Reduced soil fauna decomposition in a high background radiation area

Radium uptake by earthworms E. fetida after exposure to contaminated soil

Radium-226 is one of the most important radionuclides for assessing the radiation exposure in terrestrial ecosystems in terms of its significant contribution to the internal and total dose rates. A laboratory culture of Eisenia fetida was exposed to soil contaminated with ²²⁶Ra and ²³⁸U during two months. These nuclides entered the soil as a result of industrial radium production (Vodny, Komi Republic, Russia). The concentrations of ²²⁶Ra and ²³⁸U were 89000 ± 9000 and 2130 ± 270 Bq kg^-1 of soil. Bioaccumulation of ²²⁶Ra was investigated in E. fetida exposed to the radioactive soil or to a mixture containing the same radioactive soil diluted with peat and sand. The activity concentrations of ²²⁶Ra in E. fetida were higher after exposure to the contaminated soil compared to the mixture. The literature data on the radium accumulation in earthworms were considered also. Our experiments showed that the concentration ratio (CR) of ²²⁶Ra in E. fetida varied from 5.5 × 10^-4 to 4.5 × 10^-3 Bq kg^-1 f.w./Bq kg^-1 d.w. The average CRs were (6.7 ± 1.7) × 10^-4 for the earthworms E. fetida from the soil mixture and (3.2 ± 1.2) × 10^-3 for those from the radioactive soil. These CRs for ²²⁶Ra were up to two orders of magnitude lower than the values calculated by us from the results obtained by other researchers for natural earthworm populations in areas with lower levels radioactivity.

Radiation exposure and risk assessment to earthworms in areas contaminated with naturally occurring radionuclides

The assessment of radiation exposure on biota is one of the main parts of environment protection system. Earthworms have been recognized as an important organism group in the terrestrial ecosystems. According to many researchers the potential risks of naturally occurring radionuclides for soil invertebrates were not significant because the exposure doses to the invertebrate populations were low. Our study aimed to assess the radiation exposure and the radiological risks from naturally occurring radionuclides for earthworm populations at four sites. This research was based on three dosimetric approaches simultaneously: ERICA and RESRAD-BIOTA-the commonly used ones, and also on the original method proposed by Thomas and Liber (Environment International, 27, 341-353, 2001) for aquatic organisms. To calculate radiation dose rates to soil invertebrates inhabiting background and contaminated areas, the specific activities of radionuclides in soil, and, depending on the model, the default, or determined in this study, input mass-geometric parameters had been applied. The weighted absorbed dose rates calculated by different models and site-specific data were 0.3-1.4 μGy/h for the background and from 3.4 to 170 μGy/h for the contaminated sites. Analysis of radiation risks for earthworms indicated that ²²⁶Ra was the key contributor to the external dose rate; ²²⁶Ra and ²¹⁰Po played a dominant role in formation of internal dose rate for radioecological situations in our study. More conservative radiation risk assessments were derived from RESRAD-BIOTA tool. Dose assessments obtained using various models had shown that there are real environmental situations in which the radiological risks to reference organisms are significantly higher than the lowest benchmark protection level proposed for ecosystems.

Current ionising radiation doses in the Chernobyl Exclusion Zone do not directly impact on soil biological activity

Although soil organisms are essential for ecosystem function, the impacts of radiation on soil biological activity at highly contaminated sites has been relatively poorly studied. In April-May 2016, we conducted the first largescale deployment of bait lamina to estimate soil organism (largely soil invertebrate) feeding activity in situ at study plots in the Chernobyl Exclusion Zone (CEZ). Across our 53 study plots, estimated weighted absorbed dose rates to soil organisms ranged from 0.7 μGy h^-1 to 1753 μGy h^-1. There was no significant relationship between soil organism feeding activity and estimated weighted absorbed dose rate. Soil biological activity did show significant relationships with soil moisture content, bulk density (used as a proxy for soil organic matter) and pH. At plots in the Red Forest (an area of coniferous plantation where trees died because of high radiation exposure in 1986) soil biological activity was low compared to plots elsewhere in the CEZ. It is possible that the lower biological activity observed in the Red Forest is a residual consequence of what was in effect an acute high exposure to radiation in 1986.

Pearl millet cultivation with brackish water and organic fertilizer alters soil properties

Abstract Semi-arid regions are characterized by high evapotranspiration and low rainfall, favoring the accumulation of salts when irrigated with brackish water. The aim of this study was to evaluate the effect of pearl millet cultivation with brackish water levels and fertilized with organic fertilizer on the chemical and physical properties of the soil. A split plot randomized block design was adopted, in a factorial arrangement, with three repetitions. Plots consisted of four irrigation levels (25, 50, 75 and 100% crop evapotranspiration) and subplots consisted of four levels of organic fertilizer (0; 15; 30 and 45 Mg ha-1). At the end of the pearl millet production cycle, soil was collected from layers 0-0.20 m and 0.20-0.40 m, for physical (soil bulk density, particle density and porosity) and chemical (EC, pH, K, Na, Ca, Mg, H + Al, SB, CEC, V) properties. There was no effect of interaction of brackish water levels and organic fertilizer levels on soil chemical properties. Brackish water reduced potassium on layer 0.20-0.40 m. A negative linear effect was found for density in the 0.20-0.40 m layer under different levels of organic fertilizer. Brackish water levels and organic fertilizer levels in the cultivation of pearl millet does not alter soil chemical and physical properties at the 0-0.20 m layer. However, the use of brackish water reduces the concentration of potassium in the soil and the application of organic fertilizer reduces soil density at the 0.20-0.40 m layer.