Air Pollution and Adverse Health Implications

Introduction

The exposure to clean, good quality air is a basic health and well-being necessity^[1]. However, high levels of air pollution can result in significant negative health implications^[2]. Urbanisation, industrial activity and automobile activity are prominent sources of air pollution; emitting pollutants as a harmful byproduct, consisting of: Particulate Matter, Ozone, Nitrogen Oxide and Sulphur Dioxide^[2]. The guidelines for emission concentrations of fine particulate matter (PM2.5) in the UK is an annual mean of 10µg/m3 (micrometers per meter cubed) and for coarse particulate matter (PM10) an annual mean of 20µg/m3^[3]. In 2019, the UK is currently achieving these annual mean emission targets outlined by the World Health Organization (WHO). However, the city of London is exceeding the annual mean target of PM2.5 by 50% at 15µg/m3^[4]. Globally, the struggle for cities to limit their annual particulate matter emissions is evident with high annual PM2.5 concentrations: Los Angeles (USA) reported 18.4µg/m3, Paris (France) is 20.2µg/m3 and Beijing (China) has a reported annual equivalent of 54.75µg/m3^[5].

India are currently experiencing an air pollution crisis, with a severe pollution smog caused by farmers burning crop stubble, high volumes of automobiles on the road and the high number of fireworks used during Diwali. The PM2.5 concentration in Delhi is reported to be 533µg/m3, which is upward of 20 times over the WHO guideline limit^[6]! The urgency to improve air quality in Delhi could not be clearer due to the significant health complications caused by air pollution, especially from unprecedented PM exposure in this particular case.

Long Term Health Implications

Cardiovascular Health

Air pollution is acknowledged as a prominent risk factor associated with the development of cardiovascular disease, respiratory disease and mortality^[7]. This is supported by research highlighting a significant association between commonly emitted air pollutants and an increased risk of short term heart attack episodes^[8]. Furthermore, air pollution has been reported to contribute to the increased risk of type 2 diabetes onset by approximately 39% per 10µg/m3 of PM2.5^[9].It is theorised that air pollution increases the resistance of the body to insulin which underpins the increased vulnerability of type 2 diabetes onset^[10].

Air pollution is also acknowledged to impair cardiac and vascular health over time and increase the risk of cardiovascular disease and mortality^[11]. The adverse cardiovascular health implications associated with air pollution exposure are suggested to be incurred through a series of cardiovascular inflictions^[12], consisting of:

• Systemic (vascular) inflammation
• Vascular and organ oxidative stress
• Thrombosis and blood coagulation
• Hypertension (elevated blood pressure)
• Blood vessel dysfunction (atherosclerosis)

Respiratory Health

High concentrations of fine particulate matter (PM2.5) are acknowledged to be more harmful to lung function and linked to increased incidence of respiratory disease compared with larger particulate matter; fine particulate matter is able to penetrate deep into the lung tissue, bypassing the body’s natural filtration mechanisms whilst still transmitting harmful toxins due to a large relative surface area^[13]. Particulate matter causes airway inflammation and hyperresponsiveness which inflicts oxidative stress on respiratory tissue; for those with asthma, symptoms can be significantly exacerbated^[14]. Therefore, it is critical to ensure asthma treatments are selected to reduce respiratory irritation and the worsening of asthma related symptoms. Whilst strict governmental policy is in place to control emitted particulate matter, many industrialised and urbanised cities struggle to limit harmful fine particulate matter emissions.

Cognitive Health

Long-term exposure to high concentrations of air pollution has been associated with adverse cognitive function, where cognitive development can be impeded and maintenance of cognitive function in aging populations can be impaired^[15]. The inhalation of pollutants is reported to cause neuroinflammation in the brain through increased immune activity, a consequence of this inflammatory reaction in chronic instances is cell cycle loss and apoptosis of neurons^{[16] [17]}. PM2.5 particles have been found to travel through the bloodstream of the body directly through the olfactory pathway, entering the brain. Mice studies have shown neuropathic inflammation alongside changes in the morphology in the hippocampal region of the brain^[18], directly impacting the central nervous system. Furthermore, once present in the brain these particulates can cause neuronal degeneration and diminish white matter which increases the likelihood of the development of onset Alzheimers or Parkinsons.

Air Pollution and Alzheimers

Substances occurring in smog have also been found to increase the chances of systemic infection in individuals. This would seem to increase the presence of prefrontal brain damage, damage to the blood brain barrier and increases in the Aß42 protein, responsible for Alzheimers^[19]. It is the chronic release of these inflammatory mediators as a response to pollution that raises the risk and likelihood of developing serious health conditions or worse lead to death.

Air Pollution and IQ

It has also been demonstrated that pollution in the form of PM10 and lower can reduce the IQ of those exposed to chronically high levels of PM, however, this is most impactful for children and elderly^[20], especially those living in close proximity to busy roads. With decreases in IQ of over 5 points in some cases, this would have ramifications for the development of the child and wider society.

Air Pollution and Mental Wellbeing

Aside from the immediate impacts, pollution has also been linked to greater instances of Psychosis and other mental disorders. Research has been able to draw clear correlations between air pollution exposure and visits to the emergency department for substance abuse^[21]. In a similar study investigating Emergency Department visits for depression, a strong correlation was found between increased levels of Ozone, PM2.5 and NO2 and visits in the following days^[22]. In particular, short term increases in PM, NOx, SO2 concentrations in the atmosphere are attributed to increased suicides 1-3 days after exposure^[22]. These increases in suicide rate were small, accounting for a 2% increase in estimated suicide risk but were consistent over a period of thirty years.

Sexual Health

Air Pollution and Genetic Damage

Whilst further research is needed, there has been evidence to suggest male fertility can be impaired by long term exposure to air pollution. Reduced semen quality, characterised by increased DNA fragmentation (breaking/separation of DNA) and decreased incidence of normal sperm morphology, has emerged as a possible side effect of extensive air pollution exposure^[23].

Sperm Quality and Quantity with Air Pollution Exposure

Not only does air pollution cause genetic damage but has also been shown to distort X:Y chromosome count in the sperm of men exposed to high pollution levels^[24]. This phenomena was seen in mice but with the added effect of a substantially reduced sperm count, compared to non-exposed males.

Air Pollution and Erectile Dysfunction

Recent studies have shown some correlation between erectile dysfunction and increased rates of erectile dysfunction^[25]. Erectile Dysfunction is heavily associated with cardiovascular disease, given air pollution has a clear and measurable effect on the health of the cardiovascular system it is likely that this contributes to Erectile Dysfunction in men. Exposure to PM can cause oxidative stress and inflammation in various areas of the cardiovascular system, usually resulting in endothelial dysfunction.

Air Pollution exposure and Pregnancy

For women, it seems that there is a correlation between living near major roads and infertility. Further to this, it has been shown that exposure to particulate matter during fetal growth may likely contribute to health problems during middle age^[28]. It is thought that pollutants are inhaled and then are able to enter the maternal bloodstream. Highly bioactive toxicants such as Polycyclic Aromatic Hydrocarbons (PAHs) are likely to interfere with the development and nourishment of the fetus ^[26].

Hair Loss

Particulate matter present in the air is known to cause oxidative stress in many areas across the body, these particles can carry a number of different heavy metals such as lead and mercury alongside organic chemicals. These metals and chemicals are able to concentrate in the mitochondria of cells and then produce reactive oxidative oxygen species. PAHs are among the most common but also the most reactive. These are usually produced from vehicle emissions, asphalt roads, forest fires and industrial processes. Unfortunately, these PAHs can remain active in the air, soil and water for extensive periods of time. PAHs are able to be absorbed onto the surface of PM present in the atmosphere, these can then find themselves on the scalp, having an even worse impact on hair follicles accelerating hair loss.

It has been demonstrated that oxidative stress in hair follicles is much greater with increased pollution levels, this leads to an increase in hair shedding, similar to the mechanism of hair loss associated with androgenic alopecia^[27].

There are a number of ways to reduce the impact of air pollution. It has been suggested that regular use of an EDTA shampoo can provide a cleansing effect for the scalp, removing dirt grime and particulate matter built up over the course of a few months. It is important to let this shampoo sit for at least three minutes but ideally for five minutes. Once the scalp has been cleansed the application of coconut oil to the hair itself can provide a protective effect from further interaction with PM. It is also a good idea to combine this with a course of antioxidants, vitamins and minerals. These methods of treatment alongside small applications of minoxidil have shown to increase the density of hair follicles, and reduce the reported amount of hair loss after a four month period^[28].