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Posted: Sep 03, 2012
German Federal Environment Agency issues report on nanomaterials in the environment
(Nanowerk News) The OECD Guidelines for the Testing of Chemicals are internationally accepted standards and used for risk assessments, but their applicability to nanomaterials is not tested. Therefore the applicability of the guidelines - here especially those related to soil and sewage plant tests - was investigated in a study financed by the German Federal Environment Ministry. This publication ("Fate and behaviour of TiO2 nanomaterials in the environment, influenced by their shape, size and surface area") is only available online.
The results obtained for the three TiO2 nanomaterials are also important for closing the gap of information about environmental behaviour. The specific nanomaterials studied were UV Titan M262, which is coated with alumina and dimethicone, and the uncoated P25 and PC105. The fate and behaviour of P25 was studied in a laboratory sewage treatment plant – based on the OECD Guideline 303A. The experiments in the laboratory sewage plant were performed over a period of three weeks. Altogether 1344 mg P25 in a suspension were added in three different concentrations each for one week; first week 1 mg/L, second week 5 mg/L and third week 10 mg/L. The chemical analysis showed that only 3 – 4% of the added TiO2 was found in the effluent. The main part of the nanomaterial was adsorbed to the sludge.
The mobility of the three TiO2 nanomaterials was tested in columns with three different soil types – based on the OECD Guideline 312. The tests were carried out in duplicate. 500 mg of the nanomaterials was applied as suspension of 5 g/L to the top of each soil column. After termination of the experiments, segments of the soil and the eluate were chemically and microscopically analysed. The bulk chemical analyses of the soil segments indicate transport only for UV Titan M262. Microscopic analysis, however, showed transport of isolated TiO2agglomerates for all three nanomaterials. In the eluate no Titanium concentration > 5 /mic
g/L (LOD) was detected.
The adsorption behaviour of P25 and UV Titan M262 in different soil types was tested based on the OECD Guideline 106. 2.5 mg TiO2 were applied as suspension of 1 g/L to a soil/solution mixture consisting of 5 g soil and 22.5 mL 0.01M CaCl2 solution. The mixture was homogenised and afterwards centrifuged. The supernatant was analysed for its Titanium content to derive the non adsorbed fraction. The Titanium content in the supernatant was in all cases < 5% of that added to the system.
It can be concluded, that the OECD Guidelines 303A and 312 are applicable to nanomaterials, here specifically TiO2. Still specific recommendations should be taken into account as given in the corresponding section of the report. OECD Guideline 106 was found to be not useful for nanomaterial testing due to lack of possibilities for differentiating adsorbed from non adsorbed (agglomerated) TiO2 nanomaterial.