The antibacterial and antifungal properties of silver nanoparticles (NPs) have seen them find use in a range of industrial and consumer products. This has led to them being found increasingly in the environment and the attendant concerns over their effects once released.

Virender Sharma and co-workers, Florida Institute of Technology, USA, have found that silver nanoparticles may also be produced naturally. They find that humic acid, a mixture of organic acids formed during decay of organic material, can reduce silver ions at room temperature in 2-4 days to form spherical and polydisperse NPs. Humic acid also acted to stabilize the NPs, preventing their aggregation for up to two months.

This could explain reports of AgNPs in the environment before their widespread use and their transport over long distances. It could also lead to new routes to synthesize NPs that do not require elevated temperatures.

_{Image: (c) Wiley-VCH}

• Humic Acid-Induced Silver Nanoparticle Formation Under Environmentally Relevant Conditions
  N. Akaighe, R. I. MacCuspie, D. A. Navarro, D. S. Aga, S. Banerjee, M. Sohn, V. K. Sharma,
  Environ. Sci. Technol. 2011, 45(9), 3895–3901.
  DOI: 10.1021/es103946g