We Could Be Hurting Ourselves! Let’s Stop!

We Could Be Hurting Ourselves! Let’s Stop!

Air Pollution and its Correlation with Alzheimer’s Disease

Topic: How does air pollution exposure impact human health?

Hypothesis: More air pollution will be associated with increased incidents of neurological impairments.

Background: Earth’s atmosphere consists of 78% nitrogen, 21% oxygen, 0.9% argon, and 0.1% of other gases including carbon dioxide, methane, water vapor, and neon.¹ The atmosphere is divided into five layers based on temperature and altitude: troposphere, stratosphere, mesosphere, thermosphere, and exosphere.¹ Focusing on the first two layers, the troposphere stretches 15km above the Earth’s surface and holds the majority (75-80%) of the atmosphere’s mass. The stratosphere expands from the troposphere up to 50km high and contains a high concentration of ozone that accumulates within the ozone layer.¹ This ozone layer absorbs solar ultraviolet (UV) light and causes temperatures to increase in altitude within the stratosphere when they usually decrease in altitude.¹ When solid particles leave Earth’s surface and enter the atmosphere, they contaminate the atmosphere. This mix of particles and gases in the atmosphere is known as air pollution.²

The United States Environmental Protection Agency (EPA) identified six pollutants that, at critical levels, harm human and environmental health: carbon monoxide (CO), lead (Pb), nitrogen oxides, ground-level ozone, particle pollution (particulate matter), and sulfur oxides.³ For the purposes of this study, we will focus on particulate matter (PM). Frequently, devices use PM levels, specifically PM_2.5 and PM₁₀, to quantify air pollution. PM_2.5 is fine matter and PM₁₀ consists of larger particles. PM is made up of a mix of solid particles and liquid droplets in the air, including dust, dirt, and smoke, which we emit from construction sites, unpaved roads, fires, and complex reactions in power plants.⁴ When inhaled, PMs harm our lungs and heart and contribute to premature death due to heart or lung disease, irregular heartbeat, asthma, and respiratory irritation.⁴ Scientists have studied the respiratory affects thoroughly. However, they have only recently begun to assess the neurological effects.

Comparing world maps of air pollution and Alzheimer’s/dementia deaths, I noticed that the areas with pour air quality are the same areas with the highest Alzheimer’s and dementia death rates per 100,000 people. This is obviously not a causation, but an interesting correlation.^5,6

When we inhale air pollution, PM can accumulate in our brain by traveling through the blood stream or diffusing across the nose’s thin lining.⁷ In a recent study, researchers from the University of Southern California and Harvard Medical School concluded that air pollution was significantly associated with neurological changes affiliated with memory decline.⁸ This study included 998 women between the ages 73 and 87 who participated in the Women’s Health Initiative, a program running since 1993 to address concerns regarding heart disease, cancer, and osteoporosis.⁸  Each participant had two brain scans, five years apart. Researchers compared the participants’ brain scans to brain scans of people with Alzheimer’s disease and assigned a cognitive decline score to each scan using a machine learning model.⁸ The researchers then cross examined the data with the pollution levels in the areas the participants lived in. The researchers found an association between greater exposure to fine particle pollution (PM_2.5) and brain changes and memory problems, even after adjusting for confounding factors such as income, education, race, and lifestyle.⁸ As mentioned above, these PM_2.5 particles came from traffic exhaust, smoke, and dust–many human-caused sources.

In a long-term study conducted in Ontario, Canada between 2001 and 2012, researchers analyzed the relationship of living near major roads and the incidence of dementia, Parkinson’s disease, and multiple sclerosis (MS).⁹ The researchers compared two population-based cohorts, one consisting of 4.4 million adults 20-50 years old without multiple sclerosis, and the other with 2.2 million people 20-50 years old without dementia or Parkinson’s disease.⁹ Participants needed to be Canadian-born, Ontario residents for a minimum of five years.⁹ By assessing the proximity of each population cohort to major roadways and adjusting for confounding variables, researchers identified 243,622 incident cases of dementia, 31,577 cases of Parkinson’s disease, and 9,247 cases of MS.⁹ Upon statistical analysis, researchers concluded that living near traffic was significantly associated with a higher incidence of dementia, but not Parkinson’s disease or multiple sclerosis.⁹

Two other studies, one in England and another in China, found similar connections between air pollution and brain impairment. In the first study, researchers from China and the US analyzed a Chinese data set and found that long-term exposure to air pollution correlated with decreased performance on verbal and math tests.¹⁰ The second study analyzed 130,978 adults ages 50 to 76 from 75 medical clinics in London, England.¹⁰ Between 2005 and 2013, 2,181 of the participants developed dementia (39% Alzheimer’s disease, 29% vascular dementia, and 32% nonspecific dementia).¹⁰ Those that lived in areas with higher annual air pollution concentrations were 1.4 times more likely to get dementia, specifically Alzheimer’s disease.¹⁰ In each of these studies, researchers controlled for confounding variables, including sociodemographic factors, lifestyle, employment, clinical practices, and MRI-measured cerebrovascular disease.¹⁰

Air pollution correlates to brain impairment by altering brain composition. Magnetite particles, such as Fe₃O₄, contribute to particulate matter as a result of burning fuel. However, we also generate them naturally in our brains.⁷ Hemoglobin requires iron to bind to oxygen and transport it to tissues. When hemoglobin molecules break down, the iron in the heme group is free to react with blood oxygen. Fe₃O₄ can form as a waste product and binds to amyloid plaques during the disposal process. However, when we inhale additional amounts of magnetite and surpass the concentration our body can handle, magnetite accumulates in these plaques. In response, our bodies generate more plaques to accommodate the increased amount of magnetite. The more plaques found in the brain, the more a person’s brain resembles an Alzheimer’s brain.

Air pollution, though not necessarily the cause, significantly increases the risk of Alzheimer’s disease. Alzheimer’s is currently the sixth leading cause of death in the US.¹¹ There is no current cure or treatment. In 2016, air pollution was estimated to be the greatest major risk factor and cause of death globally.¹¹ The connection between air pollution and dementia is an emerging effect still being studied. More research is needed to quantify the burden of air pollution and to continue to make associations between exposures and diseases.

Experimental Objective: To periodically measure the levels of air pollution in Bloomington and compare them to historic trends to see how they’ve changed.

Methods:

• October: the sunset was recorded once a week for air pollution visuals and PM₅ and PM₁₀ levels were measured at the site of recording.
• October – November: PM₅ and PM₁₀ levels were measured outside and inside my apartment an average of two times each week.

Equipment: 

Data:

The PM_2.5 and PM₁₀ levels measured inside and outside of my apartment were represented in Figures 6 and 7. The inside levels were recorded as the average of the measurements taken on the main and second floors of my apartment. I wanted to compare my data to data published by a national site. The United States Environmental Protection Agency (EPA) recorded data in Bloomington for PM_2.5 levels, but not PM₁₀ levels.¹²

Long-Term Trends:

Table 1 shows how the concentrations of emitted particles have changed between 1980 and 2019. Overtime, we have greatly reduced the number of particles we’ve emitted into the atmosphere. Human-caused emissions are primary contributors to air pollution.¹³ By reducing our impact, we directly improve air quality. However, table 1 only presents changes in the national averages. There are still many people living in areas with emissions rates and air quality levels above national ambient air quality standards (NAAQS). See Table 2 for the number of people in such areas across the globe.

	1980 vs 2019	1990 vs 2019	2000 vs 2019	2010 vs 2019
Carbon Monoxide	-75	-69	-56	-27
Lead	-99	-87	-76	-30
Nitrogen Oxides (NOx)	-68	-65	-61	-41
Volatile Organic Compounds (VOC)	-59	-47	-27	-18
Direct PM10	-63	-30	-27	-17
Direct PM2.5	—	-36	-43	-20
Sulfur Dioxide	-92	-91	-88	-73

Table 1: Percent changes in emission concentrations measured from monitors located across the United States of America.¹⁴

Air Pollutant	People In Areas with Concentrations Above NAAQS
One of more pollutants above standards	81.9M
Ozone (8h average)	73.9M
PM10 (24h average)	22.5M
PM2.5 (annual and/or 24h average)	15.4M
SO2 (1h average)	2.8M
Lead (3-month average)	1.1M
CO (8h average)	0.0M
NO2 (annual and/or 1h average)	0.0M

Table 2: People living in areas across the globe with air quality concentrations in air pollutants above NAAQS in 2019.¹⁴

Figures 8 and 9 compare the trends of PM₁₀ and PM_2.5 concentrations at the municipal, state, and national levels. Although concentrations fluctuated over the years with PM₁₀, Bloomington concentrations for PM_2.5 were consistently higher than the state and national averages. In 2009, Bloomington data showed a downward trend, while Indiana data leveled off. Based on the levels I recorded, an updated Bloomington PM₁₀ would likely be similar to the historic trend, but an updated PM_2.5 trend should continue the downward trend reported in 2009.

Discussion:

Throughout October, I recorded the sunset once a week and measured the level of particulate matter at each site. I wanted to use my video of the sunset to represent a visual for what a certain PM level looked like. However, most of the evenings I recorded, the PM levels outside remained between 0 and 3 ug/m³. Although the sunset visuals changed, the level of PMs did not differ significantly. My initial plan was not effective. The visuals may have instead depended on how cloudy the sky was that evening. According to NASA, human-caused pollution impacts cloud formation, but it depends on the concentration of pollutants.¹⁶ Moderate concentrations foster cloud formation by providing just enough particles for water to condense onto, but higher concentrations generates fog and inhibits cloud formation.¹⁶

Overall, my data had a lot variation. The day-to-day fluctuations could represent changes in peoples’ daily activities. I noticed my “inside” data changed depending on whether I cleaned my apartment that day or used my roommate’s air purifier or turned on/off the air conditioning/heat. My “outside” data could have changed depending on the time of day I recorded data (peak rush hours vs early mornings or late evenings). The data could have also changed based on the wind and weather that day. Local factory emissions could have also affected my data if they were emitting more concentrations some days and less other days. One interesting thing I noticed was when my PM levels were really low outside, they were often very high inside, and vice versa. When I used my roommate’s air purifier, the PM levels inside were at their highest. Maybe that just shows that we need a new filter for the purifier. Based on my observations, it seems as though optimal environments are best outdoors when the air is crisp, cool, and breezy, and best indoors when the environment outside is damp, warm, humid, and foggy.

Compared to the data the EPA collected at Bloomington-Binford Elementary School, my data for outside concentrations was roughly similar. The slight discrepancies may have resulted from using different equipment and the location spots being a 10-minute drive apart. My indoor concentrations, however, were much higher, possibly for reasons discussed above.

According to long-term trends, air polluting emissions have decreased since 1980 and the air quality average across the USA has improved.¹⁴ However, these are averages. There are still regions with pollutant concentrations that surpass national standards.

Although national historic trends show that air quality and polluting emissions have improved, studies indicate that living in areas dense with traffic and air pollution correlates to more neurological impairments. The studies conducted in Canada, America, England, and China assess the related impacts of chronic exposure to air pollution.^8,9,10 Acute exposure also interferes with development. In an experiment conducted at the University of Southern California, researchers exposed Caenorhabditis elegans to nano-sized particulate matter (nPM) at different developmental and adult life stages.¹⁷ Acute nPM exposure did not cause mortality, but it resulted in dose-dependent size reductions in worms exposed at the first developmental stage (L1).¹⁷ Thus, acute exposure can be damaging if you get exposed early enough. Chronic exposure amplifies this effect and correlates to damages at all stages of life. If we want to minimize our health risks, we need to change our behaviors and reduce our contribution to PM_2.5 and PM₁₀ levels. It’s great that national trends are improving, but we need to make sure that all regions are below national standards, not just the national averages.

We can use this data to help us make daily decisions, such as where to live and what business to support. The further away we are from high emission sites and the more we support businesses that use sustainable methods to make their products, the more we will reduce our emission rates, improve overall air quality, and reduce our risk of neurological damage.

To improve this project in the future, I would take measurements more frequently, either three times in one day to get the average level for that day or collect data at the same time each day I record. This would minimize any potential methodological errors in my data collection.

Conclusion:

Current PM_2.5 and PM₁₀ levels are following historic downward trends. However, my hypothesis that more air pollution correlates to more neurological impairment was supported through peer-reviewed literature. Our national emission rates and air quality may have improved since 1980, but some regions remain above national standards. Areas with heavy traffic and air pollution have been significantly correlated with increasing incident cases of neurological diseases. If we wish to improve our health, we must change our behaviors and continue to improve air quality.

 

Works Cited:

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