Behavior of plutonium in floodplain soils

Abstract

It is shown that the plutonium concentration in the floodplain soils of the Techa-Iset' river system is 10-100 times higher than the level attributable to the global nuclear fallout and regularly decreases with distance from the source of contamination. As follows from the Pu-90 Sr and Pu-137 Cs ratios, the migratory ability of Pu is higher than the migratory ability of 137 Cs but lower than that of 90 Sr.The ecological impact of the unrestricted high-radioactivity discharges from the PO (Production Association) Mayak on the floodplain soils in the Techa-Iset' river system was investigated over many years, but efforts were mostly concentrated on the medical and human-health-related aspects of this problem [1]. Considerable attention has recently been focused on assessing the concentrations of the long-lived dose-producing contaminants 90 Sr and 137 Cs in the river ecosystem and establishing the specific features of their behavior [1][2][3][4][5][6][7]. However, the contamination by plutonium, which is one of the most dangerous chemical elements to health, has been studied considerably less.In this work we describe the specific features of the behavior and spatial distribution of Pu isotopes in the floodplain soils of the Techa-Iset' river system. MATERIALS AND EXPERIMENTAL TECHNIQUESThe investigations were performed in 1999-2002 in the floodplain of the middle and lower reaches of the Techa River, as well as in the floodplain of the Iset' River, located downstream from the mouth of the Techa River. Stationary sites were laid at equal distances from the contamination source on both banks of the rivers, near the following settlements ( Fig. 1): Muslyumovo (78 km), Brodokalmak (107 km), Lobanovo (158 km), Anchugovo (169 km), Shutikha (206 km), Zatechenskoe (237 km), Krasnoisetskoe (250 km), and Kovriga (277 km). The soil cover is mainly composed of alluvial-stratified and sod-grass soils; these are characterized by weakly acidic and neutral pH values of their water suspension. The humus content of the A horizon is 4.7-6.5%, and the concentrations of exchangeable Ca +2 , Mg +2 , and K + ions are 26.3-30.2, 5.9-10.4, and <1.5 mg-equiv/100 g, respectively. The granulometric composition is dominated by the fine-sand fraction (1.00-0.01 mm). Samples were taken from sections of soils made at stationary sites laid 5-15 m away from the riverbank along the uniform mesorelief, vegetation, and soil cover.To study the features of the plutonium landscape distribution, a geochemical profile was taken in the neighborhood of the large and most contaminated settlement, Brodokalmak. The profile included a nonwaterlogged riverbank (a dry valley); its regularly flooded slope; and a necked-down, swamped, floodable floodplain of the Techa River 15-20 m wide. Complete soil profiles were laid at several different localities of the terrain.In all of the cases, samples were taken from the sections layer by layer with a survey being taken for the area and the genetic horizons. The above-ground phytomass of grassy plants (motley grasses) were ...