The EPA Integrated Risk Information System (IRIS) lists safety information for many substances, including silver.
One portion of the assessment is the oral Reference Dose (RfD.) According to the EPA’s description of RfD,
“The oral Reference Dose (RfD) is based on the assumption that thresholds exist for certain toxic effects such as cellular necrosis. It is expressed in units of mg/kg-day. In general, the RfD is an estimate (with uncertainty spanning perhaps an order of magnitude) of a daily exposure to the human population (including sensitive subgroups) that is likely to be without an appreciable risk of deleterious effects during a lifetime.”
In other words, the RfD is an estimate of how much silver a person can consume on a daily basis throughout a lifetime without approaching an estimated threshold of risk.
The RfD for silver is “5E-3 mg/kg-day.” This small amount of silver (5E-3 mg equals 0.005 mg) per kilogram of body weight per day can be translated into a daily guideline for people of varying size. In the context of a silver water that contains 10 ppm (parts per million) silver, the RfD can be translated into an estimated guideline for daily 10 ppm silver water ingestion throughout a lifetime.
Listed by body weight, here is the RfD for water-based products containing 10 ppm silver:
A table like this clearly shows the importance of body weight in determining a safe level of silver ingestion. For instance, a person weighing 250 lbs can take twice the amount daily of a person weighing 125 lbs.
Importantly, this information is not intended as a dosage or recommendation of any sort. Rather, it is a mathematical extrapolation of estimates provided by the EPA. This conversion from “5E-5 mg/kg-day” into the table above is provided for quick reference and access to the RfD.
To read the full source document, please click here.