The environmental behaviour of cerium dioxide nanoparticles (CeO2) is not well known. However, they are subject to various transport and transformation processes, which significantly influence the nanoparticles' behaviour in the respective environmental compartment water, soil and air.

 

pH scale (c) DaNa TeampH scale (c) DaNa TeamUnder the prevailing conditions in natural waters, these particles do not release ions. However, the solubility of cerium dioxide depends on the pH value of the respective environment. Under acidic conditions (pH values lower than 5), which occur in some natural water bodies and in acid rain, ion release increases drastically. Likewise, the mobility of ceria nanoparticles depends on pH. An acidic environment immobilises the nanoparticles and they adsorb to other materials. In contrast, under neutral or basic conditions, which prevail in most European water bodies, mobility is increased and the transport of the nanoparticles is promoted by natural organic matter [1-3].

 

With regard to soil, the soil composition as well as nanoparticle coating affects the mobility. The cerium dioxide nanoparticles show a strong affinity for phosphates (e.g. component of fertiliser) increasing the mobility of ceria nanoparticles [4,5].

wastewater treatment plant © MariuszSzczygie / fotolia.comwastewater treatment plant © MariuszSzczygie / fotolia.com

 

In a laboratory study, a model sewage treatment plant was used to investigate the removal of metal oxide nanoparticles from wastewater. In most cases, the nanoparticles were efficiently removed from the wastewater by directly binding to the sewage sludge. Only 6 % of the original cerium dioxide nanoparticles remained in the water and ended up in the effluent in this laboratory study. In Germany, sewage sludge is either incinerated or spread on agricultural land, which is why the soil compartment is thought to be the predominant sink (see article "cerium dioxide - exposure environment").

 

However, nanoparticle suspensions with stabilising ingredients (e.g. humic acids) pose a greater challenge for the wastewater treatment. The nanoparticles are difficult to remove since the stabilisation hinders the binding of the nanoparticles to the bacteria in the sewage sludge. Moreover, the different composition of wastewater helps to stabilise cerium dioxide nanoparticles causing a lower sedimentation tendency compared to pure water [6,7].

 

 

Currently, there is no information available with regards to the behaviour of ceria nanoparticles upon release into the air. For e.g. diesel exhaust fumes a wash-out of the particles by rain is expected.

 

Overall, cerium dioxide nanoparticles do not release ions under prevailing environmental conditions. The mobility of unmodified ceria nanoparticles is low, and the majority is removed by conventional wastewater treatment processes.

 

Literature arrow down

  1. Dahle J et al. (2015), Chemosphere, 119: 1365-1371.
  2. Li, Z et al. (2011), Water Res, 45: 4409-4418.
  3. Petosa, AR et al. (2013), Water Res, 47: 5889-5900.
  4. Cornelis, G et al. (2011), Environ Sci Technol, 45, 2777–2782.
  5. Quik, JTK et al. (2010), Chemosphere, 81: 711-715.
  6. Limbach, LK et al. (2008), Environ Sci Technol, 42(15): 5828-5833.
  7. Dahle J et al. (2015), Chemosphere, 119: 1365-1371.
  8. Gomez-Rivera F et al. (2012), Bioresour Technol, 108: 300-304.

 

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