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At least 1,207 records · Page 67Linked to original sources
PubMed2001

Abatement of ammonia and hydrogen sulfide emissions from a swine lagoon using a polymer biocover.

The purpose of this research was to determine the efficiency of a polymer biocover for the abatement of H2S and NH3 emissions from an east-central Missouri swine lagoon with a total surface area of 7800 m2. The flux rate of NH3, H2S, and CH4 was monitored continuously from two adjacent, circular (d = 66 m) control and treatment plots using a nonintrusive, micrometeorological method during three independent sampling periods that ranged between 52 and 149 hr. Abatement rates were observed to undergo a temporal acclimation event in which NH3 abatement efficiency improved from 17 to 54% (p = < 0.0001 to 0.0005) and H2S abatement efficiency improved from 23 to 58% (p < 0.0001) over a 3-month period. The increase in abatement efficiency for NH3 and H2S over the sampling period was correlated with the development of a stable anaerobic floc layer on the bottom surface of the biocover that reduced mass transfer of NH3 and H2S across the surface. Analysis of methanogenesis activity showed that the biocover enhanced the rate of anaerobic digestion by 25% when compared with the control. The biocover-enhanced anaerobic digestion process was shown to represent an effective mechanism to counteract the accumulation of methanogenic substrates in the biocovered lagoon.

Agriculture↗
PubMed1987

Airway responses to nitrogen dioxide in asthmatic subjects.

Nitrogen dioxide is a common indoor air pollutant. In order to characterize the respiratory responses to this gas, 10 asthmatics (mean age +/- SD = 30 +/- 8 yrs) were exposed to air and 0.5 ppm NO2 gas for 1 h in a 30-m3 environmental chamber on different days in a double-blind randomized fashion. The forced vital capacity, (VC), functional residual capacity, forced expiratory volume in 1 s, partial expiratory flow at 40% VC (Vp 40), and specific airway conductance were measured before and after exposure. Airway reactivity to methacholine inhalation was determined after each exposure. The dose of methacholine in milligrams per milliliter to cause a 40% decrease in Vp 40 was measured. None of the subjects reported any significant symptoms after exposure. Significant potentiation of airway reactivity was noted after NO2 exposure in asthmatic subjects as a group [PD40(AIR) = 9.2 +/- SD 15.0 versus PD40(NO2) = 4.6 +/- SD 8.2 mg/ml, p = 0.042]. No significant changes were noted in other lung functions after NO2 exposure. These findings indicate that asthmatics exposed to 0.5 ppm NO2 develop heightened airway reactivity.

Adult↗
PubMed1985

A survey of typical exposures to formaldehyde in Houston area residences.

A survey of indoor air quality under warm weather conditions, in a variety of Houston area residences not selected in response to occupant complaints, revealed a distribution of indoor formaldehyde concentrations ranging from less than 0.008 ppm to 0.29 ppm, with an arithmetic mean of 0.07 ppm. Approximately 15% of the monitored residences had concentrations greater than 0.10 ppm. Formaldehyde levels were observed to depend on both age of dwelling and the structural classification of the residence. These factors are not independent and reflect the influence of more fundamental variables, such as the rate of exchange of indoor and outdoor air and the overall emission potential of indoor materials. The results of this survey suggest that considerable population exposures to excess (greater than 0.10 ppm) formaldehyde concentrations may occur in the residential environment, indicating the need for improved control strategies.

Air Pollutants↗
PubMed1985

Ambient concentrations of formaldehyde and ammonia in a screwworm fly rearing facility.

A facility for the mass rearing of sterilized screwworm flies used in fly eradication program efforts was described. Air concentrations of formaldehyde and ammonia were measured during industrial hygiene surveys conducted in the production plant which is currently the world's largest insect rearing facility. Formaldehyde, used as a bactericide and fungicide in the larvae media, was consistently found at levels below current and recommended TLVs. Ammonia, released as metabolic waste from the larvae, was occasionally found at elevated levels in some plant areas. Factors were identified which influenced the in-plant variations of ammonia air levels.

Air Pollutants, Occupational↗
PubMed1985

Ambient levels of selected gases inside swine confinement buildings.

To assess potential worker health hazards, the air in confinement structures on 21 randomly selected swine producing farms in Iowa was evaluated for selected gases. The gases measured (mean concentration) included ammonia (34 ppm), hydrogen sulfide (1.4 ppm), carbon monoxide (9.1 ppm) and carbon dioxide (1640 ppm). Ammonia (compared to other gases) most commonly exceeded the Threshold Limit Value (TLV); however, it was common to find buildings with several gases in excess of the TLV. Buildings housing younger animals were more likely to have hazardous gas levels than buildings housing older animals. This complex mixture of gases represents a potential health hazard to an estimated 400,000 individuals who work in swine confinement buildings. These data suggest that research is needed to control these exposures affecting a large number of workers.

Agriculture↗
PubMed1986

A new approach to the construction of small animal inhalation chambers: design and evaluation.

Cylindrical, all glass, inhalation chambers are described which are suitable for the exposure of small laboratory animals to atmospheric pollutants. The main feature of the design is the ability of the investigator to construct a chamber with an internal volume which best approximates the animal loading requirement and/or the availability of test material. Evaluation of the distribution of a gaseous material within the chamber has shown that animals will be exposed to a specified atmospheric concentration of the material irrespective of their position within the chamber. Catch pans for the collection of excreta can be used which do not affect the uniformity of material distribution. Preliminary evaluation of the distribution of a particulate atmosphere indicates that the same will be true for liquid and solid aerosols.

Animals↗
PubMed1986

Development and validation of personal monitoring methods for low levels of acrylonitrile in workplace atmosphere: I. Test atmosphere generation and solvent desorption methods.

The purpose of this study was to optimize monitoring methods and to investigate new technology for the determination of low levels of acrylonitrile (0.05 to 5 ppm) in workplace atmospheres. In the first phase of the study, a dynamic atmosphere generation system was developed to produce low levels of acrylonitrile in simulated workplace atmospheres. Various potential sorbents were investigated in the second phase, and the candidate methods were compared in a laboratory validation study over a concentration range from 0.05 to 5 ppm acrylonitrile in the presence of potential interferences and under relative humidity conditions from 30% to 95% RH. A collection tube containing 600 mg Pittsburgh coconut base charcoal was found to be the optimum tube for sampling for a full 8-hr shift. No breakthrough was observed over the concentrations and humidities tested. The recovery was 91.3% with a total relative precision of +/- 21% over the test range, and the recovery was not affected by storage for up to five weeks.

Acrylonitrile↗
PubMed1986

Development and validation of personal monitoring methods for low levels of acrylonitrile in workplace atmosphere: II. Thermal desorption and field validation.

Thermal desorption is a more sensitive alternative to solvent desorption for the determination of acrylonitrile in air. A dual-bed collection tube (Tenax GC and Carbosieve B) was developed for collecting and concentrating low levels of acrylonitrile. Two thermal desorption techniques were evaluated for the recovery of acrylonitrile collected on the dual-bed tubes over a concentration range from 0.05 to 5 ppm. A commercially-available system, the Century Programmable Thermal Desorption Unit, was easy to operate, allowed for multiple injections of the sample and had a recovery of 82 +/- 12% (RSD). Samples were stored for up to two months without affecting the recovery and there was not an observable effect from humidity or from the presence of other organic compounds. This system was found to have limitations at acrylonitrile concentrations above 1 ppm. A field validation study tested the sampling and analytical methods developed for monitoring low levels of acrylonitrile in the workplace. Three methods employing Pittsburgh Coconut-Base activated charcoal, Ambersorb XE-348 and Tenax-GC and Carbosieve B sampling mediums were validated for concentrations ranging from 0.05 to 5 ppm and confirmed in the field from 0.02 to 3 ppm in tests conducted at plant sites. These field studies were run over varying humidity and temperature conditions. The overall absolute recoveries and relative standard deviations found for these methods found during the field trials are 90 +/- 18% for charcoal; 85 +/- 11% for Ambersorb XE-348; and 90 +/- 19% for the Century dual-bed sorbent. These values were in quite good agreement with the 91 +/- 10%, 88 +/- 8%, and 82 +/- 12% determined in laboratory studies.

Acrylonitrile↗
PubMed1986

A laboratory evaluation of two methods for measuring low levels of formaldehyde in indoor air.

Two methods for measuring formaldehyde at ppb levels--the modified pararosaniline (PRA) and the modified chromotropic acid (CTA)--were evaluated in a laboratory study. A dynamic double dilution system was used to generate controlled test atmospheres of formaldehyde by the catalytic depolymerization of trioxane. Impinger samples were collected from the sampling manifold and analyzed accordingly. Both methods demonstrated good precision (3.5% for the PRA and 3.4% for the CTA) but differed in accuracy and collection efficiency. Accuracy was 87.7 +/- 7.5% for the PRA and 92.5 +/- 4.2% for the CTA, while collection efficiency was 91.9 +/- 6.9% and 98.7 +/- 4.7% respectively. These differences were mainly due to the use of 1% NaHSO3 as the absorbing solution in the CTA method. Additionally, the NaHSO3 solution has the advantage of long sample preservation, making the modified CTA the method of choice in most non-industrial indoor air sampling situations.

Air Pollutants, Occupational↗
PubMed1986

Use of tracer gas technique for industrial exhaust hood efficiency evaluation--where to sample?

A tracer gas technique using sulfur hexafluoride (SF6) was developed for the evaluation of industrial exhaust hood efficiency. In addition to other parameters, accuracy of this method depends on proper location of the sampling probe. The sampling probe should be located in the duct at a minimum distance from the investigated hood where the SF6 is dispersed uniformly across the duct cross section. To determine the minimum sampling distance, the SF6 dispersion in the duct in fully developed turbulent flow was studied at four duct configurations frequently found in industry: straight duct, straight duct-side branch, straight duct-one elbow, and straight duct-two elbows combinations. Based on the established SF6 dispersion factor, the minimum sampling distances were determined as follows: for straight duct, at least 50 duct diameters; for straight duct-side branch combination, at least 25 duct diameters; for straight duct-one elbow combination, 7 duct diameters; and for straight duct-two elbow combination, 4 duct diameters. Sampling at (or beyond) these distances minimizes the error caused by the non-homogeneous dispersion of SF6 in the duct and contributes to the accuracy of the tracer gas technique.

Air Pollutants, Occupational↗
PubMed1991

Comparisons of air and liquid personal cooling for intermittent heavy work in moderate temperatures.

Personal microenvironmental cooling has been used to enhance safety and extend the work capacity of laborers wearing protective clothing. Previous studies of air and liquid cooling have used either very low work rates or high environmental temperatures. Emergency work tasks frequently require high work rates and occur in moderate ambient temperatures. The purpose of this research was to examine the efficacy of intermittent personal cooling during rest and to compare liquid and air cooling systems in subjects engaged in hard work. Fourteen volunteers wearing chemical protective clothing performed treadmill walking at a metabolic rate of 430 W for 45 min followed by a 15-min rest at a wet-bulb globe temperature of 25 degrees C. During rest, volunteers received either no cooling, air cooling, or liquid cooling. Both cooling systems partially alleviated heat strain and increased work time with the air system offering slightly more effective cooling.

Adult↗
PubMed1996

Domestic magnetic field exposures in Avon.

To define a protocol for surrogate measurement of magnetic field exposure by questionnaire, a series of spot and 24-hour measurements was made at 50 houses in Avon, UK. Measurements were made with Emdex II equipment in the centres of rooms with the house power encountered at the start of the visit, and then with all power to the house isolated at the main switch. The mean spot magnetic field averaged over the 50 homes for each room varied between 0.011 and 0.023 microT with an overall mean (0.017 +/- 0.003) microT with the power 'on', and between 0.008 and 0.015 microT, giving an overall mean (0.012 +/- 0.002) microT with power 'off'. Measurements over 24 h in the three main occupancy rooms showed a distinct diurnal variation in the overall mean magnetic field of the 50 homes by a factor of three, giving a 24-hour mean of (0.044 +/- 0.06) microT; at the same time mean recorded personal exposure for the occupants monitored was (0.067 +/- 0.08) microT. These values appear low compared with, for example, USA domestic levels of magnetic field exposure demonstrated in several studies, but also show a wide variation in individual values, which could not be predicted from spot measurements.

Air Pollution, Indoor↗
PubMed2006

Impact of environmental temperature on skin thickness and microvascular blood flow in subjects with and without diabetes.

BACKGROUND: Glucose measurement from different skin areas might be influenced by changes in skin texture due to several environmental confounders. Our study was performed to investigate the effect of changes in ambient temperature on skin thickness and microvascular skin blood flow in subjects with and without diabetes at the lower forearm. METHODS: Thirteen subjects with diabetes and seven without diabetes participated in the study. The investigations were performed in a temperature- and humidity-controlled climatic chamber (EMPA, St. Gallen, Switzerland). Starting at 25 degrees C, the environmental temperature was changed in 4 degrees C steps every 40 min. Skin thickness was measured by an ultrasonic reflection technique, and microcirculation was measured by laser Doppler fluxmetry at the lower forearm. Study participants underwent the entire procedure on up to four separate study trials. RESULTS: Our study revealed a significantly reduced skin thickness (P<0.05) and microvascular blood flow (P<0.05) in patients with diabetes mellitus compared with controls without diabetes during the entire investigation. During declining ambient temperature a significant reduction in skin thickness (with diabetes, -0.09+/-0.13 mm; without diabetes, -0.06+/-0.11 mm; P<0.05) and microvascular blood flow (with diabetes, -41+/-49 arbitrary units; without diabetes, -46+/-51 arbitrary units; P<0.05) could be observed in both groups without significant differences between the two. CONCLUSIONS: Although skin thickness and microvascular skin blood flow at the lower forearm were found to be reduced in patients with diabetes compared with controls without diabetes, both groups revealed comparable dynamics in skin thickness and microvascular blood flow during changes in environmental temperature.

Adult↗
PubMed2003

Photosynthetic responses of the tropical spiny shrub Lycium nodosum (Solanaceae) to drought, soil salinity and saline spray.

Water relations and photosynthetic characteristics of plants of Lycium nodosum grown under increasing water deficit (WD), saline spray (SS) or saline irrigation (SI) were studied. Plants of this perennial, deciduous shrub growing in the coastal thorn scrubs of Venezuela show succulent leaves which persist for approx. 1 month after the beginning of the dry season; leaf succulence is higher in populations closer to the sea. These observations suggested that L. nodosum is tolerant both to WD and salinity. In the glasshouse, WD caused a marked decrease in the xylem water potential (psi), leaf osmotic potential (psi(s)) and relative water content (RWC) after 21 d; additionally, photosynthetic rate (A), carboxylation efficiency (CE) and stomatal conductance (gs) decreased by more than 90 %. In contrast, in plants treated for 21 d with a foliar spray with 35 per thousand NaCl or irrigation with a 10 % NaCl solution, psi and RWC remained nearly constant, while psi(s) decreased by 30 %, and A, CE and gs decreased by more than 80 %. An osmotic adjustment of 0.60 (SS) and 0.94 MPa (SI) was measured. Relative stomatal and mesophyll limitations to A increased with both WD and SS, but were not determined for SI-treated plants. No evidence of chronic photoinhibition due to any treatment was observed, since maximum quantum yield of PSII, Fv/Fm, did not change with either drought in the field or water or salinity stress in the glasshouse. Nevertheless, WD and SI treatments caused a decrease in the photochemical (qP) and an increase in the non-photochemical (qN) quenching coefficients relative to controls; qN was unaffected by the SS treatment. The occurrence of co-limitation of A by stomatal and non-stomatal factors in plants of L. nodosum may be associated with the extended leaf duration under water or saline stress. Additionally, osmotic adjustment may partly explain the relative maintenance of A and gs in the SS and SI treatments and the tolerance to salinity of plants of this species in coastal habitats.

Disasters↗
PubMed2004

Microgeographic genome size differentiation of the carob tree, Ceratonia siliqua, at 'Evolution Canyon', Israel.

BACKGROUND AND AIMS: We tested whether the local differences in genome size recorded earlier in the wild barley, Hordeum spontaneum, at 'Evolution Canyon', Mount Carmel, Israel, can also be found in other organisms. As a model species for our test we chose the evergreen carob tree, Ceratonia siliqua. METHODS: Genome size was measured by means of DAPI flow cytometry. KEY RESULTS: In adults, significantly more DNA was recorded in trees growing on the more illuminated, warmer, drier, microclimatically more fluctuating 'African' south-facing slope than in trees on the opposite, less illuminated, cooler and more humid, 'European' north-facing slope in spite of an interslope distance of only 100 m at the canyon bottom and 400 m at the top. The amount of DNA was significantly negatively correlated with leaf length and tree circumference. In seedlings, interslope differences in the amount of genome DNA were not found. In addition, the first cases of triploidy and tetraploidy were found in C. siliqua. CONCLUSIONS: The data on C. siliqua at 'Evolution Canyon' showed that local variability in the C-value exists in this species and that ecological stress might be a strong evolutionary driving force in shaping the amount of DNA.

Biological Evolution↗
PubMed2006

The genetic diversity of two brazilian vellozia (velloziaceae) with different patterns of spatial distribution and pollination biology.

BACKGROUND AND AIMS: The genetic structure and variability of two species of Vellozia (Velloziaceae) with restricted distribution in high-altitude quartzitic fields in south-eastern Brazil were studied. Vellozia epidendroides is short, grows on pebbly or sandy soil, and is pollinated by bees. Vellozia leptopetala is arborescent, grows on rock outcrops, and is pollinated by bees and hummingbirds. Both are self-incompatible and have a short, massive flowering strategy. The study aimed to associate differences in their genetic diversity and structure with their microhabitat distribution and pollination ecology. METHODS: Leaves from 106 and 139 plants of V. epidendroides and V. leptopetala, respectively, were collected from five patches of each species and prepared for electrophoretic analyses. KEY RESULTS: Five enzyme systems could be reliably scored for both species. Vellozia epidendroides showed 100 % of the loci polymorphic for almost all patches. The average number of alleles per locus ranged between 2.2 and 2.4 among patches. The Wright's fixation index (F) for this species was 0.226. A significant (p) value indicates that there is a reasonable genetic divergence among patches. Vellozia leptopetala presented 47.5 % of polymorphic loci. All levels of P, A, A(p) and of heterozygosities were lower than those of V. epidendroides. Vellozia leptopetala showed high inbreeding within patches. CONCLUSIONS: The relatively high values of genetic diversity indices found for V. epidendroides may be associated with its large and widespread populations. On the other hand, the low values of genetic diversity found for V. leptopetala may be related to physical isolation on outcrops and intensive foraging by territorial hummingbirds, which may hinder gene flow among patches, aggravated by the very restricted seed dispersal characteristic of the genus, that facilitates sibling mating. It is important to stress the need to preserve the specific habitats of these species of Vellozia, in particular those of V. leptopetala that has lower genetic diversity and is restricted to rock outcrop environments.

Brazil↗
PubMed2006

Stomatal oscillations in orange trees under natural climatic conditions.

BACKGROUND AND AIMS: Stomatal oscillations have been reported in many plant species, but they are usually induced by sudden step changes in the environment when plants are grown under constant conditions. This study shows that in navel orange trees (Citrus sinensis) pronounced stomatal oscillations occur and persist under natural climatic conditions. METHODS: Oscillations in stomatal conductance were measured, and related to simultaneous measurements of leaf water potential, and flow rate of sap in the stems of young, potted plants. Cycling was also observed in soil-grown, mature orchard trees, as indicated by sap flow in stem and branches. KEY RESULTS: Oscillations in stomatal conductance were caused by the rapid propagation and synchronization of changes in xylem water potential throughout the tree, without rapid changes in atmospheric conditions. CONCLUSIONS: The results show marked stomatal oscillations persisting under natural climatic conditions and underscore the need to discover why this phenomenon is so pronounced in orange trees.

Biological Clocks↗