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271.
Enteric viruses are a cause of waterborne disease worldwide, and low numbers in drinking water can present a significant risk
of infection. Because the numbers are often quite low, large volumes (100–1,000 L) of water are usually processed. The VIRADEL
method using microporous filters is most commonly used today for this purpose. Negatively charged filters require the addition
of multivalent salts and acidification of the water sample to effect virus adsorption, which can make large-volume sampling
difficult. Positively charged filters require no preconditioning of samples, and are able to concentrate viruses from water
over a greater pH range than electronegative filters. The most widely used electropositive filter is the Virosorb 1MDS; however,
the Environmental Protection Agency has added the positively charged NanoCeram filters to their proposed Method 1615. Ultrafilters
concentrate viruses based on size exclusion rather than electrokinetics, but are impractical for field sampling or processing
of turbid water. Elution (recovery) of viruses from filters following concentration is performed with organic (e.g., beef
extract) or inorganic solutions (e.g., sodium polyphosphates). Eluates are then reconcentrated to decrease the sample volume
to enhance detection methods (e.g., cell culture infectivity assays and molecular detection techniques). While the majority
of available filters have demonstrated high virus retention efficiencies, the methods to elute and reconcentrate viruses have
met with varying degrees of success due to the biological variability of viruses present in water. 相似文献
272.
Christian J. Murray Charles R. Nelson 《Journal of the Air & Waste Management Association (1995)》2013,63(7):1075-1080
ABSTRACT A portion of a population is assumed to be at risk, with the mortality hazard varying with atmospheric conditions including total suspended particulates (TSP). This at-risk population is not observed and the hazard function is unknown; we wish to estimate these from mortality count and atmospheric variables. Consideration of population dynamics leads to a state-space representation, allowing the Kalman Filter (KF) to be used for estimation. A harvesting effect is thus implied; high mortality is followed by lower mortality until the population is replenished by new arrivals. The model is applied to daily data for Philadelphia, PA, 1973-1990. The estimated hazard function rises with the level of TSP and at extremes of temperature and also reflects a positive interaction between TSP and temperature. The estimated at-risk population averages about 480 and varies seasonally. We find that lags of TSP are statistically significant, but the presence of negative coefficients suggests their role may be partially statistical rather than biological. In the population dynamics framework, the natural metric for health damage from air pollution is its impact on life expectancy. The range of hazard rates over the sample period is 0.07 to 0.085, corresponding to life expectancies of 14.3 and 11.8 days, respectively. 相似文献
273.
Charles Plourde 《Journal of Environmental Economics and Management》1979,6(2):119-126
Geometric representations of two dynamic models of replenishable natural resource harvesting are provided. A well-known simple model is presented in which the only cost of production is the opportunity foregone. That is, present consumption implies a reduction in future consumption possibilities. Diagrams show the iterations of an optimal program. A four-quadrant diagram is used to illustrate a short-run equilibrium and the dynamics that will lead to a long-run solution on the bionomic transformation curve. 相似文献
274.
International Conservation Education 总被引:1,自引:0,他引:1
Charles A. Acosta 《Conservation biology》2000,14(4):924-924
275.
Paul D. Bakke Robert Thomas Charles Parrett 《Journal of the American Water Resources Association》1999,35(4):911-921
ABSTRACT: A regional adjustment relationship was developed to estimate long-term (30-year) monthly median discharges from short term (three-year) records. This method differs from traditional approaches in that it is based on site-specific discharge data but does not require correlation of these data with discharges from a single hydrologically similar long-term gage. The method is shown to be statistically robust, and applicable to statistics other than the median. 相似文献
276.
Nares Chuersuwan Barbara J. Turpin Charles Pietarinen 《Journal of the Air & Waste Management Association (1995)》2013,63(10):1780-1789
ABSTRACT Time-resolved data is needed for public notification of unhealthful air quality and to develop an understanding of atmospheric chemistry, including insights important to control strategies. In this research, continuous fine particulate matter (PM2.5) mass concentrations were measured with tapered element oscillating microbalances (TEOMs) across New Jersey from July 1997 to June 1998. Data features indicating the influence of local sources and long-distance transport are examined, as well as differences between 1-hr maxima and 24-hr average concentrations that might be relevant to acute health effects. Continuous mass concentrations were not significantly different from filter-collected gravimetric mass concentrations with 95% confidence intervals during any season. Annual mean PM2.5 concentrations from July 1997 to June 1998 were 17.3, 16.4, 14.1, and 15.3 μg/m3 at Newark, Elizabeth, New Brunswick, and Camden, NJ, respectively. Monthly averaged 24- and 1-hr daily maximum PM2.5 concentrations suggest the existence of a high PM2.5 (May-October) and a low PM2.5 (November-April) season. PM2.5 magnitudes and temporal trends were very similar across the state during high PM2.5 events. In fact, the between-site coefficients of determination (R2) for daily PM2.5 measurements were 84-98% for June and July. Additionally, during the most pronounced PM2.5 episode, PM2.5 concentrations closely tracked the daily maximum 1-hr O3 concentrations. These observations suggest the importance of transport and atmospheric chemistry (i.e., secondary formation) to PM2.5 episodes in New Jersey. The influence of local sources was observed in diurnal concentration profiles and annual average between-site differences. Urban wintertime data illustrate that high 1-hr maximum PM2.5 concentrations can occur on low 24-hr PM2.5 days. 相似文献
277.
Xiaobo Chao Yafei Jia F. Douglas Shields Sam S.Y. Wang Charles M. Cooper 《Journal of environmental management》2010,91(7):1456-1466
A three-dimensional water quality model was developed for simulating temporal and spatial variations of phytoplankton, nutrients, and dissolved oxygen in freshwater bodies. Effects of suspended and bed sediment on the water quality processes were simulated. A formula was generated from field measurements to calculate the light attenuation coefficient by considering the effects of suspended sediment and chlorophyll. The processes of adsorption–desorption of nutrients by sediment were described using the Langmuir Equation. The release rates of nutrients from the bed were calculated based on the concentration gradient across the water–sediment interface and other variables including pH, temperature and dissolved oxygen concentration.The model was calibrated and validated by applying it to simulate the concentrations of chlorophyll and nutrients in a natural oxbow lake in Mississippi Delta. The simulated time series of phytoplankton (as chlorophyll) and nutrient concentrations were generally in agreement with field observations. Sensitivity analyses were conducted to demonstrate the impacts of varying suspended sediment concentration on lake chlorophyll levels. 相似文献
278.
Charles H. Peterson Stephen R. Fegley Christine M. Voss Sara R. Marschhauser Beth M. VanDusen 《Marine Biology》2013,160(3):629-640
Protecting eggs from predators is common practice in sea turtle conservation, but routine protection of hatchlings is not. Of 42 loggerhead hatchlings observed emerging from 10 nests on undeveloped Onslow Beach, North Carolina, 24 % were preyed on by ghost crabs. In experimental trials, ghost crabs similarly threatened and captured neonate freshwater sliders, supporting their substitution as proxy for threatened and endangered sea turtle hatchlings in field experiments testing density dependence. Exploiting natural long-shore variation in ghost crab density, we show that a 2.6-fold higher ghost crab density resulted in 5 times more nocturnal threat encounters with sliders and 3.4 times more slider captures. Sliders released in simulated group emergences experienced lower per capita capture risk by ghost crabs than solitary sliders, implying predator dilution. Non-independence of egg and hatchling depredation motivates consideration of merging sea turtle egg and hatchling stages when modeling and managing food web interactions. 相似文献
279.
Charles O. Knowles Herman J. Benezet 《Journal of environmental science and health. Part. B》2013,48(5):547-555
Abstract Amitraz and its metabolite N‘‐ (2,4‐dimethylphenyl)‐N‐methyl‐formamidine (BTS‐27271) were administered orally to white rats. Both compounds were rapidly metabolized and eliminated primarily via the urine. The cumulative percentage of the dose eliminated in the urine was 77.6 for amitraz and 88.7 for BTS‐27271 by 96 hr posttreatment. Amitraz degradation products present in urine included BTS‐27271, 2,4‐dimethylformanilide, 2,4‐dimethylaniline, 4‐formamido‐3‐methylbenzoic acid, 4‐amino‐3‐methylbenzoic acid, and several unknowns. BTS‐27271 degradation products in rat urine were similar to those found with amitraz. Tissue residues generally were low (<25 ppb) with the exception of those in liver. 相似文献
280.