Short version of this study: Colloidal silver shows promise in inhibiting SARS-CoV-2, the virus that causes covid.
They mention cytoxicity (cell toxicity) at 20 ppm. This study was appartently done in a petri dish, not a person. Many silver products are sold at 30 ppm.
From my quick read of this, I wouldn’t worry about cytotoxicity at 30 ppm because the minute you take it (via the mouth), you are diluting it with your saliva and intestinal juices. Larger particles may have more cytotoxic effects.
They do mention that lower particle size works better. So look for nano silver with small particle size over high PPM.