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Report on the Environment

Human Disease and Condition

Other Human Exposure and Health Topics

What are the trends in human disease and conditions for which environmental contaminants may be a risk factor including across population subgroups and geographic regions?

As discussed throughout the ROE, numerous human diseases and conditions have been linked with exposures to environmental contaminants, some more strongly than others. Identifying diseases that might be associated with environmental contaminants, and determining the existing data sources available for them, is a key part of the effort to better characterize links between environmental exposures and adverse health outcomes.

Tracking overall rates of disease in the nation, independent of exposure, enables the evaluation of disease patterns and emerging trends. It may identify diseases, conditions, and possible risk factors that warrant further study or intervention and can help identify where policies or interventions have been successful. Because the U.S. has a diverse population, an important component of such an analysis is identifying disparities among people of differing races and ethnicities, genders, education and income levels, and geographic locations.

EPA has selected those human diseases and conditions with well-established associations with exposures to environmental contaminants and for which national data are available, recognizing again that in most cases risk factors are multi-factorial and that the development of a particular disease or condition depends on the magnitude, duration, and timing of the exposure. The diseases and conditions addressed in this question are associated with the contaminant sources covered by the questions in the three media chapters (Chapters Air, Water, and Land) of this report. As described in the Human Health Chapter "Introduction", this question is not intended to tie human diseases and conditions to specific changes in the environment being measured at the national level. Covered health outcomes fall into the following five broad categories: cancer, cardiovascular disease, respiratory disease, infectious disease, and birth outcome. The reasons for the inclusion of each are highlighted below.

Cancer

The term “cancer” refers to diseases in which abnormal cells divide without control, losing their ability to regulate their own growth, control cell division, and communicate with other cells. Cancer is the second leading cause of death in the U.S. (General Mortality indicator). More than one in three people will develop cancer and nearly one in four will die of it.28,29 In response, scientists continue to explore the role that the exposure to environmental contaminants may play, along with other possible risk factors, in the initiation and development of cancer. Some environmental contaminant exposures are known risk factors for certain types of cancers. Examples include radon and lung cancer and arsenic and skin cancer. Though many types of cancer are suspected of being related to ambient environmental exposures, associations are not always clear because the etiology of cancer is complex and influenced by a wide range of factors. Many factors can increase individual cancer risk, such as age, genetics, existence of infectious diseases, and socioeconomic factors that can affect exposure and susceptibility.

Childhood cancers are dissimilar from cancers in adults and are therefore tracked separately. They affect different anatomic sites and may be of embryonic origin. Though overall cancer incidence rates are lower in children than in adults, childhood cancers are the third leading cause of death in children age 1-19 years.30 Children may be particularly susceptible to exposures in utero or during early childhood because their systems are rapidly developing and affected by evolving hormonal systems.31 As with many adult cancers, the causes of childhood cancers are unknown for the most part; environmental influences may be a factor and have been the subject of extensive research. Environmental exposures are difficult to evaluate because cancer is rare in children and because of challenges in identifying past exposure levels, particularly during potentially important time periods such as in utero or maternal exposures prior to conception.32

Cardiovascular Disease

More than one-third of the U.S. adult population lives with a cardiovascular disease, with more than 6 million hospitalizations each year.33 Coronary heart disease and stroke, two of the major types of cardiovascular disease, rank as the first and third leading causes of death, respectively (General Mortality indicator), and are leading causes of premature and permanent disabilities. Known risk factors include smoking, high blood pressure, high blood cholesterol, diabetes, physical inactivity, and poor nutrition. Outdoor air pollution and environmental tobacco smoke are also known risk factors for cardiovascular disease. Particulate matter, for example, has been demonstrated to be a likely causal factor in both cardiovascular disease morbidity and mortality. Collective evidence from recent studies suggests excess risk associated with short-term exposures to particulate matter and hospital admissions or emergency department visits for cardiovascular effects.34,35 Environmental tobacco smoke has been shown to be a risk factor for coronary heart disease morbidity and mortality and may contribute to stroke, though evidence is more limited.36,37

Respiratory Disease

Chronic obstructive pulmonary disease (COPD) and asthma are two prevalent chronic respiratory diseases in the U.S. Epidemiological and clinical studies have shown that ambient and indoor air pollution are risk factors in several respiratory health outcomes, including reported symptoms (nose and throat irritation), acute onset or exacerbation of existing disease (e.g., asthma), and deaths.38,39 The relationship between environmental tobacco smoke and diseases of the respiratory tract has been studied extensively in humans and in animals; environmental tobacco smoke has been shown to produce a variety of upper and lower respiratory tract disorders.40

COPD is a group of diseases characterized by airflow obstruction, resulting in breathing-related symptoms and encompasses chronic obstructive bronchitis and emphysema.41,42 COPD is the fourth leading cause of death in the U.S. and is the leading cause of hospitalization in U.S. adults, particularly in older adults. It represents a major cause of morbidity, mortality, and disability.43 Air pollution may be an important contributor to COPD, though approximately 80 to 90 percent of COPD deaths is generally attributed to smoking.44

Asthma continues to receive attention in both children and adults. Asthma prevalence increased nearly 74 percent during 1980-1996.45 During 2001-2003, an average annual 20 million people in the U.S. had asthma.46 In 2009, just over 24 million people in the U.S. reported having asthma.47,48 Environmental contaminants such as dust mites, pets, mold, and other allergens are considered important triggers for asthma.49 In addition, the relationship between environmental tobacco smoke and diseases of the respiratory tract has been studied extensively in humans and in animals; environmental tobacco smoke has been shown to produce a variety of upper and lower respiratory tract disorders.50

Infectious Disease

Infectious diseases are acute illnesses caused by bacteria, protozoa, fungi, and viruses. Food and water contaminated with pathogenic microorganisms are the major environmental sources of gastrointestinal illness. Though well-established systems for reporting food- and waterborne cases exist, data reported through these largely voluntary programs must be interpreted with caution because many factors can influence whether an infectious disease is recognized, investigated, and reported. Changes in the number of cases reported could reflect actual changes or simply changes in surveillance and reporting. In addition, many milder cases of gastrointestinal illnesses go unreported or are not diagnosed; making it difficult to estimate the number of people affected every year.

The discovery of bacterial contamination of drinking water as the cause of many cases of gastrointestinal illness represents one of the great public health success stories of the 20th century. Waterborne diseases such as typhoid fever and cholera were major health threats across the U.S. at the beginning of the 20th century. Deaths due to diarrhea-like illnesses, including typhoid, cholera, and dysentery, represented the third largest cause of death in the nation at that time. These types of diarrheal deaths dropped dramatically once scientists identified the bacteria responsible, elucidated how these bacteria were transmitted to and among humans in contaminated water supplies, and developed effective water treatment methods to remove pathogens from water supplies.

In addition to being of food - or waterborne origin, infectious disease can be airborne, arthropod-borne (spread by mosquitoes, ticks, fleas, etc.), or zoonotic (spread by rodents, dogs, cats, and other animals). Legionellosis can be contracted from naturally occurring bacteria found in water and spread through poorly maintained artificial water systems (e.g., air conditioning, ventilation systems). Arthropod-borne diseases, including Lyme disease, Rocky Mountain spotted fever, and West Nile virus, can be contracted from certain ticks and mosquitoes that acquire bacteria or viruses by biting infected mammals or birds.

Birth Outcomes

Birth defects are structural or functional anomalies that present at birth or in early childhood. Birth defects cause physical or mental disability and can be fatal. They affect approximately one out of 33 babies born each year in the U.S. and remain the leading cause of infant mortality (Infant Mortality indicator). Serious, adverse effects on health, development, and functional ability may be experienced by individuals born with birth defects.51 Birth defects have been linked with a variety of possible risk factors that can affect normal growth and development—genetic or chromosomal aberrations, as well as environmental factors such as exposure to chemicals; exposure to viruses and bacteria; and use of cigarettes, drugs, or alcohol by the mother. The causes of most birth defects are unknown, but research continues to show the possible influence of environmental exposures (e.g., prenatal exposure to high levels of contaminants such as mercury or PCBs). The relationship between exposure to lower concentrations of environmental contaminants and birth defects, however, is less clear.

Low birthweight delivery and preterm birth are considered important risk factors for infant mortality and birth defects. Low birthweight infants have a significantly increased risk of infant death, and those who survive are more likely to experience long-term developmental disabilities.52 Multiple birth babies have a low birthweight rate of more than 50 percent, compared to approximately 6 percent among singletons, among whom the low birthweight rate rose only 1 percent from 1989 to 1998.53 To eliminate the effect that multiple births may have on birth outcomes, this report presents data for singleton births only.

Environmental exposures are being investigated for possible associations with birth outcomes such as low birthweight, preterm delivery, and infant mortality. Some of the risk factors for low birthweight infants born at term include maternal smoking, weight at conception, and nutrition and weight gain during pregnancy.54 Specific examples of known or suspected environmental contaminant influences on birth outcomes include environmental tobacco smoke, lead, and air pollution. The most robust evidence exists for environmental tobacco smoke and lead.55 Environmental tobacco smoke is associated with increased risk of low birthweight, preterm delivery, and sudden infant death syndrome.56 Several studies have identified lead exposure as a risk factor for preterm delivery.57 Associations between air pollution and fetal growth and infant mortality have been documented. Recent studies report significant associations between PM10 concentration averaged over a month or a trimester of gestation and the risk of intrauterine growth reduction and low birthweight.58 Growing evidence shows exposure-response relationships between maternal exposures to air pollutants (e.g., sulfur dioxide and particulates)and preterm birth.59,60 Research continues, however, in establishing causal relationships between air pollution and low birthweight and preterm birth. Researchers also continue to examine possible associations between other contaminants as birth outcome risk factors, such as pesticides, polycyclic aromatic hydrocarbons, and others.

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