MesoCopper is .9999 pure copper nanoparticles in colloid form, a TRUE colloidal copper, which means predominantly copper particles NOT copper ions. It is an all natural mineral supplement. Made with the highest purity, sterile reagent grade deionized water. Colloidal copper does not require refrigeration after opening. MesoCopper is non toxic (see Material Data Safety Sheets). NOTE: high PPM (parts per million) does NOT necessarily mean high PSA or bioavailability. Colloidal copper concentration is 10 ppm minimum. Please see our web site "purestcolloids" or our company information here on amazon for more technical information on colloidal copper. MesoCopper is a registered trademark of Purest Colloids, Inc.