Strontium uptake in rats on alginate-supplemented diet.

Rats were fed a basic diet supplemented with sodium alginate and with tracer amounts of strontium-85 and calcium-45. Absorption of strontium was always inhibited by the alginate to a greater extent than absorption of calcium. Discrimination against strontium was greatest in alginate containing a high proportion of guluronic acid.

PEAT-CLSM: A Specific Treatment of Peatland Hydrology in the NASA Catchment Land Surface Model.

Peatlands are poorly represented in global Earth system modeling frameworks. Here we add a peatland-specific land surface hydrology module (PEAT-CLSM) to the Catchment Land Surface Model (CLSM) of the NASA Goddard Earth Observing System (GEOS) framework. The amended TOPMODEL approach of the original CLSM that uses topography characteristics to model catchment processes is discarded, and a peatland-specific model concept is realized in its place. To facilitate its utilization in operational GEOS efforts, PEAT-CLSM uses the basic structure of CLSM and the same global input data. Parameters used in PEAT-CLSM are based on literature data. A suite of CLSM and PEAT-CLSM simulations for peatland areas between 40°N and 75°N is presented and evaluated against a newly compiled data set of groundwater table depth and eddy covariance observations of latent and sensible heat fluxes in natural and seminatural peatlands. CLSM's simulated groundwater tables are too deep and variable, whereas PEAT-CLSM simulates a mean groundwater table depth of -0.20 m (snow-free unfrozen period) with moderate temporal fluctuations (standard deviation of 0.10 m), in significantly better agreement with in situ observations. Relative to an operational CLSM version that simply includes peat as a soil class, the temporal correlation coefficient is increased on average by 0.16 and reaches 0.64 for bogs and 0.66 for fens when driven with global atmospheric forcing data. In PEAT-CLSM, runoff is increased on average by 38% and evapotranspiration is reduced by 19%. The evapotranspiration reduction constitutes a significant improvement relative to eddy covariance measurements.

Changes in net ecosystem productivity with forest age following clearcutting of a coastal Douglas-fir forest: testing a mathematical model with eddy covariance measurements along a forest chronosequence.

We hypothesized that changes in net ecosystem productivity (NEP) during aging of coastal Douglas-fir (Pseudotsuga menziesii Mirb. Franco) stands could be explained by (1) changing nutrient uptake caused by different time scales for decomposition of fine, non-woody and coarse woody litter left after harvesting, (2) declines in canopy water status with lengthening of the water uptake pathway during bole and branch growth, and (3) increases in the ratio of autotrophic respiration (R (a)) to gross primary productivity (GPP) with phytomass accumulation. These hypotheses were implemented and tested in the mathematical model ecosys against eddy covariance (EC) measurements of forest CO(2) and energy exchange in a post-clearcut Douglas-fir chronosequence. Hypothesis 1 explained how (a) an initial rise in GPP observed during the first 3 years after clearcutting could be caused by nutrient mineralization from rapid decomposition of fine, non-woody litter with lower C:N ratios (assart effect), (b) a slower rise in GPP during the next 20 years could be caused by immobilization during later decomposition of coarse woody litter, and (c) a rapid rise in GPP between 20 and 40 years after clearcutting could be caused by nutrient mineralization with further decomposition of coarse woody litter and of its decomposition products. During periods (a) and (b), heterotrophic respiration (R (h)) from decomposition of fine and coarse litter greatly exceeded net primary productivity (NPP = GPP - R (a)) so that Douglas-fir stands were large sources of CO(2). During period (c), NPP exceeded R (h) so that these stands became large sinks for CO(2). Hypothesis 2 explained how declines in NPP during later growth in period (c) could be caused by lower hydraulic conductances in taller trees that would force lower canopy water potentials and hence greater sensitivity of stomatal conductances and CO(2) uptake to vapor pressure deficits. Enhanced sensitivity to vapor pressure deficits was also apparent in the EC measurements over the post-clearcut chronosequence. Hypothesis 3 did not contribute to the explanation of forest age effects on NEP.

A relationship between residual stromal damage in hematopoietic tissue and the functional activity of granulocytes.

This paper analyzes the function of mouse granulocytes in the long term, after external irradiation with x- and gamma-rays and 239Pu contamination at different gestational ages and in a variety of culture conditions. These treatments can produce persistent defects in the stroma, which regulates hematopoiesis. Superoxide-anion production has been measured in granulocytes from peripheral blood and from long-term bone marrow cultures (LTBMC). A significant enhancement of O2- is produced using single or fractionated doses of x-rays; however, little or no increase is observed with gamma-rays. With 239Pu, enhancement of O2- depends on gestational age at contamination. The absence of hydrocortisone (HC) in LTBMC and the irradiation of the adherent layer with 15 Gy stimulate O2- production. The increased production of O2- appears to be correlated with an excess of colony-stimulating factors (CSFs) released to the supernatant by stromal cells. Neutralization with anti-granulocyte-macrophage CSF (anti-GM-CSF) monoclonal antibody shows that GM-CSF is the main factor produced. In summary, conditions that lead to residual stromal damage also result in the generation of granulocytes that are functionally primed for excess superoxide-anion production.

On the late seeding of CFU-S to the spleen: 8- vs 12-day CFU-S.

Marrow from 5-fluorouracil- or cyclophosphamide-treated mice, injected into lethally irradiated recipients, gives an increasing number of spleen colonies between days 7 and 14. It has been suggested that the later-forming colonies result from the more primitive spleen colony-forming units (CFU-S), which first seed into the marrow, only later to be recirculated and form colonies in the spleen. Strontium 89 (89Sr), a bone-seeking radionuclide, was injected into recipient mice to block such putative recirculation. A dose of 89Sr, which killed at least 99.8% of CFU-S in, or entering, the bone cavities, was incapable of preventing the increase in spleen colony numbers. Similarly, the splenic environment, modified by the presence of spleen colonies and able to provide a better bed for trapping CFU-S from the peripheral circulation, yielded the same number of further CFU-S, whether or not the animal had received 89Sr. Thus, it was concluded that the 12-day CFU-S does not seed initially into the marrow spaces. Direct observation of the quality of CFU-S initially seeding into the bone marrow and spleen showed, by retransplantation into secondary irradiated mice, that a similar spectrum of CFU-S types had seeded both organs.

Long-term effects of plutonium-239 and radium-224 on the distribution and performance of pluripotent haemopoietic progenitor cells and their regulatory microenvironment.

Experiments are described which investigate the long-term damage to haemopoietic progenitor cells (CFU-S) and their microenvironment in mouse marrow resulting from the administration of leukaemogenic amounts of plutonium-239 and radium-224. 239Pu (35 Bq g-1 body weight) and 224Ra (555 Bg g-1 body weight) were injected into 10-12-week-old mice, and numbers, proliferative activity and self-renewal capacity of CFU-S were measured at different locations in femoral marrow at intervals over the following 2 years. Parallel measurements were also made of the quality of the haemopoietic microenvironment by ectopic transplantation of bone marrow cells. There was some recovery from the initial effects of 239Pu on CFU-S numbers after 3-6 months, although the recovery was not maintained in all marrow fractions. Following 224Ra administration there was an initial transient increase in CFU-S numbers in the fraction of marrow furthest from bone surfaces but a considerable depression in numbers in other regions of marrow; there was no recovery between 3 and 6 months and subsequent recovery was not complete in all regions of marrow. The differential responses of CFU-S and the haemopoietic microenvironment following 224Ra or 239Pu administration seemed in some ways related to the metabolism of the radionuclides. There was a profound reduction in the ability of marrow to generate ossicles when transplanted under the kidney capsule as a result of the administration of either 224Ra or 239Pu, with only transient recoveries from the effects of 239Pu at 4 days and at 3 months after injection.

Alpha-particle irradiation of haemopoietic tissue in pre- and postnatal mice. 1: Distribution of plutonium-239 after mid-term contamination.

Pregnant mice (at 13 days gestation) and age-matched controls were injected with 30 kBq 239Pu/kg and the distribution of plutonium in maternal and foetal tissues measured. Approximately 2% of the activity injected into the mother reached each foetus in 24 h, 95% of which was contained in membranes and placenta. The concentration of plutonium in foetal liver was 3 times the average foetal body concentration; both liver and body concentrations in the foetus increased by the end of gestation. Each pup accumulated only 0.01% extra injected activity after 9 days lactation and, as the resulting concentrations in the neonatal skeleton were low, we conclude that the greatest haemopoietic risk to the offspring from mid-term contamination in utero is in the foetal liver (which received an average dose of 10-14 mGy between the time of mid-term contamination and birth). By the end of gestation about one-quarter of the original activity was transferred to foetal tissues from the maternal liver and skeleton. No significant changes in maternal distribution were detected as a result of lactation. The results of this study are discussed, along with a compilation of previously published data.

Alpha-irradiation of haemopoietic tissue in pre- and postnatal mice: 2. Effects of mid-term contamination with 239Pu in utero.

The distribution of 239Pu in various tissues of foetal and postnatal offspring of pregnant mice, injected i.v. at 13 days gestation with 30 kBq 239Pu/kg (in some cases with 10 or 100 kBq/kg), together with the numbers of haemopoietic progenitors in the bone marrow, spleen and liver, were measured through to 1 year post-partum. The quality of the haemopoietic microenvironment in these mice was also measured using the renal-capsule implant method. The largest radiation dose received by any haemopoietic organ was that in the liver, amounting to 10-14 mGy, as reported previously. In spite of normal numbers of haemopoietic spleen colony-forming cells (CFC-S) in the liver and seeding, at birth, into the bone marrow where the level of plutonium was minimal, a long-term deficit in their number rapidly developed. The development of the stromal microenvironment, however, was also deficient, suggesting that the dose of alpha-irradiation to the foetal liver was sufficient to cause sublethal damage in those cells destined to become the precursors of the supportive haemopoietic microenvironment in bone marrow and spleen. The results of this study suggest that although the placenta affords significant shielding to the tissues of the developing foetus from maternal contamination, the long-term effects on haemopoiesis are comparable to those in mice contaminated as adults. This further implies that the developing haemopoietic tissues are exquisitely sensitive to 239Pu contamination.

Myeloid leukaemia and osteosarcoma in CBA/H mice given 224Ra.

Four groups of 400 12-week-old CBA/H mice were injected i.p. with 69, 139, 280 and 550 Bqg-1 224Ra. A further group of 400 mice were injected i.p. with diluting solution only. The mice were then allowed unrestricted access to food and water until they died or were killed. 53 cases of myeloid leukaemia and 22 cases of osteosarcoma were confirmed in the 2000 mice injected, and for both tumour types direct relationships were shown to exist between the amount of 224Ra administered and the incidence of tumours. It is concluded that mouse is at a greater risk from myeloid leukaemia than from osteosarcoma in the region of administered 224Ra below that which causes a maximum yield of osteosarcoma. These results are discussed in the light of the present acceptance of osteosarcoma as the major risk to man from bone-seeking alpha-particle emitters.

Cytogenetic effects of protracted exposures to alpha-particles from plutonium-239 and to gamma-rays from cobalt-60 compared in male mice.

Adult C3H X 101 hybrid male mice were injected intravenously with 4 muCi of 239Pu citrate per kg body weight and examined for evidence of cytogenetic damage to the testis after exposures of 21, 28 and 34 weeks, with average doses from alpha-particles estimated as 13, 18 and 18 rad respectively (mean dose rate 0.00006 rad/min). Results were compared with those obtained when equivalent males were exposed continuously and concurrently to 1128 rad 60Co gamma-irradiation over 28 weeks (0.004 rad/min). The following estimates of the relative effectiveness of the alpha- and gamma-radiation were made: 24 for reciprocal translocations and for chromosome fragments, 22 for dominant lethal mutations acting after implantation. These values (with mean of 23) are based on average testis doses, with no correction for probable non-homogeneity of alpha dose distribution. In the mice exposed to gamma-irradiation there were significant reductions in testis mass and epididymal sperm-count. Although corresponding differences from control were not significant in the alpha series, consideration of results from a previous experiment by the same authors [2] allowed the relative effectiveness of the alpha- and gamma-irradiation for testis mass reduction to be estimated as roughly 10-15. Existing data on translocation induction in mouse spermatogonia by low dose-rates of gamma-rays (down to 0.003 rad/min) were analysed. They suggested that minimum rates of induction at very low intensities were not less than 1 X 10(-5) translocations per rad. A comparison of the frequencies of induction of fragments and of sperm-head abnormalities obtained after chronic gamma-ray exposures in the present experiment with those found by other workers after acute X-ray exposures suggested that there were no marked dose-rate effects with these types of mutational effect. Finally, the special problems associated with cytogenetic studies on alpha-emitters are discussed.

Age-related and 224Ra-induced abnormalities in the teeth of male mice.

A high incidence of incisor abnormalities was found in aged control and aged 224Ra-treated male CBA mice. Visual examination of the abnormalities in both controls and treated mice revealed extreme shortening of the upper incisors and hypoplastic, grooved or undulating enamel. The administration of 865 or 1730 nCi of 224Ra hastened the onset of incisor abnormalities although no specific feature was attributable solely to radium toxicity. Radiography and histology revealed corrugated incisors, obliteration of the pulp cavity, extension and disorganized growth of incisors basally, secondary incisors, open pulp and fractures within the alveoli. There was a statistically-significant reduction in the number of molars present in animals given 432, 865 or 1730 nCi 224Ra.

A Monte-Carlo approach to the microdosimetry of 224Ra in murine compact and cancellous bone.

A method is described which allows dose calculations to be made to individual target cells in different regions of mouse bone marrow exposed to alpha particles emitted from bone. The method takes into account the variable rate of transfer of energy along the tracks of alpha particles and was applied to experiment-based values calculated for the concentration of 224Ra on bone surfaces after an injection of a leukemogenic amount of the nuclide. These calculations show a minimum dose of 11 Gy in small (less than 50-micron) marrow spaces and 10 Gy close to bone surface in the shaft of the femur. The results suggest that leukemogenic doses are likely to occur at some distance from bone surfaces in wide marrow spaces and that osteosarcoma is not likely to be induced directly in cells immediately aligning bone surfaces.

Radiation dose from plutonium deposited in marrow and bone of normal and chimaeric mice.

239Pu citrate was injected intraperitoneally into CBA mice and into CBA mice which had been made chimaeric by replacing their haematopoietic bone-marrow with that from another genetically-identical but cytologically-distinct strain. The mice were killed at three intervals up to 90 days after injection, and the deposited 239Pu was determined radiochemically in bone-marrow and in bone. The average radiation dose (integrated over 90 days) was found to be greater in the bones but lower in the marrow of chimaeric mice than in the corresponding tissues of the normal CBA mice. These results are discussed from the points of view of induction of malignant change in marrow and bone and of plutonium metabolism in the two types of mouse.

The relationship between 59Fe uptake in marrow and 239Pu deposition in bone.

The marrow in the left femur of each of 17 mice was destroyed by X-irradiation and 59Fe and 239Pu uptake into both femurs was measured 1, 3 and 7 days later. Uptake of 59Fe into marrow was depressed in the left femur 1 and 3 days after irradiation but was enhanced in the right unirradiated femur 3 days after the left femur was irradiated. There was no corresponding depression of 239Pu uptake into the left irradiated femur or enhancement into the right unirradiated femur. These results do not support the view that a functioning erythropoietic marrow is necessary for 239Pu to be deposited in bone.

The dosimetry of 224Ra in mouse bone.

Calculations are described, based on experimental findings, which show the variation of absorbed dose from 224Ra in bone marrow of CBA/H mice. These calculations indicate that, following an injection of a leukaemogenic amount of 16 kBq 224Ra into these mice, most marrow cells in the cancellous bone of femur ends are killed but most marrow cells in the femur shaft survive. The calculations also suggest that the mean leukaemogenic absorbed dose of about 1.5 Gy is received by a population of marrow cells about 30 microns from bone surface in the femur shaft.

The induction by 239Pu of myeloid leukaemia and osteosarcoma in female CBA mice.

Plutonium-239 was injected into 12-week-old female CBA/H mice in the range 1.85-18.5 kBq kg-1 either as a single injection or as 16 injections spaced at 3.5 day intervals over eight weeks. There was a highly significant increase in the yield of fully developed osteosarcomas with increased amounts of 239Pu for both modes of injection. Osteosarcomas too small to be diagnosed radiographically were also seen in many bones and small but significant yields of myeloid leukaemia were seen in animals given plutonium. Although more myeloid leukaemia was seen in the mice given plutonium in divided amounts than in those given the plutonium in a single injection it could not be shown that multiple injection significantly affected the yield of either late effect.