Water transport in zinc oxy-chloride cements

The water uptake and water loss behaviour in three different formulations of zinc oxy-chloride cement have been studied in detail. Specimens of each material were subjected to a high humidity atmosphere (93% RH) over saturated aqueous sodium sulfate, and a low humidity desiccating atmosphere over concentrated sulfuric acid. In high humidity, the cement formulated from the nominal 75% ZnCl2 solutions gained mass, eventually becoming too sticky to weigh further. The specimens at 25% and 50% ZnCl2 by contrast lost mass by a diffusion process, though by 1 week the 50% cement had stated to gain mass and was also too sticky to weigh. In low humidity, all three cements lost mass, again by a diffusion process. Both water gain and water loss followed Fick's law for a considerable time. In the case of water loss under desiccating conditions, this corresponded to values of Mt/MĄ well above 0.5. However, plots did not go through the origin, showing that there was an induction period before true diffusion began. Diffusion coefficients varied from 1.56 x 10-5 (75% ZnCl2) to 2.75 x 10-5 cm2/s (50% ZnCl2), and appeared to be influenced not simply by composition. The drying of the 25% and 50% ZnCl2 cements in high humidity conditions occurred at a much lower rate, with a value of D of 2.5 x 10-8 cm2/s for the 25% ZnCl2 cement. This cement was found to equilibrate slowly, but total water loss did not differ significantly from that of the cements stored under desiccating conditions. Equilibration times for water loss in desiccating conditions were of the order of 2-4 hours, depending on ZnCl2 content; equilibrium water losses were respectively 28.8 [25% ZnCl2], 16.2 [50%] and 12.4 [75%] which followed the order of ZnCl2 content. It is concluded that the water transport processes are strongly influenced by the ZnCl2 content of the cement.

Breast milk levels of zinc and omega-6 polyunsaturated fatty acids and growth of healthy Chinese infants

AIM: To examine the concentrations of zinc and omega-6 polyunsaturated fatty acids (omega-6 PUFAs) in breast milk, the impact of zinc on omega-6 PUFA metabolism, and the growth rate of infants. METHODS: Forty-one mother-term infant pairs from a rural area of northern Beijing, China, who were 1 month (n = 18, group I) and 3 months (n = 23, group II) old and exclusively breastfed, were studied. The dietary records and the concentrations of zinc and omega-6 PUFAs in the milk of lactating women and the increase in weight and length of their infants during 1 and 3 postnatal months were analysed. RESULTS: The dietary intakes of mothers in the two groups were the same, i.e. high in carbohydrate and low in fat, protein and energy. The maternal zinc intake was 7.5mg/d and thus reached only 34.6% of the current Recommended Nutrient Intake (RNI). The levels of zinc and arachidonic acid (AA, C20:4 omega-6) in the milk of group I were significantly higher than those in group II. Furthermore, significant positive correlations were found between the concentrations of zinc and AA in the breast milk and between the level of milk AA and weight gain. CONCLUSION: Zinc may be a co-factor and essential for essential fatty acids (EFA) metabolism. Thus suboptimal zinc intake may cause EFA imbalance. Further studies of Chinese rural mother-infant pairs are necessary to determine whether zinc supplementation should be recommended when lactation exceeds 3 months.

Invivo Changes In The Activity Of Gill ATPases And Hemolymph Ions Of Carcinus Maenas Exposed To p p'-DDT And Reduced Salinities

1. Haemolymph osmoregulation by the shore crab, Carcinus maenas was confirmed over a range of salinities. 2. Na+K+-ATPase and Mg2+-ATPase activities in gill tissue increased with a decrease in salinity. 3. Na+K+-ATPase and Mg2+-ATPase activities were inhibited after exposure to p,p′-DDT. 4. K+ ion levels of the haemolymph remained unchanged, but Na+ ion levels were affected after 7 hr when transferred from 100 to 5% SW after exposure to DDT.

Quantitative Cytochemical Effects Of 3 Metal-Ions On A Lysosomal Hydrolase Of A Hydroid

The quantitative effects of Cu8+, Cd2+ and Hg2+ on the cytochemical staining reaction for lysosomal N-acetyl-/?-D-glucosaminidase have been determined and related to the inhibitory effects of the metals on colonial growth rate in the experimentally cultured hydroid Campanularia flexuosa. Cytochemical threshold concentrations are comparable to known environmental levels and are about one order of magnitude lower than those obtained by measuring colony growth rates. Pretreatment of colonies with Cuz+ gave no indication of tolerance adaptation, although there is evidence of the cumulative toxicity of Cu2+ and the possible sequestration of this metal in endodermal cell lysosomes. There is also an indication that the Cu2+ may exert its toxic effect by decreasing the stability of the lysosomal membranes, thus increasing the level of free glucosaminidase activity.

Biogeochemical cycling of dissolved zinc along the GEOTRACES South Atlantic transect GA10 at 40°S

The biogeochemical cycle of zinc (Zn) in the South Atlantic, at 40°S, was investigated as part of the UK GEOTRACES program. To date there is little understanding of the supply of Zn, an essential requirement for phytoplankton growth, to this highly productive region. Vertical Zn profiles displayed nutrient-like distributions with distinct gradients associated with the watermasses present. Surface Zn concentrations are among the lowest reported for theworld’s oceans (<50 pM). A strong Zn-Si linear relationshipwas observed (Zn (nM)= 0.065 Si (μM), r2=0.97, n = 460). Our results suggest that the use of a global Zn-Si relationship would lead to an underestimation of dissolved Zn in deeper waters of the South Atlantic. By utilizing Si* and a new tracer Zn* our data indicate that the preferential removal of Zn in the Southern Ocean prevented a direct return path for dissolved Zn to the surface waters of the South Atlantic at 40°S and potentially the thermocline waters of the South Atlantic subtropical gyre. The importance of Zn for phytoplankton growth was evaluated using the Zn-soluble reactive phosphorus (SRP) relationship. We hypothesize that the low Zn concentrations in the South Atlantic may select for phytoplankton cells with a lower Zn requirement. In addition, a much deeper kink at ~ 500m in the Zn:SRP ratio was observed compared to other oceanic regions.

Dramatic structure in the photodetachment of inner shells of negative ions: Li-

Deep inner-shell photodetachment of negative ions is shown to differ qualitatively and quantitatively from the corresponding process in neutral atoms and positive ions. As an example, calculations of the photodetachment of Li- out of the 1s shell, using an augmented R-matrix methodology, are presented and show numerous structures over a broad energy region including a new phenomenon: Auger decay of a shape resonance. Li- was selected because it is the simplest multishell negative ion and is amenable to experimental scrutiny.