A recent article describes the mechanism of Argyria. The citation is: ACS Nano (2012), 6(11), 9887-9899. I've copied the abstract from the article here:
ABSTRACT The widespread use of silver nanoparticles (Ag-NPs) in consumer and medical products provides strong motivation for a careful assessment of their environmental and human health risks. Recent studies have shown that Ag-NPs released to the natural environment undergo profound chemical transformations that can affect silver bioavailability, toxicity, and risk. Less is known about Ag-NP chemical transformations in biological systems, though the medical literature clearly reports that chronic silver ingestion produces argyrial deposits consisting of silver-, sulfur-, and selenium-containing particulate phases. Here we show that Ag-NPs undergo a rich set of biochemical transformations, including accelerated oxidative dissolution in gastric acid, thiol binding and exchange, photoreduction of thiol- or protein-bound silver to secondary zerovalent Ag-NPs, and rapid reactions between silver surfaces and reduced selenium species. Selenide is also observed to rapidly exchange with sulfide in preformed Ag2S solid phases. The combined results allow us to propose a conceptual model for Ag-NP transformation pathways in the human body. In this model, argyrial silver deposits are not translocated engineered Ag-NPs, but rather secondary particles formed by partial dissolution in the GI tract followed by ion uptake, systemic circulation as organo-Ag complexes, and immobilization as zerovalent Ag-NPs by photoreduction in light-affected skin regions. The secondary Ag-NPs then undergo detoxifying transformations into sulfides and further into selenides or Se/S mixed phases through exchange reactions. The formation of secondary particles in biological environments implies that Ag-NPs are not only a product of industrial nanotechnology but also have long been present in the human body following exposure to more traditional chemical forms of silver. In short, silver, whether ionic or nanoparticles, is absorbed into the blood as silver ions attached mostly to proteins that contain sulfur. It is then carried to all parts of the body. Once there it can form nanoparticles once again upon exposure to light. It will also pull selenium from the blood and together silver and selenium are extremely insoluble, i.e. they stay there forever. Sunlight can photo-oxidize these particles and your skin turns gray to blue. Generally what I have read is it takes about 1 gram of silver accumulated in the body for the risk of Argyria to become high. If your body retained 100% of 10 PPM silver, it would take 100 liters to accumulate 1 gram. However, the vast majority of ingested silver passes through the body, probably much more than 90%. However, how much is absorbed and then deposited will depend upon the individual's body composition, diet, fluid intake, selenium levels, etc. So the development of argyria is not easily predicted except in extreme cases. Most of these are people working in industrial settings where they are exposed to high concentrations of silver all day. Just as an example, if a person took 50 mL (about 2 oz) of 10 PPM silver per day and retained 10% of it, it would take 5 ½ years to accumulate 1 g. Probably it is more likely that only 1% would be retained. In this case it would take 55 years to accumulate 1 gram and develop a risk (not a guarantee) for argyria. In my opinion, silver, like other antibiotics, should only be used when needed, not as a daily tonic. Then argyria colored skin should not be a problem. Hope this helps. John
