The transfer capability of long-lived Chernobyl radionuclides from surface soil to river water in dissolved forms

• Published in: Organic geochemistry 1999-01, Vol.30 (6), p.437-442
• Main Authors: Amano, H, Matsunaga, T, Nagao, S, Hanzawa, Y, Watanabe, M, Ueno, T, Onuma, Y
• Format: Article
• Language: English
• Subjects: Chernobyl 30 km zone; Cs-137; Dissolved organic materials; Earth sciences; Earth, ocean, space; Engineering and environment geology. Geothermics; Exact sciences and technology; Fulvic acid; Isotope geochemistry; Isotope geochemistry. Geochronology; Pollution, environment geology; Runoff; Speciation; Sr-90; Surface soil; Transuranic elements; Ultrafiltration
• ISSN: 0146-6380; 1873-5290
• DOI: 10.1016/S0146-6380(99)00028-5

Hydrologic runoff is one of the main processes in which radionuclides deposited in the surface environment migrate widely in both particulate and dissolved forms. This paper focuses on the transfer capability of long lived Chernobyl radionuclides from surface soil to river water in dissolved forms. First, concentration and speciation of radioactive Cs, Sr and transuranic isotopes, such as Pu and Am, were examined in undisturbed surface soil along the river in the exclusion zone (30 km zone) near the Chernobyl Nuclear Power Plant (NPP) in order to validate the radioactive contamination characteristics. Almost all radioactivities exist in the very top surface in the undisturbed soil layer. Sr-90 in the soil was estimated to be highest in the water soluble and exchangeable fractions, which were easily accessible to river water as a dissolved fraction. Pu isotopes and Am-241 are major radionuclides in free humic and free fulvic acid fractions. Secondly, surface soil near the Sahan River was extracted with distilled water, as an analogue of rain water, to estimate the dissolved fraction in runoff components from surface soil to river water. After a filtration procedure, extracted water was treated with ultra filtration techniques separating the molecular weight fractions of beyond and below 10,000 Da. Each fraction was measured for the radioactivity and the characteristics of organic materials including humic substances. Most Pu and Am exist in the molecular weight fractions beyond 10,000 Da, in spite of the fact that most of the dissolved organic fractions exist below 10,000 Da. This means that transuranic elements such as Pu and Am are associated with mobile high molecular weight materials like fulvic acids in water leachates.