are often administered in the drinking water of laboratory animals, and bottles for this purpose usually have rubber stoppers. We studied the ability of solutions of several drugs to extract copper and zinc from rubber and silicone stoppers. Water and isoniazid extracted little copper or zinc from rubber stoppers, whereas EDTA, ethambutol, tetracycline, and chlorpromazine generally extracted considerable quantities of copper and zinc from these stoppers. Neither water nor solutions of the above drugs extracted copper or zinc from silicone stoppers. We routinely use silicone stoppers on water bottles when conducting laboratory studies requiring administration of drugs, toxins, or nutrients in the drinking water.