Radiological characterisation of disposed phosphogypsum in Brazil: evaluation of the occupational exposure and environmental impact.

Phosphogypsum, a waste by-product derived from the wet process production of phosphoric acid, represents a serious problem facing the phosphate industry in Brazil. This by-product (mainly calcium sulphate dihydrate) precipitates during the reaction of sulphuric acid with phosphate rock and is stored at a rate of about 4x10(6) kg per day on several piles in Cubatão, Brazil. Contents of natural radionuclides from thorium and uranium series were measured in Brazilian phosphogypsum samples from disposal piles, using high-resolution gamma ray spectrometry and instrumental neutron activation analysis (NAA). These phosphogypsum piles present a potential threat to the surrounding environment and to the individual occupationally exposed. The results obtained in this study show that radionuclides, although present in relatively high concentrations in phosphogypsum, do not imply in significant doses for individuals occupationally exposed. The results obtained for the water activity in the monitor wells showed that the run-off of the piles is influenced by the activity present in the piles, giving indication of a possible groundwater contamination. Sediments from rivers in the area of influence of the pile presented higher concentrations of 238U and 232Th when compared with reference values.

[Assessment of risk due to the intake of uranium isotopes in mineral spring waters]. / Estimativa de risco devido à ingestão de isótopos de urânio em fontes de águas minerais.

OBJECTIVE: To complement the data of a previous research concerning the evaluation of the lifetime risk of radiation-induced cancer due to the ingestion of 226Ra, 228Ra and 222Rn in mineral spring waters from a natural highly radioactive region of Brazil. The study was performed to evaluate the lifetime risk of radiation-induced cancer due to the ingestion of 238U and 234U in the same spring waters. METHOD: It is assumed that the risk coefficient for natural U isotopes is the same as for the 226Ra-induced bone sarcomas and that the equilibrium for skeletal content is 25 times the daily ingestion of 226Ra, but 11 times the daily ingestion of long-lived uranium isotopes. Waters samples were collected seasonally over a period of one year at all the spring sites used by the local population of Aguas da Prata, S. Paulo State (Brazil). RESULTS: Concentrations ranging from 2.0 to 28.4 mBq/L and from 4.7 to 143 mBq/L were observed for 238U and 234U, respectively. Based upon the measured concentrations the lifetime risk due to the ingestion of uranium isotopes was estimated. A total of 0.3 uranium-induced cancers per 10(6) exposed persons was predicted, suggesting that chronic ingestion of uranium at the levels observed at these springs will result in an incremental increase of fatal cancers of 0.1%. CONCLUSIONS: By taking into account the uncertainties in evaluating the carcinogenic effects, it can be concluded that virtually no cancer would be expected from the ingestion of uranium in the mineral spring waters analyzed.