H51A-01
Radon Content in Ground Waters Drawn From the Metamorphic Basement, Eastern Sao Paulo State, Brazil.
Ground water drawn from granitic and metamorphic rocks frequently presents relatively high radioactivity, mostly due to the presence of uranium, radium and radon isotopes. In particular, the radon isotope 222Rn seems to have particular significance since it is normally much enriched in ground water in relation to other uranium series isotopes and is in large disequilibrium with its 226Ra mother isotope. Furthermore, radon is one of the main agents of radioactivity transfer from crust uppermost layers to lower atmosphere. At the eastern part of Sao Paulo State, southeastern Brazil, it outcrops a metamorphic terrain with a large number water bearing fractures that composes a set of fractured aquifers. Ground water is drawn from these aquifers through a large number of relatively shallow drilled wells, mostly less than 200 m deep. The radioactivity, and in particular the radon activity concentration, of the ground waters drawn from this metamorphic terrain has not yet been investigated in detail. The 222Rn activity concentration was measured in ground waters drawn from three wells drilled in different rocks of this metamorphic basement. The first well cuts a K-feldspar bearing granite, the second well cuts a granite- gneiss and the third well cuts a gneiss. The ground water samples were collected between July, 2005 and August, 2006 with a time interval of about one month between sampling campaigns. The year long mean activity concentrations were, (76 +/- 7) Bq/L for the first well, (26 +/- 3) Bq/L for the second well and (39 +/- 4) Bq/L for the third one. The activity concentrations show a time dependent variability that is interpreted as consequence of rain fall seasonal variations.
H51A-02
Occurrence of 226Ra in Ground Waters From a Granitic Aquifer at the City of Itatiba, Eastern Sao Paulo State, Brazil
Among the naturally occurring radionuclides, 226Ra play an important role in establishing the ground water radioactivity level. In this work, it is presented the 226Ra activity concentration measured in ground water drawn from a granitic fractured aquifer at the Ribeira Folded Belt, eastern Sao Paulo State, Brazil. The ground water samples were collected twice in the same well in June, 2nd and July 6th, 2005. After discarding about fifteen minutes of continuous well pumping, ground waters samples are collected in 50 L polyethylene containers, previously conditioned with nitric acid, 0.03 mol/L. The water temperature, pH and Eh are measured at the sampling site. The water samples were preserved by addition of 2.0 mL of concentrated nitric acid to lower its pH to less than 2. In laboratory, three 20 L aliquots were selected for independent radiochemical processing. Radium is precipitated from water samples in the form of barium-radium sulfate. The barium-radium precipitate is filtered and dried over the filter paper. The radium containing filter is then sealed with an adhesive plastic film and hermetically closed in a rigid polystyrene sample holder. The sample is left at rest for at least 40 days to allow the short lived daughters (222Rn, 214Pb and 214Bi) reach secular radioactive equilibrium with 226Ra. The radium activity is then indirectly measured by gamma-ray spectrometry through the full absorption peaks from the 214Pb and 214Bi. The gamma-ray spectrometry activity measurements are made by comparison with 226Ra standards. These standards were prepared by the radium precipitation from secondary standard solutions obtained by dilution of a (19.52 +/- 0.72) Bq/g 226Ra solution. The precipitate standards were prepared following the procedure adopted for the ground water samples. The observed 226Ra activity concentration were (43 +/- 2) mBq/L and (46 +/- 3) mBq/L, for the first and second water sampling campaigns, respectively.
H51A-03
Lead isotope fingerprints of childhood lead poisoning in Torreón, México
A comparison of high-precision lead isotopic ratios in blood and environmental samples was conducted to identify sources of lead contamination in thirty-four (34) children living near a silver-zinc-lead smelter plant at Torreón, Mexico. Sixty-five (65) samples of street and ceiling dust and six of atmospheric deposition to collect smelter emissions from a four (4) km2 grid covering the smelter surrounding residential areas were analyzed for lead concentrations and stable isotopic compositions. Lead concentrations in the study area ranged from 400 to 15,400 g/g and 400 to 14,500 g/g in street and ceiling dust, respectively. These indicated orders of magnitude contamination, based on regional background concentrations ranging from 15 to 35 g/g. Concentrations were greatest closest to smelter and decreased with distance from the smelter, with the highest levels southeast of the smelter corresponding with prevailing the wind direction; and atmospheric lead depositions varied between 130- 1350 g/m2d, again with highest rates within the 1 km perimeter of the smelter. Blood lead (PbB) levels in the children (ages ranges 2-17 years) ranged from 6.9 to 37.7 μg/dL with a mean of 16.3 μg/dl (sd = 8.2 μg/dL). Based on interviews, most of those children have been exposed to lead emissions from the smelter since they were in utero. In all cases, lead isotopic ratios (206Pb/207Pb: 208Pb/207Pb) on dust urban (1.200±0.009: 2.467±0.003), deposited particles (1.200±0.002: 2.466±0.002), and PbB (1.199±0.001: 2.468±0.002) were consistent with those of domestic lead ores processed at the smelter (1.199±0.007: 2.473±0.007). Consequently, both exceptionally elevated PbB concentrations of children living near the smelter and the distinctive isotopic composition of that PbB attest to pollution from the lead smelter in Torreón, México.