Chemistry behind blue skin due silver ingestion

Chemistry behind blue skin due to silver ingestion

6:28 AM, 31st October 2012
Chemistry behind blue skin due to silver ingestion
Brown scientists have figured out the complex chemistry behind argyria that turns the skin blue.

PROVIDENCE, US: Researchers from Brown University have shown for the first time how ingesting too much silver can cause argyria, a rare condition in which patients’ skin turns a striking shade of grayish blue. “It’s the first conceptual model giving the whole picture of how one develops this condition. What’s interesting here is that the particles someone ingests aren’t the particles that ultimately cause the disorder,” said Robert Hurt, Professor, Brown University.

Scientists have known for years argyria had something to do with silver. The condition has been documented in people who drink antimicrobial health tonics containing silver nanoparticles and in people who have had extensive medical treatments involving silver. Tissue samples from patients showed silver particles actually lodged deep in the skin, but it wasn’t clear how they got there.

Hurt and his team show that nanosilver is broken down in the stomach, absorbed into the bloodstream as a salt and finally deposited in the skin, where exposure to light turns the salt back into elemental silver and creates the telltale bluish hue. That final stage, oddly, involves the same photochemical reaction used to develop black-and-white photographs.

Hurt and his team found that nanosilver tends to corrode in acidic environments, giving off charged ions that can be toxic in large amounts. Jingyu Liu, Hurt’s Graduate Student, thought those same toxic ions might also be produced when silver enters the body, and could play a role in argyria.

Researchers found that nanosilver corrodes in stomach acid in much the same way it does in other acidic environments. Corrosion strips silver atoms of electrons, forming positively charged silver salt ions. Those ions can easily be taken into the bloodstream through channels that absorb other types of salt. That’s a crucial step, said Hurt. Silver metal particles themselves aren’t terribly likely to make it from the GI tract to the blood, but when they’re transformed into a salt, they’re ushered right through. Some of those ions would eventually end up in the skin, where they’d be exposed to light.

To re-create this end stage, the researchers shined ultraviolet light on collagen gel containing silver ions. The light caused electrons from the surrounding materials to jump onto the unstable ions, returning them to their original state - elemental silver. This final reaction is ultimately what turns patients’ skin blue. The photoreaction is similar to the way silver is used in black and white photography. When exposed to light, silver salts on a photographic film reduce to elemental silver and darken, creating an image.

Despite its potential toxicity, silver has been valued for centuries for its ability to kill germs, which is why silver nanoparticles are used today in everything from food packaging to bandages. There are concerns however that this nanoparticle form of silver might pose a unique health threat all its own.

“The concern in this case is the total dose of silver, not what form it’s in. This study implies that silver nanoparticles will be less toxic than an equivalent amount of silver salt, at least in this exposure scenario,” said Hurt.

© Brown University News

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