January 27, 2025 9th IER seminar of FY2024 was held. ＜International Visiting Scholar BEGUM, Professor WADA, Project Professor KONOPLEV＞
| Date & Time | Mon. Jan 27, 2024, 13:30-15:00 JST | |||||
| Venue | 6F Conference room, Main Bldg. IER/Online (Zoom) | |||||
| Speakers | International Visiting Scholar BEGUM Professor WADA Project Professor KONOPLEV | |||||
| Lecture Titles | ・Sodium Hexametaphosphate: A Chemical Dispersant and Its Binding Behavior with Soil Elements (Begum) ・Impacts of decreased fishing efforts on flatfish and other fishery resources after the Fukushima Dai-ichi Nuclear Power Plant accident (Wada) ・Long-term dynamics of dissolved 137Cs in freshwaters taking into account its seasonal fluctuations: Chornobyl and Fukushima (Konoplev) | |||||
Institute of Environmental Radioactivity (IER) regularly holds the IER seminar in which the faculty members report on their research results, with the aim of facilitating their research activities and promoting communication.
In the 9th IER seminar of this fiscal year that was held on Jan 27, 2025, three presentations were given by International Visiting Scholar Zinnat Ara BEGUM, Professor WADA Toshihiro and Project Professor Alexey KONOPLEV to 18 participating researchers and students as follows.
Dr. Zinnat Ara Begum, presented about the research that outlined the potential of using sodium hexametaphosphate (SHMP) to reduce the volume of soils contaminated with radiocesium. This process involves wet sieving to separate soil aggregates and analyzing the resulting fractions for contaminants, minerals, and organic matter. The binding reactions of SHMP may improve the solubility of certain elements linked with soil organic matter, promoting the enhanced migration of radiocesium among soil-size fractions. Ongoing research aims to comprehensively understand the binding behavior of SHMP with metal ions and its potential for reducing the volume of radiocesium-contaminated soil.
Professor Wada presented his research with the aim of evaluating the impacts of decreased fishing efforts after the FDNPP accident on demersal fish stocks off the coast of Fukushima Prefecture. Operation efforts (hours) of bottom trawls at depths of 150 to 210 m in 2012, 2013, 2014 fishery period (September to next June) was 2.0%, 2.9%, and 4.0% of pre-disaster levels, while catch per efforts (CPUE, kg/h) was calculated as 270%, 251%, and 196% of pre-disaster levels, respectively. In 2014, species-specific CPUEs at 120-130 m depth zone exceeded pre-disaster levels for many demersal fish. Bottom trawl surveys by research vessels at shallow to deep areas showed the similar increases in densities (kg/m2) for many demersal fish. The densities of several flatfish peaked in a few years following the disaster, and their size distributions in 2015 were markedly larger than those observed before the accident. In contrast, the densities and sizes of some species such as snow crab were found to decrease presumably because a part of individuals were preyed upon by increased predatory fish. These results clearly revealed the huge impacts of fishery operations on flatfish and other fishery resources.
Professor KONOPLEV presented about the long-term dynamics of dissolved 137Cs in freshwaters taking into account its seasonal fluctuations comparing Chornobyl and Fukushima. For the first time regular seasonal fluctuations of dissolved 137Cs in Pripyat-Dnieper basin were identified. Amplitude of these fluctuations was 2.5-3.5 depending on year.
Seasonal variations of dissolved 137Cs are synchronous with water temperature changes during the year and are basically caused by 137Cs remobilization from sediments due to increase of water temperature.
Obtained activation energy of 137Cs desorption for Pripyat-Dnieper rivers sediments appeared to be similar to EA for Abukuma River (Igarashi et al., 2022): 22 and 20 kJ/mol respectively.
Empirical and semi-empirical models of dissolved 137Cs long-term decline taking into account its seasonal fluctuations were suggested and compared with observational data both for Pripyat-Dnieper and Abukuma basins.
After the presentation, many questions and comments were raised by IER faculty members.
