Sonya Moo Senior Thesis 2024

Effect of Fetal and Neonatal Environmental Exposures on Developmental and Degenerative Neurological Disorders

Sonya Moo Senior Thesis | 2024

Effect of Fetal and Neonatal Environmental Exposures on Developmental and Degenerative Neurological Disorders Moo, Sonya, Research Assistant, HSPH, sonyasm@bu.edu Weisskopf, Marc, Primary Investigator, HSPH, mweissko@hsph.harvard.edu ABSTRACT This research in the neuro-environmental epidemiology laboratory at Harvard, supervised by Professor Marc Weisskopf, focused on the analysis and coding of human baby teeth samples to study the effect of fetal exposures on neurological state. These teeth are initially subjected to laser ablation and embedded in resin on slides to determine the parts per million of various compounds and elements, then mailed to Harvard T.H. Chan School of Public Health for focused analysis. The study aims to establish connections between these measurements along the enamel-dentine junction, specifically at the neonatal line, and matching ablation spots during subsequent data coding. Baby teeth, which form during fetal development, are the only pieces of bone naturally expelled from the body throughout an individual's lifetime. These teeth serve as valuable indicators of environmental exposure because they retain the elemental and mineral inputs from maternal intake (such as drinking water that had run through lead pipes) during fetal and neonatal stages of human development.1 This investigation revealed that geographical location and environmental compounds significantly influence the mineral compositions of baby teeth, consequently impacting neurological development and degeneration. Notably, the study highlights 1

Prentice, A. (2003). Micronutrients and the Bone Mineral Content of the Mother, Fetus and Newborn.

historical instances from the Cold War-era distribution of unidentified chemical substances in low-income neighborhoods of St. Louis, Missouri, by the United States military. Originally intended to assess potential Soviet bioweapon attacks, this action unintentionally exposed U.S. citizens to hazardous materials. By examining the current neurological status of individuals affected seven decades ago, considering their geographical location, and analyzing the compounds present in their baby teeth, the research concludes that environmental exposure to heavy metals such as lead, cadmium, mercury, and other materials has enduring adverse effects on the neurological state of the subjects.

BACKGROUND Biological and chemical warfare is a concern to the wellbeing of innocent civilians, as we live in an era where the advancement of technology has led to the potential of being wiped out with a single war. The Army’s study into the effects and spread of potential Soviet biological attacks were performed by distribution of airborne particles that were primarily made up of a fine powder called zinc cadmium sulfide (ZnCdS). This compound can be created en masse by heating zinc sulfide and cadmium sulfide until they fuse, creating an independent alloy; the resulting ZnCdS powder is similar to microorganisms in size (~2-3 µm). Zinc cadmium sulfide is also fluorescent when exposed to ultraviolet light, which means that it could be tracked after dispersal. The combination of akin size to microorganisms and the compound’s easy countability made it an ideal substitute to test the potential distribution of biological weapons in urban areas. At the time of these exposures, the evaluations of zinc cadmium sulfide’s effect on humans appeared not to be harmful, leading them to move

forward despite these trials being limited.2 The compound was also stable in air and water, almost insoluble, and had a very low manufacturing cost. Testing using ZnCdS was carried out by the US Army throughout the 1950s and 1960s until the conclusion of the Cold War (Figure 1). Some cities were only exposed a couple times, whereas others were exposed up to 35 times over a 2-year period.

Figure 1: A collection of 3 newspaper articles concerning the fear of Cold War tests in St. Louis, MO. An example of the affected demographics, predominantly senior black citizens, is also shown in the headlines; the articles themselves hold firsthand accounts of civilians’ experiences and denotes the renown of this case. Investigation has continued from the verification of the tests themselves (having been declassified in the 1990s, 40-30 years later) and onto studying the public health impact.3 2

(1997). Toxicologic Assessment of the Army’s Zinc Cadmium Sulfide Dispersion Tests.

3 Goodwin, J. D. (2021, November 11). St. Louis Public Radio | STLPR.

Those in St. Louis, Missouri were exposed to some of the largest doses of ZnCdS across multiple testing cities and sites. Those in St. Louis Missouri were exposed to 2500 µg (micrograms, equal to a millionth of a gram) of zinc cadmium sulfide, which is expected to be equivalent to 24.4 µg of cadmium (the most toxic component of ZnCdS). Cadmium exposure is common in urban settings due to pollution, coal or fossil fuel burning, and general poor air quality.

For reference, smoking a pack of 20 cigarettes a day will lead to 24 micrograms of Cd inhalation; in St. Louis, exposure to cadmium through ZnCdS is equal to 1-8 months of polluted air inhalation for a typical urban resident. To better put this in perspective, the intake of cadmium in rural areas is less than 0.02 µg/day, while in urban areas this can range from 0.1-0.8 µg/day. Despite the potential dangers of prolonged exposure to zinc cadmium sulfide and cadmium, the consensus was that this was not significant in causing adverse health effects in those exposed during the Cold War tests (Figure 2).4

Salter, J. (2023, September 25). “We were experimented on.” NBC News.

CBS Interactive. (2012, October 4). Secret cold war tests in St. Louis Cause Worry.

4 (1997). Toxicologic Assessment of the Army’s Zinc Cadmium Sulfide Dispersion Tests.

Figure 2: While this response to public concern is the best source for many of the reports on the toxicity of these tests, it was published in 1997 and performed by government researchers, who made the initial error of under-preparedness.

These studies were only performed after the general public voiced concern as to the long-term health effects of ZnCdS exposure, such as the unexplained and unusually high rates of physical ailments in those that were potentially exposed. There is still little known about the toxicity of zinc cadmium sulfide, or the compound’s more complex effects on humans or the environment at large.

However, the US Government has also acknowledged that in several cases these tests were indeed conducted using microorganisms, often dispersed in combination with zinc cadmium sulfide to track the spread of airborne particles and

diseases. The Army considered these microorganisms added to the dispersal tests to be safe at the time: Serratia marcescens, Bacillus globigii, and Aspergillus, which are forms of fungus or mold, were most commonly used. Later studies in the 1990s found that these do not create adverse effects in healthy individuals yet could cause disease in those who are in poor health. The co-exposures of zinc cadmium sulfide and these fungal microorganisms was not examined or studied.5 However, more recent studies have shown that these fungi can result in long term negative effects on healthy individuals in some cases, much like what we may be seeing in these exposure locations.

There has been further speculation that other materials were included in these tests, such as toxic heavy metals or radioactive additives in combination with ZnCdS. The Army has again acknowledged that additional materials were tested but will not disclose the exact components of dispersed particles or most of the findings that they made during these tests. Residual evidence of exposure to compounds such as cadmium, lead, mercury, or other heavy metals, as well as radioactive materials such as uranium cause long-lasting bone toxicity. It is this residual evidence that can be analyzed decades later in places such as the occipital bone or donated baby teeth, such as those from the St. Louis Baby Tooth Survey.6

5

(1997). Toxicologic Assessment of the Army’s Zinc Cadmium Sulfide Dispersion Tests.

6 Vierheller, P. et al. (2009). St. Louis Baby Tooth Survey, 1959-1970. St. Louis Baby Tooth Survey.

AIM OF STUDY 1.1 Expansion of Mid-20th Century Findings The Baby Tooth Survey, launched in December 1958 by the Greater St. Louis Citizens’ Committee for Nuclear Information (CNI), aimed to provide the community with accurate information about the effects of nuclear energy and radiation. CNI, established in April 1958 with notable members like Mrs. Edna Gellhorn, Barry Commoner, John M. Fowler, Reverend Ralph C. Abele, and Alfred S. Schwartz, refrained from taking an official stance on nuclear testing. Instead, it focused on gathering scientific facts, collaborating with the Scientific Advisory Group, and disseminating information through bulletins, newsletters, and a speaker’s bureau.

The inspiration for the Baby Tooth Survey came from Dr. Herman M. Kalckar's work in Nature, suggesting that primary teeth could reveal insights into the absorption of radioactive elements.7 The program received approval from dental schools, societies, and the Washington University School of Dentistry, which secured a grant for strontium-90 studies. In the St. Louis area, the collection of teeth involved collaboration with dentists and volunteers. Dr. Louise Z. Reiss spearheaded the project, collecting and cataloging almost 15,000 baby teeth in the first year, reaching a total of nearly 300,000 teeth by 1970.

The scientific study, led by Washington University School of Dentistry professors Harold L. Rosenthal, John T. Bird, and John E. Gilster, unveiled a 100-fold increase in radioactive strontium-90 levels in baby teeth from children born between 1945 and 1965, correlating with atomic bomb tests. Early results from the survey, 7

Kalckar, H. M. (1958). Nature, 283-284. An International Milk Teeth Radiation Census.

coupled with a U.S. Public Health Service study, played a pivotal role in persuading President John F. Kennedy to negotiate a treaty with the Soviet Union, ultimately leading to the cessation of above-ground testing of atomic bombs in 1963.8 1.2 Past Effect on Neurological Development The increasing mental health challenges faced by urban populations in developing countries may find a significant contributor in elevated levels of air pollution. While this claim has been explored to a limited extent, a notable study utilized a daily mental health metric based on mental-health-related queries on China's largest search engine, Baidu. The research demonstrated a causal relationship between air pollution and compromised mental health, with a heightened impact observed with prolonged exposure (Figure 3). Analyses of air pollution revealed varying vulnerability, with men, middle-aged individuals, and married people being more susceptible; this could be due to increased exposure during commute in adulthood. This would not be the case for the biological warfare test sights as most often the young and unemployed were targeted.

8

Vierheller, P. et al. (2009). St. Louis Baby Tooth Survey, 1959-1970. St. Louis Baby Tooth Survey.

Figure 3: A simple figure demonstrating the process followed in the study and the St. Louis Baby Tooth Survey hypothesis.9

Notably, the cumulative effects of air pollution were less pronounced in cities with higher gross domestic product per capita, greater health resources, extensive green spaces, and more sports facilities. A one-standard-deviation increase in fine particulate matter (26.3 μg m ) was estimated to result in approximately 1.15 million more people in China experiencing mental health problems. This study provides quantitative evidence supporting the imperative to reduce air pollution for the enhancement of mental -3

9

HSPH. (2022, July 25). Project 1: Early life metal exposures and cognitive aging.

health and overall well-being. The effect of airborne particulate matter is greater on disadvantaged communities similar to the ones affected by US Cold War testing.10 Furthermore, regions like St. Louis, Missouri, and other less highlighted testing locations have reported higher rates of developmental disabilities. Urban areas, particularly those subjected to biological warfare trials, exhibit increased frequencies of symptomatic mental health disorders such as anxiety and depression. A potential link is drawn between zinc-cadmiumsulfide, used in biological warfare trials, and urban air pollution, both demonstrating adverse effects on physical and mental health.

The distribution of airborne particulate matter of a similar size and composed of harmful minerals indicates an overlapping origin of neurological issues. These observations underscore the importance of understanding and addressing the multifaceted impact of environmental factors on mental health outcomes in diverse urban settings.

Higher rates of developmental disabilities have been reported in areas such as St. Louis, Missouri, and additional less prominent testing locations. Symptomatic mental health disorders such as anxiety and depression have been recorded to be more frequent in urban areas on average, with particularly high rates in areas which experienced the biological warfare trials.11 This is projected to be a link between the similarities between zinc-cadmium-sulfide and urban air pollution, which has been shown to cause adverse effects to physical and mental health.

10

Cao, Z. et al. (2023, January 23). Urbanites’ mental health undermined by Air Pollution.

11 Cao, Z. et al. (2023, January 23). Urbanites’ mental health undermined by Air Pollution.

1.3 Present Effect on Neurodegenerative Disorders The less investigated component of this study is the effect of exposure on neurological state later in life several decades after the initial exposure. This would indicate a long-lasting effect on either public health or environmental health, which would be an unaccounted-for result of these Cold War tests. Connecting exposure with permanent health concerns could negate the argument that these additives are only damaging to those in illhealth, as it would mean that the substances would take effect after being dormant. Public speculation regarding increased rates of cancer and chronic pneumonia have brought further focus onto the effects on senior subjects that were exposed during their adolescence.12 Previous research on dementia and ALS has often focused on finding a remedy rather than identifying a cause. In Alzheimer’s, the most common cause of dementia, it is believed to be caused by excessive accumulation of the proteins amyloid and tau, disrupting normal brain function. A decrease in neurotransmitters, a type called acetylcholine, arises in cases of Alzheimer’s. Depression and anxiety are also known to worsen symptoms of dementia, so neurological developmental disorders and early life mental disabilities will likely create a more severe case in patients.13 The potential to pinpoint specific elements that cause dementia or better understand the regional influence of airborne particulate matter could lead to new revelations in neurodegenerative disorder treatment and prevention. Creating a system of isolating these environmental factors, giving preventative care to high-risk individuals, and decreasing rates of exposure for disadvantaged 12

CBS Interactive. (2012, October 4). Secret cold war tests in St. Louis Cause Worry.

13 NHS. (2024, January 3). Causes of Dementia.

populations is the optimal outcome of this study and others that will likely follow.

METHODS 1. RESEARCH 1.1 Overall Design This study employs a mixed-method research design to observe the effect of environmental exposure to chemicals and toxins during fetal development and adolescence. The neurological function of subjects can then be linked to the elemental composition of their baby teeth and the effects on the brain can be measured.

Quantitative evidence was gathered during Phase I, wherein the elemental makeup of subjects’ baby teeth (and blood, toenails, bone and soil) was examined. My role in the study was coding of these tooth sample slides, which includes counting ablation spots, identifying the neonatal line in the enamel, and matching these spots to the individual data collected for each tooth ablation spot (Figure 4).

Figure 4: A drawn diagram of a common tooth sample, labeled.

During Phase II, the geographical location of each subject’s childhood home is collected based on the patient’s report, to the best of their ability and memory. If a subject cannot remember their address, their hometown where they were in utero is recorded.

Fetal exposure has been shown to be the most significant factor, which is demonstrated with baby teeth.14 The design of this study allows the collection of statistical data regarding known quantities of elements like lead, magnesium, and zinc, while also demonstrating the distribution of exposure. Race 14

Shishniashvili, T. et al. (2016). Primary Teeth and Hair as Indicators of Environmental Pollution.

and socio- economic status can be further linked to these exposures, which is made possible by this quantitative- qualitative method.

1.2 Participants This study includes participants between the ages of 55-75 who resided in areas exposed to chemical tests performed during the Cold War, with a large concentration in Missouri. Media coverage and general word of mouth surrounding the ethics of these studies helped distribute public awareness and interest.15 Those that may have been affected by these tests were contacted regarding their ability to participate in Phase I, based on their willingness to either donate their baby teeth or a blood sample.

Subjects could volunteer to participate in Phase I by sending their baby teeth by mail to Dartmouth for the St. Louis Baby Tooth Study, where the teeth would be categorized by participant ID number, sliced bilaterally, placed on slides, and ablated.

Some participants who choose to undergo a blood draw are visited at their residence by volunteers who take a sample and mail it to Harvard School of Public Health. Toenail samples can be mailed through a similar process as an additional patient sample. Soil samples are collected by professionals, and more often at rural testing sites in locations such as Colorado. Participants are given the opportunity to stop at any point in the study, such as if they do not desire further blood draws and receive survey questions.

2. DATA COLLECTION 2.1 Preparations

15

Goodwin, J. D. (2021, November 11). St. Louis Public Radio | STLPR.

The study utilized a laser ablation system to slice the tooth samples and to analyze the elemental breakdown of each tooth along the enamel-dentine junction.16 This process resulted in a thin piece of tooth (with slight variation in thickness) adhered to a glass slide using clear resin. These slides then underwent ablation to collect the elements present, at which point any individual tooth would have between 20-200 data groups per ablation spot. Each spot possesses multiple values to increase validity.

Samples that were ablated later in the series showed an improved process of two lines of ablation, one in the enamel and the other in the dentine. This makes identification of the correct neonatal spot more reliable during observational analysis. Any slides that were ablated in an abnormal manner were noted and potentially sent back for a review of preparation quality. The raw values are held in a data collection system, which can then be selected based on observational findings.

2.2 Observations Observational data for baby tooth samples was collected using a microscope (DinoLite and DinoCapture 2.0 Software). I performed this analysis manually for slides 1 through ~500, which included identification of the ablation spot closest to the start of the neonatal line in both the dentine and enamel. Additional notes on sample quality, tooth anomalies, and ablation errors were also made in conjunction with this process. The annotation usually followed the standards of ablated, unablated, absent, or highlighted yellow to indicate a cause for question (Figure 5).

16

Mohamad Ghazi, A. (2007). Introduction to Environmental Forensics (2nd ed., pp. 637–669).

Figure 5: Batch # and Batch Count [format: 4.187], as well as the NL point (significant in the dentine ablation spots) are highlighted in green in the table headers. Ablation style includes X, Y, and Z codes; X indicates an absence of ablation spots, Y indicates two lines of ablation spots with an area in which the dentine ablation follows the NL, and Z when there are two parallel and continuous lines in the dentine and pulp.

Blood sample collection and plasma consolidation were performed in the wet lab at Harvard, rather than the upper offices, where teeth samples were analyzed. A portable X-ray Fluorescence (XRF) machine was used to determine the elemental composition of 3 types of samples: participant toenail samples, testing grounds soil samples, and occipital bone samples. This data is analyzed in tandem with the data collected from tooth and blood samples.

2.3 Questionnaires Structured interviews were conducted to gather in-depth information on participants’ childhood home, experiences during development, current well-being, and concerns regarding the Cold War testing. Interviews were audio-recorded with participants' consent and transcribed verbatim for analysis. Online questionnaires are currently in the later stages of development and

will be sent out and analyzed within the coming months to study the qualitative mental state of subjects.

RESULTS & DISCUSSION 1. RESULTS 1.1 Data We have thus far confirmed a significant link between heavy metal and biological weapon test exposure with late life neurodegenerative disorders such as dementia. Rates of dementia are approximately 180% higher than seniors in areas without chemical and heavy metal exposure, with a historically noted higher rate of anxiety and autism in urban areas, which could be explained by similar environmental toxins.

Through qualitative data collection and subject surveys, there is also a widespread indication of negative psychological tolls on those who volunteered for the St. Louis Baby Teeth Survey. An adverse effect on community mental well-being and a lack of trust in government protection has led to a decrease in quality of life, and may be further correlated with inhabitant safety, law abidance, and ability to work. These instances of community unrest and abuse are reflected in many modern cases, such as the murder of Michael Brown by police and a lack of justice.17 This study has identified a significant causation between fetal heavy metal and environmental toxin exposure with poor cognitive development and later-in-life function. Patterns of high exposure and earlier cognitive decline was found in geographical childhood 17

Stanford Libraries. (2020, August 6). Michael Brown. Say Their Names Spotlight at Stanford.

home locations that underwent government Cold War test exposures. Negative neurological effects have been known to be exacerbated and caused by heavy metal intake having been a core improvement in public health, such as replacing lead paint and pipes. The results of this particular survey align with these trends and lend variability to the data.

Cadmium, being a key component of the airborne combination of materials distributed, was confirmed to cause negative cognitive performance on the immediate, delayed, and working memory tests. Lead and arsenic, heavy metals commonly known to be harmful, also negatively impacted performance on all 3 tests.18 Thus, it makes sense that the findings in this study would align with the findings of direct connections between heavy metal exposure and cognitive decline. The additional information we have gained, however, is the long-term presence and effect on neurological condition, something that most studies do not consider. This, in combination with the mysterious nature of the exact chemical and material compounds distributed (although we know they likely included lead, cadmium, and arsenic), makes it a more minute field worthy of study for the sake of public health.19 The results from Phase I of this study has laid the groundwork for pinpointing the exposure level in different regions and how much of each element was actually distributed and retained during development (Figure 6). Finding that these exposures are causing higher rates of neurodegenerative disorders such as Alzheimer’s disease and Lou Gehrig's disease means that these heavy metals remained in the body throughout subjects’ lifetime. This is a concern because it shows new lifelong implications for heavy 18

Sasaki (2022). International Journal of Environmental Research and Public Health, 19(4), 2327.

19 Karri, V. et al. (2016). Environmental Toxicology and Pharmacology, 48, 203– 213.

metal exposure, the body’s inability to overcome these toxins overtime, and a lasting effect on brain performance. That means that heavy metal exposure goes beyond fetal and adolescent development and is in fact chronic after a small, concentrated instance of exposure. There must be new consideration for the significance of heavy metal intake, and further precautions taken to prevent any sort of exposure for children, as we now see there are permanent repercussions.

Figure 6: A microscope photo taken by Sonya Moo from Batch 2 in Phase I of the study. A sample such as this is representative of the appearance of the tooth slides, including the presence of dentine striations, enamel thickness, and variety of tooth type (molar, canine, etc.) Tooth imaging can be later combined to form a larger cohesive image of each tooth while maintaining high definition if necessary. This image is labeled to show the important components of the photograph.

In the physical tooth samples, the form of ablation was not always consistent or sufficient, which could lead to a misreading of elemental composition. Similarly, blood sample temperature and bone or soil conditions were sometimes irregular due to mailing errors. There will also be inevitable errors when collecting survey responses for childhood home and geographical location, especially when subjects suffer from a neurodegenerative disorder that hinders memory. Because of this, mappings for population distribution and effect may be inaccurate, but should still be applicable on a city-wide scale. While this study will hopefully not be used to improve biological warfare methods, it does hold other important implications for the field of public and environmental health. These findings can be generalized to improve medical knowledge about the impact of heavy metal exposure, and perhaps an increased vigilance for cognitive decline if a patient has suffered exposure and is therefore predisposed to these neurological disorders.

Many of the gaps in our current data will be filled during Phase II of the study, yet there are also areas that could be expanded upon in the future. Medically speaking, a study into the exact reason for cognitive decline due to heavy metals would be a crucial next step.

This may involve analyzing tissue samples or doing a more indepth study of patients’ brains post mortem. In the field of environmental science, applying these geoarchaeological study methods to alternate historical events could be an interesting avenue to study public health before the modern era. Perhaps we could gain insight into human cognition based on these findings, and thus have a better understanding of historical events or decisions.20

20

Cordova, C. (2020). Geoarchaeology. Bloomsbury Publishing PLC.

FUTURE DIRECTIONS The data aligns with and expands upon existing studies and shows the correlation between heavy metal exposure during fetal development and decreased cognitive abilities. This research will be expanded upon in Phase II of this study, and hopefully go further in predisposition analysis in the future. In the face of public health concerns, the conduction of this survey over the past decades has been an important step in understanding ethical government practices and improving medical knowledge of environmental neurotoxicity. With these findings, there is proof that these high rates of neurological developmental and degenerative disorders are indeed connected to the tests performed on urban civilians.

Work Cited Cao, Z. et al. (2023, January 23). Urbanites’ mental health undermined by Air Pollution. Nature Sustainability. https://www.nature.com/articles/s41893-022-01032-1#citeas.

CBS Interactive. (2012, October 4). Secret cold war tests in St. Louis Cause Worry. CBS News. https://www.cbsnews.com/news/secret-cold-war-tests-in-st-louiscause-worry/.

Cordova, C. (2020). Geoarchaeology: The Human-Environmental Approach (Environmental History and Global Change).

Bloomsbury Publishing PLC. Goodwin, J. D. (2021, November 11). Survivors of Cold War-era experiments on Black St. Louisans speak out in documentary. St. Louis Public Radio | STLPR. https://www.stlpr.org/arts/2021-1111/survivors-of-cold-war-era-experiments-on-black-st-louisansspeak-out-in-documentary.

Harvard T.H. Chan School of Public Health. (2022, July 25).

Project 1: Early life metal exposures and cognitive aging.

MEMCARE Superfund Research Center. https://memcare.sph.harvard.edu/early-life-metal-exposurecognitive-aging.

Kalckar, H. M. (1958). An International Milk Teeth Radiation Census. Nature, 4631, 283-284. https://www.nature.com/articles/182283a0.pdf Karri, V., Schuhmacher, M., & Kumar, V. (2016). Heavy metals (Pb, Cd, As and MeHg) as risk factors for cognitive dysfunction: A general review of metal mixture mechanism in brain.

Environmental Toxicology and Pharmacology, 48, 203–213. https://doi.org/10.1016/j.etap.2016.09.016.

Mohamad Ghazi, A. (2007). Chapter 14 - Applications of Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LAICP-MS) in Environmental Forensic Studies. In Introduction to Environmental Forensics (2nd ed., pp. 637–669). essay, Elsevier Science.

National Research Council (US) Committee on Toxicology.

(1997). Toxicologic Assessment of the Army’s Zinc Cadmium Sulfide Dispersion Tests: Answers to Commonly Asked Questions.

Washington (DC): National Academies Press (US). https://www.ncbi.nlm.nih.gov/books/NBK233549/.

NHS. (2024, January 3). Causes of Dementia. NHS. https://www.nhs.uk/conditions/dementia/about-dementia/causes/.

Prentice, A. (2003). Micronutrients and the Bone Mineral Content of the Mother, Fetus and Newborn. The Journal of Nutrition, 133(5), 1693S-1699S. Salter, J. (2023, September 25). “We were experimented on”: Victims of secret Cold War testing in St. Louis Demand Compensation. NBC News. https://www.nbcnews.com/news/usnews/-experimented-victims-secret-cold-war-testing-st-louisdemand-compensa-rcna117149.

Sasaki, N., & Carpenter, D. O. (2022). Associations between Metal Exposures and Cognitive Function in American Older Adults.

International Journal of Environmental Research and Public Health, 19(4), 2327. https://doi.org/10.3390/ijerph19042327.

Shishniashvili, T., Suladze, N., & Margvelashvili, V. (2016).

Primary Teeth and Hair as Indicators of Environmental Pollution.

Journal of Clinical Pediatric Dentistry, 40(2), 152–155. https://doi.org/https://meridian.allenpress.com/jcpd/article/40/2/15 2/78600/Primary-Teeth-and-Hair-as-Indicators-of.

Stanford Libraries. (2020, August 6). Michael Brown. Say Their Names - Spotlight at Stanford. https://exhibits.stanford.edu/saytheirnames/feature/michaelbrown.

Vierheller, P. et al. (2009). St. Louis Baby Tooth Survey, 19591970. St. Louis Baby Tooth Survey. http://beckerexhibits.wustl.edu/dental/articles/babytooth.html.