Atmospheric heavy metals in tropical South America during the past 22,000 years recorded in a high altitude ice core from Sajama, Bolivia

V, Co, Cu, Zn, As, Rb, Sr, Ag, Cd, Ba, Pb, Bi and U have been analysed by inductively coupled plasma sector field mass spectrometry in various sections of a dated snow/ice core drilled at an altitude of 6542 m on the Sajama ice cap in Bolivia. The analysed sections were dated from the Last Glacial Stage ( approximately 22,000 years ago), the Mid-Holocene and the last centuries. The observed variations of crustal enrichment factors (EFc) for the various metals show contrasting situations. For V, Co, Rb, Sr and U, EFc values close to unity are observed for all sections, then showing that these elements are mainly derived from rock and soil dust. For the other metals, clear time trends are observed, with a pronounced increase of EFc values during the 19th and 20th centuries. This increase shows evidence of metal pollution associated with human activity in South America. For Pb an important contribution was from gasoline additives. For metals such as Cu, Zn, Ag and Cd an important contribution was from metal production activities, with a continuous increase of production during the 20th century in countries such as Peru, Chile and Bolivia.     

Effects of monospecific algal diets of varying biochemical composition on the growth and survival of Pacific oyster (Crassostrea gigas) larvae

Using monospecific diets of Thalassiosira pseudonana cells grown under different steady-state conditions, it was determined that higher growth rates of larval Crassostrea gigas Thunberg were obtained when fed T. pseudonana cells grown under high light. High light grown T. pseudonana cells consistently contained relatively more of the saturated fatty acids 14:0 and 16:0. Considered over three independent experiments, high light grown T. pseudonana cells were lower in protein and higher in carbohydrate than low light grown cells. Higher growth rates of larval C. gigas were obtained on diets with more of the essential fatty acid (EFA) 22:63, and less of the other EFA, 20:53. The relative requirements of C. gigas larvae for the essential fatty acids 20:53 and 22:63 are discussed. Faster growing larvae contained higher percentages of the fatty acids 14:0 and 16:0, and lower percentages of 22:2j. Oyster growth rates were correlated with their content of the fatty acids: 14:0, 16:0 and 22:2j in two experiments utilizing separately spawned batches of larvae. Fatty acid profiles are proposed as a technique for assessing larval condition. C. gigas larvae contained ten times the percent composition of the FAs 16:43, 18:17, 20:17 and 22:2j compared with their diet. Correlation analysis suggests that the dietary source of 18:17, 20:17 and 22:2j was 16:17. It is concluded that T. pseudonana cells grown under high light are a superior diet for C. gigas larvae in comparison with low light grown cells of the same species.     

黏性颗粒在滤料表面沉积的动态模拟及规律

为研究颗粒黏性对过滤除尘性能的影响,分析了颗粒沉积过程的受力情况,应用颗粒流计算软件PFC2D对颗粒在滤料表面的沉积行为进行了数值模拟。结果表明:颗粒形成粉尘层的过程中主要受到风流力、惯性力等压缩力和范德华力、滚动摩擦力偶矩等压缩阻力的作用,颗粒黏性的增加,会使颗粒间滚阻系数和摩擦系数显著增加;PFC可实现粉尘颗粒在滤料表面沉积过程的可视化,得到不同黏性颗粒在滤料表面的沉积形态,滚阻系数或摩擦系数越大,粉尘层孔隙率越大,过滤阻力越小,其中,摩擦系数的影响作用弱于滚阻系数。     

Interests and values in national nutrition policy in the united states

When scientists consider the interaction of science and value judgments, debates often occur. When public policy grows out of science, disagreements between scientists can become even more spirited. This paper examines the case of nutrition policy in the United States, which has been both at the interface between agriculture and medicine and the object of serious discord concerned with the strength and validity of the scientific evidence and the responsibility for action. The development of indirect intervention policies, designed to educate and inform the public on diet and health, is traced as a practical demonstration of the effects of involvements of nutritional scientists of different disciplines and philosophic bents. Controversies centered mainly on the issues of diet and coronary heart disease and of diet and cancer in nutritional guidelines for Americans and the recommended dietary allowances (RDAs). But the arguments turned on a complex web of values and interests as well as scientific questions. A remarkable turnaround by animal agriculture and its scientific support occurred, changing from a defensive, rightist stance to one that appears to recognize a moral responsibility to the public health. The convincing point was likely the changing market. Nutritional scientists, however, remained divided on the issue of whether a public health strategy keyed to public education should replace a strategy to identify persons of high risk and modify the risk by treatment. Our analysis suggests that the tension between libertarian and utilitarian social values of scientists is at least as important as disagreements relative to validity and strengths of the scientific evidence.     

Observations on solid phase micro-extraction for MTBE analysis

In a recent study of aqueous phase methyl tertiary butyl ether (MTBE) adsorption onto hydrophobic molecular sieves, the solid phase micro-extraction gas chromatography analytical technique was used to measure MTBE concentrations in water. The method was especially beneficial in measuring MTBE concentrations in the microg/l range, but anomalies were observed that investigators should be aware of before employing this technique. Specifically, it was observed that the calibration of the extraction fiber with known MTBE concentrations was non-linear over all concentration ranges. The technique was not suited to higher concentrations, and dilutions were necessary to increase the working range of the technique. Lastly, the fiber was observed to extract increasingly less MTBE from known standard solutions over time, requiring repeated calibrations to obtain reliable concentrations of unknown samples.     

Regional and historical variation in the nitrogen content of Racomitrium lanuginosum in Britain in relation to atmospheric nitrogen deposition

The moss Racomitrium lanuginosum (Hedw.) Brid. is an important component of the drier parts of ombrotrophic mires and montane heaths in north-western Britain. The extent and quality of the montane heaths dominated by R. lanuginosum has declined in recent decades, perhaps in part due to the effects of acidic deposition at high elevations. This paper examines the effect of atmospheric nitrogen deposition, which has increased during this century, on the nitrogen content of R. lanuginosum in Britain. The nitrogen content of the moss reflects the magnitude of the atmospheric supply being least in north-western Scotland and greatest (as much as six-fold greater) near to urban centres in northern England. This regional difference was less marked (only approx. two-fold) during the 19th century (as revealed from the analysis of herbarium specimens) when nitrogen concentrations were appreciably lower. Transplant studies both between regions and between sites within a mountain system demonstrated the importance of atmospheric deposition in determining the tissue nitrogen concentration of the moss. The results are discussed in relation to the potential importance of the enhanced atmospheric nitrogen supply to the normally nitrogen-impoverished montane heaths, and to the growth and persistence of the moss.     

The effect of polluted and leached snow melt waters on the soil bacterial community-quantitative response

The effect of polluted snow melt waters on the number of soil bacteria was determined using soil cores extracted from an upland catchment in the Cairngorm Mountains, Scotland. Total numbers of viable heterotrophic bacteria and bacterial denitrifiers were determined using plate and MPN counts. Separate soil cores were treated with simulated melt waters representative of either the composition of the first melt fraction from polluted or leached snowpacks. The number of bacteria in the Ah soil horizon (Hodgson, 1974) treated with polluted snow melt (PSM) water decreased significantly by 28-fold, but increased by 11-fold in the BC horizon. Denitrifier numbers decreased by 8-fold in the Ah horizon, but increased by over 2-fold lower down the profile. Overall the bacterial community exposed to simulated leached snow melt (LSM) waters showed little change in the Ah horizon. In the BC horizon (Hodgson, 1974), total viable bacterial numbers decreased by 20-fold, but denitrifiers numbers were unaffected.     

Feathers as a means of monitoring mercury in seabirds: Insights from stable isotope analysis

Mercury concentrations, together with nitrogen and carbon stable isotope signatures, were determined in body feather samples from northern fulmars Fulmarus glacialis and great skuas Catharacta skua, and in different flight feathers from great skuas. There were no significant relationships between trophic status, as defined using isotope analysis, and mercury concentration in the same feather type, in either species. Mercury concentrations in body feather samples were markedly different between fulmars and skuas, reflecting differences in diet, but there was no corresponding difference in trophic status as measured through nitrogen stable isotope signatures. We conclude that mercury concentrations and stable isotope values in feathers are uncoupled, mercury concentrations apparently reflecting the body pool of accumulated mercury at the time of feather growth whilst stable isotope values reflect the diet at the time of feather growth. There were significant positive correlations between the different flight feathers of great skuas for all three parameters measured. These were strongest between primary 10 and secondary 8, suggesting that these two feathers are replaced at the same time in the moult sequence in great skuas. Stable isotope analysis of different feathers may provide a means of investigating moult patterns in birds.