Tactoid formation in montmorillionite: effect on ion exchange kinetics.

Exchange between calcium from montmorillonite and hydrogen from resin is much slower than exchange between sodium from montmorillonite and hydrogen from resin. Film kinetics are prevailing in both cases, but the location of the rate-determining step is shifted from the Nernst films of the resin particles in the sodium-hydrogen exchange to the Nernst films of the clay particles in the calcium-hydrogen exchange. The increased particle size of the montmorillonite in the calcium state, caused by tactoid formation, appears to be the main reason for the shift.

Origin of life: clues from relations between chemical compositions of living organisms and natural environments.

When elemental enrichment factors in living organisms are plotted against the ionic potential of the elements, a strikingly similar pattern is found for different groups of organisms; the pattern is also similar, in its general features, to that found in seawater. These relationships support the idea that life began in a water-rich environment interfacing with the primitive atmosphere of the earth.

Iron-montmorillonite: a spectral analog of Martian soil.

Light absorption and reflectance by smectite clays containing various adsorbed ions were measured in the UV, VIS, and NIR ranges and compared to Martian dust and surface soil spectra. Structural iron in the octahedral sheet of smectites is responsible for a characteristic absorption feature in the UV at 240-260 nm, resulting from an O2 --> Fe3+ charge transfer that is similar to one observed in the Martian spectrum. Adsorbed iron affects, via crystal field absorptions, the reflectance of montmorillonite in the VIS and NIR (to 1.3 micrometers), causing stronger absorption and higher opacity in the wavelength range 0.4-0.6 micrometer, without developing any specific pronounced absorption feature. In both general appearance and presence of, or lack of, spectral features, the iron-montmorillonite reflectance spectra in the VIS and NIR are similar to the Martian spectra. At present, however, spectral similarity cannot be used as the sole criterion for constraining Martian mineralogy since several other minerals, other than Fe-smectites, show sufficient similitude to the Martian spectra; other properties have to be explored and combined to obtain a definitive identification.

The nanophase iron mineral(s) in Mars soil.

A series of surface-modified clays containing nanophase (np) iron oxide/oxyhydroxides of extremely small particle sizes, with total iron contents as high as found in Mars soil, were prepared by iron deposition on the clay surface from ferrous chloride solution. Comprehensive studies of the iron mineralogy in these "Mars-soil analogs" were conducted using chemical extractions, solubility analyses, pH and redox, x ray and electron diffractometry, electron microscopic imaging, specific surface area and particle size determinations, differential thermal analyses, magnetic properties characterization, spectral reflectance, and Viking biology simulation experiments. The clay matrix and the procedure used for synthesis produced nanophase iron oxides containing a certain proportion of divalent iron, which slowly converts to more stable, fully oxidized iron minerals. The clay acted as an effective matrix, both chemically and sterically, preventing the major part of the synthesized iron oxides from ripening, i.e., growing and developing larger crystals. The precipitated iron oxides appear as isodiametric or slightly elongated particles in the size range 1-10 nm, having large specific surface area. The noncrystalline nature of the iron compounds precipitated on the surface of the clay was verified by their complete extractability in oxalate. Lepidocrocite (gamma-FeOOH) was detected by selected area electron diffraction. It is formed from a double iron Fe(II)/Fe(III) hydroxy mineral such as "green rust," or ferrosic hydroxide. Magnetic measurements suggested that lepidocrocite converted to the more stable maghemite (gamma-Fe2O3) by mild heat treatment and then to nanophase hematite (alpha-Fe2O3) by extensive heat treatment. After mild heating, the iron-enriched clay became slightly magnetic, to the extent that it adheres to a hand-held magnet, as was observed with Mars soil. The chemical reactivity of the iron-enriched clays strongly resembles, and offers a plausible mechanism for, the somewhat puzzling observations of the Viking biology experiments. Their unique chemical reactivities are attributed to the combined catalytic effects of the iron oxide/oxyhydroxides and silicate phase surfaces. The reflectance spectrum of the clay-iron preparations in the visible range is generally similar to the reflectance curves of bright regions on Mars. This strengthens the evidence for the predominance of nanophase iron oxides/oxyhydroxides in Mars soil. The mode of formation of these nanophase iron oxides on Mars is still unknown. It is puzzling that despite the long period of time since aqueous weathering took place on Mars, they have not developed from their transitory stage to well-crystallized end-members. The possibility is suggested that these phases represent a continuously on-going, extremely slow weathering process.

Life on Mars? I. The chemical environment.

The origin of life at its abiotic evolutionary stage, requires a combination of constituents and environmental conditions that enable the synthesis of complex replicating macromolecules from simpler monomeric molecules. It is very likely that the early stages of this evolutionary process have been spontaneous, rapid and widespread on the surface of the primitive Earth, resulting in the formation of quite sophisticated living organisms within less than a billion years. To what extent did such conditions prevail on Mars? Two companion-papers (Life on Mars? I and II) will review and discuss the available information related to the chemical, physical and environmental conditions on Mars and assess it from the perspective of potential exobiological evolution.

Life on Mars? II. Physical restrictions.

The primary physical factors important to life's evolution on a planet include its temperature, pressure and radiation regimes. Temperature and pressure regulate the presence and duration of liquid water on the surface of Mars. The prolonged presence of liquid water is essential for the evolution and sustained presence of life on a planet. It has been postulated that Mars has always been a cold dry planet; it has also been postulated that early mars possessed a dense atmosphere of CO2 (> or = 1 bar) and sufficient water to cut large channels across its surface. The degree to which either of these postulates is true correlates with the suitability of Mars for life's evolution. Although radiation can destroy living systems, the high fluxes of UV radiation on the martian surface do not necessarily stop the origin and early evolution of life. The probability for life to have arisen and evolved to a significant degree on Mars, based on the postulated ranges of early martian physical factors, is almost solely related to the probability of liquid water existing on the planet for at least hundreds of millions to billions of years.

Global N2O cycles--terrestrial emissions, atmospheric accumulation and biospheric effects.

Tropospheric nitrous oxide concentration has increased by 0.2-0.4% per year over the period 1975 to 1982, amounting to net addition to the atmosphere of 2.8-5.6 Tg N2O-N per year. This perturbation, if continued into the future, will affect stratospheric chemical cycles, and the thermal balance of the Earth. In turn it will have direct and indirect global effects on the biosphere. Though the budget and cycles of N2O on Earth are not yet fully resolved, accumulating information and recent modelling efforts enable a more complete evaluation and better definition of gaps in our knowledge.

[Involvement of the subcortical structures in children with cranio-cerebral injuries]. / Porazhenie podkorkovykh struktur mozga u detei pri cherepno-mozgovoi travme.

From experience in the management of 12 cases the authors discuss the clinical picture and pathogenesis of a special form of craniocerebral trauma in children which is characterized by isolated affection of the subcortical ganglia, internal capsule, and the thalamus in the area supplied by the perforating branches of the middle cerebral artery.

[Radionuclide diagnosis of pathology of the cerebrospinal fluid system in post-traumatic conditions]. / Radionuklidnaia diagnostika patologii likvornoi sistemy pri posttravmaticheskikh sostoianiiakh.

Radionuclide cisterno-myelography was conducted in 155 patients in the posttraumatic period. Five variants of the radiological picture of liquordynamic disorders were distinguished. The signs of open internal hydrocephalus were determined. The authors note the frequency of the liquor path radiological sign--registration of radiopharmaceutical beyond the liquor channels, which points to the presence of nasal or auricular liquorrhea. Various changes of liquor circulation and resorption were revealed in posttraumatic periods. Disorders of resorption were manifested either by its acceleration or by its reduction or by sharp deceleration. Children most frequently had a radiological picture of open internal hydrocephalus. Signs of liquorrhea were a frequent component of a posttraumatic state in children. Different variants of the radiological picture were revealed in adults in the posttraumatic period: diminished draining function of the cerebral submeningeal space with compensatory drainage of the liquor in the form of nasal liquorrhea was a constant finding. Signs of open hydrocephalus were a commonly encountered component of the pathological picture of posttraumatic state in adults.

[The radionuclide diagnosis of pathology of the cerebrospinal fluid tract in posttraumatic states]. / Radionuklidnaia diagnostika patologii likvornykh putei pri posttravmaticheskikh sostoianiiakh.

Radionuclide cisternomyelography performed in 324 patients with posttraumatic injuries revealed the abnormality of the brain liquor tracts. The radiological picture of craniocerebral injury sequelae showed a great diversity of radionuclide signs, detected both morphological changes in the liquor tracts, and liquorodynamic disorders. The morphological disorders recorded by radionuclide cisternomyelography appeared as hydrocephalus, porencephalitis, arachnoidal cysts and liquorrheas. The liquorodynamic disorders recorded by this tool manifested themselves as altered liquor circulation and resorption. Radionuclide cisternomyelography provides valid data on the performance of the drainage system during operations on the liquor tracts of the brain and spine.

[Diffuse axonal damages to the brain (the clinical picture, diagnosis and outcome)]. / Diffuznye aksonal'nye povrezhdeniia golovnogo mozga (klinika, diagnostika i iskhody).

On the basis of complex clinical, computed tomographic, catamnestic, and pathomorphological examination of 336 patients with severe cerebrocranial injury the authors substantiate the need to distinguish, along with localized contusions and intracranial hematomas, diffuse axonal injuries of the brain whose biomechanics and pathogenesis are linked with trauma of angular or rotational acceleration-deceleration. The clinical manifestations and the course of diffuse axonal injuries are characterized by protracted coma occurring immediately after the injury with marked disorders of stem functions, postural motor reactions, slow recovery from coma, with the formation of a stable or transitory vegetative state, the development of syndromes of disconnection of the cerebral hemispheres and the brain stem, and severe invalidization of the patients due to mental and neurological deficits.

[Clinical and molecular genetic diagnosis of leukoencephalopathy with brainstem and spinal cord involvement and lactate elevation in children].

Leukoencephalopathy with brainstem and spinal cord involvement and lactate elevation (LBSL) is a recently described disorder with autosomal recessive model of inheritance. Mutations in the DARS2 gene, which encode mitochondrial aspartyl-tRNA synthetase, have been found. We present 31 cases with characteristic clinical and neuroimaging findings of this disorder. Patients have been stratified into two groups (early and late forms) by age-at-onset and clinical symptoms. The early form was characterized clinically by progressive pyramidal dysfunction, cerebellar and intellectual problems appeared later. Patients with the late form had cerebellar and sensitive ataxia, disturbances of muscle tonus, spastic type, mostly in the low extremities, polyneuropathic and rarely - psychoorganic syndrome. The brain MRI of all patients was characterized by inhomogeneous T2W signal abnormalities in the periventricular and deep white matter and a strikingly selective involvement of certain brainstem and spinal tracts. Most of the patients were compound-heterozygous for common mutations in the DARS2. We found 4 new mutations associated with LBSL. This is the first clinical and molecular-genetic investigation of this rare leukoencephalopathy in Russia.

[Glutaric aciduria type 1: clinical presentations, diagnostics and treatment.].

Glutaric aciduria type I is a rare autosomic recessive neurometabolic disease, which develops in the first year of life and is characterized by progressive extrapyramidal disorders as a result of the basal ganglia damage. We describe first cases of this disease in Russian population. The clinical observations are compared to the literature data. The disease usually develops after infections and features by seizures, vomiting, metabolic acidosis and deprivation of consciousness up to coma. These crises lead to the development of necroses of the basal ganglia that results in dystonias, dyskinesias and choreoatethosis. The secondary complications of the disease are difficulties with feeding, speech delay, chronic aspiration syndrome and severe delay of movement development. Diagnostics of the disease is based on urine and blood tests using methods of tandem mass spectrometry and gas chromatography. Treatment is based on dietary lysine or protein restriction and supplementation with carnitine. The data on the treatment of this disease are presented.

Secondary desertification due to salinization of intensively irrigated lands: The Israeli experience.

Secondary salinization of intensively irrigated lands is an increasingly alarming redesertification process experienced in many irrigated regions of the developed countries. The major cause is a profound interference in the geochemical/salt balances of irrigated regions. A case-in-point is the recent salinization of the Yizre'el Valley, a 20,000 ha intensively irrigated region in Israel. The extremely intensive and advanced agroecosystem developed in the region since the 1940s included pumping and importing irrigation water by the National Water Carrier, large-scale reclamation and reuse of municipal sewage water, winter flood impoundment in reservoirs for summer irrigation, and cloud seeding to enhance rainfall. Modern irrigation methods were applied, including sprinkler, trickle, moving-line, and center-pivot systems. Water use efficiency at any level was very high. Nevertheless, large-scale salinization of regional water resources and many fields had developed in the mid-1980s. Reconstructing and evaluating the water and salt balances of the Yizre'el Valley (using Cl as the representative salt constituent) shows that as water use in the valley increased to about 60 million m(3) per year, the importing of soluble salts by water totaled 15,000 tons of Cl per year. Recirculated salt - salt picked up by impounded surface water and applied to fields - increased significantly and in the late 1980s amounted to more than 9,000 tons Cl per year. The source of recirculated salts was the accumulated salts in soils and in the shallow aquifer in the valley, which were leached by floodwater or drained or infiltrated into reservoirs, grossly and adversely affecting water quality. Analysis of the Yizre'el Valley's case points to the utmost importance of maintaining the geochemical balances in addition to increasing irrigation efficiency. An irrigated region may achieve geochemical balance by the following means: limiting the extent of irrigated areas, developing a well-maintained drainage system that drains tail-water and salinized shallow-aquifer water, and devoting a significant portion of water for regional leaching. The sustained long-term productivity of irrigated lands in arid zones crucially depends on correctly managing water and soil resources. Regional management of irrigated lands to prevent secondary desertification will be aimed at carefully balancing the undisputed benefits of irrigation with the long-term (on time scales of 10 to 100 years) detrimental processes set in motion when irrigation is introduced to arid and semiarid zone soils.

Smectite clays in Mars soil: evidence for their presence and role in Viking biology experimental results.

Various chemical, physical and geological observations indicate that smectite clays are probably the major components of the Martian soil. Satisfactory ground-based chemical simulation of the Viking biology experimental results was obtained with the smectite clays nontronite and montmorillonite when they contained iron and hydrogen as adsorbed ions. Radioactive gas was released from the medium solution used in the Viking Labeled Release (LR) experiment when interacted with the clays, at rates and quantities similar to those measured by Viking on Mars. Heating of the active clay (mixed with soluble salts) to 160 degrees C in CO2 atmosphere reduced the decomposition activity considerably, again, as was observed on Mars. The decomposition reaction in LR experiment is postulated to be iron-catalyzed formate decomposition on the clay surface. The main features of the Viking Pyrolytic Release (PR) experiment were also simulated recently (Hubbard, 1979) which the iron clays, including a relatively low '1st peak' and significant '2nd peak'. The accumulated observations on various Martian soil properties and the results of simulation experiments, thus indicate that smectite clays are major and active components of the Martian soil. It now appears that many of the results of the Viking biology experiments can be explained on the basis of their surface activity in catalysis and adsorption.

Effect of adsorbed iron on thermoluminescence and electron spin resonance spectra of Ca-Fe-exchanged montmorillonite.

The electron spin resonance (ESR) spectra and the natural and gamma-induced thermoluminescence (TL) glow curves of a series of variably cation-exchanged Fe-Ca-clays prepared from SWy-1 montmorillonite were examined. The ESR signal (g = 2) intensity associated with the surface Fe was found to increase linearly with surface Fe content up to a nominal concentration of 50% exchangeable Fe. At > 50% exchangeable Fe, no appreciable increase in the signal was noted. The TL intensity decreased linearly with increasing surface Fe up to 50% nominal exchangeable Fe. At > 50%, the signal was not appreciably further diminished. The natural TL showed only a high-temperature peak, but irradiation produced an additional low-temperature peak. One month after gamma-irradiation, the integrated TL signal was still 10-100 times higher than that from the non-irradiated material. Thus, (1) surface iron clusters may form above a certain critical Fe concentration; (2) the Fe clusters are probably less effective in quenching TL than are single Fe atoms, implying interaction between surface Fe and the stored energy content of the material; and (3) the electronic energy stored in the material as the result of gamma-irradiation is only slowly dissipated.

Soil and water and its relationship to the origin of life.

Soils of the terrestrial planets form at the boundaries between lithosphere, atmosphere and hydrosphere. Biogenesis occurred in these zones; thus, it is axiomatic that some, perhaps many, stages of biogensis occurred in intimate association with the mineral constituents of soils. Because of a high surface to mass ration and, consequently, a high surface reactivity, the layer lattice clay minerals are the most important of these. According to the geological record, clay minerals appeared very early on the primordial Earth. Recent investigations have confirmed their presence in carbonaceous meteorites and have indicated their occurrence on Mars. In this paper we collect pertinent physico-chemical data and summarize the organic reactions and interactions that are induced or catalyzed by clays. Many clay-organic reactions that do not occur readily at high water contents proceed rapidly at adsorbed water contents corresponding to surface coverages of one or two molecular layers. One or two monolayers of adsorbed water correspond to extremely dry or cold planetary environments. Some consequences of these facts vis á vis biogenesis on Mars are considered.

Redistribution index and relative binding intensity of heavy metals in salt-amended soils.

Redistribution processes of heavy metals and their binding intensity in salt-amended arid-zone soils were analyzed under saturated, field capacity and wetting-drying cycle moisture regimes. Two newly developed parameters, redistribution index and reduced partitioning parameter, were used to depict the removal/attainment of metal-amended soils from/to the fractional distribution pattern in the native soils and the relative binding intensity of metals in the amended soils, respectively. Metal-amended soils, in forms of salts approached the fractional distribution pattern in the non-amended soils with time. The rates at which the metal-amended arid-zone soils approached the fractional distribution pattern characteristic of the native soil were affected by the nature and loading levels of the metals, soil properties and time. Metals in amended soils at low loading levels approach the fractional distribution pattern characteristic of non-amended soil more rapidly than at high loading levels. The sequences of approach by various metals to the fractional distribution pattern in the native soil are as follows: Cd > Cu > Ni, Zn > Cr. Moisture regime, however, did not considerably affect the metal-amended soils' overall rates of approach to the fractional distribution pattern prevailing in the non-amended soils. The binding intensity of metals in soils was affected by the nature of metal, loading level, soil properties and time. In both non-amended and amended soils, Cr had highest binding intensity, Cd lowest and Cu, Ni and Zn intermediate. The binding intensity decreased with the loading level of the metals and increased with time. The redistribution index and reduced partitioning index can quantitatively and effectively depict the kinetics of redistribution processes of metals and their relatively binding intensity in waste-amended soils.