Determination of trace elements in freshwater diatoms by neutron activation analysis

The instrumental neutron activation analysis was applied to the multielemental analysis of the freshwater diatoms taken from the head and the lower areas of Tama river. Dry samples of the diatoms were irradiated for 1 minute (for the measurement of short lived nuclides) by pneumatic tube of TRIGA-II reactor of Musashi Institute of Technology, and 12 hours (for the measurement of long lives nuclides) in F ring of TRIGA-II reactor of Rikkyo University. The analytical results of 20 elements in the samples were obtained, and the concentration of Ti showed high values in all the sample. Since it is considered that Ti is absent in algae, these high values indicate that appreciable amounts of river sediment were contained in the samples. Therefore, the analytical results were corrected for Ti contents in the samples. The concentrations of Mg, K, Zn, Mn and Co in the diatoms showed no difference between the two sampling points. The concentrations of Cr, V, As and Sb in the diatoms, however, showed difference between the two sampling points, depending on the river water quality. In Stenopsyche grisepennis, on the other hand, the concentrations of Mn and Co depend on the river water quality, and the concentrations of Cr depend on the amount of diatoms staying in the body. The concentrations of V, As and Sb in the Stenopsyche griseipennis are considered to depend both on the amount of diatoms and river sediment staying in the body. (author)