http://en.wikipedia.org/wiki/Argyria
Generally, "silver exhibits low toxicity in the human body, and minimal risk is expected due to clinical exposure," when silver or silver compounds are used in the treatment of external infections or in medical appliances. Lansdown states that "Chronic ingestion or inhalation of silver preparations (especially colloidal silver) can lead to deposition of silver metal/silver sulphide particles in the skin (argyria), eye (argyrosis) and other organs. These are not life-threatening conditions but cosmetically undesirable.” This view is supported by the Agency for Toxic Substances and Disease Registry (ATSDR) and other authorities. Only one death has been reported in the medical literature which the authors felt was due to silver toxicity. In that case a 71-year-old man developed status epilepticus after repeated oral ingestion of colloidal silver. The reference dose, published by the United States Environmental Protection Agency in 1991, which recommends
the estimated daily exposure which is unlikely to incur a appreciable risk of deleterious effects during a lifetime, is 5 µg/kg/d; meaning 5 microgram of silver per kilo of weight per person each day – about 1 liter of 10 ppm colloidal silver per month for a 66 kg person.
so, more than that