1.
Introduction and Summary
Authors
This chapter was prepared by the following individuals:
o Lawrence Baker, Ph.D., Department of Civil and Environmental Engineering, Arizona State University
o Tim Flood, M.D., Medical Director, Chronic Disease Epidemiology Section, Arizona Department of Health
Background
Over the past twenty years, this country has developed extensive regulations and policies to improve the environment. While many of these policies have resulted in improvements, other policies were developed inefficiently, in a crisis mode. For example, the 1972 Clean Water Act called for zero pollution. Two decades later we know it is a goal that could never be met.
The concern for more efficient policies has arisen for several reasons:
o The costs of environmental protection are significant and are expected to increase from about 2.1% and the Gross National Product (GNP) in 1980, to a predicted 2.8% of the GNP in the year 2000 (C & E News, 1991).
o The effectiveness of certain programs is questionable.
o Although major reductions of environmental pollution have been accomplished at reasonable costs, further reductions are likely to be far more expensive.
The Environmental Protection Agency (EPA) recognized this problem in the mid- 1980s. In an effort to make the agency less reactive and more effective at addressing environmental risks, it conducted the first nation-wide ranking of environmental risks based on scientific assessments (EPA, 1987; 1990). A notable conclusion of these assessments is that public perception and scientific assessment of risks are often different.
Since this nationwide study was published, nearly 20 states, including Arizona, have undertaken studies to analyze and rank environmental risk factors.
In Arizona, the Arizona Comparative Environmental Risk Project (ACERP) was created to develop a comprehensive ranking of environmental hazards specific to Arizona.
The ACERP effort to research and produce the environmental risk report was divided between three Technical Committees:
o Ecosystems Technical Committee
o Human Health Technical Committee
o Quality of Life Technical Committee
The role of the Committees was to develop risk assessments for environmental issues identified by the ACERP Steering Committee as important to Arizona. The Committees then ranked the issues with respect to their comparative risk.
The Technical Committees included about 20 persons each, with each member representing a broad range of technical expertise. Committee members were chosen through an application process and appointed by the Governor.
Human Health Committee
The Human Health Committee included technical experts in public health, toxicology, medicine, chemistry, hydrology, and environmental engineering. They represented universities, state, federal, and county governmental agencies, Indian tribes, consulting firms, the medical practice, and industrial groups. The technical assessments and ranking of risk factors occurred over an 18-month period, from August 1993 through May 1995.
Methodology
Creating an Issues List
One of the first tasks of the Committee was to determine what environmental hazards would be ranked, and to then create an Issues List from them.
In a broad sense, the environmental risks to human health might include all accidents, murders and assaults, communicable diseases, and many other external influences that might alter one's health. At the other extreme, one could consider environmental risks to be only those that could be regulated by traditional environmental agencies.
The Committee compromised when it developed the Issues List. It excluded, for example, the following issues:
o Hazards that would be considered largely voluntary, such as smoking. Thus, environmental tobacco smoke was a ranked issue, whereas smoking itself was not.
o Certain other risks, such as automobile accidents and communicable diseases because they have been well characterized elsewhere (McGinnis & Foege, 1993).
The final Issues List includes a broad range of potential physical, chemical, and biological threats. Some of these, including most chemical threats, are regulated. Others, such as allergens, exposure to ultraviolet light (sunlight), and natural hazards, are not.
These issues are discussed in the following chapters of this section. For perspective, the Committee has included a comparison table of ranked environmental risks relative to other human health risks in Appendix B.
Developing Risk Categories
The development of risk categories was completed in two parts.
Part One: Performing a Scientific Risk Assessment
As the first step, Committee members performed a scientific assessment for each potential hazard. The Committee used four approaches to estimate the number of people affected by an environmental risk factor. For some issues, more than one method was used. The four approaches are described in the following categories.
Approach 1: Actual Counts of Affected Persons
Certain human health impacts could be readily assessed by examining records of morbidity (illness) and mortality (death).
If the cause of the disease was well-established, the assessment was easy. For example, death records reveal precisely how many people die each year from venomous animal bites and from infectious diseases caused by animal vectors (e.g., the plague).
In this study, the following four threats were assessed using actual counts:
o Acute effects of accidental chemical releases
o Animal vector-borne diseases
o Natural hazards
o Plant poisonings
Approach 2: Toxicology Assessment
Estimates of cancer health hazards and non-cancer health hazards were calculated using this approach. These hazards are described as follows.
o Cancer: For known or suspected carcinogens (cancer-causing chemicals) the Committee used what is known as a "linear, zero-threshold model" to determine the cancer threat associated with various levels of exposure.
In this model, the threat of cancer increases linearly with increasing chemical exposure. The slopes of these lines, called potency factors, are determined from experimental studies with animals and from human studies.
A key assumption underlying this model is that there is no chemical exposure level below which there is absolutely no cancer risk. Although this assumption is being debated in scientific circles, this model is widely used and accepted by most regulatory agencies.
Finally, published potency factors tend to be conservative. Yet, because of the model's limitations, most scientists tend to believe that these figures overestimate the cancer risk associated with particular chemicals.
o Non-Cancer: For many chemicals there is a strong relationship between exposure and the development of disease. Non-carcinogenic chemicals are widely recognized as having thresholds or exposure levels below which no ill effect can be observed. For example, although elevated levels of ozone can cause eye irritation and coughing, very low levels cause no harmful effect, even with prolonged exposure.
Finally, the following health hazards were assessed using toxicological models:
o Airborne particulates (PM-10)
o Criteria air pollutants (SO2, NO, CO)
o Drinking water
o Lead
o Natural radiation
o Ozone
o Radon
o Surface water
Approach 3: Apportionment of Risk Based on Published Reports
For some issues there are no data specific to Arizona. For example, the Committee could not determine how many Arizona workers are exposed to hazardous chemicals in their jobs, or what levels of exposure are encountered. As a result, it is not possible to present a chemical-by-chemical description of the risk of cancer to workers in Arizona. Instead, the Committee used a method called apportionment.
Apportionment uses the findings of large epidemiological studies, generally conducted on a multi-city or national basis, to develop estimates of risk from various factors. The Committee applied this risk factor to Arizona to estimate how many Arizonans are at risk.
o For example, to estimate the risk of food poisoning, the Committee could not rely upon reported cases of food poisoning in Arizona because the number of reported cases is almost certainly less than the actual number of food poisonings.
Instead, researchers took an estimate of the number of food poisonings for the entire United States each year (6.5 to 24 million) and assumed that this number of cases was distributed evenly.
Since Arizona has 1.5% of the United States population, researchers estimated that Arizona also experiences the same proportion of food poisonings.
This resulted in an estimate of 97,500 to 360,000 food poisonings per year in Arizona, with a midpoint estimate around 200,000.
In this study, the following hazards were assessed using apportionment of risk:
o Asbestos
o Environmental tobacco smoke (ETS)
o Food-related illness
o Lead
o Teratogens
o Ultraviolet radiation
o Workplace exposure
Approach 4: Educated Guess
For some issues the Committee estimated a best guess of threat from each agent.
For instance, although the number of Arizonans drinking water contaminated with coliform bacteria is known, the Committee did not find a clear relationship between drinking contaminated water and contracting a waterborne disease.
However, in most documented cases of waterborne diseases caused by viruses or bacteria, the coliform standard was violated. Thus, the Committee concluded that the occurrence of a large number of water systems that exceed the coliform standard presents a significant human health threat.
In this study, the following risks were assessed using educated guesses:
o Drinking water (microbial risk)
o Environmentally-induced asthma
o Noise
o Underground storage tanks
Uncertainties and Limitations in Scientific Assessments
Four general sources of uncertainty were present in most of the risk assessments performed by the Committee:
o Estimates of cancer potency factors and other exposure response relationships were assumed to be accurate for all substances considered. For cancer risks, as mentioned above, there is increasing doubt among scientists regarding the validity of the zero threshold model.
o For some assessments, the Committee had good sources of exposure data. Data for other assessments, however, were either limited or non-existent, and other methods had to be used to estimate risk.
o A number of risk estimates were extrapolated from non-Arizona data. The non-Arizona studies were generally large epidemiological studies conducted within several cities or the entire U.S. These risk estimates may not accurately reflect the risk presented in Arizona because of differences in exposures or population characteristics.
o The Committee was conservative in attributing the cause of illness to a particular chemical or other hazard. With the possible exception of cancer risks, the magnitude of other risks is probably understated.
Part Two: Performing an Issues Assessment
After completing the Risks List, the Committee ranked the risks according to the following factors:
o The number of people affected and the severity of the outcome (ranging from mild, to temporary illness, to death)
o The degree of confidence the Committee felt in its technical analysis
o The disproportionate effect on some parts of the population
o Moral judgment
The Ranking Process
The technical assessments provided the technical core for the Committee's ranking of environmental issues.
At this point, the Committee could have taken one of two approaches:
o Conduct (at least in theory) an economic analyses such as a cost-benefit analysis. This would have allowed the Committee to estimate the cost of reducing various health risks, compared to the benefits of improved health (e.g., longer life). Although conceptually simple to understand, cost-benefit analyses have limitations:
It is necessary to assign a dollar value to human life and various ailments. This is relatively easy to do for death--economists involved in risk assessment often use values of $1-$10 million per life lost. Assigning costs for milder or long term illness, however, is more tenuous. For instance, to develop a cost-benefit analysis for urban ozone, researchers would have to assign a cost to increased coughing, a symptom of high ozone levels.
The costs of remedying the health risks must be known. While easier to accomplish than assigning the benefit of improved health, these costs are still fraught with uncertainty, particularly for low level exposures.
Cost-benefit analyses recognize only economic issues, not moral concerns such as fairness and equity.
Because of these limitations, the Committee chose to develop a comparative ranking of environmental issues affecting human health. This method used issue-by-issue technical assessments, but the ranking was tempered by moral judgments of the Committee. Factors that were considered in the final ranking include:
o Severity of outcome: The outcome of some environmental hazards can range from mild to catastrophic. The Committee defined three levels of outcome:
Adverse: Outcomes that are short-lived, moderately severe, and treatable or manageable. Examples include eye irritation, hay fever, and mild diarrhea.
Serious: Outcomes are chronic, often irreversible, difficult to manage, and greatly impair one's quality of life. An example would be a disability that would prevent one from working.
Catastrophic: Outcomes are a shortened life expectancy or severe loss of one's quality of life. Examples would include death or life- threatening cancer.
o Age at which health risks are incurred: For a given level of severity, a health problem has greater consequence if it affects a young person rather than an older person, particularly if the problem is chronic or irreversible.
o Affects on high-risk populations: The Committee recognized that certain hazards might fall disproportionately on small segments of the population. Thus, while the risk to the general population of Arizonans may be small, the risk to a particular group of individuals might be very high. Committee members were particularly sensitive to the issue of equity of environmental impacts on different socioeconomic and racial groups.
o Uncertainties: As noted above, there are considerable uncertainties in many of these analyses. These uncertainties were recognized in the final ranking of the issues.
Ranked Environmental Risks To Human Health
Following is the Committee's ranking of environmental risks to human health in Arizona. These risks are divided into the following three categories. Within each category, issues are listed in alphabetical order.
o High
o Medium
o Low
There was a strong consensus among most Committee members regarding ranking except for that of occupational exposures, which generated considerable disagreement.
High Risk Category
Allergens and Cocci (Valley Fever)
Central and Southern Arizona have growing seasons more than 10 months long, allowing a proliferation of pollens from trees, grasses and other plants to be dispersed among the populace. These substances result in allergic responses among hundreds of thousands of Arizonans.
Indigenous to the desert soil in Central and Southern Arizona is a fungus called Coccidioides immitis, or "cocci." Cocci spores are dispersed in the air and inhaled by people, causing subclinical infection in thousands of Arizonans, clinical infection in hundreds, and approximately 30 deaths. Serious illness occurs in many persons at risk, such as dark-skinned persons and those with impaired immune responses.
Despite its status as a reportable disease in Arizona, cocci is under-reported. For example, vacationers in Arizona may contract the disease here and return to their home states, where the illness may not be recognized by local physicians.
Environmental Tobacco Smoke (ETS)
Non-smoker exposure to chemicals and irritants from second-hand and sidestream smoke can cause a number of adverse effects, including increases in heart disease, lung cancer, respiratory tract infections, asthma, and infant mortality.
To study this hazard, Committee researchers extrapolated EPA data for the U.S. population and applied this data in proportion to the Arizona population and number of adult smokers. They also used ADHS data for infant mortality. The predicted annual consequences of environmental tobacco smoke to non-smokers include:
o 31 infant deaths
o 35 lung cancer deaths
o 189 to 239 heart disease deaths
o 2,200 to 4,400 respiratory tract infections in children
o 2,950 to 14,700 asthmatic children with increased frequency of attacks and severity of symptoms
o Increased risk of heart disease
o Increases in respiratory infections and distress
Uncertainties in these results include a lack of detailed exposure data in Arizona and the underlying assumptions and methods used in the EPA report.
Fine Particulate Matter in Air
Airborne particulates are mixtures of solid and liquid droplets of materials that vary in size and origin. Since only very small particles (particulate matter less than 10 microns in size, called "PM-10") can be inhaled into the respiratory tract, they are of the most biologically threatening to humans.
The smallest of the particles (less than 2.5 microns in size) are thought to be the most damaging since they are breathed deeply into the lungs. Adverse health effects resulting from exposure to fine particulate matter may include:
o Increases in hospital admissions from respiratory problems
o Increases in emergency room visits for asthma and chronic obstructive pulmonary disease
o Asthma episodes
o Lower and upper respiratory symptoms (including cough)
o Death
The causal link between exposure to fine particulate matter and adverse health effects is well established. Making quantitative estimates of the actual number of these events and health effects that may occur in Arizona as a result of particulate exposure, however, is difficult.
While numerous studies have found statistical associations between fine particulate pollution and mortality, none of the epidemiological studies prove a causal effect. When considered together, however, the studies indicate that a causal association exists, particularly among susceptible subgroups such as the elderly and those already suffering from a cardiopulmonary or respiratory disorder.
The methodology used to estimate the number of deaths that may occur in Arizona due to particulate pollution uses recent published research, information from the ADHS annual vital statistics reports, and air quality data from the ADEQ (1991). The method that was selected comes from Dockery and Pope (1994).
The estimated number of premature deaths due to PM-10 in Arizona is 963 per year. Those affected are primarily the elderly and those already suffering from a cardiopulmonary or respiratory disorder.
Uncertainties in the estimate include the methods used to derive the dose-response number and the assumption that there is no threshold of effect. The estimate includes particulate matter from natural and man-made origins.
Food Safety
The four sources of risks considered for food safety were:
o Pesticide residues
o Microbial contamination
o Naturally-occurring toxins
o Antibiotics used on animals
Data for Arizona were extrapolated from national statistics because there is known under-reporting of food poisoning in Arizona.
The extrapolation indicates that:
o 100,000 to 369,000 Arizonans get food-borne illnesses annually.
o The majority of the illnesses resulted in minor symptoms, such as simple diarrhea, and would not affect normal activities of daily living.
o 140 Arizonans die each year from food-borne illnesses.
o Many of the deaths occur in persons who are immuno-deficient, including the aged and infants.
The Committee had no information about the types and amounts of pesticides found on foods consumed in Arizona. This lack of data limited the Committee's ability to conduct the risk assessment.
Surveys performed across the country by the Food and Drug Administration (FDA) show that there are minute, but now measurable, amounts of pesticide residues on about 40% of the foods tested.
Pesticides that have been banned for use on foods by the FDA were found in about 5% of imported food samples. The amounts of pesticides reached violative levels on less than 1% of the samples.
Since 1990, when laws mandated the reporting of pesticide poisoning in Arizona, health professions have reported no instances of consumers becoming ill by consuming foods with pesticide residues.
By applying the results of an analysis of pesticide residue levels conducted by the EPA to Arizona's population, the Committee estimated that there may be 1.3 to 8.6 additional cancer deaths per year as a result of people consuming foods with pesticide residues.
However, this assessment assumes that humans respond in the same way as laboratory animals that have been exposed to much larger doses.
The EPA notes that the true risk may be as low as zero additional cancers. An effect, if one occurs at all, would likely be immeasurable at the consumer level because the amount of pesticides consumed is so small and the link between pesticides and adverse effects has been so difficult to establish.
The Committee is confident about this assessment.
Dioxin
The most recent EPA dioxin report indicates that the major route of human exposure is through ingestion of foods containing minute quantities of dioxin-like compounds.
It is known that essentially all U.S. residents are exposed to a predictable range of dioxin because of the uniformity of levels in the food supply. While the effect of this exposure level is not known for non-cancer end points, an estimation can be made of the excess cancer risk based on annual dose-response models. This calculation would predict an upper bound of five cases per year in Arizona.
Ionizing Radiation Excluding Radon
Everyone is exposed to several natural sources of ionizing radiation, including:
o Cosmic radiation
o Radiation from naturally-occurring radioactive material in the earth
o Naturally-occurring radioactive material which is ingested and inhaled
The predominant health effect from this radiation exposure is a higher risk of cancer.
To assess the risks, the Committee used the national average annual radiation doses, estimated by the National Council on Radiological Protection. Potency factors for radiation were obtained from estimates by the International Commission on Radiological Protection, which studied human populations exposed to large doses of radiation.
In Arizona, the Committee estimated that approximately 170 cancer deaths may result each year from natural radiation sources other than radon.
The main uncertainty in this assessment is extrapolating the risk from high dose exposures to natural exposures. No reliable studies have demonstrated risk at natural background levels.
Lead Poisoning from Environmental Exposures
Children with elevated blood lead levels are at risk of developing neurological damage, including peripheral neuropathy, hyperactivity, and cognitive deficits (decreased IQ).
When blood lead levels in young children reaches 10 microns/dL, it is considered the "action level." This level indicates that a response from the government is or should be forthcoming.
An estimate of the number of Arizona children with elevated blood lead was made using an EPA model, data from a statistically-based national survey of blood lead levels, and non-statistical data on blood lead levels in Arizona children.
In Arizona, the estimated number of children with blood lead levels in excess of 10 microns/dL is 6,350.
o An estimated 235 of these children may have severely elevated blood lead (greater than 20 microns/dL).
Considerable progress has been made in reducing childhood exposure to lead through the phase-out of leaded gasoline, lead-soldered cans, and lead-based paint. However, residual lead contamination in houses with old lead-based paint remains in some residential areas in Arizona.
The EPA model predicts that up to 30% of very young children living in homes with lead-based paint may have blood lead levels above the action level. While there are a number of media through which children may be exposed to lead, eliminating exposure to lead-based paint and lead-contaminated soils would substantially reduce lead exposure in children.
Radon
Radon is a naturally-occurring radioactive gas which accumulates in indoor air. Radon levels vary with building construction, ventilation, and building site geology. Exposure is assumed to increase the risk of lung cancer.
The risk assessment for radon was conducted using measurements of radon in Arizona homes with radon potency factors from the EPA, National Research Council, and the International Commission in Radiological Protection. These risk factors were derived from studies of lung cancer in underground miners exposed to high doses of radon.
The Committee estimates that approximately 250 Arizonans die of lung cancer each year from residential radon exposure. The hazards to smokers appears to be ten times greater than for non-smokers.
The main uncertainty in the risk assessment is applying the extrapolation of cancer risks for the miners to cancer risks for the general population. The general population experiences much lower exposures than the underground miners.
This extrapolation has been questioned, especially because of differences between mines and homes. A difference which may affect risk includes the presence of silicon, metals, and organic vapors in mines.
Ultraviolet Radiation (UVR)
Ultraviolet radiation (UVR) in sunlight is considered a high risk since it is a recognized cause of skin cancer and premature aging of the skin. Arizona receives a high amount of sunlight compared to other states. Infants, children, and fair- complexioned persons are at increased risk because they burn easily.
The Committee estimates that exposure to UVR is associated with about 12,000 skin cancers each year in Arizona.
o At least 200 of these skin cancers are melanomas.
o About 90 persons die each year from skin cancers related to the UVR exposure.
o Melanoma rates in southern Arizona have increased over the past two decades. The increase is thought to be caused by intentional exposure and clothing habits.
The main uncertainty about this issue is the Committee's assumption regarding the proportion of skin cancers attributable to UVR: 50% of the melanomas and 90% of non-melanoma cancers.
Similarly, many scientists are worried that chlorofluorocarbons may deplete the atmospheric ozone layer and increase the rate of skin cancer. While major ozone depletion has occurred in the Antarctic and Arctic regions, and most scientists attribute this to chlorofluorocarbons, changes in the ozone layer above Arizona have not yet been observed.
Medium Risk Category
Drinking Water
The drinking water risk assessment included:
o Public water supplies; used by 95% of Arizona's population
o Private domestic wells; used by 5% of Arizona's population
A comprehensive water quality data base is available for public water systems, but very little data are available for private wells.
Findings for the study of public water systems in Arizona include:
o Around 10% of Arizonans who drink public water supplies are exposed to microbial contamination in excess of federal and state standards. Most of these violations are infrequent.
o About 2% of the population served by public water supplies drinks water that regularly exceeded the standard by more than three violations per year.
o Major outbreaks of waterborne disease in Arizona are infrequent; only one major outbreak has occurred since 1986.
Individuals who drink microbially-contaminated water probably experience a higher incidence of gastrointestinal disturbances resulting in stomach ache and diarrhea.
Outbreaks of viral and bacterial waterborne diseases are nearly always accompanied by violations of the coliform standard. However, the coliform standard is not a good predictor of outbreaks caused by protozoan diseases such as Cryptosporidia.
The Committee did not find any information on microbial contamination of domestic wells.
The Committee assessed the cancer risk associated with drinking water by using a zero-threshold model which may overestimate risks at very low exposure levels.
Using that model, the Committee estimated that no more than 20 cancers per year were caused by drinking water contaminants in public water supplies.
o These contaminants were primarily arsenic and trihalomethanes.
The cancer risk from consuming arsenic in public water supplies was much higher in Yavapai County than in other parts of the state.
The major non-cancer risk associated with drinking water results from exposure to elevated nitrate concentrations. About 12,700 Arizonans are served by public water supplies that regularly exceed the maximum contaminants level for nitrate.
Many domestic wells are also contaminated with nitrate. The maximum level is based upon the risk of infants getting methemoglobinemia, which is a type of blue- baby syndrome that can lead to death.
Although methemoglobinemia has been observed in infants drinking water with 10 mg/L nitrate, it is very rare, even at much higher nitrate concentrations.
One reason for the lack of known cases of methemoglobinemia in Arizona may be that public water systems are required to notify users when there are maximum contamination level violations. This notice informs people of the risks to infants of drinking high-nitrate water and, presumably, leads parents to use alternative sources such as bottled water for their infants.
Hazardous Air Pollutants (HAPs)
Over 1,000 chemical compounds and elements have been identified as potential hazardous air pollutants (HAPs). These pollutants, also known as "air toxins," are released into the air by a variety of sources such as industry, vehicle emissions, agricultural activities, and home heating.
Unfortunately only a fraction of HAPs are measurable at levels that occur in the atmosphere. Thus, modeled estimates of ambient levels and consequent public exposure were used.
Using this approach, the Committee estimates:
o 24 cancer deaths per year occur from exposure to HAPs.
16 occur from exposure to indoor air
1 - 8 occur from exposure to outdoor air
The assessment has high uncertainty because of a lack of reliable human exposure data and the absence of risk information for many suspected HAPs.
Medical Exposure to Ionizing Radiation
Use of x-ray equipment and radioactive material in medicine results in the patient being exposed to ionizing radiation. The predominant health effect from ionizing radiation exposure is excess risk of cancer.
In the assessment of this risk, the Committee used the average annual medical radiation dose for the nation, estimated by the National Council on Radiological Protection. Similarly, potency factors for radiation were obtained from estimates by the International Commission on Radiological Protection. These risk factors were estimated from human populations exposed to large doses of radiation.
In Arizona, it is estimated that approximately 50 cancer deaths may result each year from medical radiation exposure.
Natural Hazards
Natural hazards are events that present unique threats to human health, including flooding, lightning and temperature extremes.
Because these outcomes are frequently catastrophic, death certificates for selected causes of death during the 1990-1993 period were analyzed. During this period:
o The annual mean number of deaths due to natural hazards was 45.
91% were due to the effects of extreme temperatures
The Committee is highly confident of this estimate.
Occupational Exposure to Toxic Materials
This report estimated the risks associated with exposure to toxic materials in the workplace.
Data in the report were derived from two sources:
o A report by the Industrial Commission of Arizona that estimates the number of work-related illnesses in the state. The report was derived from sampling workplaces in Arizona.
For the year 1991, the Industrial Commission report estimates that there were 1,172 illnesses related to the workplace environment. These illnesses were not related to injury or repeated trauma.
Of the 1,172 illnesses, there were:
62 poisonings
377 respiratory conditions due to toxic agents
42 dust diseases of the lung
o A national report published in 1981 by Doll and Peto, who address the issue of work-related cancers. This landmark report concludes that about 4% of all cancer deaths in the U.S. were related to exposures to chemicals in the workplace.
The Committee explored other sources for information on work-related cancers, including the Industrial Commission of Arizona, State Workers Compensation, the Arizona Division of Occupational Safety and Health, and the ADEQ. Detailed information on this topic was not available, however, so the Committee applied Doll and Peto's figure of 4% to Arizona's 7,648 cancer deaths in 1993.
o In Arizona, according to the calculation, 305 cancer deaths could be attributable to work-related exposures in 1993.
While many scientists cite Doll and Peto's study, there have been surprisingly few comparative reviews of the etiology of cancer similar to it. Much has changed since 1981:
o The workforce has become less industrialized.
o Workplace exposure levels have dropped in response to restrictive regulations.
o Manufacturers have voluntarily eliminated their use of many toxic chemicals, switched to less toxic chemicals, or adopted closed systems that reduce worker exposures.
o New technologies have introduced new chemical agents into the workplace.
Additional studies have been published that both strengthen and weaken concern about the relationship between workplace chemicals and cancer.
Given the uncertainties of the effect of the changes over the past 14 years, the Committee has a high degree of uncertainty about quantifying cancer and the workplace.
Low Risk Issues
Accidental Releases of Toxic Substances
Accidental releases of hazardous substances can cause adverse health effects among exposed individuals, especially among first responders like firemen and hazardous materials teams, and among employees and members of the general public.
This analysis uses data from the ADEQ Emergency Response Unit and from Hall, et al. (1994) at the Agency for Toxic Substances and Disease Registry. The data are used to evaluate the potential health effects as a result of exposure to hazardous substances during emergency events in Arizona.
As a result of the study, the Committee made the following estimates for Arizona:
o 75 persons may be injured each year during emergency events involving hazardous substances.
o 127 persons may experience some of the following health effects each year due to emergency events involving hazardous substances:
Respiratory irritation
Eye irritation
Nausea
o The estimated number of annual deaths as a result of these events is 0.5.
Animal Vectors of Human Diseases
The major, serious diseases transmitted by animals to humans include:
o Rabies by bats, skunks, dogs, cats
o Plague by rabbits and other rodents
o Hantavirus pulmonary syndrome by deer mice and other rodents
o Encephalitis borne by mosquitoes (Culix tarsalis)
o Brucellosis from unpasteurized dairy products
Hantavirus Pulmonary Syndrome
Hantavirus Pulmonary Syndrome was identified in 1993. An aggressive disease control program at ADHS has kept the number of deaths from all animal vectors to about three per year. The Committee has high confidence in this estimate.
Asbestos
Asbestos refers to a group of fibrous minerals that have enjoyed wide use because of their high tensile strength, resistance to chemical degradation and incombustible nature. They were used primarily as insulation, fire-proofing agents and in brake products.
Asbestos can cause lung cancer and pleural mesothelioma, and possibly cancer of other organs like the larynx and gastrointestinal tract.
Studies show that current exposure to asbestos can have the following effects:
o Exposure in schools between ages 5 and 18 might add 0.07 to 0.68 cancers per year.
o Exposure in public buildings between ages 25 and 45 might add 0.07 to 0.67 cancers per year.
o Occupational exposure between ages 25 and 45 might add 0.25 cancers per year.
By making a worst case assumption and combining all the high-end estimates, the Committee estimated that there may be 3.43 cancers of lung and pleural mesothelium per year in Arizona due to asbestos. High-risk groups include installers of asbestos products like brake repairman, building repair personnel, and occupants of asbestos- contaminated buildings.
The risk of cancer among cigarette smokers exposed to asbestos is ten times higher than the risk to non-smokers.
Risk of asbestos contamination can be reduced by proper maintenance of asbestos- containing products such as buildings. Proper maintenance reduces dispersion of asbestos and reduces exposure.
CERCLA and WQARF Superfund Sites
As of fiscal year 1994, there were 63 CERCLA (federal superfund), WQARF (State of Arizona superfund), or Department of Defense superfund sites in Arizona.
o 31 sites are located in the Phoenix area
o 12 sites are located in the Tucson area
o 20 sites are located in the remaining portions of Arizona
The sites are primarily affected by groundwater contamination, although some have surface soil and surface water contamination.
Contaminated media at these sites include surface soils, subsurface soils, surface water, and groundwater. In addition, air may become contaminated at some sites through wind erosion of contaminated surface soils, or diffusion of organic contaminants from surface soils.
Groundwater is the medium most frequently contaminated at sites in Arizona.
The calculated incremental increase in the number of cancer cases in Arizona as a result of exposure to contaminants from waste sites was between 0.01 and 0.04 cases each year.
Uncertainties in the analysis combine to create uncertainty of approximately two or three orders of magnitude. Taking the extreme of the calculated range as point estimates, the actual number of excess cancer cases is likely to be less than one per year.
Criteria Air Pollutants Other than Lead and Fine Particulates
Criteria air pollutants include ozone, carbon monoxide, nitrogen oxides, and sulfur oxides. The main concern, however, is ozone.
Ozone
Ozone is both a naturally-occurring and a man-made gas. It has an electrical-like odor. It is the main oxidant in photochemical smog.
Ozone is a strong irritant that primarily affects the respiratory tract, with symptoms such as irritation of the skin, eyes and mucus membranes. Other symptoms include an increased respiratory rate, shallow breathing, cough, bronchitis, and pulmonary edema (Sittig, 1991). Neurological symptoms may include fatigue, dizziness, and headache.
The regions of Arizona that periodically approach or exceed the National Ambient Air Quality Standard for ozone include the Phoenix, Tucson and Yuma metropolitan areas.
The formula used in this study to calculate the ozone risk calculates the number of Minor Restricted Activity Days (MRADs) from outdoor ozone exposure.
o MRADs are events in which human activity is reduced, but not severely restricted. Health effects that may occur during MRADs include sore throat, mild cough, headache, chest discomfort, and eye irritation.
Applying Arizona data from 1993 (ADEQ, 1995) to the formula results in an estimate of about 1,600,000 minimal restriction activity days per year in Arizona as a result of exposure to outdoor ozone.
Uncertainties in the assessment include the dose-response estimate and the number of people exposed to elevated ozone levels.
Other Criteria Air Pollutants
Ambient levels of carbon monoxide, sulfur oxides, and nitrogen oxides found in Arizona generally would not result in adverse health effects.
Farm Worker Exposure to Pesticides
It was difficult to determine which pesticides are used in the state and how many workers are exposed. Therefore, the Committee used the following national EPA estimates:
o 20,000 to 300,000 illnesses each year are associated with occupational use of pesticides on farms.
The Committee applied these estimates to Arizona's population of farmers.
o Arizona has 50,000 farm workers, about 1% of the national total.
o In the most conservative estimate, there are about 20,000 pesticide illnesses nationally each year.
Given these estimates, Arizona should have at least 200 cases of pesticide illness each year. However, reported cases for 1994 are considerably fewer:
o Of 32 suspected pesticide poisonings, only 14 were agriculturally-related; of those 14, only four were confirmed.
Under-reporting of pesticide poisoning appears to be a problem.
Adequate toxicology data for many pesticides is also lacking, particularly to characterize chronic (long-term) risk among highly exposed individuals. The cumulative contribution of total intake of carcinogenic pesticides to overall cancer risk is also poorly understood. The potential health impacts of multiple, synergistic, or cumulative exposures are not well characterized, but such exposures occur and may pose a significant health risk.
The Committee ranked this issue as low, but the uncertainty is high because of the lack of available data.
Ionizing Radiation from Man-Made Non-Medical Activities
Everyone is exposed to small doses of radiation from a number of human activities. These doses come from occupational radiation exposure, uranium mines and mills, nuclear power generation, radiation from consumer products, weapons test fallout, and transportation of radioactive materials.
The main health effect from radiation exposure is excess risk of cancer.
To assess most of these sources of radiation exposure, the Committee used the following resources:
o Average annual radiation doses for the nation, as estimated by the National Council on Radiological Protection
o Data for the Palo Verde Nuclear Generating Station were used for nuclear power
o Data for Arizona uranium mines and mills
o Potency factors for radiation were obtained from estimates by the International Commission on Radiological Protection. These risk factors were estimated from human populations exposed to large doses of radiation.
The Committee estimated that 15 cancer deaths may result in Arizona each year from the radiation sources listed above. Of these 15, consumer products account for 13 of the deaths.
The predominate uncertainty in this assessment is from extrapolation of risk from high dose exposure. No reliable studies have demonstrated risk at low level exposure.
Leaking Underground Storage Tanks (USTs)
About 2,500 underground storage tanks have leaked some or all of their contents. Nearly all of these are petroleum storage tanks, and roughly 10-20% of these are believed to have contaminated the groundwater. Since public water supplies are tightly monitored, any exposure to these contaminants would occur by private domestic wells.
Noise
The public is increasingly aware of the problem of noise pollution.
Noise from a jet flyover at 1,000 feet is 103 decibels (Db). Average city traffic noise is 80 Db. The EPA has proposed a sound level of 55 Db in neighborhoods as protective of public health.
Studies of human volunteers have tended to support a relationship between noise and diastolic blood pressure elevations in both normotensive and hypertensive individuals.
The Committee's educated guess is that noise raises the prevalence of hypertension by 2%. If so, there are about 8,944 such cases of blood pressure elevations in Arizona.
Resource Conservation and Recovery Act (RCRA) Sites
The Resource Conservation and Recovery Act (RCRA) was passed in 1976 to safely handle and dispose of hazardous waste nation-wide. The goals of RCRA are to:
o Protect human health and the environment
o Reduce waste and conserve energy and natural resources
o Reduce or eliminate the generation of solid and hazardous waste as expeditiously as possible
The health risk analysis for exposure to emissions from transportation and storage disposal facilities and from generator activities uses:
o Risk information developed by EPA Region IX
o Information about the number and types of waste facilities and generators in Arizona, using the EPA Region IX RCRIS database (ADEQ, 1994)
The analysis uses risk calculations developed by EPA for each facility category (USEPA, 1990).
The estimated incremental increase in the number of cancer cases as a result of exposure to contaminants from RCRA facilities in Arizona is approximately 0.04 cases/year.
Assumptions in this analysis combine to create uncertainty of approximately two or three orders of magnitude (high uncertainty). Taking 0.04 cases/year as a point estimate, the actual number of excess cancer cases is likely to be less than one per year.
Surface Water Contact
Potable use of untreated surface water is limited in Arizona, but probably accounts for several hundred cases of Giardiasis per year. Some dermal contact and incidental ingestion of contaminated surface water may occur at Lake Havasu or in the Middle Gila River downstream from Phoenix.
The potential for contamination of surface waters is illustrated by the extensive recent bacterial contamination at Lake Havasu.
Issues Not Ranked
Health Effects of Exposure to Electromagnetic Fields
The public is exposed to electromagnetic energy in a wide range of frequencies including microwaves, radio-waves, and low frequency fields from the transmission and use of electric power.
Recently, exposure to electromagnetic fields from transmission wires and use of electric power has been linked to childhood leukemia and other cancers, although these possible effects remain controversial.
Results of epidemiological studies have been inconsistent, and studies that demonstrate positive correlations have been criticized for inadequately describing the fields to which individuals were exposed and any possible confounding factors.
Relative risk factors reported have been less than three, with large confidence intervals. As a result of the controversy surrounding potential health effects of exposure to electromagnetic fields, the Committee has decided that it is premature to conduct a comprehensive risk assessment on this issue.
Reproduction Problems
At this time it is not possible to accurately estimate the number of cases of reproductive problems that occur as a result of environmental factors.
Scientists report that infectious diseases can cause miscarriage and about 2% of birth defects. Exposure to medicines and other environmental chemicals has been associated with about 1.5% of birth defects.
The Committee, however, judged the current information to be inadequate to estimate the number of adverse reproduction outcomes that result from exposure to environmental chemicals. Therefore, this issue was not ranked.
Transboundary Exposures
Information concerning transboundary exposures between Mexico and the U.S. is scanty. The Committee felt that there was insufficient data with which to make an assessment and ranking.
Summary and Comparison of Risks
The table in Appendix B shows a summary of some of the catastrophic and non- ranked environmental health risks described above. Catastrophic outcomes for several other human health risks are presented for comparison. As shown in Appendix B, some highly-ranked environmental risks are comparable in magnitude to several well-documented health risks that have traditionally been major focal points for various government agencies involved with improving human health.
Deaths from Environmental Hazards
Approximately 30,810 Arizonans died in 1992. Ranked environmental risks, including both cancer and non-cancer, caused or contributed to around 7% of all these deaths.
Cancer Risk
Of the 30,814 Arizonans who died in 1992, there were 7,331 who died of cancer. Ranked environmental health risks resulted in no more than 934 cancer deaths, about 13% of all cancer deaths for 1992. It is significant that over one-half of these are the result of such non-chemical risks as radiation from radon, UVR, and natural ionizing radiation.
Non-Cancer Catastrophic Health Risks
Catastrophic health outcomes other than cancer are also significant. Of particular note is the high number of premature deaths that result from fine particulate air pollution events. Although the number of deaths is uncertain, the evidence that PM- 10 events cause premature mortality is growing.
Many on the Committee were surprised at the magnitude of food poisoning, but the uncertainty of this estimate is very low. Much of the food poisoning occurs in the home.
Several lines of evidence support the contention that between 2-3% of Arizona's children have elevated levels of lead in their blood (greater than 10 microns/dL). Several hundred have blood lead levels that should cause clinical symptoms of toxicity (20 microns/dL). Results from a model-based study indicate that approximately 30% of children living in older homes with lead-based paint might experience elevated blood lead levels.
Use/ Misuse of Environmental Risk Ranking
A comparative analysis of environmental risks to human health is one of many tools that should be used in developing priorities for environmental protection.
The information provided in this report will be used by the Public Advisory Committee (PAC), which will also review results from the Quality of Life and Ecosystems Technical Committees. The PAC will also consider broader moral issues as well as economics in developing its recommendations for future environmental policy in Arizona.
The Committee offers the following points regarding the appropriate use and misuse of the results of this study:
o The results are a snapshot of environmental risks to human health, taken in the early 1990s.
Just because an issue is ranked low does not mean one can assume that regulations regarding that risk should be loosened. For example, one reason that pesticides present a very modest risk is because an extensive regulatory framework restricts the use of pesticides that might pose greater risk. Because of this, the use of pesticides today is far safer than it was in the past.
Similarly, since we have not incurred outbreaks of typhoid and cholera in recent years in Arizona, one might incorrectly conclude that chlorination of public water supplies is no longer necessary. If we decided to not regulate chlorination, we would quickly discover that these deadly diseases would reappear.
o Conversely, just because an issue is ranked high does not necessarily mean that it should receive high priority.
The Committee made no attempt to evaluate the costs of reducing these risks, and it may be that public funds might be spent more effectively on health issues that the Committee did not evaluate. For example, many public health officials agree that far greater health risks are caused by voluntary actions such as smoking, over-consumption of alcohol, and over-eating than by environmental risks.
Programs to reduce these voluntary risks may be more cost-effective in terms of cost per life saved or improved than programs to reduce some of the highly ranked environmental risks.
o The Committee did not consider possible direct deleterious effects of imposing regulations to reduce high-ranked environmental issues.
For example, a policy to reduce air pollution by increasing bicycle commuting might result in more accidental injuries and deaths of cyclists than the illness and death caused by the air pollution.
o Moral judgment was involved in the Committee's ranking. Those involved with developing environmental regulation should dwell further on moral issues, such as generational and racial equity, the balance between governmental protection from the actions of our neighbors versus individual rights, and the proper relationship between humans and their environment.
Need for Further Research
Further research needs to be conducted on several issues. Some of these issues would be better addressed at the national level, while others could be addressed within the state.
National-Scale Issues
o Cancer risk assessment. A major uncertainty in human health risks to carcinogens is the "zero threshold" concept. This issue is being addressed by toxicologists around the country, and it seems likely that a better model of cancer toxicology will evolve over the next decade.
o Occupational exposure. The Committee was surprised that there are no national data on occupational exposures to chemicals. Its assessment of risk was based on a single major review of the epidemiology of occupational risks written in 1981. Given the potential significance of health risks caused by prolonged exposure to multiple chemicals in some work environments, better information on worker exposure is needed.
o Particulate air pollution. The evidence that fine particulate matter causes disease is growing, but models to predict the effects of PM-10 have large uncertainties.
o Drinking water microbes. The coliform test is a fairly crude predictor of the potential of waterborne disease outbreaks. A better microbial indicator would greatly improve our ability to predict the occurrence of waterborne disease.
State-Level Issues
o Background PM-10 Levels. A better understanding of natural background PM-10 concentrations in Arizona would be helpful in determining contributions of human activities to overall PM-10 levels. We also need to more fully understand the effects of particulates and other air pollutants on Arizona's population, which has a relatively high proportion of individuals with respiratory problems.
o Valley Fever. The epidemiology of Valley Fever should be better understood. There is some concern that measures taken to reduce dust at construction sites may contribute to the problem, but this has not been proven.
o Lead Poisoning. The Committee estimated that several hundred children had blood levels in excess of 20 microns/dL. Given the severity of the outcome, a statistically-based study of blood lead levels should be conducted to refine this estimate and better identify high-risk populations.