Rhizospheric mobilization and plant uptake of radiocesium from weathered micas: I. Influence of potassium depletion.

Potassium depletion in the soil solution around plant roots promotes the root uptake of radiocesium. However, it can also induce the transformation of mica through the release of interlayer K. In bulk soil, the formation of frayed edge sites (FES) with a high selectivity for Cs adsorption is usually related with mica weathering. We studied the effect of K level in the nutrient solution on the root-induced weathering of phlogopite as well as on the root uptake of radiocesium by willow (Salix viminalis L. var. Orm). The willows were grown for 7 wk in column lysimeters filled with a quartz-phlogopite mixed substrate continuously irrigated with nutrient solutions differing in K concentration (0-2 mM). From a potassium supply of 0.4 mM downward, we observed a decrease in root uptake of potassium as well as an increase in (i) potassium release from phlogopite, (ii) degree of transformation of phlogopite into vermiculite, and (iii) root uptake of radiocesium. Increasing K depletion had thus two effects: a decrease of the root uptake of potassium and an increase of phlogopite weathering in the rhizosphere, both of which promoted the root uptake of radiocesium.

Radiocaesium soil-to-wood transfer in commercial willow short rotation coppice on contaminated farm land.

The feasibility of willow short rotation coppice (SRC) for energy production as a revaluation tool for severely radiocaesium-contaminated land was studied. The effects of crop age, clone and soil type on the radiocaesium levels in the wood were assessed following sampling in 14 existing willow SRC fields, planted on radiocaesium-contaminated land in Sweden following Chernobyl deposition. There was only one plot where willow stands of different maturity (R6S2 and R5S4: R, root age and S, shoot age) and clone (Rapp and L78183 both of age category R5S4) were sampled and no significant differences were found. The soils differed among others in clay fraction (3-34%), radiocaesium interception potential (515-6884 meq kg(-1)), soil solution K (0.09-0.95 mM), exchangeable K (0.58-5.77 meq kg(-1)) and cation exchange capacity (31-250 meq kg(-1)). The soil-to-wood transfer factor (TF) of radiocaesium differed significantly between soil types. The TF recorded was generally small (0.00086-0.016 kg kg(-1)), except for willows established on sandy soil (0.19-0.46 kg kg(-1)). Apart from the weak yet significant exponential correlation between the Cs-TF and the solid/liquid distribution coefficient (R2 = 0.54) or the radiocaesium interception potential, RIP (R2 = 0.66), no single significant correlations between soil characteristics and TF were found. The wood-soil solution 137Cs concentration factor (CF) was significantly related to the potassium concentration in the soil solution. A different relation was, however, found between the sandy Trödje soils (CF = 1078.8 x m(K)(-1.83), R2 = 0.99) and the other soils (CF = 35.75 x m(K)(-0.61), R2 =0.61). Differences in the ageing rate of radiocaesium in the soil (hypothesised fraction of bioavailable caesium subjected to fast ageing for Trödje soils only 1% compared to other soils), exchangeable soil K (0.8-1.8 meq kg(-1) for Trödje soils and 1.5-5.8 meq kg(-1) for the other soils) and the ammonium concentration in the soil solution (0.09-0.31 mM NH4+ for the Trödje soils compared to 0.003-0.11 mM NH4+ for the other soils) are put forward as potential factors explaining the higher CF and TF observed for the Trödje soils. Though from the dataset available it was not possible to unequivocally predict the Cs-soil-to-wood-transfer, the generally low TFs observed point to the particular suitability for establishment of SRC on radiocaesium-contaminated land.

Short rotation coppice for revaluation of contaminated land.

When dealing with large-scale environmental contamination, as following the Chernobyl accident, changed land use such that the products of the land are radiologically acceptable and sustain an economic return from the land is a potentially sustainable remediation option. In this paper, willow short rotation coppice (SRC) is evaluated on radiological, technical and economic grounds for W. European and Belarus site conditions. Radiocaesium uptake was studied in a newly established and existing SRC. Only for light-texture soils with low soil potassium should cultivation be restricted to soils with contamination levels below 100-370 kBq m-2 given the TFs on these soils (5 x 10(-4) and 2 x 10(-3) m2 kg-1) and considering the Belarus exemption limit for firewood (740 Bq kg-1). In the case of high wood contamination levels (> 1000 Bq kg-1), power plant personnel working in the vicinity of ash conveyers should be subjected to radiation protection measures. For appropriate soil conditions, potential SRC yields are high. In Belarus, most soils are sandy with a low water retention, for which yield estimates are too low to make production profitable without irrigation. The economic viability should be thoroughly calculated for the prevailing conditions. In W. Europe, SRC production or conversion is not profitable without price incentives. For Belarus, the profitability of SRC on the production side largely depends on crop yield and price of the delivered bio-fuel. Large-scale heat conversion systems seem the most profitable and revenue may be considerable. Electricity routes are usually unprofitable. It could be concluded that energy production from SRC is potentially a radiologically and economically sustainable land use option for contaminated agricultural land.

A note on 'aging-pharmacodynamics' with application to the analysis of the age-dynamics of adipocyte response to epinephrine and insulin.

This note aims at clearing some semantic problems in the literature concerning the analysis of the effect of age on dose-response curves as well as standardize the way such data should be presented. In particular it is shown how to assess the age-dynamics (i.e. the pattern of change as a mathematical function of age) of the sensitivity of a receptor system to a given agent, of the quantitative overall changes of the cellular response apparatus which affect response capacity, and of the interaction between different simultaneously acting agents. The concepts and theory are illustrated using as an example the in vitro isolated rat fat cell (or adipocyte) which we have recently studied extensively with regards to the age-dynamics of its lipolytic response to epinephrine and insulin. This 'aging-pharmacodynamics' analysis has led to the surprising conclusion of a rebound effect of age (decrease at maturity followed by increase at old age) on the sensitivity of the fat cell to epinephrine and to its antagonist (with respect to lipolysis) insulin, as well as a negative correlation of these sensitivities with fat cell size.

Changes in lipolytic activity of isolated adipocytes from rats throughout life span.

The lipolytic response of isolated adipocytes from 1 1/2-, 6-, 24- and 32-month-old rats to various doses of epinephrine was studied. Both the basal and the maximal stimulated glycerol release were largest in the mature rats (6 months old) which had the largest adipocytes. Expressing glycerol release per unit cell surface area (which was drastically reduced with age) eliminated the difference between mature and senescent rats both in absence of epinephrine and at high doses of the hormone. However, at low epinephrine doses the adipocytes of the very young and the very old rats showed an enhanced response per unit surface area. A simple pharmacodynamic analysis based on the occupancy theory of drug-receptor interaction suggests that the sensitivity of rat adipocyte receptors is increased during senescence; this increase may be related to the decreased surface of old adipocytes. On the other hand, the decreased maximal lipolytic response during senescence may be due in part to a reduced number of receptors and to a reduced sensitivity of the cellular enzymatic system underlying lipolysis.

In vitro effect of thyroid hormones on lipolysis of rat fat cells during aging.

The in vitro effect of triiodothyronine (T3) 10(-5) M upon lipolysis was studied on white fat cells isolated from 1.5-6- and 30-month-old rats. We couldn't see any consistent effect of this hormone upon the basal lipolysis. We observed a T3 effect on epinephrine-stimulated lipolysis on the three groups of animals. After 1 h of incubation the increase of glycerol release varies with the dose of epinephrine; after 3 h the T3 effect persisted only in the 6-month and 30-month groups.

Morphological and metabolic alterations in adipose tissue of very old rats.

Body weight, epididymal adipose tissue weight, fat cell size, and metabolic activity of fat depot were studied in 30-month-old Wistar rats and compared with rats aged 6 and 24 months old. In very old age a significant reduction of body weight was observed and was paralleled with a decline of adipose mass and a decrease in cell volume. In vitro metabolic studies, with and without insulin, showed a greater oxidation of D-U-14C glucose to 14CO2 and a greater incorporation into triglycerides than in the 24-month-old animals when the data were expressed per cell or per cm2 surface area. The resistance to insulin was elevated in spite of a significant decrease of adipocyte size in very old rats.

[Prolonged effects of training on adipose tissue glucose metabolism and insulin responsiveness in adult rats (author's transl)]. / Effets prolongés de l'entrainement physique sur le métabolisme du glucose du tissu adipeux et sa sensibilité a l'insuline chez le rat adulte.

Physical training (forced swimming for 6 weeks) led in resting adult rats modifications of circulating hormones, fuels and substrates, of epididymal adipose tissue composition and of its glucose metabolism. Plasma concentrations of free fatty acids, cholesterol and insulin were decreased by training. The weight of the epididymal fat pad, its triglyceride content and the mean cell size of adipocytes were significantly diminished. Twenty four hours after the end of the final exercise period, incorporation of D-U-14C-glucose into triglycerides was reduced (P less than 0.01) but the response to insulin was greatly enhanced for swimming rats both for oxidation of labelled glucose (P less than 0.001) and its incorporation into lipids (P less than 0.001) (respectively 215 and 225%). This enhancement of insulin sensitivity by training persisted and became more marked one week after the end of the exercise period (respectively 258 and 363%).

Organ culture of the Islets of Langerhans from young and senescent rats.

The B-cells of the endocrine pancreas constitute an adequate model for in vitro study of the aging process in highly differentiated cells. In the present study, collagenase-isolated islets of Langerhans from young and senescent rats were cultured up to 28 days. The response of the B-cells to the stimulatory conditions of the culture medium involved the nucleus, ribosomes, endoplasmic reticulum, Golgi apparatus, and secretory granules. Correlated data from light microscopy, electron microscopy, and insulin radioimmunoassay show that the differentiation and function of senescent B-cells are maintained in culture, as it has been proven for the B-cells of younger animals. On the other hand, signs of cytological deficiency not directly concerned with the specific function of B-cells were observed: abnormal mitochondria and lysosomes are more numerous in the senescent B-cells. The proliferative capacity of the B-cells of aged rats is reduced.

Effect of maturation and senescence on carbohydrate utilization and insulin responsiveness of rat adipose tissue.

The aim of the present investigation was to study the effect of aging upon the metabolism and the responsiveness to insulin of epididymal adipose tissue from rats (6 weeks, 6 and 24 months). Basal glucose metabolism by these tissues and adipocytes was positively related to cell size, for each age group. But age per se plays an important role: for the same diameter, the U-14C-glucose oxidation to CO2 and its incorporation into triglycerides described markedly between 6 weeks and 6 months, as reported peviously, and decreased still further between 6 months and 24 months, for any diameter. In contrast, insulin responsiveness of adipose tissue fragments and fat cells was negatively correlated to adipose cell size, when we analyzed the role of cell diameter for a group of given age. When comparing the sensitivity to hormone for a given cell volume but at different ages, it appeared that insulin resistance increased considerably between 6 weeks and 6 months and was still more marked in old age. The mechanisms underlying these facts have been discussed.

[The effect of age on the in vitro insulin response in the rat. II. Glucose metabolism in epididymal adipose tissue (author's transl)]. / Effet de l'âge sur la réponse à l'insuline in vitro chez le rat. II. Métabolisme glucidique du tissu adipeux épididymaire

A decrease of the basal glucose metabolism with sensescence in the isolated rat adipose tissue has been demonstrated. In the presence of insulin, the oxidation of (U14C)-D-glucose and its incorporation into triglycerides are significantly increased at all ages studied. No significant difference between groups of animals was noted when the insulin-stimulating effect was related to basal metabolism. The synthesis of fatty acids from glucose is highly enhanced by insulin at 6 weeks, poorly at 6 months and no more at 24 months. It is concluded that the insulin sensitivity of the rat adipose tissue is not affected by ageing. Nevertheless, as far as fatty acid synthesis is concerned, a different metabolic pathway could be involved.

[The effect of age on the in vitro response to insulin in the rat. I. Glucose metabolism on the diaphragm (author's transl)]. / Effet de l'âge sur la réponse à l'insuline in vitro chez le rat. I. Métabolisme glucidique du tissu diaphragmatique

No modification in basal radioglucose metabolism by isolated rat diaphragm could be seen with senescence. Insulin increased the production of 14CO2 only in growing animals. On the opposite, incorporation of radioglucose into glycogen is enhanced in the different age groups; nevertheless, the response in 3-month-old animals was lower than in 6-week-old ones. No significant difference has been detected between the adult and the old rats. Therefore, it is concluded that a diminution of insulin sensitivity appeared during the period of transition between growing up and maturity without any further modification during old age.

Effect of ageing on insulin and insulin-glucose sensitivity tests in rats.

Insulin tolerance tests have shown old rats to respond to injection of the hormone by a sharp and lasting drop in blood sugar. The difference between these animals and young and adult ones lies in their inability to restore a normal blood glucose level. Glucose tolerance and insulin-glucose tolerance tests show that glucose uptake under the influence of the hormone is significantly reduced with age in absolute terms. However, the difference in glucose assimilation coefficient in the absence or presence of insulin (deltaK) is comparable in all age groups; thus senile rats were found to be as sensitive even to small doses of hormone as the adult ones, if basal levels are taken into account.