Almera Proficiency Test Determination of Naturally Occurring Radionuclides in Phosphogypsum and Water

Phosphogypsum is generated as a by-product of the phosphoric acid based fertilizer industry. The discharge of phosphogypsum on earth surface deposits is a potential source of enhanced natural radiation and heavy metals, and the resulting environmental impact should be considered carefully to ensure safety and compliance with environmental regulations. A reliable determination of technologically enhanced naturally occurring radioactive materials in phosphogypsum is necessary to comply with the radiation protection and environmental regulations. This proficiency test (PT) is one of the series of the ALMERA network proficiency tests organised on a regular basis by the Chemistry Unit of the IAEA Terrestrial Environment Laboratory. These proficiency tests are designed to identify analytical problems, to support Member States laboratories to maintain their preparedness and to provide rapid and reliable analytical results. In this PT, the test item set consisted of six samples: one phosphogypsum (the IAEA-434 reference material) and five water samples spiked with natural radionuclides. The main task of the participating laboratories was to identify and quantify the activity levels of radionuclides present in these matrices. The tasks of IAEA were to prepare and distribute the samples to the participating laboratories, to collect and interpret analysis results and to compile a comprehensive report. The certified massic activity values of all radionuclides used in this PT were fulfilling the requirements of metrological traceability to international standards of radioactivity. In this PT, 306 test items (reference materials) were prepared and distributed to 52 participants from 40 countries in November 2008. The deadline for receiving the results from the participants was set to15 May 2009. For gross alpha/beta results the deadline was one working day from the date of sample delivery. The participating laboratories were requested to analyse Ra-226, U-234 and U-238 in water samples 01 and 02, and gross alpha/beta in water samples 03, 04 and 05. In the phosphogypsum sample number 06 the participants were asked to analyse Pb-210, Ra-226, Th-230, U-234 and U-238. Fifty two laboratories registered to take part in the proficiency test. Of these, 49 laboratories reported their results to the IAEA. The analytical results of the participating laboratories were compared with the reference values assigned to the reference materials, and a rating system was applied. The summary evaluation of this PT has shown that 67% of the overall reported analytical results fulfilled the evaluation criteria applied in this PT