Final Report: Effects of Prenatal Exposure to Inhaled Methanol on Nonhuman Primates and Their Infant Offspring

EPA Grant Number: R828112C089
Subproject: this is subproject number 089 , established and managed by the Center Director under grant R828112
(EPA does not fund or establish subprojects; EPA awards and manages the overall grant for this center).

Center: Health Effects Institute (2000 — 2005)
Center Director: Greenbaum, Daniel S.
Title: Effects of Prenatal Exposure to Inhaled Methanol on Nonhuman Primates and Their Infant Offspring
Investigators: Burbacher, Thomas
Institution: University of Washington
EPA Project Officer: Chung, Serena
Project Period: April 1, 2000 through March 31, 2005
RFA: Health Effects Institute (1996) RFA Text |  Recipients Lists
Research Category: Health Effects , Air

Objective:

In an effort to improve air quality and decrease dependence on petroleum, the federal government, industry, and other groups have encouraged development of alternative fuels such as methanol to substitute for gasoline or diesel fuel. Methanol is also a candidate to provide the hydrogen for fuel cells, which are being developed for a variety of power sources (including motor vehicle engines). Before people are exposed to increased concentrations of methanol, the potential health effects of such exposures require study.

Methanol, a simple alcohol containing one carbon atom, occurs naturally in plants and animals and participates in human metabolism. People regularly consume low doses of methanol in fruits, vegetables, and fermented beverages as well as soft drinks and foods sweetened with aspartame (which breaks down to methanol in the gastrointestinal tract). Despite its ubiquitous presence, methanol can be highly toxic if sufficient quantities are consumed. Ingestion of methanol (usually in the form of wood alcohol or tainted alcoholic beverages) can result in metabolic acidosis, blindness, and even death. Although the body has the capacity to metabolize the low doses of methanol to which people are regularly exposed, it cannot handle high doses because too much methanol overwhelms the body?s ability to remove a toxic metabolite (formate). When formate accumulates, methanol poisoning occurs. One factor that regulates the rate at which formate is removed is the liver level of a derivative of the vitamin folic acid. People who are deficient in folic acid (including 15% to 30% of pregnant women) may be particularly susceptible to the toxic effects of methanol.

If methanol were to be widely adopted as a fuel, environmental exposures would increase through ingestion of contaminated drinking water, inhalation of vapors from evaporative and other emissions, and dermal contact. Current concentrations of methanol in ambient air are very low, 1 to 30 parts per billion (ppb). If all motor vehicles in the United States were converted to 100% methanol fuel, methanol levels in ambient air are estimated to increase approximately 1,000-fold (to 1 to 10 ppm in cities) and in a worst-case situation could occasionally reach concentrations as high as 200 ppm in enclosed spaces (HEI 1987). Inhaling these concentrations of methanol for short periods of time is not predicted to affect formate production and thus should not present a health risk. However, little is known about the consequences of long-term inhalation of methanol vapors, especially in susceptible populations of pregnant women and developing fetuses. HEI, therefore, developed a research program to address this information gap.

Summary/Accomplishments (Outputs/Outcomes):

In an effort to improve air quality and decrease dependence on petroleum, the federal government, industry, and other groups have encouraged development of alternative fuels such as methanol to substitute for gasoline or diesel fuel. Methanol is also a candidate to provide the hydrogen for fuel cells, which are being developed for a variety of power sources (including motor vehicle engines). Before people are exposed to increased concentrations of methanol, the potential health effects of such exposures require study.

Methanol, a simple alcohol containing one carbon atom, occurs naturally in plants and animals and participates in human metabolism. People regularly consume low doses of methanol in fruits, vegetables, and fermented beverages as well as soft drinks and foods sweetened with aspartame (which breaks down to methanol in the gastrointestinal tract). Despite its ubiquitous presence, methanol can be highly toxic if sufficient quantities are consumed. Ingestion of methanol (usually in the form of wood alcohol or tainted alcoholic beverages) can result in metabolic acidosis, blindness, and even death. Although the body has the capacity to metabolize the low doses of methanol to which people are regularly exposed, it cannot handle high doses because too much methanol overwhelms the body?s ability to remove a toxic metabolite (formate). When formate accumulates, methanol poisoning occurs. One factor that regulates the rate at which formate is removed is the liver level of a derivative of the vitamin folic acid. People who are deficient in folic acid (including 15% to 30% of pregnant women) may be particularly susceptible to the toxic effects of methanol.

If methanol were to be widely adopted as a fuel, environmental exposures would increase through ingestion of contaminated drinking water, inhalation of vapors from evaporative and other emissions, and dermal contact. Current concentrations of methanol in ambient air are very low, 1 to 30 parts per billion (ppb). If all motor vehicles in the United States were converted to 100% methanol fuel, methanol levels in ambient air are estimated to increase approximately 1,000-fold (to 1 to 10 ppm in cities) and in a worst-case situation could occasionally reach concentrations as high as 200 ppm in enclosed spaces (HEI 1987). Inhaling these concentrations of methanol for short periods of time is not predicted to affect formate production and thus should not present a health risk. However, little is known about the consequences of long-term inhalation of methanol vapors, especially in susceptible populations of pregnant women and developing fetuses. HEI, therefore, developed a research program to address this information gap.

Dr. Thomas Burbacher and colleagues of the University of Washington studied the effects of long-term exposure to methanol vapors on metabolism and reproduction in adult female monkeys (Macaca fascicularis) and developmental effects in their offspring, who were exposed prenatally to methanol.

The investigators exposed adult female monkeys (11 to 12 animals/group) to one of four concentrations of methanol vapors (0, 200, 600, and 1,800 ppm) for 2.5 hours a day, seven days a week during the following periods: (1) before breeding, (2) during breeding, and (3) during pregnancy. They collected blood from the adults at regular intervals to monitor methanol levels (which served as a marker of internal dose) and formate concentrations. They also conducted pharmacokinetic studies to determine whether methanol disposition (which includes absorption, distribution, metabolism, and excretion) was altered as a result of repeated methanol exposures and to assess pregnancy-related changes. Because high doses of methanol damage the central nervous system, the infants (8 to 9 animals/group) were examined at regular intervals during the first nine months of life to assess their growth and neurobehavioral development.

Exposure to methanol vapors did not affect the health of the adult monkeys prior to or during pregnancy. Single 2.5-hour exposures to methanol vapors caused short-term elevations in blood methanol concentrations of approximately 0- to 2-fold in the 200 ppm exposure group, 3- to 4-fold in the 600 ppm group, and 13- to 16-fold in the 1,800 ppm group. After long-term exposures, peak blood methanol concentrations declined slightly over the first month and remained constant thereafter. The concentrations of plasma formate (the toxic intermediate) remained at baseline levels during the entire course of the study in all exposure groups. Pregnancy had no effect on methanol disposition. Serum folate concentrations were not affected by pregnancy and methanol exposure.

Methanol exposure had no effect on most measures of reproductive performance, including menstrual cycles, conception rate, and live-birth delivery rate. However, all methanol-exposed animals had a decrease of about six to eight days in the duration of pregnancy compared to the control animals. It is not clear whether this decrease was related to methanol exposure as there was no dose response and no differences among offspring groups in body weight or other physical parameters. Prenatal exposure to methanol had no effect on infant growth and physical development for the first year of life. An unexplained wasting syndrome, characterized by growth retardation, malnutrition, and gastroenteritis, occurred after one year of age in two female offspring exposed in utero to 1,800 ppm methanol.

The investigators reported no systematic effects of prenatal methanol exposure on most of the measures used to test infant neurobehavioral development (neonatal behavior, early reflex responses, infant gross motor development, spatial memory, and social behavior). The investigators reported two possible methanol-related effects, one on visually directed reaching in male infants (a test of sensorimotor development), and one on novelty preference (a test of memory and cognitive function). Care must be taken in interpreting these results because a large number of neurobehavioral endpoints were analyzed and these results were based on a small number of subjects. Random fluctuations in the data may have appeared to be statistically significant. At the same time, however, both observations warrant further investigation as these central nervous system functions are complex perceptual processes that take time to develop and may be subject to latent neurotoxic effects.

This study adds substantially to our understanding of the effects of long-term exposure to inhaled methanol vapors. Because of the high quality of the study, the relevance of the animal model, the opportunities for dose-response analyses, and the availability of a marker of internal methanol dose, the results are appropriate for use in risk assessment. They can be readily used to predict the response of nutritionally competent people; they do not necessarily apply to women who are folate deficient.

The investigators? findings suggest that repeated inhalation exposure to concentrations of methanol vapors as high as 1,800 ppm would not result in accumulation of blood formate above baseline levels. With the exception of an unexplained shortening of gestation, methanol exposure had no effect on reproductive performance. The most significant result to emerge from this study was the wasting observed in two monkeys exposed in utero to 1,800 ppm methanol. Although this observation raises concern for prenatal exposures of this magnitude, pregnant women are unlikely to be exposed to such extremely high concentrations of methanol for prolonged periods of time.

Overall, the results provide no evidence of a robust effect of prenatal methanol exposure on the neurobehavioral development of nonhuman primate infants during the first nine months of life. However, improved understanding of methanol neurobehavioral toxicity will result from evaluation at later stages of development when more sophisticated tests of cognitive performance can be conducted and when latent effects may emerge. Such studies are now under way in the same monkeys at 4 to 5 years of age.

Supplemental Keywords:

Prenatal Exposure, Air, particulate matter, air toxics, mobile sources, epidemiology, health effects, alternative fuel, Methanol, ambient air quality, animal model, drinking water., RFA, Health, Scientific Discipline, Air, particulate matter, Toxicology, air toxics, Environmental Chemistry, Health Risk Assessment, Risk Assessments, mobile sources, Biochemistry, ambient air quality, particulates, neurotoxic, motor vehicles, air pollutants, inhalability, lung, vehicle emissions, aerosol particles, motor vehicle emissions, prenatal exposure, exposure and effects, engines, animal model, motor vehicle exhaust, automotive emissions, metabloic study, metabolic study, air pollution, automobiles, automotive exhaust, emissions, environmental health effects, monkey, inhalation, lung inflammation, particulate exposure, ambient particle health effects, metabolic studies, diesel, inhaled, vehicular exhaust, inhalation toxicology, Formaldehyde

Progress and Final Reports:

Original Abstract
  • 2000
  • 2001
  • 2002
  • 2003

  • Main Center Abstract and Reports:

    R828112    Health Effects Institute (2000 — 2005)

    Subprojects under this Center: (EPA does not fund or establish subprojects; EPA awards and manages the overall grant for this center).
    R828112C042 Does Inhalation of Methanol Vapor Affect Human Neurobehavior?
    R828112C043 Human Responses to Nitrogen Dioxide
    R828112C044 The Role of Inflammation in Ozone-Induced Lung Injury
    R828112C045 How Does Exercise Affect the Dose of Inhaled Air Pollutants?
    R828112C046 How Do Chemicals in Diesel Engine Exhaust Damage DNA?
    R828112C047 Effect of Nitrogen Dioxide on Bacterial Respiratory infection in Mice
    R828112C048 Effects of Ozone Exposure on Airway Epithelium
    R828112C049 Inhalation of Aldehydes and Effects on Breathing
    R828112C050 Does Ozone Cause Precancerous Changes in Cells?
    R828112C051 Effects of Formaldehyde on Human Airway Epithelial Cells Exposed in a Novel Culture System
    R828112C052 Carbon Monoxide and Cardiac Arrhythmias
    R828112C053 Effects of Formaldehyde and Particle-Bound Formaldehyde on Lung Macrophage Functions
    R828112C054 Mechanisms for Protecting Lung Epithelial Cells Against Oxidant Injury
    R828112C055 Relationship of Nitropyrene-Derived DNA Adducts to Carcinogenesis
    R828112C056 Particle Trap Effects on Heavy-Duty Diesel Engine Emissions
    R828112C057 Carbon Monoxide and Atherosclerosis
    R828112C058 Nitrogen Dioxide and Respiratory Illness in Children
    R828112C059 Noninvasive Methods for Measuring Ventilation in Mobile Subjects
    R828112C060 Oxidant Air Pollutants and Lung Cancer: An Animal Model
    R828112C061 Detection of Carcinogen-DNA Adducts: Development of New Methods
    R828112C062 Effects of Carbon Monoxide on Heart Muscle Cells
    R828112C063 Development of Personal Ozone Samplers: Three Approaches
    R828112C064 Development of Biomarkers to Monitor Carcinogen Exposure
    R828112C065 Effects of Prolonged Ozone Inhalation on Collagen Structure and Content in Rat Lungs
    R828112C065II Prolonged Ozone Exposure and the Contractile Properties of Isolated Rat Airways
    R828112C065III Changes in Complex Carbohydrate Content and Structure in Rat Lungs Caused by Prolonged Ozone Inhalation
    R828112C065IV Genetic Control of Connective Tissue Protein Synthesis After Prolonged Ozone Inhalation
    R828112C065V Pulmonary Function Alterations in Rats After Chronic Ozone Inhalation
    R828112C065VII Prolonged Ozone Exposure Leads to Functional and Structural Changes in the Rat Nose
    R828112C065VIII - IX Studies of Changes in Lung Structure and Enzyme Activitiesin Rats After Prolonged Exposure to Ozone
    R828112C065X An Innovative Approach to Analyzing Multiple Experimental Outcomes: A Case Study of Rats Exposed to Ozone
    R828112C065XI The Consequences of Prolonged Inhalation of Ozone on Rats: An Integrative Summary of the Results of Eight Collaborative Studies
    R828112C066 Interactive Effects of Nitropyrenes in Diesel Exhaust
    R828112C067 Detection of Formaldehyde–DNA Adducts: Development of New Methods
    R828112C068I Comparison of the Carcinogenicity of Diesel Exhaust and Carbon Black in Rat Lungs
    R828112C068II An Investigation of DNA Damage in the Lungs of Rats Exposed to Diesel Exhaust
    R828112C068III No Evidence For Genetic Mutations Found In Lung Tumors From Rats Exposed To Diesel Exhaust or Carbon Black
    R828112C069 Noninvasive Determination of Respiratory Ozone Absorption: The Bolus-Response Method
    R828112C070 The Effects of Inhaled Oxidants and Acid Aerosols on Pulmonary Function
    R828112C071 Biochemical Consequences of Ozone Reacting with Membrane Fatty Acids
    R828112C072 DNA Mutations in Rats Treated with a Carcinogen Present in Diesel Exhaust
    R828112C073 Developmental Neurotoxicity of Inhaled Methanol in Rats
    R828112C074 Methanol Distribution in Non Pregnant and Pregnant Rodents
    R828112C075 Is Increased Mortality Associated with Ozone Exposure in Mexico City?
    R828112C076 Effects of Fuel Modification and Emission Control Devices on Heavy-Duty Diesel Engine Emissions
    R828112C077 Metabolic Studies in Monkeys Exposed to Methanol Vapors
    R828112C078 Effects of Ozone on Pulmonary Function and Airway Inflammation in Normal and Potentially Sensitive Human Subjects
    R828112C079 Improvement of a Respiratory Ozone Analyzer
    R828112C080 Mechanism of Oxidative Stress from Low Levels of Carbon Monoxide
    R828112C081 Long-Term Exposure to Ozone: Development of Methods to Estimate Past Exposures and Health Outcomes
    R828112C082 Effects of Ambient Ozone on Healthy, Wheezy, and Asthmatic Children
    R828112C083 Daily Changes in Oxygen Saturation and Pulse Rate Associated with Particulate Air Pollution and Barometric Pressure
    R828112C084 Evaluation of The Potential Health Effects of the Atmospheric Reaction Products of Polycyclic Aromatic Hydrocarbons
    R828112C085 Mechanisms of Response to Ozone Exposure: The Role of Mast Cells in Mice
    R828112C086 Statistical Methods for Epidemiologic Studies of the Health Effects of Air Pollution
    R828112C087 Development of New Methods to Measure Benzene Biomarkers
    R828112C088 Alveolar Changes in Rat Lungs After Long-Term Exposure to Nitric Oxide
    R828112C089 Effects of Prenatal Exposure to Inhaled Methanol on Nonhuman Primates and Their Infant Offspring
    R828112C090 A Pilot Study of Potential Biomarkers of Ozone Exposure
    R828112C091 Effects of Concentrated Ambient Particles on the Cardiac and Pulmonary Systems of Dogs
    R828112C092 Cancer, Mutations, and Adducts in Rats and Mice Exposed to Butadiene and Its Metabolites
    R828112C093 Effects of Concentrated Ambient Particles in Rats and Hamsters: An Exploratory Study
    R828112C094I The National Morbidity, Mortality, and Air Pollution Study: Methods and Methodologic Issues
    R828112C094II The National Morbidity, Mortality, and Air Pollution Study: Morbidity and Mortality from Air Pollution in the United States
    R828112C095 Association of Particulate Matter Components with Daily Mortality and Morbidity in Urban Populations
    R828112C096 Acute Pulmonary Effects of Ultrafine Particles in Rats and Mice
    R828112C097 Identifying Subgroups of the General Population That May Be Susceptible to Short-Term Increases in Particulate Air Pollution
    R828112C098 Daily Mortality and Fine and Ultrafine Particles in Erfurt, Germany
    R828112C099 A Case-Crossover Analysis of Fine Particulate Matter Air Pollution and Out-of-Hospital Sudden Cardiac Arrest
    R828112C100 Effects of Mexico City Air on Rat Nose
    R828112C101 Penetration of Lung Lining and Clearance of Particles Containing Benzo[a]pyrene
    R828112C102 Metabolism of Ether Oxygenates Added to Gasoline
    R828112C103 Characterization and Mechanisms of Chromosomal Alterations Induced by Benzene in Mice and Humans
    R828112C104 Acute Cardiovascular Effects in Rats from Exposure to Urban Ambient Particles
    R828112C105 Genetic Differences in Induction of Acute Lung Injury and Inflammation in Mice
    R828112C106 Effects on Mice of Exposure to Ozone and Ambient Particle Pollution
    R828112C107 Emissions from Diesel and Gasoline Engines Measured in Highway Tunnels
    R828112C108 Case-Cohort Study of Styrene Exposure and Ischemic Heart Disease Investigators
    R828112C110 Effects of Metals Bound to Particulate Matter on Human Lung Epithelial Cells
    R828112C111 Effect of Concentrated Ambient Particulate Matter on Blood Coagulation Parameters in Rats
    R828112C112 Health Effects of Acute Exposure to Air Pollution
    R828112C113 Benzene Metabolism in Rodents at Doses Relevant to Human Exposure from Urban Air
    R828112C114 A Personal Particle Speciation Sampler
    R828112C115 Validation and Evaluation of Biomarkers in Workers Exposed to Benzene in China
    R828112C116 Biomarkers in Czech Workers Exposed to 1,3-Butadiene: A Transitional Epidemiologic Study
    R828112C117 Peroxides and Macrophages in the Toxicity of Fine Particulate Matter in Rats
    R828112C118 Controlled Exposures of Healthy and Asthmatic Volunteers to Concentrated Ambient Particles in Metropolitan Los Angeles
    R828112C119 Manganese Toxicokinetics at the Blood-Brain Barrier
    R828112C120 Effects of Exposure to Concentrated Ambient Particles from Detroit Air on Healthy Rats and Rats with Features of Asthma or Mild Bronchitis
    R828112C121 Field Evaluation of Nanofilm Detectors for Measuring Acidic Particles in Indoor and Outdoor Air
    R828112C123 Time-Series Analysis of Air Pollution and Mortality: A Statistical Review
    R828112C126 Effects of Exposure to Ultrafine Carbon Particles in Healthy Subjects and Subjects with Asthma
    R828112C128 Neurogenic Responses of Rat Lung to Diesel Exhaust
    R828112C130-I Relationships of Indoor, Outdoor, and Personal Air (RIOPA). Part I. Collection Methods and Descriptive Analyses
    R828112C132 An Updated Study of Mortality Among North American Synthetic Rubber Industry Workers