ABSTRACT: Sustained interest in and concern about the health status of the aquatic environment has resulted in extensive research focused on (1) effects of pollution on survival, growth, and reproduction of resource species at all life stages; (2) diseases of fish and shellfish, as they may be related to pollution and as they may serve as indicators of environmental stress; and (3) contaminant body burdens in fish and shellfish - their effects on the aquatic animals and their potential effects on humans. Effects, lethal and sublethal, of pollutants on life history stages of fish and shellfish have been documented, as have impacts on local stocks in badly degraded habitats, but as yet there has been no adequate quantitative demonstration of effects on entire aquatic species - probably because of the difficulty in sorting out relative effects of the many environmental factors that influence abundance. Sublethal effects, especially those that result in disease, have been examined intensively, and some diseases and disease syndromes have been associated statistically with pollution. Other pollution indicators (biochemical, physiological, genetic, behavioral, and ecological) have also received some attention, as have body burdens of contaminants in aquatic species. Research, especially that conducted during the past decade, has done much to clarify the many pathways and toxic effects of contaminants on aquatic animals, and has also helped to identify mechanisms for survival of fish and shellfish in the presence of environmental changes caused by human activities. 相似文献
The transport from the upper mixed layer into the pycnocline of particles with negative buoyancy is considered. Assuming the
hydrodynamic parameters to be time- independent, an adjoint model is resorted to that provides a general expression of the
residence time in the mixed layer of the constituent under study. It is seen that the residence time decreases as the settling
velocity increases or the diffusivity decreases. Furthermore, it is demonstrated that the residence time must be larger than
z/w and smaller than h/w, where z, h and w denote the distance to the pycnocline, the thickness of the mixed layer and the sinking velocity. In the vicinity of the
pycnocline, the residence time is not necessarily zero; its behaviour critically depends on the eddy diffusivity profile in
this region. Closed-form solutions are obtained for constant and quadratic diffusivity profiles, which allows for an analysis
of the sensitivity of the residence time to the Peclet number. Finally, an approximate value is suggested of the depth-averaged
value of the residence time. 相似文献
This paper is concerned with health effects from the inhalation of particulate matter (PM) emitted from the combustion of coal, and from the co-combustion of refuse derived fuel (RDF) and pulverized coal mixtures, under both normal and low NOx conditions. Specific issues focus on whether the addition of RDF to coal has an effect on PM toxicity, and whether the application of staged combustion (for low NOx) may also be a factor in this regard.
Ash particles were sampled and collected from a pilot scale combustion unit and then re-suspended and diluted to concentrations of 1000 μg/m3. These particles were inhaled by mice, which were held in a nose-only exposure configuration. Exposure tests were for 1 h per day, and involved three sets (eight mice per set) of mice. These three sets were exposed over 8, 16, and 24 consecutive days, respectively. Pathological lung damage was measured in terms of increases in lung permeability.
Results show that the re-suspended coal/RDF ash appeared to cause very different effects on lung permeability than did coal ash alone. In addition, it was also shown that a “snapshot” of lung properties after a fixed number of daily 1-h exposures, can be misleading, since apparent repair mechanisms cause lung properties to change over a period of time. For the coal/RDF, the greatest lung damage (in terms of lung permeability increase) occurred at the short exposure period of 8 days, and thereafter appeared to be gradually repaired. Ash from staged (low NOx) combustion of coal/RDF appeared to cause greater lung injury than that from unstaged (high NOx) coal/RDF combustion, although the temporal behavior and (apparent) repair processes in each case were similar. In contrast to this, coal ash alone showed a slight decrease of lung permeability after 1 and 3 days, and this disappeared after 12 days. These observations are interpreted in the light of mechanisms proposed in the literature. The results all suggest that the composition of particles actually inhaled is important in determining lung injury. Particle size segregated leachability measurements showed that water soluble sulfur, zinc, and vanadium, but not iron, were present in the coal/RDF ash particles, which caused lung permeabilities to increase. However, the differences in health effects between unstaged and staged coal/RDF combustion could not be attributed to variations in pH values of the leachate. 相似文献
The numerical time-dependent three-dimensional model [Kovalets, I.V. and Maderich, V.S.: 2001, Int. J. Fluid Mech. Res. 30, 410–429] of the heavy gas dispersion in the atmospheric boundary layer has been improved by parameterizing momentum and
heat fluxes on the surface of Earth using Monin–Obukhov similarity theory. Three parameterizations of heat exchange with the
surface of Earth were considered: (A) formula of Yaglom A.M. and Kader B.A. [1974, J. Fluid Mech. 62, 601–623] for forced convection, (B) interpolation formula for mixed convection and (C) similarity relationship for mixed
convection [Kader, B.A. and Yaglom, A.M.: 1990, J. Fluid Mech. 212, 637–662]. Two case studies were considered. In the first study based on experiment of Zhu et al., J. Hazard Mater62, 161–186], the interaction of an isothermal heavy gas plume with an atmospheric surface layer was simulated. It was found
that stable stratification in the cloud essentially suppresses the turbulence in the plume, reducing the turbulent momentum
flux by a factor of down to 1/5 in comparison with the undisturbed value. This reduction essentially influences velocities
in the atmospheric boundary layer above the cloud, increasing the mean velocity by a factor of up to 1.3 in comparison with
the undisturbed value. A simulation of cold heavy gas dispersion was carried out in the second case based on field experiment
BURRO 8. It was shown that both forced and free convections under moderate wind speeds significantly influence the plume.
The relative rms and bias errors of prediction the plume’s height were σH ≈ 30% and ɛH = − 10%, respectively, for parameterization B, while for A and C the errors were σH ≈ 80% and ɛH ≈ − 65%. It is therefore advised to use the simple parameterization B in dense gas dispersion models. 相似文献
Plant–herbivore interactions are complex and affect herbivore fitness components and life history traits in many different
ways. In this paper, we present results from an experiment studying the effects of leaf quality on pupal survival and duration
of pupation (as measured by time-to-emergence) in the winter moth. Because only surviving pupae are at risk of emerging, analysis
of time-to-emergence should exclude the dead pupae. However, due to right censoring, the survival status could not be determined
for each individual. This failure to determine the group of moths at risk of emerging a priori motivated the development of
a joint model of both survival probability and time-to-emergence. We formulate the model in a Bayesian framework and apply
Monte Carlo Markov Chain (MCMC) to obtain posterior distributions. Time-to-emergence is modeled by a Cox Proportional Hazards
(CPH) model where only the surviving pupae are at risk of emergence. Probability of pupal survival was modeled by a Generalized
Linear Mixed Model (GLMM). The censored individuals were included in the analysis as a missing value in the GLMM. The GLMM
then generated prior distributions of survival probabilties—and thus of the probability of being at risk of emergence—for
these 19 individuals, conditional on the model parameters. The CPH model was formulated as a count process and the binary
frailty was incorporated as a zero-inflated Poisson model. Zeros in this model represent the non-survivors. Leaf quality did
not appear to influence time-to-emergence. Pupal survival was affected in a complex and unexpected way showing opposite effects
in males and females. We also explored the robustness of our model against increased levels of censoring. While the degree
of censoring was low in our study (< 1%), we artificially increased it to 67%. Although further study is required to study
the generality of these results in a theoretical framework, our explorations suggest that the newly proposed technique may
be widely applicable in a variety of situations where the identification of the at risk population cannot be done in a straightforward
way.
Received: January 2005 / Revised: June 2005 相似文献
This article presents results from the particulate monitoringcampaign conducted at Qalabotjha in South Africa during the winter of 1997. Combustion of D-grade domestic coal and low-smoke fuels were compared in a residential neighborhood to evaluate the extent of air quality improvement by switchinghousehold cooking and heating fuels.Comparisons are drawn between the gravimetric results from the two types of filter substrates (Teflon-membrane and quartz-fiber) as well as between the integrated and continuous samplers. It is demonstrated that the quartz-fiber filters reported 5 to 10% greater particulate mass than the Teflon-membrane filters, mainly due to the adsorption of organic gases onto the quartz-fiber filters. Due to heating of sampling stream to 50 °C in the TEOM continuous sampler and the high volatile content of the samples, approximately 15% of the particulate mass was lost during sampling.The USEPA 24-hr PM2.5 and PM10 National Ambient Air Quality Standards (NAAQS) of 65 g m-3 and 150 g m-3, respectively, were exceeded on several occasions during the 30-day field campaign. Average PMconcentrations are highest when D-grade domestic coal was used, and lowest between day 11 and day 20 of the experiment when a majority of the low-smoke fuels were phased in. Source impacts from residential coal combustion are also found to be influenced by changes in meteorology, especially wind velocity.PM2.5 and PM10 mass, elements, water-soluble cations (sodium, potassium, and ammonium), anions (chloride, nitrate, and sulfate), as well as organic and elemental carbonwere measured on 15 selected days during the field campaign. PM2.5 constituted more than 85% of PM10 at three Qalabotjha residential sites, and more than 70% of PM10 at the gradient site in the adjacent community of Villiers. Carbonaceous aerosol is by far the most abundant component, accounting for more than half of PM mass at the three Qalabotjha sites, and for more than a third of PM mass at the gradient site. Secondary aerosols such as sulfate, nitrate,and ammonium are also significant, constituting 8 to 12% of PM mass at the three Qalabotjha sites and 15 to 20% at the Villiers gradient site. 相似文献