Establishing a database of radionuclide transfer parameters for freshwater wildlife

Environmental assessments to evaluate potentials risks to humans and wildlife often involve modelling to predict contaminant exposure through key pathways. Such models require input of parameter values, including concentration ratios, to estimate contaminant concentrations in biota based on measurements or estimates of concentrations in environmental media, such as water. Due to the diversity of species and the range in physicochemical conditions in natural ecosystems, concentration ratios can vary by orders of magnitude, even within similar species. Therefore, to improve model input parameter values for application in aquatic systems, freshwater concentration ratios were collated or calculated from national grey literature, Russian language publications, and refereed papers. Collated data were then input into an international database that is being established by the International Atomic Energy Agency. The freshwater database enables entry of information for all radionuclides listed in ICRP (1983), in addition to the corresponding stable elements, and comprises a total of more than 16,500 concentration ratio (CRwo-water) values. Although data were available for all broad wildlife groups (with the exception of birds), data were sparse for many organism types. For example, zooplankton, crustaceans, insects and insect larvae, amphibians, and mammals, for which there were CRwo-water values for less than eight elements. Coverage was most comprehensive for fish, vascular plants, and molluscs. To our knowledge, the freshwater database that has now been established represents the most comprehensive set of CRwo-water values for freshwater species currently available for use in radiological environmental assessments.

Background dose-rates to reference animals and plants arising from exposure to naturally occurring radionuclides in aquatic environments

In order to put dose-rates derived in environmental impact assessments into context, the International Commission on Radiological Protection (ICRP) has recommended the structuring of effects data according to background exposure levels. The ICRP has also recommended a suite of reference animals and plants (RAPs), including seven aquatic organisms, for use within their developing framework. In light of these propositions, the objective of this work was to collate information on activity concentrations of naturally occurring primordial radionuclides for marine and freshwater ecosystems and apply appropriate dosimetry models to derive absorbed dose-rates. Although coverage of activity concentration data is comprehensive for sediment and water, few, or in some cases no, data were found for some RAPs, e.g. for frogs (Ranidae) and freshwater grasses (Poaceae) for most radionuclides. The activity concentrations for individual radionuclides in both organisms and their habitat often exhibit standard deviations that are substantially greater than arithmetic mean values, reflecting large variability in activity concentrations. To take account of variability a probabilistic approach was adopted. The dominating radionuclides contributing to exposure in the RAPs are (40)K, (210)Po and (226)Ra. The mean unweighted and weighted dose-rates for aquatic RAPs are in the ranges 0.07-0.39 microGy h(-1) and 0.37-1.9 microGy h(-1) respectively.

Platelet activation by healing ePTFE grafts

The purpose of this study was to examine the effect of the in vivo maturing ePTFE graft surface on platelet activation. Ten canines were randomized to receive either a carotid to infrarenal aorta ePTFE graft or sham operation. Animals were sampled at specific time points up to 3 months postoperatively. Whole blood platelet aggregometry (arachidonic acid, ADP, and collagen agonists) and ATP secretion (in response to arachidonic acid, ADP, collagen, and thrombin) were measured. Additionally, complete hematologic analysis and histology were performed. With time, graft animals showed significantly more decrease in platelet aggregation in response to ADP compared to sham animals (P = .023). The total amount of ATP per platelet was not different, as demonstrated by equivalent ATP release per platelet in response to thrombin. Over the first week, grafted dogs developed a decrease in systemic platelet count of 50% (P < .001) that persisted over the 3-month follow-up period. With time, overall regression model slopes of graft and sham platelet count data were not statistically different (P = .29). Histologically, the grafts demonstrated limited cellular ingrowth at both anastomoses, with fibrin matrix along the remainder of the blood-biomaterial interface. These data suggest that, similar to Dacron, exposure to an ePTFE surface results in significant changes in platelet biology, and these platelet-ePTFE interactions persist even after the graft has formed a mature pseudointima. The pseudointima appears to be the primary determinant of the blood-biomaterial interaction.

Gastrointestinal colonization and systemic dissemination by Candida albicans and Candida tropicalis in intact and immunocompromised mice

Gastrointestinal colonization and systemic dissemination by Candida albicans and Candida tropicalis were compared in intact and immunocompromised mice. Five-day-old CFW mice were inoculated by the oral-intragastric route with 1.0 x 10(7) CFU of two C. albicans and two C. tropicalis strains isolated from the blood of patients with acute leukemia and with C. albicans 4918 and its cerulenin-resistant mutant 4918-10. C. albicans and C. tropicalis spread to the lungs, liver, and kidneys within 30 min postinoculation, and organ CFU of the two species were comparable over the following 10 days. Close association of blastoconidia with the villous surface of the small intestine resulted in lysis of microvilli and then progressive invasion of villi. Blastoconidia within villi were surrounded by a conspicuous zone of clearing. Persistent colonization of the small and large intestines by C. albicans blood isolates and strains 4918 and 4918-10 was similar for 31 days after inoculation, but consistently exceeded that of C. tropicalis. In mice colonized with C. albicans, immunosuppression with cortisone acetate and cyclophosphamide on days 30 and 33 after inoculation increased stomach CFU 40- to 370-fold and intestinal CFU 30- to 80-fold. In contrast, persistent colonization by C. tropicalis was undetectable before immunosuppression and only became apparent after treatment. C. albicans disseminated more frequently and with higher organ CFU than C. tropicalis. Despite this fact, 20% of mice infected with C. tropicalis died, compared with 4% infected with C. albicans blood isolates. Indirect immunofluorescence revealed penetrative growth by Candida hyphae exclusively in the mucosa and submucosa of the stomach from immunosuppressed, persistently colonized mice. Taken together, the data indicate that C. tropicalis appears to be more virulent than C. albicans and that factors responsible for gastrointestinal colonization, systemic dissemination, and mortality in immunocompromised mice may not be identical.

Chlamydospore-like cells of Candida albicans in the gastrointestinal tract of infected, immunocompromised mice

We have demonstrated in a previously described murine model of gastrointestinal (GI) and systemic candidiasis that the antifungal angent cilofungin was efficacious in clearing infection of body organs when administered subcutaneously by infusion, but permitted large numbers of Candida albicans in the GI tract to persist. Yeast and hyphae in these animals were associated primarily with the stratified squamous epithelium of the stomach. Administration of immunocompromising drugs (cyclophosphamide plus cortisone acetate) to animals with persistent GI infection resulted in relapse of systemic candidiasis. Histological examination of the gastric mucosa revealed invasive hyphal elements and yeast as well as multiple chlamydospore-like cells. Comparative histochemical and electron-microscopic examinations of these latter cells produced in host tissue and chlamydospores formed in vitro were conducted. The results suggested that similarities in wall and cytoplasmic composition and ultrastructure exist between these in vivo and in vitro produced C. albicans cells. Exposure of C. albicans to cyclophosphamide during in vitro growth resulted in stimulation of chlamydospore production. No significant effect of cortisone acetate on C. albicans morphogenesis was detected. The murine model used in this study permits investigation of the formation of chlamydospore-like cells of C. albicans during early stages of fungal invasion of cyclophosphamide-treated mice, and of the possible influence of these cells on immunological response of the host to persistent candidiasis of the GI tract.