The removal of arsenate from water using iron-modified diatomite (D-Fe): isotherm and column experiments.

Iron hydroxide supported onto porous diatomite (D-Fe) is a low-cost material with potential to remove arsenic from contaminated water due to its affinity for the arsenate ion. This affinity was tested under varying conditions of pH, contact time, iron content in D-Fe and the presence of competitive ions, silicate and phosphate. Batch and column experiments were conducted to derive adsorption isotherms and breakthrough behaviours (50 µg L(-1)) for an initial concentration of 1,000 µg L(-1). Maximum capacity at pH 4 and 17% iron was 18.12-40.82 mg of arsenic/g of D-Fe and at pH 4 and 10% iron was 18.48-29.07 mg of arsenic/g of D-Fe. Adsorption decreased in the presence of phosphate and silicate ions. The difference in column adsorption behaviour between 10% and 17% iron was very pronounced, outweighing the impact of all other measured parameters. There was insufficient evidence of a correlation between iron content and arsenic content in isotherm experiments, suggesting that ion exchange is a negligible process occurring in arsenate adsorption using D-Fe nor is there co-precipitation of arsenate by rising iron content of the solute above saturation.

Assessment of the radiological impact of gamma and radon dose rates at former U mining sites in Central Asia.

An assessment of the radiological situation due to exposure to gamma radiation, radon and thoron was carried out at selected former uranium mining and processing sites in the Central Asian countries of Kazakhstan, Kyrgyzstan, Uzbekistan and Tajikistan. Gamma dose rate measurements were made using various field instruments and radon/thoron measurements were carried out using discriminative radon ((222)Rn)/thoron ((220)Rn) solid state nuclear track detectors (SSNTD). The detectors were exposed for an extended period of time, including at least three seasonal periods in a year, in different outdoor and indoor public and residential environments at the selected uranium legacy sites. The results showed that gamma, Rn and Tn doses were in general low, which consequently implies a low/relatively low radiological risk. The major radiation hazard is represented by abandoned radioactive filtration material that was being used as insulation by some Minkush residents (Kyrgyzstan) for a longer period of time. Annual radiation doses of several hundred mSv could be received as a consequence of using this material domestically. In addition, the gamma and Rn/Tn dose rates at Digmai, Tajikistan, could reach values of several 10 mSv/a. The doses of ionizing radiation deriving from external radiation (gamma dose rate), indoor radon and thoron with their short-lived progenies in several cases exceeded the recommended annual effective dose threshold level of 10 mSv. At none of the sites investigated did the individual annual effective doses exceed 30 mSv, the internationally recommended value for considering intervention. Current doses of ionizing radiation do not represent a serious hazard to the health of the resident public, but this issue should be adequately addressed to further reduce needless exposure of the resident public to ionizing radiation.

Childhood exposures to Rn-222 and background gamma radiation in the uranium provinces of south Kazakhstan and northern Kyrgyzstan.

The project was undertaken in southern Kazakhstan and Kyrgyzstan. It was speculated that the radiation doses in these areas would be sufficiently high and dispersed to facilitate a case-control study where the radiation doses to leukaemia subjects/their siblings could be compared with those received by control children. As a precursor a pilot project was undertaken to confirm radiation exposures in the region. This was undertaken in association with regional childhood cancer treatment centres. Children from families affected by childhood leukaemia were monitored for 1 month for external γ-radiation dose and for exposure to radon gas. 28 children from families in Kazakhstan and from 31 families in Kyrgyzstan were monitored. The median measured radon in air concentration recorded in Kazakhstan was 123 Bq m(-3) and in Kyrgyzstan was 177 Bq m(-3). These represent 24-h average indoor/outdoor values. In the case of the γ-doses the mean annual dose was 1.2 mGy for Kazakhstan and 2.1 mGy for Kyrgyzstan. Overall, the results suggest that the populations studied receive similar annual radiation doses to those received by populations living in other areas with enhanced natural radioactivity and that further study of Kazakh and Kyrgyz populations would not facilitate a successful case-control study for childhood leukaemia.

In-vitro analysis of the dissolution kinetics and systemic availability of plutonium ingested in the form of 'hot' particles from the Semipalatinsk NTS.

In-vitro leaching of radioactive 'hot' particles isolated from soils sampled at the Semipalatinsk Nuclear Test Site has been carried out in order to evaluate the fraction of plutonium activity released into simulated human stomach and small intestine fluids during digestion. Characterisation of the particles (10-100 Bq(239,240)Pu) and investigation of their dissolution kinetics in simulated fluids has been accomplished using a combination of high-resolution alpha-spectrometry, gamma-spectrometry and liquid scintillation counting. The results of these analyses indicate that plutonium transfer across the human gut following the ingestion of 'hot' particles can be up to two orders of magnitude lower than that expected for plutonium in a more soluble form, and show that for areas affected by local fallout, use of published ingestion dose coefficients, together with bulk radionuclide concentrations in soil, may lead to a considerable overestimation of systemic uptake via the ingestion pathway.

Americium, plutonium and uranium contamination and speciation in well waters, streams and atomic lakes in the Sarzhal region of the Semipalatinsk Nuclear Test Site, Kazakhstan.

New data are reported on the concentrations, isotopic composition and speciation of americium, plutonium and uranium in surface and ground waters in the Sarzhal region of the Semipalatinsk Test Site, and an adjacent area including the settlement of Sarzhal. The data relate to filtered water and suspended particulate from (a) streams originating in the Degelen Mountains, (b) the Tel'kem 1 and Tel'kem 2 atomic craters, and (c) wells on farms located within the study area and at Sarzhal. The measurements show that (241)Am, (239,240)Pu and (238)U concentrations in well waters within the study area are in the range 0.04-87mBq dm(-3), 0.7-99mBq dm(-3), and 74-213mBq dm(-3), respectively, and for (241)Am and (239,240)Pu are elevated above the levels expected solely on the basis of global fallout. Concentrations in streams sourced in the Degelen Mountains are similar, while concentrations in the two water-filled atomic craters are somewhat higher. Suspended particulate concentrations in well waters vary considerably, though median values are very low, at 0.01mBq dm(-3), 0.08mBq dm(-3) and 0.32mBq dm(-3) for (241)Am, (239,240)Pu and (238)U, respectively. The (235)U/(238)U isotopic ratio in almost all well and stream waters is slightly elevated above the 'best estimate' value for natural uranium worldwide, suggesting that some of the uranium in these waters is of test-site provenance. Redox analysis shows that on average most of the plutonium present in the microfiltered fraction of these waters is in a chemically reduced form (mean 69%; 95% confidence interval 53-85%). In the case of the atomic craters, the proportion is even higher. As expected, all of the americium present appears to be in a reduced form. Calculations suggest that annual committed effective doses to individual adults arising from the daily ingestion of these well waters are in the range 11-42microSv (mean 21microSv). Presently, the ground water feeding these wells would not appear to be contaminated with radioactivity from past underground testing in the Degelen Mountains or from the Tel'kem explosions.

Source-term characterisation and solid speciation of plutonium at the Semipalatinsk NTS, Kazakhstan.

New data on the concentrations of key fission/activation products and transuranium nuclides in samples of soil and water from the Semipalatinsk Nuclear Test Site are presented and interpreted. Sampling was carried out at Ground Zero, Lake Balapan, the Tel'kem craters and reference locations within the test site boundary well removed from localised sources. Radionuclide ratios have been used to characterise the source term(s) at each of these sites. The geochemical partitioning of plutonium has also been examined and it is shown that the bulk of the plutonium contamination at most of the sites examined is in a highly refractory, non-labile form.