Analytical Performance of 14 Laboratories Taking Part in Proficiency Test for the Determination of Caesium-137 and Total Lead-210 in Spiked Soil Samples

One of the most widespread threats to agricultural development is soil erosion. Soil erosion further impoverishes low-income farm households by reducing soil quality and consequently agricultural yields. It also affects productivity in irrigated farming systems by contributing suspended sediment to waterways and reducing storage capacity of reservoirs. The costs of these effects are substantial in many developing and developed countries. To combat soil erosion there is an urgent need for reliable quantitative data on the extent and rates of soil erosion and sedimentation. Fallout radiouclides (FRN) 210Pb and 137Cs are widely used for soil erosion and sedimentation studies. FRN measurements for soil redistribution involve gamma analysis on soil samples. It is therefore important that the analytical data are correct to ensure that the conclusions of such studies are based on reliable and validated analytical results and to ensure the comparability of the results of different countries. Through a collaboration between the Chemistry Unit and the Soil Science Unit of the IAEA's laboratories IAEA organized an intercomparison exercise in order to assess the validity and reliability of the analytical measurements of 137Cs and total 210Pb carried out by the different laboratories participating in the IAEA Co-ordinated Research Project D1.50.08 'Assessing the effectiveness of soil conservation measures for sustainable watershed management using fallout radionuclides' lead by the Soil Water Management and Crop Nutrition Section of the Joint FAO/IAEA Division of Nuclear Techniques in Food and Agriculture. In this proficiency test 90 samples (Proficiency Test (PT) materials) were distributed to the participating laboratories. The laboratories were requested to analyse the samples employing the same methods used in their daily routine gamma measurements. In total 14 out of 18 initially registered laboratories reported their results. The analytical results of the laboratories were compared with the reference values assigned to the PT materials, and a rating system was applied. In the case of 137Cs, the analytical results were satisfactory with 66% of the participants producing acceptable results (only the sample with low 137Cs activity 2.6±0.2 Bq kg-1 gave less accurate results) while the 210Pb analysis indicated a clear need for corrective actions in the analytical process. 63% of the laboratories involved in the proficiency test did not fulfil the proficiency test criteria for total 210Pb, while this was only 21% for 137Cs. It is recommended that further inter-comparison exercises be organized by IAEA or regional laboratories to ensure the quality of the analytical data produced in Member States through Co-ordinated Research Projects and Technical Co-operation Projects. (author)