A final report entitled Exposure assessment for engineered silver nanoparticles throughout the rivers of England and Wales (CB0433) was published by the Centre for Ecology and Hydrology UK (CEH). The report is the result of a year-long study of the concentration of nanosilver particles in English and Welsh rivers and sewer systems.
The effect of nanosilver on the environment is not known very well due to the fact that the concentration of it in the environment is not known. The toxicity of nano- and colloidal silver is high in high concentrations. This study measured that concentration and compared it with the model based on the commercial and residential use of nano-silver products.
In order to model the concentration of nano-silver in rivers a Low Flows 2000 (LF2000) WQX (Water Quality eXtension) model was used. This model is commonly used to model the river flows and regional water resources. 'Based on our knowledge of their consumption, predicted nano silver concentrations are much lower than total particulate silver concentration, by approximately a factor of 10'. Predictions for Themes and Trent river from the model are 10 to 30 ng/L for total particulate silver and 0 to 3ng/L for nano-silver.
Experimentally the concentration of silver particles was measured in sewage. Three particle size ranges were isolated and sampled for the study:
- Large particulate fraction (>450 nm),
- The dissolved fraction (<2 nm) and
- The colloidal fraction (2-450 nm), which includes the nanosilver fraction
The results of theory and measurements produced a discrepancy between the values. A significantly lower concentration of nanosilver was found experimentally in rivers. The measured concentration of nanosilver particles was found to be approximately 1/10 of that expected from the sewage discharge. The authors questioned the commercial market penetration of nanosilver products in the UK as an explanation for the discrepancy.
The article also points out that the nanosilver is thought to react to form sulphide. 'The implication of this sulphide reaction is to make much of the current ecotoxicology data on silver of questionable relevance, since the majority of silver will reach the environment only following sewage treatment and interaction with sulphide'.
The article concludes by saying: 'given our current ecotoxicological knowledge these predicted river concentrations are below levels where acute harmful effects on wildlife might be expected. The known reactivity of silver with anions, particularly sulphide, or organic macromolecules in the environment will likely reduce the risks still further'.
For more information please follow this link to the original of the report.
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