Almost all studies on the radioactive content of mushrooms have been centered on 137Cs and, to a lesser extent, on 40K. Other alpha and beta emitters have not been fully investigated and, therefore, their contribution to the dose due to consumption of mushrooms is not taken into consideration. We have studied the incorporation of several radionuclides: into mushrooms using two approaches — laboratory and natural conditions. Pleurotus eryngii was cultured under controlled laboratory conditions, and was found that 134Cs was incorporated to a greater extent in the mushroom than the rest of radionuclides, and 239Pu at least. These results were confirmed by the uptake under natural conditions: 137Cs > 228,230,232Th
90Sr >> 239+240Pu. The contribution of thorium and uranium to the dose due to mushroom consumption in Spain is of the same order of magnitude as that of 137Cs.
We describe the procedure developed for the electrolytic concentration of3H in water, together with systematically applied checks to guarantee the reproducibility of the process and to minimize the
variability between water samples concentrated simultaneously in the different electrolytic cells. Starting from initial volume
of 250 ml water, we obtained enrichment parameters normally greater than 70%, with a dispersion always less than 5%. Measuring
the concentrated and the unelectrolyzed samples under the same conditions, we found that the lowest detectable activities
had been improved from around 1.5 to 0.3 Bq/l. This allowed us to quantify the3H activity levels of 100% of the rainwater samples collected in Cáceres from 1994 to 1996. The resulting average value for
this period was (0.79±0.38) Bq/l.
A certified reference material (CRM) for radionuclides in seawater, IAEA-381 (Irish Sea Water), is described and the results of certification are presented. The material has been certified for nine radionuclides (40K, 90Sr, 137Cs, 237Np, 238Pu, 239Pu,240Pu, 239,240Pu and 241Am). Information on massic activities with the corresponding 95% confidence intervals are given for eight radionuclides (3H, 125Sb, 234U, 235U, 236U, 238U, 241Pu and 244Cm). Less reported radionuclides include 60Co, 99Tc, and 242Pu. The CRM may be used for quality assurance/quality control of the analysis of radionuclides in environmental water samples, for the development and validation of analytical methods and for training purposes. The material is available from the IAEA in 5 kg units.
From 1994 to 1996 we have studied a number of radioactive (total b and residual b-activity levels and 3H activity) and physico-chemical (pH, conductivity, and natural potassium content) parameters in the water of two Alcántara and Guadiloba reservoirs, which are artificially connected by interbasin transfers. The analysis of the results showed the existence of major correlations between the two systems for tritium activity, conductivity, and stable potassium content. A model based on the water balance in the Guadiloba reservoir was also elaborated which allowed us to forecast its effective surface area monthly, which varied extraordinarily between 0.405 and 135 km2.
Authors:A. Baeza, M. Del Rio, C. Miro, and J. Paniagua
With the object of quantifying the radiological impact that the Almaraz Nuclear Power Station, situated beside the Tajo river in Spain, induces on its ecosystem, since 1986 we have been carrying out multiple gamma-spectrometric studies and determinations of90Sr concentrations on the receptor media: surface waters, sediments, fishes, aerosols, and soils, in the two likeliest critical transmission pathways of transmission of the radioactive contamination. The principal results are summarized in the present work, and they allow the impact to be quantified, as well as the most probable source to be assigned for each of the levels detected.
Authors:A. Baeza, M. Del Rio, C. Miro, and J. Paniagua
An analysis has been made of the surface distribution of137Cs and90Sr in soils of the province of Cáceres (Spain), of some 20.000 km2 area, situated on the frontier with Portugal. From the distribution of depth profiles of concentrations of these radionuclides and their fit to a negative exponential, determination was made of the mean values of the respective inventories and of the corresponding137Cs/90Sr ratio. The external dose rates from the presence of these man-made isotopes in the soil are calculated and compared with that originating from the concentrations of natural radioisotopes.
Authors:A. Baeza, L. del Río, E. García, A. Jiménez, C. Miró, J. Paniagua, and M. Rufo
We have quantified the evolution during 1994 of the impact on the Tagus river of liquid releases of3H (51.3 TBq in the cited year), originating from the functioning of the Almaraz Nuclear Power Plant, and conditioned by the management of the cooling reservoir water. Taking into account, on the one hand, that tritiated water is hydrodynamically indistinguishable from untritiated water when both form part of the same mass of liquid, and, on the other, the practically null stratification and forced circulation of the water in the cited cooling reservoir, together with the hydrological fluxes interchanged between the said reservoir and the Tagus river (which is entirely regulated in the section under study and, because of prolonged drought, had a relatively small flow during the study period), we were able to model satisfactorily the temporal evolution of the3H activity in the cooling reservoir.
Authors:A. Baeza, L. Delrío, A. Jiménez, C. Miró, J. Paniagua, and M. Rufo
The mean weekly levels of7Be in the atmosphere of Cáceres (Spain) was measured for three consecutive years, from 1992 to 1994. The values showed a strongly seasonal behavior, conditioned fundamentally by two effects: (1) the incorporation of7Be into the low layers of the troposphere due to the displacement of masses of air from higher layers caused by the solar irradiation, and (2) the washing of7Be out of the atmosphere by rain. From the quantification of these two effects, the residence time of7Be was determined in the atmosphere at ground level as 10.3 days, with an interval for the standard error of 9.0 and 12.1 days. Modelling the temporal evolution of this radionuclide we were able to explain 90.72% of the variance of the measured activity levels. Using the effective residence time of7Be, we were able to justify the diversity of values obtained for the deposition of137Cs in different soils of the province of Cáceres due to the fallout from atmospheric nuclear blasts.
Authors:A. Baeza, M. Del Rio, A. Jimenez, C. Miro, and J. Paniagua
The radioactive concentrations of226Ra,232Th,235U and40K in surface soil of the province of Cáceres (Spain) were studied as a function of the geology and grain size. The activities of the four radionuclides in granitic and metamorphic soils have normal frequency distributions, with the mean value being significantly higher for the granitic soils than for the metamorphic soils. Sedimentary soils present asymmetric distributions, and their activities lie between the previous two types. The specific activities of the four radionuclides rises as the particle radius decreases. The equationAe=(P1/R)+P2 describes the dependence of the specific activityAe on radiusR, P1 andP2 being parameters that are related to the surface area and volume activities of the grains. The isotopes226Ra,232Th and235U accumulate with greater intensity on the surface of the grains than40K. This effect is more pronounced in granitic and sedimentary soils than in metamorphic soils.