When the environment cries, humans suffer

(Image: Michigan Creative)

Our natural environment easily supports life and nurtures human health. However, pollution in the air, water, soil, and plants can lead to severe health problems and congenital disabilities. The list of potential diseases caused or impacted by pollution is long. It includes allergies, cancers, skin and lung diseases, fertility problems, heart disease, immune deficiency diseases, kidney diseases, poisoning, nervous system disorders, and reproductive disorders.

One need look no further than the recent tragedy of the Flint water crisis to experience the impact of human-induced pollution on human health. Other environmental disasters caused by humans include the nuclear meltdowns at Chernobyl and Fukushima (in Ukraine and Japan, respectively) and the Deepwater Horizon oil spill in the U.S., to name just a few.

Catastrophic environmental-pollution events are not the only culprits impacting human health. Other types of environmentally induced health challenges include:

• Lifestyle factors like poor nutrition, tobacco use, or lack of physical activity
• Naturally occurring exposures to ultraviolet light, radon gas, and other infectious agents
• Medical treatments like radiation, chemotherapy, hormone drugs, and drugs that suppress the immune system
• Exposure to detrimental pollutants in the workplace
• Exposure to detrimental pollutants in the household
• Environmental pollution to air, water, and soil

Environmental pollution impacts on health

Maintaining a healthy environment is central to increasing the quality of one’s life expectancy. Globally, about 23 percent of all deaths (roughly 12.6 million per year), and 26 percent of deaths among children under age 5 can be attributed to preventable environmental factors like hazardous substances in air, water, soil, and food; natural and technological disasters; climate change disasters; occupational hazards; and built-environment hazards.

(Source: World Health Organization.)

Poor environmental quality exerts its most significant impact on people whose health status is already at risk: the sick, the young, and the elderly.

The World Health Organization (WHO) regularly documents environmentally induced health concerns and deaths. The most recent WHO report, published in 2018 for the calendar year 2017, shows most environment-induced deaths locate in South East Asia, Africa, and the Far East, areas with the highest number of people living in poverty.

Causes of death from environmental pollution

This pie chart (below) shows the top seven causes of death due to environmental pollution. Men are slightly more affected due to occupational risks and injuries, while women bear higher exposures to traditional environmental threats, such as smoke from cooking with solid fuels or carrying water. Nearly 4.9 million adults between age 50-75 die due to noncommunicable diseases and injuries. Nearly 1.7 million children under the age of 5 die due to respiratory infections and diarrheal diseases related to environmental pollution.

Controlled burns and forest fires set by humans release pollutants into the atmosphere.

Air pollution: A major source of death and health concerns

Air pollution ranks as the number-one cause, followed closely by water pollution, of pollution-induced deaths. We can classify the factors responsible for releasing pollutants into the atmosphere into two basic categories: man-made and natural.

Man-man air pollution includes:

• Controlled burning in agriculture, farming, and prairie restoration
• Forest fires set by humans
• Fossil-fuel burning from stationary sources that include factories and waste incinerators, as well as furnaces and other types of fuel-burning heating devices
• Exhaust gases from motor vehicles, marine vessels, and aircraft
• Fumes from hair spray, varnish, aerosol sprays, and other solvents
• Waste deposition in landfills, which generates methane
• Military resources, such as nuclear weapons, toxic gases, germ warfare, and rocketry

Natural air-pollution sources include the following:

• Dust from natural sources, usually large areas of land with little or no vegetation
• Methane, emitted by animals digesting their food (cattle, for example)
• Radon gas from radioactive decay within the Earth’s crust
• Smoke and carbon monoxide from naturally occurring wildfires
• Vegetation (Plants can emit environmentally significant amounts of volatile organic compounds — VOCs — in the form of gas. Black gum, poplar, oak, and willow are some examples of vegetation that can produce abundant VOCs in hot weather.)
• Volcanic activity

Air pollutants can be solid particles, liquid droplets, or gases and classify as primary or secondary. Primary pollutants are usually the byproduct of a process: ash from a volcanic eruption, carbon monoxide gas from motor vehicle exhaust, or sulfur dioxide released as exhaust, mostly from factories.

The top seven causes of environmental pollution.

Examples of primary air-pollutants

• Carbon dioxide (CO₂) is a greenhouse gas and a natural component of the atmosphere. The primary source of atmospheric CO₂ comes from burning fossil fuels. Currently, CO₂ forms about 410 parts per million (ppm) of the Earth’s atmosphere -– almost twice the amount (280 ppm) recorded during pre-industrial times.

• Sulfur oxides (SOx), particularly sulphur dioxide, SO₂, is produced by burning coal and petroleum–containing sulfur compounds. When SO₂ oxidizes in the presence of nitrogen dioxide (NO₂), it forms H₂SO₄ (sulfuric acid), known as acid rain.
• Nitrogen oxides (NOx), particularly nitrogen dioxide (NO₂), is expelled from the high-temperature combustion of fossil fuels. It also can be produced during thunderstorms by electric discharge.
• Carbon monoxide (CO) is a colorless, odorless, and toxic (yet non-irritating) gas produced during combustion of natural gas, coal, or wood. Vehicular exhaust contributes to the majority of atmospheric CO.
• Volatile organic compounds (VOCs) are air pollutants categorized as either methane (CH₄, a greenhouse gas) or non-methane (NMVOCs).
• Particulate matter (PM) occurs naturally, originating from volcanoes, dust storms, forest and grassland fires, living vegetation, and sea spray. Burning of fossil fuels in vehicles, power plants, and various industrial processes generates significant amounts of PMs.
• Chlorofluorocarbons (CFCs) are gases released from air conditioners, refrigerators, and aerosol sprays. They are banned in the U.S.
• Ammonia (NH₃) gases are emitted from agricultural processes, both caustic and hazardous.

Secondary pollutants

Secondary pollutants are not emitted directly into the atmosphere. Rather, they form in the air when primary pollutants react or interact. They also include particulates created from gaseous primary pollutants and compounds. Ground-level ozone is a prominent example of a secondary pollutant. Smog represents another example of a secondary pollutant. It results from burning coal and from vehicular and industrial emissions that are acted on in the atmosphere by ultraviolet light from the sun.

Most air pollutants are carcinogenic

Cancer is caused by changes in a cell’s DNA, its genetic “blueprint.” Some of these changes are inherited while others may be caused by direct or indirect environmental exposures. Substances and exposures that can lead to cancer are called carcinogens. Some carcinogens do not affect DNA directly but lead to cancer in other ways. For example, they may cause cells to divide at a faster than normal rate, which could increase the chances that DNA changes will occur.

Carcinogens do not cause cancer in every case, all the time. Substances labeled as carcinogens may have different levels of cancer-causing potential for different people. Some carcinogens may cause cancer only after prolonged, high levels of exposure. For any particular person, the risk of developing cancer depends on many factors, including how one is exposed to the carcinogen, the length and intensity of the exposure, and the person’s genetic makeup.

How do researchers determine if an air pollutant is a carcinogen?

Testing to see if an air pollutant can cause cancer is complicated. It is not ethical to test a substance by exposing people to a potential carcinogen. Thus, scientists use other types of tests, which do not always produce definitive results.

Lab studies

Scientists get much of their data about environmental pollutants and cancer from lab studies in cell cultures and animals.

The use of animals in research is not without its attending problems, however, including the ethical question of using animals in biomedical research. There are several reasons why the use of animals is critical for biomedical research.

Researchers have yet to discover anything that can substitute for the complex functions of a living, breathing, whole-organ system with pulmonary and circulatory structures like those in humans. Until such a discovery, animals continue to play a critical role in biomedical-environmental research. About 95 percent of all animals used for biomedical research in the United States are rodents (rats and mice) bred specifically for laboratory use. Nevertheless, there are accelerating efforts to discover new, novel ways to study pollution effects that do not involve animals. This cannot come too soon, in my opinion.

Human studies

Another way to identify human carcinogens is through epidemiologic studies. However, these studies also have limits. Humans are exposed to many substances at any given time, including those they encounter at work, school, or home; and in the food they eat and the air they breathe. Moreover, many years or decades often pass between exposure to a carcinogen and the development of cancer. Therefore, it can be very challenging to link definitively any particular pollutant exposure to cancer.

By combining data from different types of studies, scientists do their best to make an educated assessment of a substance’s cancer-causing ability. When the evidence is conclusive, the substance labels as a carcinogen. When the available evidence is compelling but not conclusive, the substance may be considered to be a probable carcinogen. In many cases, there isn’t enough information to be certain one way or the other.

Perhaps not surprisingly, based on how hard it can be to test these candidate carcinogens, most are listed as being of probable, possible, or unknown risk. (iStock.)

Identifying carcinogens

The most widely used system for classifying carcinogens comes from the International Agency for Research on Cancer (IARC), part of the World Health Organization. During the past 30 years, the IARC has evaluated the cancer-causing potential of more than 900 likely candidates, placing them into one of the following groups:

• Group 1: Carcinogenic to humans
• Group 2A: Probably carcinogenic to humans
• Group 2B: Possibly carcinogenic to humans
• Group 3: Unclassifiable as to carcinogenicity in humans
• Group 4: Probably not carcinogenic to humans

Not surprisingly, most potential carcinogens are identified as being of probable, possible, or unknown risk. Only a little over 100 pollutant agents are classified as carcinogenic to humans, and most are linked only with certain kinds of cancer, not all types.

It is important to note that while research attempts to describe the level of evidence that a particular air pollutant can cause cancer, it does not describe how likely it is that a specific substance will cause cancer in any particular person. For example, there is overwhelming evidence showing that both tobacco smoking and eating processed meat can cause cancer, so both classify as “carcinogenic to humans.” But smoking is overwhelmingly more likely to cause cancer than eating processed meat, even though both are in the same cancer-causing category. To complicate matters, different carcinogens do not cause cancer at all times, under all circumstances. Some may only be carcinogenic if a person is exposed under certain conditions and with a certain genetic makeup. Some pollutants may lead to cancer after only a very small exposure, while others might require intense exposure over many years.

Even if a pollutant is known or suspected to cause cancer, this does not necessarily mean that it can or should be avoided at all costs. For example, exposure to ultraviolet (UV) radiation from sunlight is known to cause cancer, but it’s not practical (or advisable) to avoid the sun completely.

What we can do to improve air quality

There is much we can do to improve our air quality and reduce pollution and disease. For sure, we all can become advocates to encourage our politicians, lawmakers, and business partners to do the following:

• Apply low-carbon strategies in industry, energy, and housing
• Use more active and public transportation
• Introduce clean fuels and technologies for cooking, heating, and lighting
• Reduce occupational exposure to pollution
• Change consumption patterns to lower the use of harmful chemicals; minimize waste production and save energy
• Implement interventions that can increase protection from the sun
• Pass smoking bans to reduce exposure to second-hand tobacco smoke
• Encourage policymakers to use a “health-first doctrine” to create healthier environments and prevent disease

References

• “Air pollution: Everything you need to know.” 
• Air Pollution: National Institute of Environmental Health Sciences. 
• “Climate 101: Air pollution.”
• Lewtas, J. 1993. “Airborne carcinogens.” Pharmacology and Toxicology; 72 Suppl 1:55.”
  
• Muñoz, X., et al. 2019. “Diesel exhausts particles: Their role in increasing the incidence of asthma. Reviewing the evidence of a causal link.” Science of the Total Environment; 652:1129.
  
• Popovic, I., et al. 2018. “A systematic literature review and critical appraisal of epidemiological studies on outdoor air pollution and tuberculosis outcomes.” Environmental Research; 170:33-45.
  
• Qin, F., et al. 2018. “Exercise and air pollutants exposure: A systematic review and meta-analysis.” Life Sciences; Dec. 21. pii: S0024-3205(18)30830-0.
  
• Vrijheid, M., et al. 2016. “Environmental pollutants and child health: A review of recent concerns.” International Journal of Hygiene and Environmental Health; 219(4-5):331.