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R W Morgan

Publications and source records attributed to R W Morgan.

At least 55 records · Page 3Linked to original sources
PubMed1988

An epidemiologic investigation of the relationship between DBCP contamination in drinking water and birth rates in Fresno County, California.

This report describes an epidemiologic investigation of the relationship between DBCP (dibromochloropropane) contamination in drinking water and birth rates between 1978 and 1982 in Fresno County, California. Census tracts in the county were categorized according to DBCP level in their drinking water. Standardized birth ratios and relative birth ratios (adjusted for age, race, per cent Hispanic, and parity) were calculated for these census tracts. No relation between birth ratios and DBCP contamination in drinking water was found.

Adult↗
PubMed1988

Problems associated with collecting drinking water quality data for community studies: a case example, Fresno County, California.

This paper discusses methodology in developing exposure data for the water supply contaminant dibromochloropropane (DBCP) in Fresno County, California. There are 532 drinking water systems (49 large and 483 small) within Fresno County plus 14,000 private wells. We determined the number of wells per system, the output per well, and the population served by each system. The task of deriving water quality estimates for each census tract was complicated by the fact that a single census tract can be served by more than one system; each system usually has more than one well; and a single well can have several episodes of testing for various contaminants. We calculated a series of weighted averages for concentrations of DBCP, arsenic, and nitrates for each census tract, using water production figures for each well as the weighting factor. Water quality data were derived from a total of 14,861 laboratory reports, although the majority did not report on all contaminants. Mean DBCP levels ranged from 0.0041 ppb to 5.7543 ppb among the census tracts. We found no correlation between DBCP levels per census tract compared to either arsenic or nitrates. We believe that we made as complete an exposure assessment as practically feasible.

Arsenic↗
PubMed1987

Functional significance of histologic alterations induced by Escherichia coli pig-specific, mouse-negative, heat-stable enterotoxin (STb).

In contrast to cholera enterotoxin and other Escherichia coli enterotoxins, a pig-specific, heat-stable E. coli enterotoxin (STb) causes morphologic lesions (loss of villous epithelial cells and partial villous atrophy). These lesions reflect a loss of absorptive cells and thus suggest that STb causes impaired absorption as well as inducing net secretion. The present studies assess functional significance of morphologic changes induced by STb. Net fluid movement, mucosal surface area, sucrase activity and the electrical response induced by alanine were measured in swine jejunal loops exposed to E. coli culture filtrates with and without STb. Net fluid secretion (-11.1 +/- 1.1 ml) occurred in some STb loops (secretors) and net absorption (2.7 +/- 0.3 ml) in others (nonsecretors), but net absorption occurred in all control loops (4.9 +/- 0.2 ml). The mucosal surface area of STb loops was about 20% less than that of controls (P less than 0.01). Sucrase activity was also lower (about 15%) in STb loops than in control loops (P less than 0.01). The electrical response induced by alanine in mucosa from nonsecreting STb loops did not differ from that induced in mucosa from control loops. However, the response to alanine in mucosa from secreting STb loops was reduced about 70% from that in mucosa from nonsecreting STb loops or from control loops (P less than 0.05). It is concluded that reduced sucrase activity is a functional correlate to villous atrophy induced by STb, that STb impairs alanine absorption in some loops (secretors), and that the impaired alanine absorption is independent of the decreased surface area caused by STb. Because the impaired alanine absorption occurred independent of the decreases in surface area, it is suggested that the secretory response to STb is associated with an impairment of active absorption of alanine.

Animals↗
PubMed1987

Reconstructive materials for endodontically treated teeth.

A review of the literature on restoration of endodontically treated teeth was presented. The advantages and disadvantages of current methods and materials were described, and a detailed technique was suggested for the newer glass-ionomer restorative materials. An all-purpose material suited for the restoration of endodontically treated teeth is still unavailable. Each patient requires individual consideration. However, Ketac Silver material may be an excellent choice in select patients.

Cermet Cements↗
PubMed1987

Investigation and work-up of tight building syndrome.

In recent years, incidents involving health-related complaints due to poor indoor air quality have increased dramatically. These problems have generally occurred in new or remodeled buildings. Following relocation to a new building, some employees began to experience health complaints, including upper respiratory tract irritation, headaches, fatigue, and eye irritation. A questionnaire was designed which elicited information about specific work locations, symptom experience, and timing of such symptoms. Although no causative agent(s) could be isolated, the data collected indicate that over the 5-week time period of investigation the rate and persistence of new symptoms decreased. The health complaints experienced appeared to be neither persistent nor pervasive enough to constitute an ongoing health and safety hazard at the facility. Reasons were proposed why some new and/or remodeled buildings have this type of problem while others do not.

Adult↗
PubMed1986

Hydrogen peroxide-inducible proteins in Salmonella typhimurium overlap with heat shock and other stress proteins.

Hydrogen peroxide treatment induces the synthesis of 30 proteins in Salmonella typhimurium. Five of these proteins are also induced by heat shock, including the highly conserved DnaK protein. The induction of one of these five proteins by heat shock is dependent on oxyR, a positive regulator of hydrogen peroxide-inducible genes, while the induction of the other four by heat shock is oxyR independent. Five of the 30 hydrogen peroxide-inducible proteins have been identified, and their structural genes have been mapped. Other stresses such as nalidixic acid, ethanol, or cumene hydroperoxide treatment also induce subsets of the 30 hydrogen peroxide-inducible proteins as well as additional proteins. Hydrogen peroxide-inducible proteins are shown to be largely different from those proteins induced by aerobiosis. In addition, the expression of the katG (catalase) gene is shown to be regulated by oxyR at the level of mRNA.

Adaptation, Physiological↗
PubMed1986

An epidemiological study of petroleum refinery employees.

A cohort study of 14179 current and former Chevron USA employees at the Richmond and El Segundo, California, refineries was conducted. The cohort consisted of everyone working at either refinery for a minimum of one year. The observed mortality of the cohort, by cause, was compared with the expected based on the United States mortality rates, standardised for age, race, sex, and calendar time. Analyses by refinery, job category, hire date, duration of employment, and latency were performed. For the entire cohort, mortality from all causes was 72.4% of that expected, a deficit that was statistically significant. In addition, a significantly lower mortality was found for all forms of cancer combined, digestive cancer, lung cancer, heart disease, non-malignant respiratory disease, diseases of the digestive system, and accidents. Only lymphopoietic cancer showed a pattern of increased risk suggestive of a possible relation to an occupational exposure. The excess appears confined to cancer of lymphatic tissue (not leukaemias) at Richmond, and only among those hired before 1948. A follow up case analysis of the deaths from lymphatic cancer failed to identify a common exposure pattern.

Brain Neoplasms↗
PubMed1985

An epidemiologic surveillance program for evaluating occupational reproductive hazards.

A noninvasive and inexpensive epidemiologic program for evaluating the possible effects of occupational exposures on fertility is proposed. This surveillance program utilizes reproductive information obtainable from a short questionnaire (1-2 pages in length) or directly from existing medical, employment, or insurance records, and results can be generated readily on a routine basis. This program examines the reproductive experience of the exposed workers in terms of live births compared with that of the US general population with the proper statistical adjustments. It calculates the standardized birth ratios (SBR), adjusting for maternal age, parity, calendar time, and race. Such an analysis will detect whether there is a significant decrease in fertility among a group of employees, and is, therefore, a useful surveillance tool. The proposed method should be viewed as a mechanism to provide an early signal for any potential hazard and to direct priority for other more in-depth epidemiologic or physiologic studies. The procedure is illustrated with data from individuals exposed to EDB, DBCP, and waste-water treatment plant processes. The method can be modified to compare the reproductive performance of an exposed group to that of an internal control group. With an internal control group, additional confounding factors can be taken into consideration. The relative merits of this approach compared to another method of fertility evaluation, semen analysis, are discussed.

Adult↗
PubMed1985

Positive control of a regulon for defenses against oxidative stress and some heat-shock proteins in Salmonella typhimurium.

S. typhimurium become resistant to killing by hydrogen peroxide and other oxidants when pretreated with nonlethal levels of hydrogen peroxide. During adaptation to hydrogen peroxide, 30 proteins are induced. Nine are constitutively overexpressed in dominant hydrogen peroxide-resistant oxyR mutants. Mutant oxyR1 is resistant to a variety of oxidizing agents and overexpresses at least five enzyme activities involved in defenses against oxidative damage. Deletions of oxyR are recessive and uninducible by hydrogen peroxide for the nine proteins overexpressed in oxyR1, demonstrating that oxyR is a positive regulatory element. The oxyR1 mutant is also more resistant than the wild-type parent to killing by heat, and it constitutively overexpresses three heat-shock proteins. The oxyR regulatory network is a previously uncharacterized global regulatory system in enteric bacteria.

Adaptation, Physiological↗
PubMed1985

Mortality of paint and coatings industry workers. A follow-up study.

Extensive follow-up of production workers in the paint and coatings industry failed to indicate any important hazard that was previously unsuspected. The authors are more confident of the results of their original study since studying a subsample of persons lost to follow-up in the original study. Some efforts to investigate certain diseases (skin and liver cancer) more vigorously met with failure, which illustrates the problem of attempting retrospective studies by using death certificates for case ascertainment. Of the successful studies, the leukemia case-control analysis showed a possible relationship to lacquer production, which probably included benzene exposure. For lung cancer, no exposure category was associated with increased risk. The bowel cancer excesses, concentrated in three plants, are probably not job related and in any case do not represent an industry-wide problem. Cerebrovascular accidents showed a mild elevation of risk for vehicle workers. Although strong statements concerning the safety of this industry probably await more studies or further follow-up of this cohort, there is every indication that it is an industry without a major excess of any job-related disease. In drawing this conclusion, however, one must be aware that an individual job or individual plant could harbor health problems that would not be detected by a study of this type.

California↗
PubMed1985

Mortality among members of a heavy construction equipment operators union with potential exposure to diesel exhaust emissions.

A historical prospective mortality study was conducted on a cohort of 34 156 male members of a heavy construction equipment operators union with potential exposure to diesel exhaust emissions. This cohort comprised all individuals who were members of the International Union of Operating Engineers, Locals 3 and 3A, for at least one year between 1 January 1964 and 31 December 1978. The mortality experience of the entire cohort and several subcohorts was compared with that of United States white men, adjusted for age and calendar time. The comparison statistic was the commonly used standardised mortality ratio (SMR). Historical environmental measurements did not exist, but partial work histories were available for some cohort members through the union dispatch computer tapes. An attempt was made to relate mortality experience to the union members' dispatch histories. Overall mortality for the entire cohort and several subgroups was significantly lower than expected. When cause specific mortality was examined, however, the study provided suggestive evidence for the existence of several potential health problems in this cohort. Mortality from liver cancer for the entire cohort was significantly high. Although mortality from lung cancer for the entire cohort was similar to expected, a positive trend by latency was observed for lung cancer. A significant excess of mortality from lung cancer was found among the retirees and the group for whom no dispatch histories were available. Other dispatch groups showed no evidence of lung cancer excess. In addition, the total cohort experienced significant mortality excess from emphysema and accidental deaths.

Accidents, Occupational↗
PubMed1985

Comparison of SMR, PMR, and PCMR in a cohort of union members potentially exposed to diesel exhaust emissions.

A comparison of cause specific standarised mortality ratios (SMRs) and proportionate mortality ratios (PMRs) or proportionate cancer mortality ratios (PCMRs) was made based on the mortality experience of a cohort of 34 156 members of a heavy equipment operators union. Two types of PMRs or PCMRs were used in the comparison: those based on all deaths and those based on deaths known to the union only. The comparison indicated that, for the entire cohort, both types of PMRs were poor indicators for cancer risk and produced a large number of false positives. On the other hand, PCMRs appeared to be better than PMRs for assessing the direction of site specific cancer risk, but they tended to overstate the magnitude of risk. Analysis by duration of union membership or latency indicated that PMRs or PCMRs based on deaths known to the union tended to overestimate the risk of lung cancer by disproportionately larger amounts in groups with shorter time than in groups with longer time. This differential bias had the net effect of reducing the gradient of any trend or eliminating the trend entirely. In conclusion, PMR or PCMR, based on reasonably sufficient death ascertainment, has a certain usefulness in generating hypotheses, but they are not useful or reliable in measuring the magnitude of risk or in detecting trends in dose response analysis. No conclusion should be drawn from either PMR or PCMR.

Air Pollutants, Occupational↗
PubMed1985

Asbestos and gastrointestinal cancer. A review of the literature.

Exposure to asbestos is among several factors cited as possible causes of esophageal, gastric and colorectal cancer. More than 45 published studies have presented mortality data on asbestos-exposed workers. For each cohort, we listed the observed and expected rates of deaths from types of gastrointestinal cancer based on the latest published follow-up. Summary standardized mortality ratios (SMRs) were then derived. Finally, we calculated summary SMRs for total gastrointestinal tract cancer for three occupational groups: asbestos factory workers, insulators/shipyard workers and asbestos miners. Statistically significant elevations in summary SMRs were found for esophageal, stomach and total gastrointestinal tract cancer in all asbestos-exposed workers. Esophageal cancer summary SMRs remained significantly elevated when data were reanalyzed to include only those cohorts with death certificate diagnoses for cause of observed deaths. However, summary SMRs were not statistically significant for stomach and total gastrointestinal tract cancer after reanalysis. Summary SMRs by occupational group showed a significant elevation for total gastrointestinal cancer in insulators/shipyard workers. The elevation was not significant after reanalysis. Based on the results after reanalysis, the elevations in summary SMRs for stomach and total gastrointestinal tract cancer are of a magnitude that could result from diagnostic and investigator error. We conclude that more studies are required before stomach and colorectal cancers are documented as asbestos-related diseases.

Asbestos↗
PubMed1984

Review: putative mutagens and carcinogens in foods. V. Cycad azoxyglycosides.

Cycasin is a member of a family of azoxyglycosides produced by cycads. It is mutagenic and carcinogenic only when deglucosylated to release its principal metabolite, methylazoxymethanol (MAM). Methylazoxymethanol is also the aglycone of other cycad azoxyglycosides and is responsible for their toxicologic properties. The way in which people can be exposed to cycad azoxyglycosides is through the consumption of foods prepared from cycads. MAM induces genetic alterations in various test systems in bacteria, yeast, plants, Drosophila, and mammalian cells. An important aspect of the biological activities of cycasin and MAM is the intimate connection between their metabolism and their toxicologic effects. In adult mammals, the deglucosylation of cycasin is catalyzed only by enzymes of the microflora of the gut. Cycasin is therefore active when administered orally but not when administered parenterally. In contrast, MAM is active regardless of the route of exposure. Major uncertainties remain regarding the intermediates generated from MAM spontaneously and metabolically. More knowledge of these intermediates is required for a better understanding of the molecular mechanisms underlying the toxicity of cycasin, MAM, and related compounds.

Animals↗
PubMed1984

Fetal loss and work in a waste water treatment plant.

We investigated pregnancy outcomes in 101 wives of workers employed in a waste water treatment plant (WWTP), and verified fetal losses by hospital records. Paternal work histories were compiled and each of the 210 pregnancies was assigned a paternal exposure category. The relative risk of fetal loss was increased when paternal exposure to the WWTP occurred around the time of conception.

Abortion, Spontaneous↗
PubMed1983

Exogenous estrogens and development of breast and endometrial cancer.

The risk of breast cancer and endometrial cancer in 1483 menopausal and postmenopausal women who had received estrogen therapy for other than contraceptive use was examined. The incidence and mortality rates of the study cohort (cohort A) were compared with the age-specific cancer incidence and mortality rates of the female populations of Ontario (cohort B) and of Saskatchewan (cohort C). A significant difference was found in each of the two comparisons between the observed and expected survival curves for breast cancer incidence and breast cancer mortality. However, the incidence rate of endometrial cancer in the study cohort (cohort A) did not differ significantly from the rates of the reference populations (cohorts B and C). The results suggest that the women in the study may have received some protective effect against breast cancer by taking estrogens, but the estrogens did not protect them against endometrial cancer and may indeed have predisposed them to this cancer.

Adult↗