Sensitivity analysis of the asymptotic behavior of a model for the environmental movement of radionuclides

The asymptotic behavior of a linear compartment model for the environmental movement of radionuclides is investigated. Here, the expression asymptotic behavior is used to designate the behavior of q(t) as t → ∞, where q is the solution of a vector differential equation of the form dq/dt = h + Kq. The asymptotic behavior of such equations is described. For the model and conditions under consideration, each element of q converges monotonically to a steady-state value. A hydrologic system is defined and used to illustrate this behavior. An approach to sensitivity analysis employing Latin hypercube sampling, rank transformations and stepwise regression is presented and then applied to this system. A total of 20 independent variables is introduced and the following dependent variables are investigated for the various components of the system: amount of radionuclide present at steady state. concentration of radionuclide at steady state, and time required to reach 90% of steady state. Finally, an application of asymptotic behavior in the analysis of a hypothetical site for the geologic isolation of high-level radioactive waste is described and a brief discussion of differential sensitivity analysis is given.     

Plasma pharmacokinetics of the mycotoxin deoxynivalenol following oral and intravenous administration to sheep

The pharmacokinetics of deoxynivalenol (DON) were studied in sheep after administrating intravenous and oral doses (0.5 and 5.0 mg/kg, respectively). The plasma concentrations were measured using an electron-capture gas chromatographic method. After iv administration DON plasma levels were found to decrease biexponentially, showing a rapid distribution phase (t 1/2 alpha = 12-23 min), followed by a slower elimination phase (t 1/2 beta = 57-78 min). Only trace levels of DON could be detected in plasma 7 hr post-dosing. Further pharmacokinetic data suggest that DON was confined mainly to extracellular fluid, and did not appear to undergo any significant binding or uptake by tissue. After oral dosing, DON was quickly absorbed (t-max 4.0-5.3 hr), but had a systemic bioavailability of only 7.5%; due in part to its rapid and efficient metabolism by rumen microorganisms. Half-life of elimination (t 1/2 beta) was 100-125 min following oral administration, and depending on the animal, required 20-30 hr to be cleared from the system. The metabolic formation of the glucuronide conjugate after iv and oral administration of DON appeared to occur quite efficiently (iv, 21%; oral, 75%), and its elimination half-lives (iv, 150-200 min; oral 6.1-7.1 hr) were considerably longer than that of the parent toxin. Detection in plasma of the de-epoxide metabolite, DOM-1, accounted for only a minor portion of the dose after either dosing regimen (iv, less than 2.0%; oral, less than 0.3%), occurring predominantly as the glucuronide conjugate.     

Nitrite and Freshwater Fish

Nitrite occurs naturally in fresh waters as a result of nitrification of ammonia and denitrification of nitrate, and its concentration can be enhanced by partial oxidation of ammoniacal discharges. Nitrite is toxic to vertebrates including fish and a principal effect is the conversion of haemoglobin to methaemoglobin which is incapable of oxygen transport although there are circulatory and tissue effects as well. The toxic species is the nitrite ion (NO₂) which is believed to enter the blood via the branchial chloride/bicarbonate exchange and fish such as salmonids with high chloride uptake rates are more susceptible than those with low chloride uptake rates, for example carp. Nitrite toxicity is strongly aleviated by chloride and the concentration ratio of these ions is of great importance in assessing toxicity. Short term and long term toxicity data for a variety of fish species are presented. There are no field data on fish populations in waters where nitrite was the only pollutant. However extensive field surveys indicated that, waters with a mean chloride concentration of 25 mg l^-1 in good salmon fisheries were associated with concentrations of nitrite below 50 μg l^-1 N · NO₂, good coarse fisheries below 100 μg l^-1 N · NO₂.     

Inhibition of trout gill and soybean lipoxygenases by organotin compounds

Activity of trout gill and soybean lipoxygenase was inhibited by various low concentrations of tri-n-butyltin, di-n-butyltin and n-butyltin chlorides at pH 7.8. Tri-n-butyltin (0.044-0.19 mM; 8-100% inhibition) was significantly more inhibitory against trout gill lipoxygenase than di-n-butyltin (0.1-0.27 mM; 17-39% inhibition) or n-butyltin (1.2-3.6 mM; 26-43% inhibition). Soybean lipoxygenase displayed a similar sensitivity to the inhibitory effects of organotin compounds at pH 7.8. Although tri-n-butyltin (0.067-0.2 mM; 13-68% inhibition) was less inhibitory to soybean lipoxygenase, di-n-butyltin (0.134-0.537 mM; 51-75% inhibition) and n-butyltin (0.41-1.23 mM; 33-75% inhibition) were more inhibitory towards soybean lipoxygenase compared with trout gill lipoxygenase. Concentrations of butyltins required to provide substantial inhibition of trout gill lipoxygenase were of the order of magnitude of those reported for lethal water exposure concentrations of these compounds for trout and other fishes when bioaccumulation factors are considered. Thus, it is proposed that inhibition of lipoxygenase likely contributes to the biocidal activity of organotin compounds.     

Comparative floorplan-analysis as a means to develop design guidelines

This study explores the usefulness of comparative floorplan-analysis for the development of spatio-organizational concepts in architectural design processes.Each floorplan can be considered as a reflection of the goals and activities of the users as interpreted by the architect. By comparing a wide range of building layouts for similar organizations one may achieve a good understanding of the way organizational characteristics are (can be) expressed in spatial solutions. In the study reported here, in which 50 Dutch health centres were analysed comparatively, definite relationships between organizational and spatial concepts were found. This information is used both as a means to make organizational principles more explicit as well as data for briefwriting and design guidelines.     

Applying the Declining Population Paradigm: Diagnosing Causes of Poor Reproduction in the Marbled Murrelet

Abstract:  We identified six approaches to diagnosing causes of population declines and illustrate the use of the most general one ("multiple competing hypotheses") to determine which of three candidate limiting factors—food availability, nesting site availability, and nest predation—were responsible for the exceptionally poor reproduction of Marbled Murrelets (  Brachyramphus marmoratus ) in central California. We predicted how six attributes of murrelet demography, behavior, and physiology should be affected by the candidate limiting factors and tested predictions with field data collected over 2 years. The average proportion of breeders, as estimated with radiotelemetry, was low (0.31) and varied significantly between years: 0.11 in 2000 and 0.50 in 2001. Murrelets spent significantly more time foraging in 2000 than in 2001, suggesting that low food availability limited breeding in 2000. In 2001, 50% of radio-marked murrelets nested and 67% of females were in breeding condition, suggesting that enough nest sites existed for much of the population to breed. However, rates of nest failure and nest predation were high (0.84 and 0.67–0.81, respectively) and few young were produced, even when a relatively high proportion of murrelets bred. Thus, we suggest that reproduction of Marbled Murrelets in central California is limited by food availability in some years and by nest predation in others, but apparently is not limited by availability of nesting sites. The multiple-competing-hypotheses approach provides a rigorous framework for identifying causes of population declines because it integrates multiple types of data sets and can incorporate elements of other commonly used approaches.     

Evaluating Causes of Population Change in North American Insectivorous Songbirds

Although the North American Breeding Bird Survey (BBS) is a principal source of information regarding populations of most North American bird species, many features of the survey complicate analysis of population change. Correlation studies based on BBS data cannot be used to define cause and effect relationships unambiguously. Recently, Böhning-Gaese et al. (1993) presented an analysis of population trends in insectivorous songbirds using data from the BBS. They concluded that predation has played an important role in influencing population trends. We review aspects of the analysis methods for estimating population trends (e.g., observer effects, data subset) and for associating mean trends with species attributes (e.g., confounding of attributes). Using alternative analyses of the same BBS data, we demonstrate that the evidence that predation is associated with population declines is weaker than they suggested. Based on our analyses the only factor among those tested that was consistently associated with population trends was migration status (short-distance migrant/resident versus long-distance migrant) during the period 1978–1987. Also, we present evidence that the harsh winters of the mid-1970s severely depressed populations of short-distance migrant species and may have been responsible for the observed associations between migration status and population trends.