Norbert Miekeley

Groundwater colloid properties: a global approach

This study presents and discusses groundwater colloid results from various geological formations ranging from crystalline to sedimentary, from organic rich to organic poor systems and from subsurface to very deep aquifers. Colloid presence and their potential mobility are justified on the basis of colloid stability properties in the investigated groundwaters. The colloid concentration is a function of pH, redox potential, concentrations of Na, K, Ca, Mg and organic carbon, as well as the status of the chemical and physical steady state of the hydrogeochemical system. The colloid properties are discussed with a non-site specific approach.

Chemical and physical characterization of suspended particles and colloids in waters from the Osamu Utsumi mine and Morro do Ferro analogue study sites, Poços de Caldas, Brazil

Data are presented on suspended particles and colloids in groundwaters from the Osamu Utsumi mine and the Morro do Ferro analogue study sites. Cross-flow ultrafiltration with membranes of different pore sizes (450 nm to 1.5 nm) was used to prepare colloid concentrates and ultrafiltrates for analyses of major and trace elements and U- and Th-isotopic compositions. Additional characterization of colloidal and particulate material was performed by ESCA, SEM and X-ray diffraction. The results indicate the presence of low concentrations of colloids in these waters (typically < 500 μg/l), composed mainly of iron/organic species. Minor portions of uranium and other trace elements, but significant fractions of the total concentrations of Th and REE in prefiltered waters (< 450 nm) were associated with these colloids. Suspended particles (> 450 nm), also composed mainly of hydrous ferric oxides and humic-like compounds, show the same trend as the colloids with respect to U, Th and REE associations, but elemental concentrations were typically higher by a factor of 1,000 or more. In waters of low pH and with high sulphate content, these associations are considerably lower. Due to the low concentrations of suspended particles in groundwaters from the Osamu Utsumi uranium mine (typically <0.5 mg/l), these particles carry only a minor fraction of U and the REE (<10% of the total concentrations in unfiltered groundwaters), but a significant, usually predominant fraction of Th (30–70%). The suspended particle load in groundwaters from the Morro do Ferro environment is typically higher than in those from the mine by a factor of 5 to 10. This suggests that U, Th and the REE could be transported predominantly by particulate matter. However, these particles and colloids seem to have a low capacity for migration.

A contribution to the chemical characterization of rivers in the Rio Negro Basin, Brazil

Water samples were collected in Middle Amazonia from the Amazon River, Rio Negro and 17 tributaries of Rio Negro. The analyses consisted of pH, conductivity, and dissolved organic (DOC) measurements, as well as plasma source mass spectrometry (ICP-MS). Factor analysis revealed three factors, which explained 94% of the total variance. A plot of factor scores presented a cluster containing mostly samples from the Rio Negro Basin. Ultrafiltration tests confirmed that organics from the Rio Negro have higher molecular mass than in the Amazon, and that some metals are associated with these compounds. Heavy rare-earth elements (REE) are enriched relative to light REE in the dissolved fraction of most rivers of the Negro Basin; the opposite occurred in suspended matter.

Elemental anomalies in hair as indicators of endocrinologic pathologies and deficiencies in calcium and bone metabolism.

Analytical results obtained by ICP-MS of hair samples from a group of women from Rio de Janeiro city show that abnormal Ca and P concentrations in this compartment can be an indication of pathologies affecting the metabolism of these elements. The study was conducted initially on 900 women (outpatients, >40 years). From this group, approx. 24% showed anomalously high or low Ca concentrations in hair, in some cases correlated to anomalies of other elements. In 144 cases (16%), very high concentrations of Ca (up to 8,285 mg/kg) were measured, frequently correlated with a high concentration of P (up to 4,720 mg/kg), exceeding by far the reference intervals for this age/sex group. Follow-up studies of a few individuals from this group gave first indications that their abnormal hair compositions were related to endocrinologic pathologies affecting calcium/bone metabolism. Very low hair Ca-concentrations were observed in older women (72 cases, age >60 years) and related to senile osteoporosis. Complementary investigations of patients with recognized endocrinologic pathologies (hyperthyroidism, hyper- and hypoparathyroidism) and osteomalacia gave statistical support for the hypothesis that hair concentrations of Ca, P and various other trace elements are influenced characteristically by these diseases. In patients with hyperparathyroidism and hyperthyroidism, both elements showed significant increase in hair, whereas patients with rickets/osteomalacia had only elevated Ca concentrations, together with suspiciously high toxic levels of Cd and various other elements (Fe, Mn, Mg, Sr, Ba). Patients with hypoparathyroidism had significantly decreased Ca and P concentrations in hair. Statistical evaluation of these data by multivariant analysis (MANOVA) using a contrast matrix and by discriminant analysis showed that elemental hair anomalies can be used to diagnose correctly the above-mentioned pathologies, demonstrating the usefulness of hair analysis as a complementary tool for the detection of disturbances in calcium/bone metabolism.

Rare-earth elements in groundwaters from the Osamu Utsumi mine and Morro do Ferro analogue study sites, Poços de Caldas, Brazil

Abstract Data are presented on rare-earth elements (REE) in prefiltered ( 450 nm) from the Osamu Utsumi uranium mine and the Morro do Ferro thorium-REE-deposit. Groundwaters from both sites typically contain between 1–50 μg/l of total REE, but can reach values of up to 160 μg/l in the deepest borehole F4 (U-Mine: 150–415 m). Even higher REE concentrations of up to 29 mg/l were measured in acidic, sulfate-rich near-surface waters of the same site. The chondrite-normalized REE patterns in deeper, more reducing groundwaters and in their corresponding suspended particle fractions are similar to those observed in the bedrock (phonolites), indicating that bedrock leaching and secondary mineral sorption occurred without significant fractionation between these elements, in accordance with the only small variations in the stability constants of the expected REE-sulfate complexes in these waters. Groundwaters from the unsaturated zone of both sites show a very characteristic cerium depletion (less pronounced than that observed in the corresponding suspended particulate fractions), which is most probably related to the oxidation of Ce (III) under the prevailing E h -conditions of these waters (600 to 800 mV), and to sorption/precipitation reactions of the much less soluble Ce(IV) species. Coarse particulate matter (>450 nm ), composed mainly of amorphous ferric hydrous oxides, has a strong capacity for sorption of REE. This is shown by its very high REE concentrations, in some boreholes > 8,000 μg/g (total REE), and by the calculated association ratios R a (ml/g), which are in the order of 10 5 to 10 6 . The implications of these findings for the migration behavior of REE in both environments are discussed.

Molecular mass distributions of dissolved organic carbon and associated metals in waters from Rio Negro and Rio Solimões

Abstract Waters from two tributaries of the Amazon River, the Rio Negro and Rio Solimoes, were collected near Manaus (Brazil), and their dissolved organic carbon (DOC) were concentrated and size fractionated by ultrafiltration. Hollow fiber ultrafiltration columns were used to separate humic compounds (and associated metal ions) from larger volumes of water in the field. The metal composition of each fraction was determined primarily by ICP-AES, after preconcentration. Flat membrane ultrafiltration was used to obtain sharper molecular mass cut-off levels in the laboratory. About 30–40% of the DOC in the Rio Negro water was within the mass range of 1–10 kDa. This fraction was composed mainly of humic compounds, which are the carriers for most of the metal ions studied (e.g. Al, Fe, Ti, Cu, Mn, Zn, Ca, Mg). Humic and fulvic acids, isolated from these waters, were characterized by IR-spectrometry and potentiometric titrations. Water from the Rio Solimoes showed lower retention of DOC ( ≊ 20% ) and associated metal ions, probably due to the more pronounced sorption of the high-molecular mass humic compounds on suspended particles. Despite the high load of clay particles in this water, no evidence of such particles in colloidal size ranges was observed.

Determination of minor and trace elements in obsidian rock samples and archaeological artifacts by laser ablation inductively coupled plasma mass spectrometry using synthetic obsidian standards

Abstract Accuracy and repeatability of analytical results obtained by laser ablation (LA) inductively coupled plasma mass spectrometry (ICP-MS) critically depends on the availability of calibration standards, which should ideally have a matrix composition very close to the samples being analyzed. The preparation of synthetic obsidian standards (SOS) is described in this work, their minor and trace element composition (>40 elements), determined by solution nebulization ICP-MS and inductively coupled plasma optical emission spectrometry is presented and their performance in the quantitative and semiquantitative analysis of obsidians by LA-ICP-MS is discussed. Due to matrix matching of SOS and natural obsidians, internal standardization of the analyte intensities by 27Al or 29Si had no significant effect on the final results. Good analytical curves (r2>0.995) were obtained with the SOS series, permitting quantitative determination of a large number of trace elements in geological and archaeological samples with repeatabilities typically between 5 and 10% and adequate accuracies, as shown by the generally good agreement between solution nebulization and laser ablation data for the same samples. Results obtained in the fast semiquantitative mode of calibration were in most cases statistically not different from those obtained by the quantitative mode. This, for the routine analysis of a large number of samples attractive feature, was achieved by the use of 47 quantified elements in SOS for updating of the response factors. An example for the application of analytical methodologies introduced in this work is shown in provenance studies of archaeological obsidian artifacts from Ecuador.

Natural decay series studies of the redox front system in the Poços de Caldas uranium mineralization

Abstract As part of a major natural analogue study of relevance to radioactive waste disposal, natural decay series disequilibrium techniques were used to provide information on the mechanisms and rates of processes occurring at redox fronts in an extensive uranium deposit near Pocos de Caldas, Brazil. This topic is of direct relevance to waste disposal safety assessment in view of the postulated development of radiolysis-induced oxidizing conditions in respositories. The study confirmed the downwards displacement of uranium by oxidizing groundwater interacting with the reduced rock, resulting in downwards movement of the redox front, with associated cyclical oxidation-induced dissolution and reduction-induced redeposition of uranium generating enhanced uranium concentrations at the redox fronts. Deposition of uranium occurs on both sides of the redox fronts, with reduction to insoluble U4+ in the reduced rock and scavenging by secondary iron oxides being identified as the respective mechanisms of deposition. Radioactive disequilibrium considerations indicate that, while the uranium deposited in the oxidized rock is retained for times of at least 106 y, some slow redissolution does occur, possibly involving mainly preferential loss of 234U. Sequential leaching indicates that the redeposited uranium in both the oxidized and the reduced rock is more readily dissolved than the uranium in the unaltered reduced rock. It is concluded that the observed distributions of uranium were produced by diffusion in both directions away from the redox fronts in conjunction with groundwater flow downward along the direction of the fronts. Limited redistribution of thorium has occurred, but at a level at least two orders of magnitude less intense than that of uranium and there is a systematic separation of uranium from thorium with increasing depth in the rock. At two locations where the oxidized rock overlies the reduced rock, natural decay series disequilibrium indicated a rate of movement of the front of 2–20 m in 106 y, suggesting that the rate of movement of the redox front is controlled by the rate of regional erosion (about 12 m in 106 y). At a location where the reduced rock overlies the oxidized rock, the front was estimated to have moved less than 1 cm in 106 y. This location was also the site of the most intense mineralization of uranium in the samples studied. 226Ra mobility over distances of the order of 10 m was observed, along with preferential transfer of 226Ra from the reduced to the oxidized rock at the deeper redox fronts. The postulated maximum rate of far-field movement of a repository-related redox front of about 50 m in 106 y is concluded to be a realistic value for use in models. Scavenging of radionuclides by secondary minerals forming in oxidized rocks is identified as a potentially important retardation process which might not be apparent from purely thermodynamic considerations. The effect of a repository-related redox front would be initially to retard radionuclide movement by at least partial deposition at the front. If such a redox front were to penetrate a sufficient distance through the far field, it could, however, result in the breakthrough of a pulse of radionuclides to the near-surface zone.

Intervalos de referência para elementos menores e traço em cabelo humano para a população da cidade do Rio de Janeiro - Brasil

Inductively coupled plasma mass spectrometry (ICP-MS) has been used for the determination of twenty minor and trace elements in hair samples from an urban population group (N = 1775), aiming at the establishment of reliable hair reference intervals. Statistical evaluation of the data with respect to age, sex and anatomic region was performed by multivariant analysis and according to recommendations of the International Federation of Clinical Chemistry (IFCC). The results show that mainly age and anatomic region (scalp or pubis) influence significantly the concentration of several elements. Comparison of the here calculated reference intervals with those previously published and used by clinical laboratories for this population showed larger discrepancies and the need for an urgent revision of these data.

Ultrafiltration of humic compounds through low molecular mass cut-off level membranes

Abstract During ultrafiltration of humic compounds through Amicon YM2 flat membranes (cut-off level: 1 kDa), humic acid solutions presented retentions of 80–90% and fulvic acid of 60–70%. Fulvic acid retention on this membrane depends directly on pH and inversely on ionic strength. Calcein (2,7-Bis[bis(carboxymethyl)-aminomethyl]-fluorescein; 623 g/mol), an organic molecule tested for comparative purposes, exhibited a similar behavior. Experiments with humic acid were handicapped by precipitation or aggregation processes under low pH or high ionic strength conditions. Humic acid retention on PM10 membrane (cut-off level: 10 kDa) is the same as on YM2, despite the difference in cut-off levels. This anomalous result is attributed to the lipophilic character of the PM10 membrane. Both membranes are, therefore, highly efficient for the concentration of humic acid from typical freshwaters; a good recovery is also attained with fulvic acid on the YM2 membrane. Although YM2 is considered a hydrophilic, non-ionic membrane, salts containing polyvalent anions show high retentions under low ionic strength conditions, and the retention is proportional to the anion charge.