COMPARISON OF NEUTRON-ACTIVATION ANALYSIS AND ICP-MS USED FOR RIVER WATER-POLLUTION CONTROL

This paper compares the performance and limitations of two analytical methods for samples from the environment: Instrumental Neutron Activat ion Analysis (INAA) and Inductively Coupled Plasma with Mass Spectrome try (ICP-MS). A Brazilian river, the Das Velhas, was chosen as the tes t-site. This river runs through a Fe, Mn and Au mining area. The two m ethods were initially tested on three international reference material s: SLRS-3 (riverine water, Research Council Canada), GS-N (granite, AN RT, France) and SOIL-7 (soil, International Atomic Energy Agency, Vien na, Austria). Actual river samples (water and sediments) were analysed next. The INAA and ICP-MS results were generally in good agreement. H owever, ICP-MS analysis occasionally suffered from random flask contam ination (e.g. Zn). The concentrations obtained by ICP-MS for certain e lements (e.g. Zr) were lower than the certified values and results fro m INAA, probably because the dissolution of their natural forms (oxide s) was not complete. For INAA, only one irradiation run was used. Some elements with short half-life radioisotopes (e.g. Mn, Mg or V) and us ually analysable by NAA were not detected. The results obtained for th e Das Velhas river showed a strong relationship between mining activit y and pollutant concentrations. Increased concentrations of certain me tals corresponded to passage of the river through the industrial minin g area. The use of both INAA and ICP-MS enabled accurate results for w ater and sediment samples to be obtained for approximately 50 elements . For water analysis, ICP-MS was clearly the most convenient method, a s INAA was handicapped by the effect of radiolysis which prevented irr adiation of liquid samples. For sediment analysis, sample preparation time for ICP-MS was time consuming. INAA avoided these problems and co uld be used as a reference method. Routinely, a particular method was selected for each element.