The IAEA-450 CRM is a unicellular microalga (Scenedesmus obliquus). Two batches of algae were grown in an outdoor bioreactor, one batch on a standard nutrient solution (natural contamination level), the second batch on a nutrient solution containing elevated levels of As, Cd, Cr, Hg, Ni, Pb, and Pt. After harvesting, the bulk material was gamma ray irradiated at the IAEA's laboratories to avoid a bacterial deterioration, and tested for homogeneity.Thereafter, in order to adjust the Pt mass fraction to the level of environmental pollution in road dust, the two materials were mixed in a ratio of 1:100 (high Pt: low Pt). Using high purity methanol, slurries of the two algae materials were produced and merged under constant stirring in 200 g batches. After 72 hours drying at 60°C, the dry material was homogenized using a shaking device for 8 hours. Then the bulk material was combined/mixed into one batch and homogenized for 1 week in a 50 L drum homogenizer containing 20 ceramic balls of 2 cm diameter.Bottling of IAEA-450 was carried out under normal laboratory conditions. Portions of 10 g were filled into plastic bottles, sealed with security polyethylene caps and labelled with the code IAEA-450.After bottling, the material was sterilized by gamma-ray irradiation with a total dose of 25 kGy using a 60Co source according to EN ISO 13485:2003 in an irradiation facility. keywords: Biological material, Plant material, trace elements , heavy metals, Environmental material |
