8.14 - Pollution and Human Health

Learning Objectives

I. Routes of Exposure

• Lead (Pb): Can enter the body through water pipes, or through paint chips and dust that children in older homes inhale or ingest. Lead was used in paint for a long time.

• Mercury (Hg): Exposure happens through eating seafood, especially tuna and other high trophic level organisms where mercury has bioaccumulated.

• Carbon Monoxide (CO): Mostly comes from indoor biomass combustion of subsistence fuels like charcoal or wood in developing nations.

• Particulate Matter (PM): Materials like dust or pollen enter the respiratory tract just from being in the air.

• Arsenic (As): Found in rice, which accumulates it in its tissues. It’s also found in groundwater that’s been exposed to arsenic through natural decay of rocks or release from wood treating facilities.

II. Synergism

• It’s difficult to isolate the effect of one specific pollutant because humans are exposed to so many different toxicants at once.

• Examples: Asthma caused by particulate matter from a coal power plant could be making the lung damage from COVID-19 worse. Similarly, it’s hard to isolate whether lung cancer came from asbestos exposure or from smoking cigarettes.

• Synergism makes it hard for epidemiologists to pinpoint the exact cause of an illness or disease.

• How scientists study it: Since it’s unethical to expose people to pollutants on purpose, scientists use epidemiological studies. They follow large groups of people, compare those with more exposure to those with less, and use statistics to account for other factors like smoking, age, and income. For example, the Harvard Six Cities Study (1993) followed more than 8,000 adults for 14 to 16 years and found that people in the city with the most fine particulate pollution had about 26% higher death rates than people in the cleanest city. Even a study like this shows a strong link (correlation), not absolute proof of cause.

III. Major Health Issues Linked to Pollution Sources

• An intestinal infection that causes bloody diarrhea. It’s usually caused by Shigella bacteria (and sometimes by an amoeba), which spread through food or water contaminated with raw, untreated sewage (feces). It’s common in developing nations that lack widespread access to sewage and water treatment.

• Dysentery causes severe intestinal swelling and infection and promotes violent diarrhea as the body tries to flush out the pathogen.

• That leads to severe dehydration, which is especially deadly for young children. Shigella alone killed an estimated 212,000 people in 2016, about 64,000 of them children under 5, mostly in developing nations.

• Prevention comes mainly through filtration of water sources and expanding clean water access.

• A specific type of cancer caused primarily by asbestos exposure.

• When asbestos fibers are inhaled, they lodge in the body and can lead to cancerous tumors in the mesothelium, the thin lining that surrounds the lungs (most common), the abdominal cavity, and the heart. It usually shows up 20 to 50 years after exposure, which makes it hard to trace back to the source.

• The primary route of exposure is disturbed old insulation, like in attics, ceilings, or around water heaters.

• Asbestos removal has to be done by trained professionals wearing proper equipment (respirator, body suit) in an area that’s completely sealed off with good ventilation, so the particles don’t spread. The replacement insulation should be asbestos free.

• A general respiratory irritant.

• $\text{O}_3$ decreases lung function, can cause a burning sensation in the throat and severe headaches, and can worsen pre-existing respiratory conditions like asthma, COPD, or emphysema.

• Sources include $\text{NO}_2$ emissions from vehicle exhaust and coal-fired power plants reacting with sunlight to produce $\text{O}_3$ (see 7.2).