Surface chemical and physical behavior of chrysotile asbestos in natural waters and water treatment

Chrysotile asbestos fibers enter California waters from physical weathering of magnesium-silicate, serpentine rocks in mountains of the northern and central portions of the state. Chrysotile particles, initially positively charged below pH 8.9 because of their magnesium-hydroxide surface, become negatively charged due to dissolution and adsorption of organic matter. Chrysotile suspended in 0.1 M inorganic electrolyte at pH 7-10 for up to five days dissolves with magnesium being released in excess of the 3:2 Mg:Si to silica molar ratio in the solid. The rate of magnesium release exhibits a fractional dependence on hydrogen-ion concentration: r = k_1'[H^+]^(0.24) The observed rate constant, k_l', depends on dissolution mechanism, specific surface area of the solid and charge-potential relation at the surface. Interpreted in terms of a site-binding model for adsorption and desorption of protons on the surface, the fractional dependence implies that dissolution is limited by a chemical reaction involving an average of less than one adsorbed proton per magnesium ion released into solution. Silica release from chrysotile shows no clear pH dependence. The rate of magnesium release is independent of the anions NO^(3-), Cl^- , SO_4^(2-), HCO_3^-, oxalate or catechol. Oxalate inhibited and catechol slightly enhanced silica release over the pH range 7.5-8.5; other anions had no systematic effect. Chrysotile's dissolution rate (10^(-15.7) mol/cm^2·s at pH 8) is consistent with observations on other magnesium silicates and brucite. Catechol adsorption onto chrysotile or aluminum oxide (pH 7.5-8.5) does not reach equilibrium but increases over five days. After one day the maximum adsorption density (Langmuir adsorption equation) on chrysotile is 0.7 x 10^(-9) mol/cm^2 (50 x 10^(-6) mg C/cm^2), approximately one-third of the estimated number of surface sites available for proton exchange. The maximum adsorption density for natural organic matter was near 30 x 10^(-6) mg C/cm^2 on both chrysotile and aluminum oxide. Chrysotile adsorbs sufficient catechol, oxalate, phthalate or natural organic matter within one day to reverse its surface charge. The extent of reversal is larger than observed for adsorption of the same organics on aluminum oxide, because of selective dissolution of chrysoti1e's outer magnesium-hydroxide layer. In reservoirs, submicron-sized chrysoti1e particles coagulate with larger (>2 μm), negatively-charged particles that subsequently settle out. The rate at which freshly-suspended, positively-charged chrysotile fibers coagulate is at least ten-fold greater than the rate for aged, negatively-charged fibers coagulate. Removal of chrysotile particles in water treatment occurs by deposition of fibers onto sand grains in filtration. Capture efficiency for single fibers is low; removal is enhanced 10-fold or more by incorporating fibers into larger flocs. Removal of chrysotile fibers in water filtration to levels near detection limits (typically 10^5-10^6 fibers/L) is possible; consistent achievement of this level will require a higher removal efficiency than is routinely achieved in treatment plants receiving water from the California aqueduct

Evapotranspiration Mapping for Forest Management in California's Sierra Nevada

We assessed the response of densely forested watersheds with little apparent annual water limitation to forest disturbance and climate variability, by studying how past wildfires changed forest evapotranspiration, and what past evapotranspiration patterns imply for the availability of subsurface water storage for drought resistance. We determined annual spatial patterns of evapotranspiration using a top-down statistical model, correlating measured annual evapotranspiration from eddycovariance towers across California with NDVI (Normalized Difference Vegetation Index) measured by satellite, and with annual precipitation. The study area was the Yuba and American River watersheds, two densely forested watersheds in the northern Sierra Nevada. Wildfires in the 1985-2015 period resulted in significant post-fire reductions in evapotranspiration for at least 5 years, and in some cases for more than 20 years. The levels of biomass removed in medium-intensity fires (25- 75% basal area loss), similar to magnitudes expected from forest treatments for fuels reduction and forest health, reduced evapotranspiration by as much 150-200 mm yr-1 for the first 5 years. Rates of recovery in post-wildfire evapotranspiration confirm the need for follow-up forest treatments at intervals of 5-20 years to sustain lower evapotranspiration, depending on local landscape attributes and interannual climate. Using the metric of cumulative precipitation minus evapotranspiration (P-ET) during multi-year dry periods, we found that forests in the study area showed little evidence of moisture stress during the 1985-2018 period of our analysis, owing to relatively small reliance on interannual subsurface water storage to meet dry-year evapotranspiration needs of vegetation. However, more-severe or sustained drought periods will push some lower-elevation forests in the area studied toward the cumulative P-ET thresholds previously associated with widespread forest mortality in the southern Sierra Nevada

Atmosphere-snow transfer function for H2O2: microphysical considerations

H2O2 analyses of polar ice cores show an increase in concentration from 200 years to the present. In order to quantitatively relate the observed trend in the ice to atmospheric levels, the atmosphere-snow transfer behavior and postdepositional changes must be known. Atmosphere-snow transfer was studied by investigating uptake and release of H2O2 in a series of laboratory column experiments in the temperature range −3°C to −45°C. Experiments consisted of passing H2O2-containing air through a column packed with 200-μm diameter ice spheres and measuring the change in gas phase H2O2 concentration with time. The uptake of H2O2 was a slow process requiring several hours to reach equilibrium. Uptake involved incorporation of H2O2 into the bulk ice as well as surface accumulation. The amount of H2O2 taken up by the ice was greater at the lower temperatures. The sticking coefficient for H2O2 on ice in the same experiments was estimated to be of the order of 0.02 to 0.5. Release of H2O2 from the ice occurred upon passing H2O2-free air through the packed columns, with the time scale for degassing similar to that for uptake. These results suggest that systematic losses of H2O2 from polar snow could occur under similar conditions, when atmospheric concentrations of H2O2 are low, that is, in the winter

Annual net snow accumulation over southern Greenland from 1975 to 1998

As part of NASA's Program for Arctic Regional Climate Assessment (PARCA), extensive ice core measurements of annual net water-equivalent accumulation have been made recently around the southern Greenland ice sheet. Analysis of these measurements demonstrates that annual and seasonal accumulation patterns are sometimes regional, with temporal variability in accumulation correlated over large areas. Using this unique, widely distributed set of contemporaneous accumulation measurements, as well as available previously published observations, we developed maps of annual net snow accumulation south of �73° N for each year from 1975 to 1998. Here net snow accumulation is defined as snow accumulation minus ablation. In order to achieve a more consistent spatial distibution of core measurements for each of the 24 years in the study period, some of the observed records were extrapolated up to 5 years using empirical relationships between monthly precipitation measured at coastal stations and the observed ice core net accumulation records. Initial comparisons between the maps of annual net snow accumulation and similar maps of net accumulation derived from meteorological model simulations show excellent agreement in the temporal variability of accumulation, although significant differences in the magnitude of accumulation remain. Both measurements and model simulations indicate that annual net accumulation, averaged over all higher-elevation regions (above 2000 m) of the southern ice sheet, varies significantly from one year to the next. The maximum year-to-year change during the 24-year study period occurred between calendar years 1995 and 1996, when the average annual net snow accumulation increased by 101 and 172 kg m-2 yr-1, or 37 and 57, for observations and model simulations, respectively. Taken alone, this 1-year change in average net snow accumulation corresponds to a drop in sea level of �0.16 and �0.28 mm yr-1. Copyright 2001 by the American Geophysical Union

Annual accumulation for Greenland updated using ice core data developed during 2000-2006 and analysis of daily coastal meteorological data

An updated accumulation map for Greenland is presented on the basis of 39 new ice core estimates of accumulation, 256 ice sheet estimates from ice cores and snow pits used in previous maps, and reanalysis of time series data from 20 coastal weather stations. The period 1950-2000 is better represented by the data than are earlier periods. Ice-sheetwide accumulation was estimated based on kriging. The average accumulation (95 confidence interval, or ±2 times standard error) over the Greenland ice sheet is 30.0 ± 2.4 g cm -2 a-1, with the average accumulation above 2000-m elevation being essentially the same, 29.9 ± 2.2 g cm-2 a -1. At higher elevations the new accumulation map maintains the main features shown in previous maps. However, there are five coastal areas with obvious differences: southwest, northwest, and eastern regions, where the accumulation values are 20-50 lower than previously estimated, and southeast and northeast regions, where the accumulation values are 20-50 higher than previously estimated. These differences are almost entirely due to new coastal data. The much lower accumulation in the southwest and the much higher accumulation in the southeast indicated by the current map mean that long-term mass balance in both catchments is closer to steady state than previously estimated. However, uncertainty in these areas remains high owing to strong gradients in precipitation from the coast inland. A significant and sustained precipitation measurement program will be needed to resolve this uncertainty. Copyright 2009 by the American Geophysical Union

Diel variations of H2O2 in Greenland: A discussion of the cause and effect relationship

Atmospheric hydrogen peroxide (H2O2) measurements at Summit, Greenland, in May–June, 1993 exhibited a diel variation, with afternoon highs typically 1–2 parts per billion by volume (ppbv) and nighttime lows about 0.5 ppbv lower. This variation closely followed that for temperature; specific humidity exhibited the same general trend. During a 17-day snowfall-free period, surface snow was accumulating H2O2, apparently from nighttime cocondensation of H2O and H2O2. Previous photochemical modeling (Neftel et al., 1995) suggests that daytime H2O2 should be about 1 ppbv, significantly lower than our measured values. Previous equilibrium partitioning measurements between ice and gas phase (Conklin et al., 1993) suggest that air in equilibrium with H2O2 concentrations measured in surface snow (15–18 μM) should have an H2O2 concentration 2–3 times what we measured 0.2–3.5 m above the snow surface. A simple eddy diffusion model, with vertical eddy diffusion coefficients calculated from balloon soundings, suggested that atmospheric H2O2 concentrations should be affected by any H2O2 degassed from surface snow. However, field measurements showed the absence of either high concentrations of H2O2 or a measurable concentration gradient between inlets 0.2 and 3 m above the snow. A surface resistance to degassing, that is, slow release of H2O2 from the ice matrix, is a plausible explanation for the differences between observations and modeled atmospheric profiles. Degassing of H2O2 at a rate below our detection limit would still influence measured atmospheric concentrations and help explain the difference between measurements and photochemical modeling. The cumulative evidence suggests that surface snow adjusts slowly to drops in atmospheric H2O2 concentration, over timescales of at least weeks. The H2O2 losses previously observed in pits sampled over more than 1 year are thought to have occurred later in the summer or fall, after the May–July field season

Maternal Weaning Modulates Emotional Behavior and Regulates the Gut-Brain Axis.

Evidence shows that nutritional and environmental stress stimuli during postnatal period influence brain development and interactions between gut and brain. In this study we show that in rats, prevention of weaning from maternal milk results in depressive-like behavior, which is accompanied by changes in the gut bacteria and host metabolism. Depressive-like behavior was studied using the forced-swim test on postnatal day (PND) 25 in rats either weaned on PND 21, or left with their mother until PND 25 (non-weaned). Non-weaned rats showed an increased immobility time consistent with a depressive phenotype. Fluorescence in situ hybridization showed non-weaned rats to harbor significantly lowered Clostridium histolyticum bacterial groups but exhibit marked stress-induced increases. Metabonomic analysis of urine from these animals revealed significant differences in the metabolic profiles, with biochemical phenotypes indicative of depression in the non-weaned animals. In addition, non-weaned rats showed resistance to stress-induced modulation of oxytocin receptors in amygdala nuclei, which is indicative of passive stress-coping mechanism. We conclude that delaying weaning results in alterations to the gut microbiota and global metabolic profiles which may contribute to a depressive phenotype and raise the issue that mood disorders at early developmental ages may reflect interplay between mammalian host and resident bacteria

siRNA-Based Targeting of Cyclin E Overexpression Inhibits Breast Cancer Cell Growth and Suppresses Tumor Development in Breast Cancer Mouse Model

Cyclin E is aberrantly expressed in many types of cancer including breast cancer. High levels of the full length as well as the low molecular weight isoforms of cyclin E are associated with poor prognosis of breast cancer patients. Notably, cyclin E overexpression is also correlated with triple-negative basal-like breast cancers, which lack specific therapeutic targets. In this study, we used siRNA to target cyclin E overexpression and assessed its ability to suppress breast cancer growth in nude mice. Our results revealed that cyclin E siRNA could effectively inhibit overexpression of both full length and low molecular weight isoforms of cyclin E. We found that depletion of cyclin E promoted apoptosis of cyclin E-overexpressing cells and blocked their proliferation and transformation phenotypes. Significantly, we further demonstrated that administration of cyclin E siRNA could inhibit breast tumor growth in nude mice. In addition, we found that cyclin E siRNA synergistically enhanced the cell killing effects of doxorubicin in cell culture and this combination greatly suppressed the tumor growth in mice. In conclusion, our results indicate that cyclin E, which is overexpressed in 30% of breast cancer, may serve as a novel and effective therapeutic target. More importantly, our study clearly demonstrates a very promising therapeutic potential of cyclin E siRNA for treating the cyclin E-overexpressing breast cancers, including the very malignant triple-negative breast cancers