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Results for “multiple exposures”

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At least 307 records · Page 17Linked to original sources
PubMed2005

Growth inhibition as indicator of stress because of atrazine following multiple toxicant exposure of the freshwater macrophyte, Juncus effusus L.

Atrazine is a herbicide used most frequently in North America, but it usually is encountered in mixtures of agrochemicals. Few atrazine exposure studies have been conducted using mixed pesticides; therefore, little data are available to suggest reliable means of discerning effects attributable to atrazine. The common freshwater macrophyte, Juncus effusus L., was exposed in 66 mesocosms to atrazine at two nominal concentrations (96 and 192 microg/L) with varying concentrations of chlorpyrifos, monosodium methanearsonate, and monomethylmercury. Exposure levels represented typical levels that might follow runoff or direct-spray application in enclosed waterbodies. Using shoot density and number of shoots shorter than 25 cm per unit area as response measurements, the growth effects of atrazine, even in varying pesticide mixes, could be detected as early as 16 d after initial exposure. Further growth effects specifically caused by atrazine also could be detected following a second exposure to the same toxicant mixture. Mesocosm tests offer greater control of natural variability than would be found in the natural environment and offer more realistic conditions than traditional laboratory/greenhouse studies. Therefore, in field testing, growth measurements should be accompanied by other confirmatory tests, such as pesticide concentrations in tissue and, possibly, chlorophyll concentrations, for measuring specific toxic effects of atrazine and other pesticides.

Animals↗
PubMed2005

Emotion and motor control: movement attributes following affective picture processing.

The authors investigated the impact of emotion on the performance of a square-tracing task after participants (N = 40) were exposed to pleasant (P), unpleasant (U), and neutral (N) pictures. Physiological and self-report measures indexed affective valence and arousal. In Experiment 1, greater error followed exposure to 4 consecutive U images than exposure to 4 consecutive P images. Speed of performance did not vary as a function of valence. In Experiment 2, participants viewed 1 slide per trial within a modified exposure protocol. Speed of performance varied as a function of valence; faster performance followed U relative to P stimuli. Accuracy of performance did not vary between conditions. Corresponding self-report and physiological measures generally corroborated previous evidence. Findings collectively indicated that the length of exposure to affective stimuli mediates speed and accuracy of motor performance; compared with P stimuli, U stimuli led to either increased error (short exposure) or increased speed (multiple exposures). The authors conclude that brief and extended exposures to affective pictures have direct behavioral consequences, and they discuss the implications of that finding.

Adolescent↗
PubMed1999

Multiple human exposures to a rabid bear cub at a petting zoo and barnwarming--Iowa, August 1999.

On August 27, 1999, a black bear cub, approximately 5-6 months old, died after several hours of acute central nervous system symptoms; preliminary test results available on August 28 indicated the bear had rabies. The bear was part of the Swenson's Wild Midwest Exotic Petting Zoo in Clermont, Iowa (northeastern Iowa). At the petting zoo, visitors fed, wrestled, and may have been nipped by the bear. The bear also was taken to an August 14 barnwarming at the Tharp barn in Holy Cross, Iowa (eastern Iowa), where it reportedly nipped people. An estimated 400 people from 10 states (Arizona, California, Florida, Illinois, Iowa, Minnesota, New Mexico, New York, Ohio, and Wisconsin) and Australia had contact with the bear cub at either the petting zoo or the barnwarming during the 28 days before its death, during which the bear may have transmitted rabies virus.

Animals↗
PubMed1989

[Cytochrome P-450 dependent drug metabolism--use of an in vitro test system in multiple chemical exposure].

Investigations of the influence of an actual exposure on the in-vitro-activities and the inducibility of cytochrom P-450 dependent enzymes have not been described in the literature until now. First results gained from mitogen-stimulated lymphocytes of exposed and not-exposed individuals suggest such an influence of the given mixture of noxious agents on the basic deethylational ability of the examined cells acting in the sense of inhibition. Possible causes for this phenomenon are discussed.

Air Pollutants, Occupational↗
PubMed1988

Multiple, small exposures of far-ultraviolet or mid-ultraviolet light change the sensitivity to acute ultraviolet exposures measured by cell lethality and mutagenesis in V79 Chinese hamster cells.

Chinese hamster V79 cells (subline MI2G) were exposed repeatedly to fractionated doses of germicidal 254 nm light (far-uv) at 6 J.m-2/fraction/day or sunlight-simulating 290-330 nm (mid-uv) at 150 J.m-2/fraction/day and sensitivities to cell killing action and mutation of far-uv and mid-uv were examined. As the number of exposure fractions increased, the cell cultures became resistant to cell killing induced by both far-uv and mid-uv. Increases in both Do and Dq were observed. Treatment with exposures of 6 J.m-2 far-uv is more efficient in yielding cell cultures that are resistant than exposures of 150 J.m-2 mid-uv. In contrast to the cells exposed to repeated far-uv, the cells exposed to repeated mid-uv were relatively more resistant to cell killing effects of mid-uv than far-uv, suggesting a possible role of photolesions other than pyrimidine dimers. When mutants resistant to 6-thioguanine were assayed during repeated exposure to far- or mid-uv light, the yield was initially linear with accumulating dose. At high total accumulated doses, the frequency decreased gradually (6 J.m-2 mid-uv) or reached a plateau (150 J.m-2 mid-uv). The sensitivity of N80 cells (exposed to 80 fractions of mid-uv) to mutation induction by uv light is higher than that of the original MI2G cells, whereas U81 cells (exposed to 81 fractions of far-uv) have a sensitivity similar to that of the original cells. Although an initial decrease in resistance to cell killing was observed, resistant cells retained their characteristics after 100 days in culture without further exposure. Cross-resistance to X rays was not shown. The data in this paper suggest that the capacity for repair of photolesions in DNA by repair processes was enhanced in cell cultures by repeated exposure to far-uv or mid-uv and that this altered the cells' ability to cope with lethal and mutagenic lesions. It remains to be seen if these changes in cell sensitivity were brought about by selective or inductive processes or a combination of both.

Animals↗
PubMedDate not supplied

[Physical endurance of the rat during multiple intensive exposures to a constant magnetic field].

Variations in physical endurance of rats exposed to a constant magnetic field of 1.6 T for 3 hours a day during 30 days were investigated. The parameter was measured as the time of swimming with a load making 10% of body weight until complete arrest. The rats exposed once, 5 or 15 times showed a longer time of swimming than the controls. On the 30th day of exposure there was no difference between the experimental and control animals. The data obtained suggest that exposure to a constant magnetic field produces a stimulating effect on physical work capacity during the first 15 days.

Animals↗
PubMed1984

Multiple dose exposure effects on the tissue distribution of lead in the preweanling rat.

The time dependent tissue/organ distribution of Pb resulting from repeated intragastric exposure of the preweanling rat to Pb acetate was investigated. On the day of parturition, 12 dams were assigned randomly either to control (nonhandled) or Pb-treated groups and their litters were culled to 8 pups. On days 6, 9, 12, 15, and 18 post partum, the experimental groups received 50 mg Pb (as Pb acetate)/kg body weight containing 50 microCi of 210Pb. By day 7 (N = 15), the liver had accumulated 1.48 +/- 0.14 micrograms Pb/g wet weight (avg. +/- SE) and the kidney, 1.21 +/- 0.20 micrograms/g. However, most of the Pb was found in the intestine (129.07 +/- 20.90 micrograms/g) and intestinal contents (8.31 +/- 1.16 total Pb). By day 14 (N = 14), bone had accumulated 20.86 +/- 1.05 micrograms/g Pb while the liver and kidney levels had increased to 2.59 +/- 0.22 and 2.51 +/- 0.08 micrograms/g, respectively. At this time, blood was found to contain 0.87 +/- 0.07 micrograms/g and brain, 0.14 +/- 0.03 micrograms/g. On day 14, the greatest quantities of Pb were again found in the intestine and intestinal contents; 45.87 +/- 4.93 and 441.26 +/- 23.77 micrograms/g, respectively. By day 21 (N = 32), the concentration of Pb in liver, intestine, intestinal contents, and blood had decreased to 1.03 +/- 0.02, 4.22 +/- 1.68, 1.03 +/- 0.02 and 0.29 +/- 0.02 micrograms/g, respectively, while that in kidney remained unchanged (2.38 +/- 0.07 micrograms/g). By day 21, the concentration of Pb in bone and brain increased to 43.85 +/- 1.18 and 0.31 +/- 0.02 micrograms/g, respectively. However, it is to be noted that brain Pb levels were relatively low. There was no accumulation of Pb in lung, heart, stomach, or spleen at any time. Although the spleen did not accumulate any Pb, it was effected by Pb exposure as evidenced by a significant decrease in wet weight. Body weights of Pb-treated animals were comparable to those of control animals throughout the period of preweanling development.

Age Factors↗
PubMed1982

Chemotherapy sensitivity assessment of leukemic colony-forming cells with in vitro simultaneous exposure to multiple drugs: clinical correlations in acute nonlymphocytic leukemia.

For 13 patients with acute nonlymphocytic leukemia receiving four-drug combination chemotherapy (14 chemotherapy trials), leukemic bone marrow cells were obtained before treatment and were exposed in vitro to all four-drug-mixture solutions simultaneously followed by the survival assessment of leukemic colony-forming cells (L-CFU). Survival of normal marrow colony-forming cells (CFU-C) was also assessed concurrently, and the sensitivity index (SI) of leukemic cells was determined as the ratio of the survival of CFU-C to that of L-CFU. Correlations of in vitro results to clinical results were excellent: four of five trials resulting in complete remission had high SI and eight of nine trials without complete remission had low SI (P = 0.02). The potential advantages of this method of exposing cells to drug mixture are discussed in terms of detecting drug synergism and improving the efficiency of in vitro chemotherapy sensitivity studies.

Acute Disease↗
PubMed1983

Hydroa vacciniforme: induction of lesions with ultraviolet A.

Hydroa vacciniforme is a rare photosensitivity disorder with onset in childhood. The distinctive lesion is a vesicle which heals with scarring. We report a case of hydroa vacciniforme in which an abnormal minimal erythema dose to wavelengths of 322 to 370 nm within the ultraviolet A (UVA) range was demonstrated. Vesicles could be induced only with multiple exposures to UVA. Increased tolerance to UVA erythema was induced by multiple UVB exposures, although tanning was poor. Of note were the presence of several halo nevi and a history of the loss of ability to tan. The clinical features and appropriate laboratory evaluation of hydroa vacciniforme are reviewed.

Adult↗
PubMed1985

A multi-route exposure assessment of chemically contaminated drinking water.

This report provides an example of how a single source of contamination could potentially contribute to all routes of exposure. A modeling approach was used to estimate multiple exposure routes in an attempt to assess the health significance of gasoline-contaminated drinking water supplies. This model consisted of a two-compartment, indoor air quality equation that calculates the contribution made by ambient and indoor air contaminated by a pollutant volatilized from drinking water to that pollutant's inhalation burden. In addition, the model uses the traditional equations for assessing a pollutant's oral and dermal burdens. Benzene, toluene and xylene were used as surrogates for gasoline contamination to determine the contribution of contaminated water to adult and child body burdens from indoor air, oral (drinking water and food) and dermal exposure routes. The contribution thus calculated for each chemical was compared to the EPA's Office of Drinking Water Health Advisories. In terms of acute exposure, the use of chemically contaminated water for showering purposes may generate vapor in the confined area of the bathroom at levels sufficient to cause or contribute to mucous tissue irritation, as commonly reported in affected homes. High temperatures and humidity may also contribute to these effects, especially in the bathroom. In terms of chronic exposure, the use of chemically contaminated water at EPA-recommended guideline amounts in an affected home may result in inhalation, oral and dermal exposures leading to cumulative doses exceeding adult and child total daily body burdens based on EPA's Health Advisories. Thus, this model indicates that the traditional standard/guidelines derivation processes should be reevaluated to consider the pollutant contribution from multiple routes of exposure. The New Jersey Departments of Health and Environmental Protection conducted a study in which concentrations of several pollutants including benzene in the breathing zone were measured during a 15-minute shower in homes with contaminated water. The findings suggest that the air quality model used in the present study may satisfactorily predict the airborne concentrations of pollutants in, at least, the bathroom after showering with contaminated water (Pearson rank correlation coefficient of 0.773 with p = 0.0012 for n = 14). The findings of the present study support the use of an adjustment factor for all exposure durations to account for exposures to other sources of the contaminant, i.e., urban, occupational, and food. A value of 20% seems appropriate based on the study's findings.(ABSTRACT TRUNCATED AT 400 WORDS)

Aerosols↗