Neutron Activation Analyses of Selenium and Mercury Marine Products from along the Coast of Shikoku Island

Abstract

The selenium (Se) and mercury (Hg) contents of marine fish and weeds obtained from along the coast of Shikoku Island were determined by neutron activation analysis. To measure the Se content, freeze-dried samples were irradiated for 10 sec and then the radioactivities were counted at the energy peak of ^77mSe (162 keV, half life 17.5 sec) for 30 see with a Ge (Li) detector. As for Hg determination, the samples were irradiated for 5 hr and cooled for an ap-propriate period (2_??_3 weeks) prior to the measurement. The Hg contents were evaluated by subtracting the contribution of 75Se from the total activities of both ²⁰³Hg (279 keV, half life 47 d) and ⁷⁵Se (279.6 keV, half life 120 d). In most of the samples tested, both elements could be measured without any chemical treatment before or after irradiation. However, for the samples containing less than 0.04 μg of Se or Hg, concentration processes were conducted by precipitating the metals after irradiation of the samples. The Se and Hg contents of fish samples were in the ranges of 0.12_??_0.45 ppm and 0.01_??_0.13 ppm, respectively, on a wet weight basis. The sea weeds tested contained very low levels of these elements.