Skip to main content
eScholarship
Open Access Publications from the University of California

Scholarly Works (28 results)

  • Peer Reviewed
UC Berkeley Previously Published Works (2019)
Dental amalgam fillings, which contain about 50% mercury, have been used since the early 19th century. However, their use has been controversial, particularly because they continually release small amounts of mercury. Inorganic mercury is known to be highly toxic, particularly to the nervous system and kidneys, but exposures from amalgam fillings are generally well below those established as toxic. However, uncertainties about threshold concentrations of effect and the nature of any long-term exposure effects remain. Considering the long-standing and widespread use of these fillings, there has been remarkably little investigation of their safety and most epidemiologic studies have been relatively recent. In general, investigations to date have shown little evidence of effects on general chronic disease incidence or mortality. There have been few studies so far of neurodegenerative diseases and results have been equivocal. Assessments of the safety of dental amalgam have mainly been based on studies of occupationally exposed populations. However, the amalgam-exposed population contains a broader, potentially more susceptible, spectrum of people. In that regard, a number of studies of children that have found no evidence of health effects have provided some reassurance.
    Cover page: Dental Amalgam Fillings: An Under-Investigated Source of Mercury Exposure☆
    • Article
    • Peer Reviewed
    Berkeley Research Impact Initiative (BRII) (2015)
    Results have been conflicting whether long-term ambient hydrogen sulfide (H2S) affects lung function or is a risk factor for asthma or chronic obstructive pulmonary disease (COPD). Rotorua city, New Zealand, has the world’s largest population exposed to ambient H2S—from geothermal sources.
      • Article
      • Peer Reviewed
      UC Berkeley Previously Published Works (2017)
      The mechanism of toxicity of hydrogen sulfide (H2S) gas is thought mainly to operate through effects on the nervous system. The gas has high acute toxicity, but whether chronic exposure causes effects, including peripheral neuropathy, is yet unclear. The city of Rotorua, New Zealand, sits on an active geothermal field and the population has some of the highest measured ambient H2S exposures. A previous study in Rotorua provided evidence that H2S is associated with peripheral neuropathy. Using clinical methods, the present study sought to investigate and possibly confirm this association in the Rotorua population. The study population comprised 1635 adult residents of Rotorua, aged 18-65. Collected data relevant to the peripheral neuropathy investigation included symptoms, ankle stretch reflex, vibration sensitivity, as measured by the timed-tuning fork test and a Bio-Thesiometer (Bio-Medical Instrument Co., Ohio), and light touch sensitivity measured by monofilaments. An exposure metric, estimating time-weighted H2S exposure across the last 30 years was used. Principal components analysis was used to combine data across the various indicators of possible peripheral neuropathy. The main data analysis used linear regression to examine associations between the peripheral nerve function indicators and H2S exposure. None of the peripheral nerve function indicators were associated with H2S exposure, providing no evidence that H2S exposure at levels found in Rotorua is a cause of peripheral neuropathy. The earlier association between H2S exposure and peripheral neuropathy diagnoses may be attributable to the ecological study design used. The possibility that H2S exposure misclassification could account for the lack of association found cannot be entirely excluded.
        Cover page: Ambient geothermal hydrogen sulfide exposure and peripheral neuropathy
        • Article
        • Peer Reviewed
        UC San Francisco Previously Published Works (2013)

        Background

        Whether long-term, low-level hydrogen sulfide (H2S) gas is a cause of health effects, including asthma, is uncertain. Rotorua city, New Zealand, has the largest population exposed, from geothermal sources, to relatively high ambient levels of H2S. In a cross-sectional study, the authors investigated associations with asthma in this population.

        Methods

        A total of 1637 adults, aged 18-65 years, were enrolled during 2008-2010. Residences and workplaces were geocoded. H2S exposures at homes and workplaces were estimated using city-wide networks of passive H2S samplers and kriging to create exposure surfaces. Exposure metrics were based on (1) time-weighted exposures at home and work; and (2) the maximum exposure (home or work). Exposure estimates were entered as quartiles into regression models, with covariate data.

        Results

        Neither exposure metric showed evidence of increased asthma risk from H2S. However, some suggestion of exposure-related reduced risks for diagnosed asthma and asthma symptoms, particularly wheezing during the last 12 months, emerged. With the maximum exposure metric, the prevalence ratio for wheeze in the highest exposure quartile was 0.80 (0.65, 0.99) and, for current asthma treatment, 0.75 (0.52, 1.08). There was no evidence that this was caused by a "survivor effect".

        Conclusions

        The study provided no evidence that asthma risk increases with H2S exposure. Suggestions of a reduced risk in the higher exposure areas are consistent with recent evidence that H2S has signaling functions in the body, including induction of smooth muscle relaxation and reduction of inflammation. Study limitations, including possible confounding, preclude definitive conclusions.
          Cover page: Associations of ambient hydrogen sulfide exposure with self-reported asthma and asthma symptoms
          • Thesis
          • Peer Reviewed
          UC Berkeley Electronic Theses and Dissertations (2010)

          This dissertation examines the level of two major pollutants in the kitchens from biomass, kerosene and liquefied petroleum gas (LPG) stoves, and two health problems associated with use of biomass and kerosene compared with LPG stove in Nepal. Its chapter a) characterizes the exposure levels of two pollutants-fine particles (PM2.5) and naphthalene from three cookstoves, b) validate exposure questionnaire used in two epidemiological studies with the gold standard, c) showcase method to estimate sample size (duration of measurements) to reliably characterize levels of PM2.5 across rural households from continuously measured PM2.5 data, and d) examines the association of use of biomass and kerosene fuel with pre-clinical damage of lens (lens opacity) and tuberculosis in women.

          Divided on 5 chapters, the chapter 1 gives an overview of the dissertation. Chapter 2 provides a detailed background, materials and methods and results of validity study, and measurement results of naphthalene and PM2.5 from passive samplers. Similarly chapter 2 validates method for determining sample size from continuously measured PM2.5 data. Although there exist studies of associations of TB and cataracts from use of biomass fuel but the possible associations of TB and cataracts with the use of kerosene fuel are virtually uninvestigated. Chapter 3 investigates association between biomass and kerosene fuel use and pre-clinical damage of lens (lens opacity) in women and chapter 4 investigates the association between biomass and kerosene fuel use and TB in women. The chapter 5 summarizes the main findings of chapters 2, 3 and 4.

          The results of the three main chapters suggest that in Nepal cooks who use unvented biomass cookstoves experience very high mean and peak exposure of PM2.5 compared with kerosene and LPG stoves. By contrast, the cooks experience higher exposure of naphthalene from both kerosene and biomass cookstoves compared with LPG cookstoves. Current and past use of biomass cookstoves is associated with an increase risk of nuclear opacity and use of biomass as a heating fuel and kerosene, either in stoves or in lamps, is a risk factor for TB. Thus, promotion of low-emission biomass stoves, such as semi-gasifier stoves or other cleaner burning fuels (biogas or LPG) for cooking and heating, and promotion of solar lamps or cleaner burning devises for lighting could minimize the risk of lens opacity and TB in women in rural areas of Nepal.

            Cover page: Pre-clinical Measures of Eye Damage (Lens Opacity), Case-control Study of Tuberculosis, and Indicators of Indoor Air Pollution from Biomass Smoke
            • Article
            • Peer Reviewed
            UC Berkeley Previously Published Works (2008)

            Background

            Studies from developed countries have reported on host-related risk factors for extra-pulmonary tuberculosis (EPTB). However, similar studies from high-burden countries like Nepal are lacking. Therefore, we carried out this study to compare demographic, life-style and clinical characteristics between EPTB and PTB patients.

            Methods

            A retrospective analysis was carried out on 474 Tuberculosis (TB) patients diagnosed in a tertiary care hospital in western Nepal. Characteristics of demography, life-style and clinical features were obtained from medical case records. Risk factors for being an EPTB patient relative to a PTB patient were identified using logistic regression analysis.

            Results

            The age distribution of the TB patients had a bimodal distribution. The male to female ratio for PTB was 2.29. EPTB was more common at younger ages (< 25 years) and in females. Common sites for EPTB were lymph nodes (42.6%) and peritoneum and/or intestines (14.8%). By logistic regression analysis, age less than 25 years (OR 2.11 95% CI 1.12-3.68) and female gender (OR 1.69, 95% CI 1.12-2.56) were associated with EPTB. Smoking, use of immunosuppressive drugs/steroids, diabetes and past history of TB were more likely to be associated with PTB.

            Conclusion

            Results suggest that younger age and female gender may be independent risk factors for EPTB in a high-burden country like Nepal. TB control programmes may target young and female populations for EPTB case-finding. Further studies are necessary in other high-burden countries to confirm our findings.
              Cover page: Comparison of pulmonary and extrapulmonary tuberculosis in Nepal- a hospital-based retrospective study
              • Article
              • Peer Reviewed
              UC Berkeley Previously Published Works (2019)
              Automotive technicians are commonly exposed to organic and chlorinated solvents, particularly through use of cleaning products. Mainly during the period 1989-2002, n-hexane was a component of some of these products. In other occupational contexts, n-hexane has been shown to be a cause of peripheral neuropathy. The purpose of the present study was to investigate whether previous exposures to low concentrations of n-hexane were a cause of persistent peripheral neuropathy in automotive technicians. Enrolled in the study were 830 San Francisco Bay Area automotive technicians. Each participant underwent a battery of tests to investigate peripheral nervous system impairment. Test results regressed against estimated hexane and total solvent exposures showed only limited evidence of association with solvent exposures. Exposures to both hexane and general solvents were well below their occupational exposure limits. Generally, our results provide reassurance about persistent peripheral neuropathic effects in automotive technicians who previously used hexane-containing automotive cleaning products. This may reflect repair processes, since the exposures occurred some years previous to the study. However, we cannot exclude the possibility that the absence of observed effect in this study may be attributable to low exposures, exposure misclassification and/or the healthy worker survivor effect.
                Cover page: Hexane exposure and persistent peripheral neuropathy in automotive technicians
                • Article
                • Peer Reviewed
                UC Berkeley Previously Published Works (2018)
                Evidence suggests that early-life exposure to pesticides inside the home may be associated with childhood leukemia, however data from Latin American countries are limited. We examined whether self-reported maternal residential pesticide use and nearby pesticide applications-before and after child's birth-were associated with acute lymphoblastic leukemia (ALL) in the Costa Rican Childhood Leukemia Study (CRCLS), a population-based case-control study (2001-2003). Cases (n = 251 ALL) were diagnosed between 1995 and 2000 (age <15 years at diagnosis) and were identified through the Costa Rican Cancer Registry and National Children's Hospital. Population controls (n = 577) were drawn from the National Birth Registry. We fitted unconditional logistic regression models adjusted for child sex, birth year, and socioeconomic status to estimate the exposure-outcome associations and also stratified by child sex. We observed that self-reported maternal insecticide use inside the home in the year before pregnancy, during pregnancy, and while breastfeeding was associated with increased odds of ALL among boys [adjusted Odds Ratio (aOR) = 1.63 (95% confidence interval [95% CI]: 1.05-2.53), 1.75 (1.13-2.73), and 1.75 (1.12-2.73), respectively. We also found evidence of exposure-response relationships between more frequent maternal insecticide use inside the home and increased odds of ALL among boys and girls combined. Maternal report of pesticide applications on farms or companies near the home during pregnancy and at any time period were also associated with ALL. Our study in Costa Rica highlights the need for education to minimize pesticide exposures inside and around the home, particularly during pregnancy and breastfeeding.
                  Cover page: Maternal residential pesticide use and risk of childhood leukemia in Costa Rica
                  • Article
                  • Peer Reviewed
                  UC Berkeley Previously Published Works (2005)
                  Human biomonitoring investigations have provided data on a wide array of chemicals in blood and urine and in other tissues and fluids such as hair and human milk. These data have prompted questions such as a) What is the relationship between levels of environmental chemicals in humans and external exposures? b) What is the baseline or "background" level against which individual levels should be compared? and c) How can internal levels be used to draw conclusions about individual and/or population health? An interdisciplinary panel was convened for a 1-day workshop in November 2004 with the charge of focusing on three specific aspects of biomonitoring: characteristics of scientifically robust biomonitoring studies, interpretation of human biomonitoring data for potential risks to human health, and communication of results, uncertainties, and limitations of biomonitoring studies. In this report we describe the recommendations of the panel.
                    Cover page: Workgroup Report: Biomonitoring Study Design, Interpretation, and Communication—Lessons Learned and Path Forward
                    • Article
                    • Peer Reviewed
                    UC Berkeley Previously Published Works (2020)
                    OBJECTIVE:To investigate whether heavy load carrying, wearing a patuka, and body position at work are risk factors for uterine prolapse among Nepali women. METHODS:Community-based case-control study of 448 women (170 cases of uterine prolapse; 278 controls) aged 18-60 years in Kaski district, Nepal was conducted. Women diagnosed with uterine prolapse were cases. Two controls were recruited for each case, frequency-matched by residential area and age. Multivariate logistic regression was used to investigate associations between outcome and exposures. RESULTS:No association of heavy load carrying with uterine prolapse was observed; women who never used a patuka had lower odds of uterine prolapse (odds ratio = 0.18, 95% confidence interval = 0.05-0.71). Women working in a sitting position had higher odds than those working in a standing position (odds ratio = 2.94, 95% confidence interval = 1.74-4.96), as did women who mainly worked in a bending position (odds ratio = 2.45, 95% confidence interval = 1.12-5.34). Housewives were more prone to uterine prolapse than women engaged in farming (odds ratio = 2.13, 95% confidence interval = 1.31-3.47). CONCLUSION:Using a patuka, occupation, and body position during work were all associated with uterine prolapse. No association was found with heavy load carrying, although that might be attributable to the cross-sectional nature of study recruitment.
                      Cover page: Bio-mechanical risk factors for uterine prolapse among women living in the hills of west Nepal: A case-control study.
                      Top