Sorption of Strontium to Uraninite and Uranium(IV)-Silicate Nanoparticles

Spent nuclear fuel contains both uranium (U) and high yield fission products, including strontium-90 (⁹⁰Sr), a key radioactive contaminant at nuclear facilities. Both U and ⁹⁰Sr will be present where spent nuclear fuel has been processed, including in storage ponds and tanks. However, the interactions between Sr and U phases under ambient conditions are not well understood. Over a pH range of 4-14, we investigate Sr sorption behavior in contact with two nuclear fuel cycle relevant U(IV) phases: nano-uraninite (UO₂) and U(IV)-silicate nanoparticles. Nano-UO₂ is a product of the anaerobic corrosion of metallic uranium fuel, and UO₂ is also the predominant form of U in ceramic fuels. U(IV)-silicates form stable colloids under the neutral to alkaline pH conditions highly relevant to nuclear fuel storage ponds and geodisposal scenarios. In sorption experiments, Sr had the highest affinity for UO₂, although significant Sr sorption also occurred to U(IV)-silicate phases at pH ≥ 6. Extended X-ray absorption fine structure (EXAFS) spectroscopy, transmission electron microscopy, and desorption data for the UO₂ system suggested that Sr interacted with UO₂ via a near surface, highly coordinated complex at pH ≥ 10. EXAFS measurements for the U(IV)-silicate samples showed outer-sphere Sr sorption dominated at acidic and near-neutral pH with intrinsic Sr-silicates forming at pH ≥ 12. These complex interactions of Sr with important U(IV) phases highlight a largely unrecognized control on ⁹⁰Sr mobility in environments of relevance to spent nuclear fuel management and storage.

N-cadherin haploinsufficiency increases survival in a mouse model of pancreatic cancer

Pancreatic ductal adenocarcinoma (PDA) is often detected at a late stage, hence the identification of new therapies that have potential to block tumor progression is critical for this lethal disease. N-cadherin upregulation has been observed in many cancers including PDA, however, a causal role for this cell adhesion receptor in disease progression has yet to be defined. The concomitant expression of oncogenic Kras(G12D) and mutant p53 (Trp53(R172H)) in the murine pancreas results in metastatic PDA that recapitulates the cognate features of human pancreatic cancer providing an excellent animal model to identify genes required for tumor progression. Here we determine the consequences of genetically manipulating N-cadherin expression in a mouse model of PDA. Remarkably, mice with reduced N-cadherin expression (that is, Ncad(-/+)) survived 25% longer (177 vs 142 days, P<0.05) than animals expressing two wild-type N-cadherin (Cdh2) alleles. The survival benefit is likely due to a cumulative effect of N-cadherin's role in different aspects of tumorigenesis including tumor-cell survival, growth, migration and invasion. Interestingly, reduced hedgehog signaling may contribute to the better prognosis for the Ncad(-/+) mice. Moreover, the matrix metalloproteinase MMP-7, associated with poor prognosis in PDA, was reduced in Ncad(-/+) tumors. Finally, Ncad(-/+) tumor cells exhibited decreased FGF-stimulated ERK1/2 activation consistent with N-cadherin's ability to promote FGFR signaling. These data support a critical role for N-cadherin in PDA and its potential prognostic value. Additionally, this study provides in vivo genetic evidence that the cell-surface protein N-cadherin represents a promising therapeutic target for the treatment of pancreatic cancer.

"A bucket of cold water": a follow-up study in a residential special school

This paper reports the initial findings of a follow-up study of the 75 young men who were admitted in their early teens to a residential school for maladjusted boys over a five year period. Sixty were traced and interviewed in depth, using an approach based on methods established at the Institute of Psychiatry. A structured interview was used which covered the individual's recollections of family, peer experiences, schools and adult life, with a special section on the residential therapeutic environment. The data allowed an assessment of their overall psycho-social adjustment. The preliminary analysis indicates that two-thirds had no current problems of note, and that just under two-fifths had had no history of problems since leaving. With only a few exceptions, the ex-boys' evaluation of the school's regime was positive.