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Clean Water (clean + water)
Terms modified by Clean Water Selected AbstractsPollution by conspecifics as a component of intraspecific competition among Aedes aegypti larvaeECOLOGICAL ENTOMOLOGY, Issue 1 2005Stéphanie Bédhomme Abstract., 1. The role of pollution by conspecifics in the costs associated with larval intraspecific competition was investigated for Aedes aegypti (Diptera: Culicidae). 2. The growth of larval A. aegypti mosquitoes reared in clean water and water in which another larva had previously grown was compared; this procedure eliminates interactions through food consumption between competitors and allows the effects of other processes to be expressed. 3. A cost of growing in polluted water was found: this cost was expressed as an increase in developmental time and a reduction of adult longevity when starved, starved adult dry weight, and wing length. 4. Contrary to previously reported results of an experiment allowing for competition for food, these costs were not expressed in a sex-specific manner and were independent of the sex of the polluter. 5. It was thus demonstrated that competition arises from both resource depletion and other effects that result in deterioration of the environment, with chemical pollution of the environment being the most likely cause. [source] The acute and chronic toxicity of cadmium and zinc to two hydra speciesENVIRONMENTAL TOXICOLOGY, Issue 6 2001Douglas A. Holdway Abstract The potential of two hydra species, Hydra vulgaris (pink) and Hydra viridissima (green), for use as invertebrate models for toxicity testing of waterborne metals was investigated. The acute and subchronic toxicities of cadmium (a nonessential metal) and zinc (an essential metal) were determined. Results showed that both the hydra species were more sensitive to cadmium than to zinc, and that green hydra were more sensitive than pink hydra. The mean (SE) 96 h LC50 values of cadmium and zinc for pink hydra were 83 (8.5) and 2300 (150) ,g/L, respectively. For green hydra, the respective 96 h LC50 values for cadmium and zinc were 3.0 (0.0) and 935 (46.5) ,g/L. The respective 7-day no-observed-effect-concentrations (NOEC) and lowest-observed-effect-concentrations (LOEC) for pink hydra were <13 and 13 ,g/L for cadmium, and <250 and 250 ,g/L for zinc. The respective 7-day NOEC and LOEC values for green hydra were 0.4 and 0.8, ,g/L for cadmium, and 38 and 75 ,g/L for zinc. Neither 1, 2, or 3 × 90-min pulse-exposures to 0.4, 0.8, or 1.5 ,g/L of cadmium had any significant deleterious effect on total green hydra numbers after seven days in clean water. Green hydra appeared to be excellent freshwater invertebrate models for testing dissolved metals based on their sensitivity and the ability to rapidly assess population reproduction in the laboratory. © 2001 John Wiley & Sons, Inc. Environ Toxicol 16: 557,565, 2001 [source] The effects of continuous and pulsed exposures of suspended clay on the survival, growth, and reproduction of Daphnia magnaENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 1 2010Sarah E. Robinson Abstract Suspended sediments are a natural component of aquatic ecosystems, but anthropogenic activity such as land development can result in significant increases, especially after rain events. Continuous exposures of suspended clay and silt have been shown to affect growth and reproduction of Cladocera, leading to a decrease in population growth rate. The mechanism of clay toxicity in these filter-feeding organisms is clogging of the gut tract, resulting in decreased food uptake and assimilation. When placed in clean water, daphnids can purge clay from their gut and recover. In many surface waters, aquatic organisms experience episodic exposures of high concentrations of suspended solids driven by rain events. However, little is known about the consequences of pulsed exposures on individuals and populations. The objective of the present study was to characterize the effects of continuous and pulsed exposures of natural and defined clays on survival, growth, and reproduction of Daphnia magna. Two defined clays, montmorillonite and kaolinite, as well as clay isolated from the Piedmont region of South Carolina, USA, were used. Continuous exposures of clays elicited a dose dependent decrease in survival. Toxicity varied depending on clay source with montmorillonite,>,natural clay,>,kaolinite. Pulsed exposures caused a decrease in survival in a 24 h exposure of 734 mg/L kaolinite. Exposure to 73.9 mg/L also caused an increase in the time to gravidity, although there was not a corresponding decrease in neonate production over 21 d. No significant effects resulted from 12 h exposures even at 730 mg/L, almost 10 times the 24-h reproductive effects concentration. This suggests that exposure duration impacted toxicity more than exposure concentration in these pulsed exposures. Environ. Toxicol. Chem. 2010;29:168,175. © 2009 SETAC [source] Reversibility of estrogenic sex changes in zebrafish (Danio Rerio),ENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 8 2009Mia G. Larsen Abstract Development of male zebrafish (Danio rerio) courtship behavior was studied following estrogenic disruption of sexual differentiation. Sixty zebrafish were exposed at 28C to 5 ng/L (nominal concentration) of 17,-ethinylestradiol (EE2) from the egg stage until adulthood at four months of age, resulting in a female-biased sex ratio. Twenty-five EE2 -exposed phenotypic female zebrafish were subsequently held in clean water for eight months. During this period, eight phenotypic males developed. These phenotypic males demonstrated significant behavioral aberrations and a low fertilization rate compared to control males. [source] Uptake and elimination of hydrophobic organic contaminants in estuarine copepods: An experimental studyENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 2 2009Kévin Cailleaud Abstract Polycyclic aromatic hydrocarbons (PAHs) are considered to be rapidly biotransformed by organisms, whereas poly-chlorinated biphenyls (PCBs) are strongly bioaccumulated. In the present study, the estuarine copepod Eurytemora affinis was exposed in a continuous flow-through system to dissolved PAH (500 ng/L) and PCB (300 ng/L) mixtures for 86 h, whereas control groups were placed in a continuous flow-through system with clean water. Both PCB and PAH body residues were measured and compared in exposed and in nonexposed copepods to assess the uptake and the elimination of these two contaminant classes in this copepod species. After the exposure, exposed copepods exhibited concentration factors, based on a dry-weight basis, of 25, 750, and 1,200, respectively, for total PCBs and PAHs. The lower concentrations of PAHs in the nonexposed versus exposed copepods in contrast to small differences for PCBs suggest a higher rate of metabolism of PAHs compared with PCBs and could explain the differences observed in the accumulation. Furthermore, uptake as well as elimination of both PCBs and PAHs were compound selective in E. affinis. Therefore, higher-molecular-weight PCBs and PAHs were preferentially accumulated, while lower-molecular-weight compounds were preferentially eliminated. These results suggest the importance of copepods in the biogeochemical cycles of hydrophobic organic contaminants in estuarine ecosystems. [source] Effects of dilution on the exposure in sediment toxicity tests,buffering of freely dissolved concentrations and changes in mixture compositionENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 10 2007Thomas L. ter Laak Abstract Some sediment toxicity tests, such as the Microtox® test, are conducted by diluting either contaminated sediment or an aqueous phase with clean water. The present study aims to clarify how the dilution procedure affects the exposure of organisms. It is shown that freely dissolved concentrations of hydrophobic compounds are buffered by desorption from the sediment matrix when sediment is diluted with water. The buffering depends on the properties of the sediment matrix and contaminant. Consequently, the composition of a contaminant mixture changes with dilution, and the exposure in a sediment dilution toxicity test is poorly defined. This questions the application and subsequent assessments of such tests. Additionally, the often-observed higher toxicity in sediment dilution tests relative to elutriate dilution tests is not sufficient to claim direct contact exposure, because the enhanced sensitivity in sediment dilution tests also can be explained by buffering from the sediment matrix. In applying these tests, one should be aware of the fundamental differences between the sediment dilution strategy and the dilution of an aqueous phase and of the consequences it has for the outcome of the test. [source] Toxicokinetics of waterborne bisphenol a in landlocked salmon (Salmo salar m. Sebago) eggs at various temperaturesENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 10 2001Jani O. Honkanen Abstract Eye-pigmented eggs of landlocked salmon were exposed to waterbone [14C]-labeled bisphenol A at four temperatures (2, 6, 8, and 12°C). Both in accumulation and depuration experiments, the eggs were exposed to a bisphenol A concentration of 1 ,g/L for 196 h. In the depuration experiment, the exposed eggs were placed into clean water for 96 h. At each sampling time, the eggs were dissected into three parts (eggshell, embryo, and yolk sac), and all of these parts were weighed and analyzed separately in a liquid scintillation counter. The results show that waterborne bisphenol A accumulates in developing salmon eggs. Accumulation of bisphenol A showed a clear trend both in whole eggs and in dissected parts: the higher the temperature, the higher the uptake rate constant and the concentration of bisphenol A. Steady state was reached only in the embryos at the lowest temperature; in other cases, accumulation was linear. Depuration was significant only in the embryos at 2 and 6°C. As the accumulation and the depuration results show, the elimination of bisphenol A was evidently more significant at lower temperatures. [source] Health Status of Temporary Migrants in Urban Areas in Vietnam1INTERNATIONAL MIGRATION, Issue 4 2007Liem T. Nguyen ABSTRACT The rapid economic growth after economic reform, known in Viet Nam as "Doi Moi", and the growing scope of urban migration raise specific questions for social policy, including migration and health policies. This paper compares issues of health status and its determinants as they affect temporary urban migrants versus permanent urban migrants and non-migrants. The analyses utilize multivariate logistic regression and data from the 1997 Vietnam Migration and Health Survey. The results show that temporary migrants staying in guest houses are most vulnerable to health problems. Though most of them are initially healthier, their reported health deteriorates faster than other groups of urban residents. The findings also present important implications for the current migration and health policies in Vietnam: 1) A special attention should be given to temporary migrants in guest houses; 2) Different priorities in health policy should be applied to different groups of migrants and non-migrants; 3) The current population management policy by registration system needs to be reviewed; 4) Providing clean water is one of the most important ways to improve health of temporary migrants; 5) Targeting educational investments and reducing unemployment would likely to improve overall health; 6) A higher priority on health policies targeting women would likely pay dividends, and; 7) Improving management and collaboration between government offices and interested partners is important to improving health status and reducing inequity. [source] Soil conservation in Polylepis mountain forests of Central Argentina: Is livestock reducing our natural capital?AUSTRAL ECOLOGY, Issue 4 2010DANIEL RENISON Abstract Mountain forests and their soils provide ecological services such as maintenance of biodiversity, provision of clean water, carbon capture and forage for livestock rearing, which is one of the principal economic activities in mountain areas. However, surprisingly little is known about livestock impact in South American mountain forest soils. With the aim of understanding how livestock and topography influence patterns of forest cover, soil compaction, soil loss and soil chemical properties, we analysed these parameters in 100 Polylepis australis woodland plots situated in the humid subtropical mountains of Central Argentina. We used distance from the nearest ranch as an objective index of historical livestock impact and measured standard topographic variables. Our main results reveal that distance from ranch in all cases partly explains tree canopy cover, soil loss, soil compaction and soil chemical properties; suggesting a strong negative effect of livestock. Intermediate altitudes had more tree canopy cover, while landscape roughness , a measure of the variability in slope inclination and aspect , was negatively associated to soil impedance and acidity, and positively associated to soil organic matter content. Finally, flatter areas were more acid. We conclude that livestock has had a substantial influence on forest soil degradation in the Mountains of Central Argentina and possibly other similar South American mountains. Soil degradation should be incorporated into decision making when considering long-term forest sustainability, or when taking into account retaining livestock for biodiversity conservation reasons. Where soil loss and degradation are ongoing, we recommend drastic reductions in livestock density. [source] A simple method to estimate the contribution of biological floc and reactor-solution to mass transfer of oxygen in activated sludge processesBIOTECHNOLOGY & BIOENGINEERING, Issue 4 2005Venkatram Mahendraker Abstract In this study, the mass transfer coefficient of biological floc (KLabf) was estimated from the mass transfer coefficient of the mixed-liquor (KLaf) and the reactor-solution (KLae). The biological floc resistance (BFR) and reactor-solution resistance (SR) were defined as the reciprocal of KLabf and KLae, respectively, by applying the concept of serial-resistance originally presented in two-film theory (Lewis and Whitman (1924) Ind Eng Chem 16:1215,1220). The specific biological floc resistance (SBFR) was defined as biological floc resistance per unit biomass concentration. The data indicated that an activated sludge process yielding low BFR/MLR and BFR/SR tended to produce higher oxygen transfer efficiency. Surprisingly, the reactor-solution posed the same level of resistance as clean water in all experiments, except in a 5-day SRT, non-nitrifying, completely mixed activated sludge (CMAS) process run. Furthermore, SBFR successfully represented biological floc and showed a positive correlation to sludge volume index (SVI). In addition, SBFR/SR and oxygen transfer efficiency (OTEf) followed an exponential relationship for the complete data set. The method of separating the mixed-liquor into biological floc and reactor-solution improved the understanding of oxygen transfer under process conditions, without resorting to intrusive techniques or direct handling of fragile biological floc. © 2005 Wiley Periodicals, Inc. [source] Biological cost of tolerance to heavy metals in the mosquito Anopheles gambiaeMEDICAL AND VETERINARY ENTOMOLOGY, Issue 2 2010P. O. MIREJI The global rate of heavy metal pollution is rapidly increasing in various habitats. Anopheles malaria vector species (Diptera: Culicidae) appear to tolerate many aquatic habitats with metal pollutants, despite their normal proclivity for ,clean' water (i.e. low levels of organic matter). Investigations were conducted to establish whether there are biological costs for tolerance to heavy metals in Anopheles gambiae Giles sensu stricto and to assess the potential impact of heavy metal pollution on mosquito ecology. Anopheles gambiae s.s. were selected for cadmium, copper or lead tolerance through chronic exposure of immature stages to solutions of the metals for three successive generations. Biological costs were assessed in the fourth generation by horizontal life table analysis. Tolerance in larvae to cadmium (as cadmium chloride, CdCl2), copper [as copper II nitrate hydrate, Cu(NO3)2 2.5 H2O] and lead [as lead II nitrate, Pb(NO3)2], monitored by changes in LC50 concentrations of the metals, changed from 6.07 µg/L, 12.42 µg/L and 493.32 µg/L to 4.45 µg/L, 25.02 µg/L and 516.69 µg/L, respectively, after three generations of exposure. The metal-selected strains had a significantly lower magnitude of egg viability, larval and pupal survivorship, adult emergence, fecundity and net reproductive rate than the control strain. The population doubling times were significantly longer and the instantaneous birth rates lower in most metal-selected strains relative to the control strain. Our results suggest that although An. gambiae s.s. displays the potential to develop tolerance to heavy metals, particularly copper, this may occur at a significant biological cost, which can adversely affect its ecological fitness. [source] | ||||||||||