Artificial and natural radionuclides are commonly found in several compartments of the earth's crust. Some mushroom species have a high capacity to absorb radionuclides and toxic elements from the soil. Diet is considered as one of the main routes of radioactive contamination. Therefore, radioactivity measurements in the environment and in food are extremely important to monitor the radiation levels that human can be exposed to either directly or indirectly. Environmental biomonitoring has demonstrated that diverse organisms such as crustaceans, fish and mushrooms are useful when evaluating both the contamination and the quality of the ecosystems. There are actually several radionuclides that can be accumulated in mushrooms, including 40 K, 137 Cs, 232 Th and 238 U. There are few studies in the Southern hemisphere countries, on the natural and artificial radioactivity levels in mushrooms. The present study evaluated 40 K, 137 Cs, 232 Th and 238 U in commercialized edible mushrooms in the state of São Paulo, Brazil. The edible mushroom samples were acquired in different commercial establishments in the São Paulo metropolitan region, specifically in Municipal Markets. Some samples were acquired directly from producers located in the cities of Mogi das Cruzes, Mirandópolis, Suzano and Juquitiba. About 400g were colleted for each edible mushroom species, which included Agaricus sp, Pleurotus sp and Lentinula sp species. All the samples were prepared and stored in polyethylene bottles for approximately 35 days, so that secular equilibrium could be established before counting. The 40 K, 137 Cs, 232 Th and 238 U gamma activities were measured by gamma spectrometry. The equipment consisted of a Hiperpure Germanium detector connected to an electronic system. The detector efficiency was obtained from measurements of reference materials: IAEA-300, IAEA-327 and IAEA-375. The results for the specific activities in edible mushrooms samples ranged from 461 to 1535 Bq kg-1 , 1.4 to 10.6 Bq kg-1 , 6.2 to 54.2 Bq kg-1 and 14 to 66 Bq kg-1 d.w., for 40 K, 137 Cs, 232 Th e 238 U, respectively. The 137 Cs levels are in accordance with the Southern hemisphere radioactive fallout, the concentrations are below the maximum levels established by CNEN. Comparing the result values with these found in published literature, the values of the activities found for natural radionuclides are within the normal radioactivity levels for this kind of food. Hence, the studied mushroom species can be consumed without risk of contamination. The employed methodology in this study showed adequate to estimate 232 Th and 238 U specific activities and to determine 40 K and 137 Cs activities in biological samples. This study marks the first time that edible mushrooms in Brazil have been studied to evaluate their radioactivity contents and as such is a contribution for future research in this area.
