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Results for “Light Pollution”

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At least 451 records · Page 25Linked to original sources
PubMed2002

Aqueous photodegradation of polycyclic aromatic hydrocarbons.

Photodegradation of 12 polycyclic aromatic hydrocarbons was studied in aerated pure water, solutions of Suwannee River fulvic acid, and natural waters using polychromatic light (>290 nm). Quantum yields in pure water varied from 3.2 x 10(-5) to 9.2 x 10(-3). No obvious relationships were evident among the quantum yields and molecular properties. Photodegradation rate constants in solutions of Suwannee River fulvic acid or natural waters were largely unchanged compared to rate constants in pure water. Estimates of PAH photodegradation rates in natural waters can thus be obtained employing the quantum yields in pure water, PAH absorption, and solar irradiance. Calculated rate constants for photodegradation in surface waters during the summertime at mid-latitude varied from 3.2 x 10(-3) to 7.6 h(-1).

Absorption↗
PubMed2005

Growth dilution of metals in microalgal biofilms.

Despite the key role microalgae play in introducing toxicants into aquatic food webs, little is known about the effects of environmental factors on metal accumulation by these primary producers. Environmental factors such as light and nutrients alter growth rates and may consequently influence metal concentrations in microalgae through growth dilution. Laboratory experiments suggested that metal uptake and elimination by microalgal biofilms were gradual enough to enable dilution of metals within the biofilms by photosynthetically accrued carbon, and a simple kinetic model of metal accumulation predicted significant variation in metal content due to growth dilution over the natural range of microalgal growth rates. The ratio of metal uptake to carbon uptake by microalgal biofilms decreased exponentially with increasing light in short-term laboratory experiments because photosynthesis was much more sensitive to a light gradient than was metal uptake. The effect of light on biofilm metal concentrations was confirmed in situ with a long-term experiment in which experimental shading of biofilms in a metal-contaminated stream decreased biofilm growth rates and caused a 3x increase in biofilm concentrations of twelve metals, including methylmercury. Slow growth at the primary producer level is a likely contributor to higher biotic metal concentrations in shaded, oligotrophic, or cold ecosystems.

Biofilms↗
PubMed2005

No down-regulation of leaf photosynthesis in mature forest trees after three years of exposure to elevated CO2.

The photosynthetic responses of six species of mature forest trees to long-term exposure to elevated CO2 (ca. 530 ppm) were determined at the Swiss Canopy Crane (SCC) site near Basel, Switzerland. In the third year of growth in elevated CO2, using web-FACE technology, net photosynthesis (As) in fully sunlit, upper canopy foliage was stimulated by ca. 40% compared to ambient controls. This enhancement did not differ from the instantaneous increase in As found in ambient-grown leaves that were temporarily measured at elevated CO2. A complete lack of down-regulation of photosynthesis was found in all species and in both the early and the late growing season. Neither was leaf nitrogen content significantly affected by long-term exposure to elevated CO2. Our results document a persistent enhancement in leaf level photosynthesis in response to elevated CO2 in mature forest trees over a period of three years. Circumstantial evidence suggests that the additional assimilates feed into large sinks other than stem and shoot growth.

Air Pollutants↗
PubMed2002

Naphthalene removal from aqueous systems by Sagittarius sp..

Naphthalene is a polyaromatic hydrocarbon (PAH) present in many sediment-water systems. The uptake of naphthalene by an aquatic plant, arrowhead (Sagittaria sp.), was studied in a series of batch systems and continuous flow systems. Batch experiments were conducted in a fed-batch mode, and naphthalene was administered in consecutive spike doses. Results from batch experiments indicated that the rate of naphthalene removal by arrowhead in the presence of light was 0.114+/-0.061 h(-1), at a 90% confidence interval. Naphthalene removal by arrowhead occurred even in the absence of light, although this rate was about 25% of that in the presence of light. Results indicated that repeated exposures to naphthalene for a single arrowhead plant may decrease its capacity for naphthalene uptake, particularly after the first exposure. Naphthalene tended to deposit out in CSTRs where no arrowhead was present, indicating that while the naphthalene may not have been present in the water column, it was not removed from the system. Results from CSTR experiments indicated that under well-mixed quasi-steady state conditions, naphthalene removal by arrowhead in the presence of light was about 40%. Photolytic degradation of naphthalene in the absence of arrowhead was about 15%, when additional mixing was provided to simulate scouring.

Biodegradation, Environmental↗
PubMed2003

The built environment and mental health.

The built environment has direct and indirect effects on mental health. High-rise housing is inimical to the psychological well-being of women with young children. Poor-quality housing appears to increase psychological distress, but methodological issues make it difficult to draw clear conclusions. Mental health of psychiatric patients has been linked to design elements that affect their ability to regulate social interaction (e.g., furniture configuration, privacy). Alzheimer's patients adjust better to small-scale, homier facilities that also have lower levels of stimulation. They are also better adjusted in buildings that accommodate physical wandering. Residential crowding (number of people per room) and loud exterior noise sources (e.g., airports) elevate psychological distress but do not produce serious mental illness. Malodorous air pollutants heighten negative affect, and some toxins (e.g., lead, solvents) cause behavioral disturbances (e.g., self-regulatory ability, aggression). Insufficient daylight is reliably associated with increased depressive symptoms. Indirectly, the physical environment may influence mental health by altering psychosocial processes with known mental health sequelae. Personal control, socially supportive relationships, and restoration from stress and fatigue are all affected by properties of the built environment. More prospective, longitudinal studies and, where feasible, randomized experiments are needed to examine the potential role of the physical environment in mental health. Even more challenging is the task of developing underlying models of how the built environment can affect mental health. It is also likely that some individuals may be more vulnerable to mental health impacts of the built environment. Because exposure to poor environmental conditions is not randomly distributed and tends to concentrate among the poor and ethnic minorities, we also need to focus more attention on the health implications of multiple environmental risk exposure.

Air Pollution↗
PubMed1987

Assessing dose equivalent from intensive short-term U product inhalation.

Intensive exposure of a product packaging operator to U product dust resulted in the uncontrolled inhalation of natural U. In-vivo counting yielded an estimate of about 40 mg of natural U initially deposited in the lung. An effective committed dose equivalent in the range of 67 mSv and 137 mSv was calculated to correspond to this lung contamination, using a single exponential lung clearance and the modified ICRP models, respectively. The effective committed dose equivalent of a person 47 y old involved in this incident can hardly be used to quantify the risk, and therefore committed and annual dose equivalent systems were discussed in light of risk assessment.

Adult↗
PubMed2000

Removal of nitrate from groundwater by cyanobacteria: quantitative assessment of factors influencing nitrate uptake.

The feasibility of biologically removing nitrate from groundwater was tested by using cyanobacterial cultures in batch mode under laboratory conditions. Results demonstrated that nitrate-contaminated groundwater, when supplemented with phosphate and some trace elements, can be used as growth medium supporting vigorous growth of several strains of cyanobacteria. As cyanobacteria grew, nitrate was removed from the water. Of three species tested, Synechococcus sp. strain PCC 7942 displayed the highest nitrate uptake rate, but all species showed rapid removal of nitrate from groundwater. The nitrate uptake rate increased proportionally with increasing light intensity up to 100 micromol of photons m(-2) s(-1), which parallels photosynthetic activity. The nitrate uptake rate was affected by inoculum size (i.e., cell density), fixed-nitrogen level in the cells in the inoculum, and aeration rate, with vigorously aerated, nitrate-sufficient cells in mid-logarithmic phase having the highest long-term nitrate uptake rate. Average nitrate uptake rates up to 0.05 mM NO(3-) h(-1) could be achieved at a culture optical density at 730 nm of 0.5 to 1. 0 over a 2-day culture period. This result compares favorably with those reported for nitrate removal by other cyanobacteria and algae, and therefore effective nitrate removal from groundwater using this organism could be anticipated on large-scale operations.

Biomass↗
PubMed2006

Bio-optical properties and ocean color algorithms for coastal waters influenced by the Mississippi River during a cold front.

During the passage of a cold front in March 2002, bio-optical properties examined in coastal waters impacted by the Mississippi River indicated that westward advective flows and increasing river discharge containing high concentrations of nonalgal particles contributed significantly to surface optical variability. A comparison of seasonal data from three cruises indicated spectral models of absorption and scattering to be generally consistent with other coastal environments, while their parameterization in terms of chlorophyll (Chl) alpha concentration showed seasonal variability. The exponential slope of the colored dissolved organic matter (CDOM) averaged 0.0161+/-0.00054 nm(-1) and nonalgal absorption averaged 0.011 nm(-1) with deviations from general trends observed due to anomalous water properties. Although the phytoplankton specific absorption coefficients varied over a wide range [0.02 to 0.1 m2 (mg Chl)(-1) at 443 nm] being higher in offshore surface waters, values of phytoplankton absorption spectra at the Sea-Viewing Wide Field-of-View Sensor (SeaWiFS) wave bands were highly correlated to modeled values. Particulate scattering characteristics were similar to observations for other coastal waters, while backscattering ratios were on average lower in phytoplankton-dominated surface waters (0.011+/-0.003) and higher in low Chl near-bottom waters (0.0191+/-0.0045). Average percent differences in remote sensing reflectance Rrs derived from modeled and in-water radiometric measurements were highest in the blue wave bands (52%) and at locations with more stratified water columns. SeaWiFS estimates of Chl and CDOM absorption derived using regional empirical algorithms were highly correlated to in situ data.

Algorithms↗
PubMed2004

[Study of photoelectrocatalytic oxidation of benzoic acid].

This study reports the photoelectrocatalytic oxidation of benzoic acid in a three-electrode photoelectroreactor. The effects of the anode bias potential, the atmosphere of reaction and the basis material for photocatalyst preparation on the removal efficiency of benzoic acid were researched. The photoelectrocatalysis was compared with photolysis, photocatalysis and electrolysis. The results of the experiments indicated the removal efficiency of benzoic acid after the photoelectrocatalytic oxidation process for 1 h could be more than 85%, much higher than the efficiency of photolysis (48%), photocatalysis (30%) and electrolysis (nearly having no effect). The synergetic effect of the photoelectricity was obvious. The working electrode and the counter electrode were arranged as two concentric columns whose diameters were different. The results showed that this kind of arrangement mode was very effective. In nitrogen atmosphere the removal efficiency of benzoic acid could be 98% when TiO2/Ti acted as the anode of the photoelectrocatalytic oxidation process for 1 h, much better than the TiO2/Al did (85%). While in oxygen atmosphere the two kinds of electrodes were both effective and the removal efficiency of benzoic acid could approach 100%.

Benzoic Acid↗
PubMed2004

[Microwave assisted UV electrodeless discharge lamp photochemical degradation of 4-chlorophenol in aquatic solutions].

A microwave assisted UV electrodeless discharge lamp system (MW/UV) was used for photo-degradation of 4CP simulated wastewater. In order to evaluate the degradation efficiency of 4CP, UV spectrophotometry and ion chromatography were used for determination of 4CP and Cl- respectively. The degradation rate in MW/UV system was higher than that in the UV system within 120min, which were 52.40% and 21.56% respectively. The degradation efficiency was improved by increasing pH value of the solution, aerating O2 gas, enhancing light intensity, or adding H2O2 oxidant. The degradation of 4CP under MW/UV accords with the first order kinetics equation.

Chlorophenols↗