Transfer Of 65Zn Research Articles

Effect of the physicochemical parameters of soils on the biological availability of natural and radioactive zinc

The relationship between the main physicochemical properties of soils and the accumulation of natural Zn and 65Zn radionuclide has been studied, and the capacity of soils to limit the mobility of the element in the soil–plant system has been assessed. The contribution of each of the selected soil state parameters to the accumulation of zinc by barley has been determined, and the soil state parameters have been ranked. It has been found that the largest contributions to the variation of the resulting parameter (65Zn accumulation coefficient, Ka) are made by mobile Fe (25%), free carbonates (21%), and acid-soluble Zn (18%). The largest contributions to the ZnacKa are made by free carbonates (13%) and mobile Fe (8%). The contributions of physical clay and organic carbon in soils and qualitative composition of humic substances are almost similar (4% for each). No differences in the inactivating capacity of different soils (soddy-podzolic soils, gray forest soils, and chernozems) for 65Zn are observed. This is related to the fact that the transfer of 65Zn to plants is statistically significantly controlled by the contents of free carbonates, mobile iron, and potentially plantavailable forms of stable natural Zn (carrier of 65Zn) rather than the quantitative and qualitative composition of organic matter and the degree of dispersion of mineral particles. The analysis of the ZnacKa/65Zn Ka ratios has shown that the share of plant-available Zn in the acid-soluble form of the metal (1 M HCl) is 0.61 on the average for the studied soils, and its share in the total Zn content in the soils is only 0.14.

Selective Transport of Zinc, Manganese, Nickel, Cobalt and Cadmium in the Root System and Transfer to the Leaves in Young Wheat Plants

The uptake, translocation and redistribution of the heavy metals zinc, manganese, nickel, cobalt and cadmium are relevant for plant nutrition as well as for the quality of harvested plant products. The long-distance transport of these heavy metals within the root system and the release to the shoot in young wheat (Triticum aestivum 'Arina') plants were investigated. After the application of 65Zn, 54Mn, 63Ni, 57Co and 109Cd for 24 h to one seminal root (the other seminal roots being excised) of 54-h-old wheat seedlings, the labelled plants were incubated for several days in hydroponic culture on a medium without radionuclides. The content of 65Zn decreased quickly in the labelled part of the root. After the transfer of 65Zn from the roots to the shoot, a further redistribution in the phloem from older to younger leaves was observed. In contrast to 65Zn, 109Cd was released more slowly from the roots to the leaves and was subsequently redistributed in the phloem to the youngest leaves only at trace levels. The content of 63Ni decreased quickly in the labelled part of the root, moving to the newly formed parts of the root system and also accumulating transiently in the expanding leaves. The 54Mn content decreased quickly in the labelled part of the root and increased simultaneously in leaf 1. A strong retention in the labelled part of the root was observed after supplying 57Co. The dynamics of redistribution of 65Zn, 54Mn, 63Ni, 57Co and 109Cd differed considerably. The rapid redistribution of 63Ni from older to younger leaves throughout the experiment indicated a high mobility in the phloem, while 54Mn was mobile only in the xylem and 57Co was retained in the labelled root without being loaded into the xylem.

Intestinal absorption of zinc: competitive interactions with iron, cobalt, and copper in mice with sex-linked anemia (sla)

Duodenal uptake and transfer of 59Fe and 65Zn and absorptive interactions between iron, zinc, cobalt, and copper were studied in sla mice and in genetically normal Swiss albino control mice. Genetically normal mice with a high iron-absorbing capacity, induced by being fed an iron-deficient diet, showed greater uptake and transfer of 65Zn in duodenum but not ileum, compared with mice with a low iron-absorbing capacity. 59Fe transfer from the duodenal mucosa to the body was lower in sla mice compared with controls and bleeding stimulated the capacity to absorb 59Fe less in sla mice relative to normal controls. In contrast, 65Zn transfer in sla was no different from controls and was not stimulated by bleeding in sla or in control mice. Iron or cobalt in a 10-fold molar excess predominantly lowered 65Zn transfer in both sla and controls, but in a study of the effect of zinc on iron transport only the uptake of 59Fe in sla mice was lowered by excess zinc in the perfusate. The effect of added copper on 65Zn transport was paradoxical; in both sla and control mice copper markedly increased 65Zn uptake relative to perfusates containing 65Zn alone, but transfer in normal mice was lowered whereas it was increased in sla animals. The interaction between zinc and iron does not appear to take place at the site of the genetic defect in sla mice. The lesion in iron transport in these mice is likely due to defective binding and transfer sites in the basolateral membrane; these sites are apparently exclusive for iron and not shared by zinc.

Kinetics of zinc absorption by the rat jejunum: effects of adrenalectomy and dexamethasone.

Effects of dexamethasone and adrenalectomy on the kinetics of jejunal 65Zn uptake and absorption were studied in the anesthetized adult rat. The jejunal lumen was perfused in situ with 5 mM glucose in 150 mM saline containing 65Zn and [14C]polyethylene glycol as volume marker. Over the 30-min perfusion period, the rate of net 65Zn removal from the perfusate was biexponential due to the establishment of a return flux to the lumen. An open two-compartment model satisfactorily describes these observations: (formula; see text) Dexamethasone (2 mg/kg ip 7 h before perfusion) increased k12 by 75% (P less than 0.0002) and decreased k20 by 45% (P less than 0.04). Both effects were independent of adrenalectomy. Mathematical simulations using the compartmental model and experimentally determined kinetic constants predicted that transfer of 65Zn into the body should be enhanced by adrenalectomy and retarded by dexamethasone administered to adrenalectomized rats. Dexamethasone and adrenalectomy thus differentially affect Zn uptake and absorption in this system, suggesting a possible adrenocortical hormone involvement in the regulation of Zn absorption. These changes are apparently not mediated via metallothionein.

Bioaccumulation et elimination du 65Zn par Gammarus aequicauda martimov

Uptake of 65Zn by Gammarus aequicauda results in a concentration factor of approximately 50 and it is characterised by a maximal accumulation level attained as early as the third day of the experiment. After ingestion by the gammarids of twenty contaminated meals which are distributed over a 45-day period, a transfer of 65Zn between the food and the consumer can be observed but there is no sign of the biomagnification phenomenon. The retention rate of the radionuclide is only about 1·5% and the 65Zn concentration in the gammarids remains markedly inferior to that of the ingested food. The elimination of the 65Zn fixed directly from water takes place according to an exponential model which corresponds to the existence of three biological half-lives of the radionuclide, Tb 1 ⋍ 0·5 day, Tb 2 ⋍ 3·5 days and Tb 3 ⋍ days . The excretion of 65Zn accumulated from food is a simple exponential phenomenon which corresponds to only one biological half-life of approximately 17 days.

Transfer of 65Zn through Placenta and Milk in Mice

Transfer of 65Zn through Placenta and Milk in Mice

Transfer of 65Zn from sediments by marine polychaete worms

Silty marine sediments spiked with 65Zn lose only small fractions of their radioactivity when exposed to slowly flowing seawater for several weeks. However, polychaete worms (Nereis diversicolor), burrowing through the sediment, cause 65Zn losses 3 to 7 times higher than in sediment without worms. Long-term experiments on the uptake and loss of 65Zn by the polychaete Hermione hystrix indicate that 60 or more days exposure are required for this worm to approach steady state with 65Zn in the sediment. Biological half-life estimates for 65Zn accumulated from sediment by H. hystrix are extremely variable (52 to 197 days), depending on the loss-time interval chosen for the calculation. Following 5 days exposure to 16 cm3 of radioactive sediment, N. diversicolor individuals contained an average of 0.2% of the total 65Zn in the sediment. When these worms were transferred to non-radioactive sediment, estimates of biological half-life for 65Zn averaged 14 to 17 days during the loss period Day 3 to Day 15. Based on these experimental results, it is estimated that a population of N. diversicolor could cause an annual loss of 3% or more of the 65Zn in the upper 2 cm of the sediment of a hypothetical radioactive estuary.

Experimental studies on the transfer of 65Zn in high concentration by euphausiids

The uptake and elimination of 65Zn by Euphausia pacifica, in ‘clean’ sea water and in several concentrations of radioactive phytoplankton food, have been measured at 10 °C. Measurement was done on time schedules to simulate those which vertically-migrating euphausiids would spend in and out of a hypothetical 65Zn pool at the sea surface at different seasons of the year in temperate latitudes. From a knowledge of the total 65Zn body burdens reached at any time t, and of the mechanisms and rates of loss of 65Zn in radioactive and non-radioactive water, transfer of 65Zn via euphausiids from the ‘hot’ surface pool to non-radioactive water below may be assessed. With inital concentrations of 25μ Ci 65Zn/l, equilibrium body burdens were achieved in ‘clean’ sea water in about four days under all time schedules. The level of equilibrium body burden was a function of time schedule (time spent in the radioactive solution). In radioactive food, equilibrium body burdens were not reached in five days. Below about 10 5 cells/ml, uptake through food was a function of food concentration, but was not apparently affected by food concentrations above 10 5 cells/ml. When uptake was from ‘clean’ sea water, elimination was by molting of the animal's chitinous exoskeleton and by exchange with non-radioactive water. When uptake was from labelled food, elimination was from fecal pellet deposition as well as molting and exchange. Molting, exchange, and fecal pellet deposition represented different percentage losses from total body burden, depending largely upon the time the animal spent in and out of 65Zn and the source of 65Zn (water or food). Summations of these losses have been used to estimate transfer of 65Zn by euphausiids from a ‘hot’ surface pool to waters below the pool.

Distribution of 65Zn In Tissues of Two Marine Crustaceans Determined by Autoradiography

In the benthic amphipod Anonyx sp., and the euphausiid Euphausia pacifica Hansen, 65Zn accumulated from seawater was shown by autoradiography to be localized predominantly in the exoskeleton and interstitial spaces of the myofibrils. Also, the gut and hepatopancreas of Anonyx sp. and the eye of E. pacifica contained 65Zn. The presence of 65Zn in crustacean exoskeletons may affect the efficiency of transfer of 65Zn through the food web and the vertical distribution of 65Zn in the Pacific Ocean along the Oregon coast.