A new study shows that silver nanoparticles have the potential to inhibit nitrifying bacteria in wastewater treatment works. Nitrifying bacteria play an important role in breaking down sewage. The study raises further concern about the widespread use of nano-silver in consumer products.

Nitrifying bacteria oxidise ammonia to give nitrate ions. The researchers exposed ammonia-oxidising bacteria to silver nanoparticles coated with citrate, gum arabic, and polyvinylpyrrolidone (PVP). Those coated in gum arabic and PVP were the strongest inhibitors of nitrification by Nitrosomonas europaea bacteria. “Coating plays a very important role in determining silver dissolution and ultimately toxicity to nitrifiers,” said the researchers.

The study was published in Environmental Science and Technology by researchers from the Center for Environmental Implications of Nano Technology (CEINT) in North Carolina, US.