Silver nanoparticles are not very stable under environmental conditions and are modified due to the influence of various factors (e.g. aging). An important factor is the solubility of the particles that release silver ions in dependence of ambient conditions.

 

An essential characteristic for estimating the environmental behaviour of nanomaterials is their stability under environmental conditions. Simplified, it is assumed that a high stability leads to a high accumulation in the environment and to better transport properties. Silver nanoparticles are considered an unstable nanomaterial. In an aqueous environment, they tend to dissolve or react with other substances present in the environment. Here, the interaction of environmental factors (e.g. pH) with the particle properties (e.g. surface modification) decides on whether and how quickly certain processes (e.g. sedimentation) occur. Dissolved organic carbon, for example, affects the solubility of silver and thus both the behaviour of the particles and their effects on environmental organisms. Similarly, the type of surface modification of nano silver alters the behaviour with respect to solubility and agglomeration [1,2].

Colorful facades © huxflux / fotolia.com

 

Release from facade paint

The release of silver nanoparticles from facade paint was investigated by simulating typical environmental conditions (rain, UV light). After one year, about 30 % of the silver contained in the original paint was washed out. The released nanoparticles were not present individually, but firmly embedded in remnants of the paint matrix (see cross-cutting issues – nanoparticles in paints) [3].

 

Behaviour in waste water treatment plants / wastewater

Wastewater treatment plant from aboveWastewater treatment plant from aboveSewage treatment plants, which purify polluted wastewater from households or industry, are a potential source for nanomaterials being released into the environment. This can occur either via purified wastewater or by application of sewage sludge as fertiliser on fields (as done in some regions). First and foremost, the release of nano silver depends on the incorporation into the respective product (see cross-cutting issues - nanoparticles in textiles).

For silver-containing textiles, it was shown as part of the UMSICHT project that some products released almost no silver, whereas others released high silver amounts into the sewage. Released nanosilver was effectively transported through the sewers to the treatment plant. So far, the concern on a disruption of bacterial treatment of wastewater by silver nanoparticles has not been confirmed. Furthermore, silver nanoparticles are effectively separated from the wastewater and subjected to dissolution- and modification processes. The majority of the particles will adsorb to solids and thus ends up in sewage sludge (see cross-cutting issues - nanoparticles in wastewater treatment plants) [4-8].Section of grass and soil. © andreusK / fotolia.com

 

 

Behaviour in soils

Assessing the behaviour of nanomaterials in soils is a challenging task because appropriate methods are still missing. Both the nature of the silver nanoparticles as well as the composition of the soil can vary greatly, which likewise affects the interaction between soil and particles. For example, by comparing 16 natural soils the distribution and solubility of nano silver varied greatly depending on the soil type. The distribution of nano silver in soil differs significantly from the distribution of both of the dissolved silver as well as coarser silver particles [9,10].

 

 

Silver nanoparticles are considered as unstable under environmental conditions. A variety of processes leads to the dissolution or to modifications of the particle surface. In this respect, both the environmental conditions as well as the particle characteristics determine whether and how quickly these processes occur.

 

 

Literature arrow down

  1. Kennedy, AJ et al. (2012), Environ Sci Technol, 46(19): 10772-10780.
  2. Tejamaya, M et al. (2012), Environ Sci Technol, 46(13): 7011-7017.
  3. Kaegi, R et al. (2010), Environ Pollut, 158(9): 2900-2905.
  4. Kaegi, R et al. (2013), Water Res, 47(12): 3866-3877.
  5. Doolette, CL et al. (2013), Chem Cent J, 7(1): 46.
  6. Li, LXY et al. (2013), Environ Sci Technol, 47(13): 7317-7323.
  7. Kim, B et al. (2010), Environ Sci Technol, 44(19): 7509-7514.
  8. Kaegi, R et al. (2011), Environ Sci Technol, 45(9): 3902-3908.
  9. Cornelis, G et al. (2012), Soil Sci Soc Am J, 76(3): 891-902.
  10. Cornelis, G et al. (2010), Environ Chem, 7(3): 298-308.

 

 

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