Environmentally Mediated Health Disparities

Abstract

We describe important settings where environmental exposure leads to disease disparities. Lead exposure in urban settings disproportionately impacts the urban black poor. Native Americans have been forcibly relocated to areas of the west that have arsenic-contaminated groundwater or exposure to radionuclides near mines and nuclear development. Latino farm workers are disproportionately exposed to pesticides and herbicides. These chemicals are associated with cancer, neuropsychiatric disorders, renal failure, and respiratory disorders. The rural poor, both white and of color, are disproportionately impacted by hydraulic fracturing exposing residents to volatile organic compounds such as toluene and benzene, and heavy metals such as lead and arsenic. The urban and rural poor are both exposed to air pollution that significantly impact health. Short- and long-term ambient air pollution exposure has been associated with all-cause cardiovascular disease, stroke, blood pressure and ischemic heart disease. Cancer due to air pollution has disproportionately impacted poor communities like ‘Cancer Alley’ where numerous industrial sources are geographically clustered. Understanding local environmental hazards and available resources to address them can enhance the quality of medical care.

Introduction

There is recent awareness that low income and racial/ ethnic minorities suffer disproportionately from environmental pollution^1,2. This review provides internists with several specific environmental toxicant exposures they need to be aware of when caring for patients from vulnerable populations that can help them improve the quality of the medical care rendered.

As physicians appreciate social determinants of health and incorporate them into patient evaluation and therapeutic decisions, so too should the environmental conditions in which patients live and work be considered. Although assessing exposures is not a core skill taught in most medical schools³, its importance has become increasingly recognized as the science linking environmental exposure and disease has evolved. Patients may raise questions regarding hazardous chemicals or sources of pollution in their communities or may be completely unaware of their exposures. Especially when patients are unaware, physicians need to recognize and appreciate the implications of environmental toxicants. Our aim is to describe several important settings where environmental exposure and disease disparities occur and provide resources that physicians can use to improve the care of their patients.

Lead Toxicity and the Urban Black Poor

Studies have shown that low-income communities of color bear the highest burden of environmental exposure. The presence of lead and its toxic effects in these communities have been a recurrent finding whether in Flint⁴, Chicago⁵, or Philadelphia⁶. Although similar, these cities differ in the relative contribution from each lead source; so while in Flint, the water supply was a major contributor, in Philadelphia, lead paint and dust in old buildings and lead soil contamination that occurs when old buildings containing lead are demolished play a larger role. Lead toxicity has been found to have a strong association with impaired neurodevelopment and increased incidence of preeclampsia. Lead contamination in air has also been empirically connected to increased crime prevalence⁷. Lead is the oldest developmental neurotoxicant known. It crosses the blood brain barrier to cause apoptosis and excitotoxicity of neurons and glial cells impairing learning, memory and mood development. A study using NHANES data found African-American children had up to a 5.6 times higher odds of having an elevated blood lead level (>5ug/dl) than other children⁸. The CDC recommends that all children that meet its risk criteria: living or spending time in a house or building built before 1978, are from low-income households, are immigrants, refugees, or recently adopted from less developed countries, live or spend time with someone who works with lead or has hobbies that expose them to lead be tested for lead⁹. Some cities (Philadelphia, Pittsburgh) and states (Maryland, New York, Connecticut, Delaware, New Jersey), recognizing that the majority of their populations fit at least one of the CDC’s criteria have passed ordinances requiring testing of children for lead at around age 1 and 2. Lead toxicity may also impact the adult population and bone lead may be an important biomarker in chronic disorders¹⁰(10). Cumulative exposure to lead in adults has been associated with an increased risk (OR=3.21) of developing Parkinson’s disease in studies in Boston¹¹ and Detroit¹². The mechanism is likely impaired dopamine release, reduced receptor sensitivity, and peroxidation leading to the denaturing of α-synuclein¹³. Cumulative exposure to lead is associated with negative neurobehavioral, renal, and cardiovascular outcomes later in life¹⁴. Identification of occupational exposure may lead to interventions interrupting ongoing exposure reducing total cumulative exposure.

Native Americans in the American West: Mining, Metals and Radionuclides

The forceful relocation of Native Americans to the American West often placed them near mining locations and subsequently nuclear development sites, bringing them into contact with a variety of environmental toxicants¹⁵. Children living in or near mining towns had marked elevation of lead levels regardless of ethnicity correlating with high lead soil and dust levels¹⁶. But this is hardly the only environmental toxin they are exposed too. Five native American tribes were relocated downwind from the Hanford nuclear development site including the Spokane and Yakima tribes¹⁷. Cancer rates in these populations exceed state rates by 40% or more. The Navaho nation was exposed to radionuclides in their drinking water. Nuclear waste sites from uranium mining remain on their lands which are mostly in Arizona and New Mexico. Arapaho Native Americans living on the Wind River Reservation have nuclear contaminated water, a tenfold incidence in cancer prevalence and an increased prevalence of kidney disease¹⁸. Another significant environmental contaminant to water in the West and Southwest US is naturally occurring arsenic. Arsenic is a known human carcinogen and has been associated with obesity and diabetes. A recent USGS survey of the Colorado Plateau Aquifer revealed that 36% of the wells in Arizona and 30% of the wells in New Mexico had moderate or high concentrations of arsenic¹⁹. Arsenic can be removed by filtration, but this can be costly. There are no EPA point-of-use certified filters for uranium contamination of drinking water. Physicians should advise all patients with private well water to have their water tested.

Migrant Latino Workers and Pesticides in the South

Migrant and native workers on farms are exposed to pesticides and herbicides in excess of the general population. The Community & Migrant Health Center Network in 2019, found that 61% of migrants seeking care at their clinics had an income level at or below the poverty line, 89% were Latino, and 64% were best served in a language other than English²⁰. Low English literacy creates a barrier to engaging with health protective instructions about personal protective equipment and medical treatment in some settings. A study of urinary samples of Latino farm workers in North Carolina found that they had frequent substantial exposure to insecticides and pesticides²¹. These toxicants include glyphosate, organophosphates, organochlorines, and others, many of which are endocrine disrupting chemicals that produce a wide range of illnesses including cancer, birth defects in offspring, neuropsychiatric disorders including depression, renal failure, and respiratory disorders. Protective equipment may not always be available or used optimally. Less of these toxicants may be needed with alternative cropping systems that are less reliant on pesticides. Physicians should be aware of pesticide exposures in this population. Specialty consultation is available at an Association of Occupational and Environmental Clinic²² or a poison control center.

Fracking, Well Water, Noise Pollution, and the Rural Poor

There is also evidence that hydraulic fracturing (fracking), the horizontal drilling technique used for natural gas extraction, occurs in locations most often proximate to low income communities of color in states such as Texas and Louisiana, while in rural Pennsylvania fracking wells are predominantly located on land near low income white populations including the elderly²³. Fracking may expose those in its vicinity to a plethora of toxicants including volatile organic compounds such as toluene and benzene, and heavy metals such as lead, arsenic, and cadmium²⁴. Soil and water contamination may involve these toxicants and even naturally occurring radionuclides which are brought to the surface during the fracking process. Health impacts include an increased risk of cancers such as multiple myeloma, respiratory illnesses including asthma, and neurotoxicity including Alzheimer’s disease²⁵. A recent study in Pennsylvania found that children born to families that had residences within 2 kilometers of a fracking well had nearly twice the incidence of acute lymphoblastic leukemia²⁶. Noise from compressors and light pollution from flaring can lead to sleep disturbance, hypertension and cardiovascular disease²⁷. EPA estimates that more than 23 million households rely on private wells for drinking water in the US²⁸. Well water is not routinely tested by any government agency. The EPA maintains a map of the density of private domestic wells which can be consulted to determine local likelihood of well water²⁹. Everyone whose drinking water source is a private well should have their water tested every few years. People living in areas where fracking occurs should test their drinking water regularly for the chemicals used in fracking in their region. A non-profit maintains a voluntary registry of fracking chemicals used in wells mapped geographically called Fracfocus³⁰.

Air Pollutants: Urban and Rural Poor

Numerous studies document that low income communities face higher concentrations of air pollution³¹. Air pollution is a complex mixture that varies in its proportional content but often contains particulates that adhere numerous heavy metals and chemicals and gaseous pollutants such as sulfur dioxide, nitrogen oxides, ozone, and hazardous air pollutants. Emissions due to traffic represent a significant component of air pollution in urban settings. However, particulates generated in agricultural activities in the summer in rural settings have been shown to have similar oxidative potential, a measure of toxicity, as particulates from transportation sources³². Some settings, such as the San Joaquin Valley in California are impacted by particulate pollution from transportation and agricultural sources. Although the frequency of wildfires has not increased in the US, the extent of wildfires (burned areas) has been increasing since 2000³³. Preliminary observational data suggest that increased PM2.5 exposure from wildfires is associated with higher rates of respiratory hospitalizations than the same increase in PM2.5 from non-wildfire sources³⁴. Air pollution has been established as a known human carcinogen by the World Health Organization’s International Agency for Research on Cancer (IARC)³⁵. Although many carcinogens exist in air pollution from combustion sources, some carcinogens emanate from industrial sources. Some communities like ‘Cancer Alley’, the area along the Mississippi River between Baton Rouge and New Orleans, LA, have numerous industrial sources clustered geographically. A recent study showed how existing regulatory frameworks allow for clustering of hazardous industry in particular in low income communities of color³⁶.

A recent review identified strong evidence for higher short-and long-term ambient air pollution exposure with all cause cardiovascular disease, stroke, blood pressure and ischemic heart disease. Detrimental effects of air pollution on the cardiovascular system have been attributed to vasomotor dysfunction, inhibition of fibrinolysis, and impaired cardiac function. The respiratory system’s impacts from air pollution have been airway inflammation, increased airway responsiveness, increased risk of respiratory infection and the development and exacerbation of asthma³⁷. Particulate matter (PM2.5) exposure during pregnancy has been associated with low birth weight and spontaneous abortion³⁸. Sulfur dioxide and nitrogen dioxide have also been associated with low birth weight^39.40.

Conclusions

Although some environmental exposures may not be under personal control, understanding their contribution and impact may prove helpful to the clinician in defining and modifying treatment regimens. For example, maintaining a course of treatment for symptomatic asthma during a week of poor air quality may prove essential. Tapering down the therapy a week later when there is no longer a poor air quality contribution may be more feasible. Identifying occupational exposures may result in improved control of chronic disorders and reduction of cancer risk. The populations that are most likely to reap the benefits of expanded consideration of environmental exposure reduction are those with the greatest health disparities, low income communities of color. The informed clinician can better care for her/his patients when aware of the impact of environmental toxicants on the wide range of chronic and acute disorders.

Environmentally sensitive medical care starts with taking an exposure history. Asking questions about community, home, hobbies, occupation, personal habits, diet and drugs are essential⁴¹. Knowledge of the environmental hazards of the community served is essential and several resources are available to identify them. The EPA has created an online Environmental Justice Screening and Mapping Tool which demonstrates 12 environmental indicators including air, water and hazardous waste pollution and combines these with 7 socioeconomic indicators. Searching a patient’s home address on EJ Screen will quickly provide greater insight into their local environmental exposures(https://www.epa.gov/ejscreen). TOXNET, the NLM database containing chemical exposure and toxicology information has been retired, yet its content is still accessible through this link: https://www.nlm.nih.gov/toxnet/index.html. The ATSDR Toxicologic Profiles for individual chemicals compile toxicologic literature by pathway of exposure which provides a comprehensive view of published literature in easy to find sections⁴².

Subspecialty referral to trained occupational and environmental specialists may sometimes be needed for adequate expertise in diagnosis and treatment of environmental toxicants akin to other subspecialty referral. The Association of Occupational and Environmental Clinics is a non-profit organization that has a network of clinics http://www.aoec.org/index.htm. In addition, the American College of Occupational and Environmental Medicine has an on-line Directory. https://acoem.org/Find-a-Provider. Developing our clinical skills to better identify environmental exposures and their effects is increasingly important in the service of our patients whose environmental risks are substantial and increasing in today’s environment.

Clinical Significance.

• Lead exposures occur from water, soil, homes and air in poor especially black communities

• Native Americans experience radionuclide as well as metal toxicant exposure

• Latino farm workers have significant herbicide and pesticide exposure with multiple toxic effects

• Proximity to hydraulic fracturing leads to water, air and noise pollution for rural poor

• Thorough clinical care requires a knowledge of toxicant exposure and its impact on health