The concentration-response relationship between daily ambient inhalable particle (particulate matter less than or equal to 10 micro m; PM(10)) concentrations and daily mortality typically shows no evidence of a threshold concentration below which no relationship is observed. However, the power to assess a relationship at very low concentrations of PM(10) has been limited in studies to date. The concentrations of PM(10) and other air pollutants in Vancouver, British Columbia, Canada, from January 1994 through December 1996 were very low: the 50th and 90th percentiles of daily average PM(10) concentrations were 13 and 23 micro g/m(3), respectively, and 27 and 39 ppb, respectively, for 1-hr maximum ozone. Analyses of 3 years of daily pollution (PM(10), ozone, sulfur dioxide, nitrogen dioxide, and carbon monoxide) concentrations and mortality counts showed that the dominant associations were between ozone and total mortality and respiratory and cardiovascular mortality in the summer, and between nitrogen dioxide and total mortality in the winter, although some association with PM(10) may also have been present. We conclude that increases in low concentrations of air pollution are associated with increased daily mortality. These findings may support the notion that no threshold pollutant concentrations are present, but they also raise concern that these effects may not be effects of the measured pollutants themselves, but rather of some other factor(s) present in the air pollution-meteorology mix.
Exposure atmospheres for a rodent inhalation toxicology study were generated from the exhaust of a 2000 Cummins ISB 5.9L diesel engine coupled to a dynamometer and operated on a slightly modified heavy-duty Federal Test Procedure cycle. Exposures were conducted to one clean air control and four diesel exhaust levels maintained at four different dilution rates (300:1, 100:1, 30:1, 10:1) that yielded particulate mass concentrations of 30, 100, 300, and 1000 microg/m3. Exposures at the four dilutions were characterized for particle mass, particle size distribution (reported elsewhere), detailed chemical speciation of gaseous, semivolatile, and particle-phase inorganic and organic compounds. Target analytes included metals, inorganic ions and gases, organic and elemental carbon, alkanes, alkenes, aromatic and aliphatic acids, aromatic hydrocarbons, polycyclic aromatic hydrocarbons (PAH), oxygenated PAH, nitrogenated PAH, isoprenoids, carbonyls, methoxyphenols, sugar derivatives, and sterols. The majority of the mass of material in the exposure atmospheres was gaseous nitrogen oxides and carbon monoxide, with lesser amounts of volatile organics and particle mass (PM) composed of carbon (approximately 90% of PM) and ions (approximately 10% of PM). Measured particle organic species accounted for about 10% of total organic particle mass and were mostly alkanes and aliphatic acids. Several of the components in the exposure atmosphere scaled in concentration with dilution but did not scale precisely with the dilution rate because of background from the rodents and scrubbed dilution air, interaction of animal derived emissions with diesel exhaust components, and day-to-day variability in the output of the engine. Rodent-derived ammonia reacted with exhaust to form secondary inorganic particles (at different rates dependent on dilution), and rodent respiration accounted for volatile organics (especially carbonyls and acids) in the same range as the diesel exhaust at the lowest exhaust exposure concentrations. Day-to-day variability in the engine output was implicated partially for differences of several components, including some of the particle bound organics. Though these observations have likely occurred in nearly all inhalation exposure atmospheres that contain complex mixtures of material, the speciations conducted here illustrate many of them for the first time.
Herbicides are widely applied along highways to control roadside vegetation, and surface water is frequently nearby. To determine whether herbicide runoff along highways threatens water quality, a field study was conducted at two sites in northern California for three rainy seasons. The herbicides oryzalin, isoxaben, diuron, glyphosate, and clopyralid were selected for study to include compounds with significant variation in physical/chemical properties. Concentrations of herbicides in runoff were monitored for up to 11 storms following herbicide application, and 24 samples were collected per storm, providing unprecedented temporal detail. Flow-weighted event mean concentrations were calculated for each herbicide in each storm and ranged from below detection limits to 43.13 microg/L for oryzalin. The least soluble compounds, isoxaben and oryzalin, were detected in all storms monitored while the more soluble compounds, diuron and clopyralid, declined to levels below detection limits before monitoring was concluded. Very small amounts of glyphosate were mobilized, but its transformation product aminomethylphosphonic acid was detected at higher concentrations, in more storm events, and at greater depth in the soil profile. A first-order model successfully described the declining herbicide concentrations in spray zone soil and in surface runoff for all sites and herbicides. Fitted first-order coefficients were always higher for runoff than for soil, indicating that the herbicide that persists in the source zone becomes less available for runoff as the time since application increases. The percentage of the applied herbicide that was detected in surface runoff over a season ranged from 0.05% to 43.5%, and the most critical variables in controlling the variation were the solubility of the herbicide and the runoff volume. For a given herbicide and site, the most critical factors in determining seasonal herbicide loss to surface water were the timing and intensity of the first storm following application, affecting total seasonal runoff by up to 2 orders of magnitude. Minimizing runoff of herbicides along highways will thus require careful attention to the intrinsic mobility of the compound and the timing of its application.
There is increasing interest in diesel fuels derived from plant oils or animal fats ("biodiesel"), but little information on the toxicity of biodiesel emissions other than bacterial mutagenicity. F344 rats were exposed by inhalation 6 h/day, 5 days/wk for 13 wk to 1 of 3 dilutions of emissions from a diesel engine burning 100% soybean oil-derived fuel, or to clean air as controls. Whole emissions were diluted to nominal NO(x) concentrations of 5, 25, or 50 ppm, corresponding to approximately 0.04, 0.2, and 0.5 mg particles/m(3), respectively. Biologically significant, exposure-related effects were limited to the lung, were greater in females than in males, and were observed primarily at the highest exposure level. There was a dose-related increase in the numbers of alveolar macrophages and the numbers of particles in the macrophages, as expected from repeated exposure, but no neutrophil response even at the highest exposure level. The macrophage response was reduced 28 days after cessation of the exposure. Among the high-level females, the group mean lung weight/body weight ratio was increased, and minimal, multifocal bronchiolar metaplasia of alveolar ducts was observed in 4 of 30 rats. Lung weights were not significantly increased, and metaplasia of the alveolar ducts was not observed in males. An increase in particle-laden macrophages was the only exposure-related finding in lungs at the intermediate and low levels, with fewer macrophages and fewer particles per macrophage at the low level. Alveolar histiocytosis was observed in a few rats in both exposed and control groups. There were statistically significant, but minor and not consistently exposure-related, differences in body weight, nonpulmonary organ weights, serum chemistry, and glial fibrillary acidic protein in the brain. There were no significant exposure-related effects on survival, clinical signs, feed consumption, ocular toxicity, hematology, neurohistology, micronuclei in bone marrow, sister chromatid exchanges in peripheral blood lymphocytes, fertility, reproductive toxicity, or teratology. This study demonstrated modest adverse effects at the highest exposure level, and none other than the expected physiological macrophage response to repeated particle exposure at the intermediate level.
A single-cylinder engine diesel exhaust exposure system was constructed to conduct laboratory health effects studies. The singlecylinder engine was selected to provide a cost-effective and easyto-operate biological exposure system as an alternative to larger engines operated on chassis or test stand dynamometers. The engine was a 5500-watt diesel generator operated at load by connection to a bank of 11 500 watt light sources. The engine was isolated from the rodent and cell exposure chambers to ameliorate excessive noise and heat in the exposure room. Exhaust was diluted approximately 100:1 and routed to a 1 m 3 flow-through exposure chamber where the exhaust composition was assessed in detail. Measurements included particle mass, particle size distribution (based on both number and mass), carbon monoxide, nitrogen oxides, particle carbon (organic and elemental), particle sulfate/nitrate, metals, total and speciated volatile hydrocarbons, and speciated semivolatile and particle-phase polycyclic aromatic hydrocarbons. The exhaust
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.