Two new alarming research studies from the United States have highlighted serious concerns about the toxicity of nano-silver to aquatic microorganisms, plants and animals – with inevitable consequences to human food sources and health.

Nano-silver is a powerful antimicrobial used in a wide range of consumer goods, from shoes, socks, underpants, hairbrushes, toothbrushes, fridges, washing machines and more. Retailers such as as K-Mart, Rebel Sport, BigW, Priceline and Kathmandu are now selling nano-silver products, marketed as “odour-controlling” and “anti-microbial”. Last year, leading Australian microbiologists raised concerns about nano-silver breeding further antibiotic resistance in superbugs and driving increases in childhood allergies.

In a study published earlier this year, scientists from the California NanoSystems Institute (CNSI) and the University of California, Los Angeles (UCLA) tested the idea that nano-silver toxicity is mostly caused by the gradual release of silver ions from the larger crystals of nano-silver. These silver ions are able to block certain key enzymes in some types of cells and create powerful free radicals, which can oxidise and further damage enzymes, other proteins and DNA.

The team began by examining the toxicity of differents sorts of silver nanoparticles in fish gill cells and zebrafish embryos. All the particles were toxic at high doses. However, this research found for the first time that the toxicity of nano-silver is also partly based on the shape of the nanomaterial. In particular, silver nanoplates were much more toxic than silver nanorods and nanospheres. This was due to the higher rate of surface defects in the stacking of silver within the crystal structure of nanoplates, which are very efficient at creating free radicals. Taking a step back, this discovery suggests further implications for the previously under-estimated potential of impurities in all nanomaterials to create free radicals.

Researchers at Duke University took a broader approach to the real-world fate of nano-silver in a study published last month. In this study, the researchers created miniature ecosystems to simulate for the first time how nano-silver changes after release into the environment. A key finding was that nano-silver tended to form into new chemical compounds and settle in the soil and underwater sediments, creating reservoirs. However, over time these silver compounds were taken up by plants, insects and fish in these miniature ecosystems, with silver even passing from mother fish to her embryos. This evidence of bioaccumulation adds to a growing number of studies that raise concerns about their widespread use of nano-silver as a widespread anti-microbial in consumer goods.