Polycyclic aromatic hydrocarbons (PAHs) and their effect of general and periodontal health

Introduction

Polycyclic aromatic hydrocarbons (PAHs) are a group of organic compounds composed of multiple aromatic rings. They are primarily formed during the incomplete combustion of organic materials such as coal, oil, gas, wood, and tobacco. PAHs are known environmental pollutants and have been associated with various adverse health effects, including respiratory diseases, cardiovascular diseases, and cancers. They are often found in soil, water, and air, and can pose significant health risks due to their toxic, mutagenic, and carcinogenic properties.

Effect of polycyclic aromatic hydrocarbons on general health

PAHs are well-known for their carcinogenic potential. Long-term exposure has been linked to various cancers, including lung, skin, bladder, liver, and stomach cancers. Workers in industries such as coal tar production, asphalt paving, and aluminum production are at higher risk due to prolonged exposure to PAHs. Respiratory effects of PAHs are more prominent. Exposure to PAHs can lead to reduced lung function and exacerbate conditions like asthma. Increased rates of obstructive lung diseases have been observed in populations exposed to high levels of PAHs. The PAHs have significant effect on cardiovascular system. Long-term exposure to PAHs has been associated with an increased risk of cardiovascular diseases (References available in book). PAHs can weaken the immune system, making individuals more susceptible to infections. Direct contact with PAHs can cause skin irritation and dermatitis. Along with this, some PAHs can increase the skin’s sensitivity to sunlight, leading to phototoxic reactions. PAHs also adversely affect the reproductive system. Animal studies have shown that PAHs can affect reproductive health, including reduced fertility and developmental issues in offspring (References available in book). Limited evidence suggests that PAH exposure may adversely affect cognitive and behavioral functions in children.

Possible Mechanisms explaining adverse effects of PAHs on health

Polycyclic aromatic hydrocarbons (PAHs) affect general health through several mechanisms, primarily involving oxidative stress, inflammation, DNA damage, and disruption of cellular processes. Here’s a detailed look at how PAHs exert their toxic effects on general health:

Oxidative Stress

PAHs can generate reactive oxygen species (ROS) during their metabolic activation. These ROS cause oxidative stress, leading to cellular damage, lipid peroxidation, protein oxidation, and DNA damage. The imbalance between ROS production and the body’s antioxidant defenses results in oxidative stress, which is implicated in various diseases.

Inflammation

PAHs can activate inflammatory pathways, leading to chronic inflammation. This occurs through several mechanisms:

Activation of Aryl Hydrocarbon Receptor (AhR): PAHs bind to AhR, a transcription factor that regulates the expression of genes involved in detoxification and immune responses. Activation of AhR by PAHs can lead to the production of pro-inflammatory cytokines.

Nuclear Factor Kappa B (NF-κB) Pathway: PAHs can activate the NF-κB pathway, a key regulator of the immune response, resulting in the production of inflammatory mediators such as cytokines and chemokines.

DNA Damage and Mutagenesis

PAHs are metabolized in the body to form reactive intermediates that can bind to DNA, forming PAH-DNA adducts. These adducts cause mutations and chromosomal aberrations, which can initiate carcinogenesis. PAHs are classified as genotoxic carcinogens due to their ability to cause mutations and contribute to cancer development.

Endocrine Disruption

Some PAHs have endocrine-disrupting properties, meaning they can interfere with hormone signaling. They can mimic or antagonize the action of hormones, leading to altered endocrine function. This can affect reproductive health, development, and metabolic processes.

Immune System Modulation

PAHs can modulate the immune system, either suppressing or enhancing immune responses. This can lead to an increased susceptibility to infections, autoimmune diseases, and other immune-related conditions.

Cellular Toxicity

PAHs can exert direct cytotoxic effects on various cell types. This includes inducing apoptosis (programmed cell death), necrosis (uncontrolled cell death), and impairing cellular functions such as proliferation, differentiation, and communication.

Association between Polycyclic aromatic hydrocarbons and periodontal disease

Recent studies have highlighted a significant association between exposure to polycyclic aromatic hydrocarbons (PAHs) and periodontal health issues, particularly periodontitis. Research involving 1880 participants from the National Health and Nutrition Examination Survey (NHANES) found that exposure to multiple PAHs was positively associated with an increased risk of periodontitis (References available in book). Another study showed a gradual increase in periodontitis risk with higher levels of PAH exposure. For example, participants in the highest quartile of exposure to certain PAHs had significantly higher odds of developing periodontitis compared to those in the lowest quartile. PAHs can induce inflammatory responses in the body, which can exacerbate periodontal disease. One study identified blood neutrophils as partial mediators of the effects of specific PAHs, such as 3-hydroxyfluorene (3-OHF) and 2-hydroxyfluorene (2-OHF), on periodontitis (References available in book). Reducing exposure to PAHs through improved air quality, smoking cessation, and safer industrial practices can help mitigate the risk of periodontitis. Increasing public awareness about the sources and health impacts of PAHs is crucial for promoting better periodontal health.

Possible Mechanisms Linking PAHs to Periodontitis

Inflammation and Immune Response: PAHs can induce systemic inflammation and modulate immune responses. They can activate pathways such as the aryl hydrocarbon receptor (AhR) pathway, leading to the production of pro-inflammatory cytokines. This systemic inflammation may contribute to the inflammatory processes in the periodontal tissues.

Oxidative Stress: PAHs can generate reactive oxygen species (ROS), leading to oxidative stress. Oxidative stress is a key factor in the pathogenesis of periodontitis, as it can damage periodontal tissues and exacerbate the inflammatory response.

Microbiome Alteration: Exposure to PAHs may alter the composition of the oral microbiome, promoting the growth of pathogenic bacteria associated with periodontitis. This dysbiosis can enhance the susceptibility to periodontal disease.

Direct Toxicity: PAHs can exert direct toxic effects on periodontal cells, impairing their function and viability. This can weaken the periodontal support structures and facilitate disease progression.

Methods to prevent production of Polycyclic aromatic hydrocarbons

Preventing the production of polycyclic aromatic hydrocarbons (PAHs) involves reducing their formation at the source, which primarily occurs during the incomplete combustion of organic materials. The methods to reduce PAH production include the following,

Improve Combustion Efficiency

We should use advanced combustion technologies that ensure complete combustion of fuels. For example, high-efficiency burners, stoves, and engines can reduce the formation of PAHs. Regular maintenance of combustion equipment (e.g., engines, furnaces, stoves) should be done to ensure they operate efficiently and produce fewer PAHs. Another important measure is maintaining optimal combustion conditions, including appropriate temperature, oxygen supply, and mixing of fuel and air to minimize incomplete combustion.

Use Cleaner Fuels

We should switch to clean energy sources. Use cleaner energy sources such as natural gas, electricity, and renewable energy (solar, wind, hydropower) instead of coal, wood, and oil can significantly reduce the production of PAHs. Use refined fuels with lower impurity levels also reduced PAH production. For example, low-sulfur diesel and gasoline produce fewer PAHs during combustion. Along with this, we should consider using alternative fuels like biodiesel and ethanol, which produce fewer PAHs compared to traditional fossil fuels.

Implement Emission Control Technologies

Use catalytic converters in vehicles and industrial processes can reduce PAH emissions. These devices convert harmful pollutants into less harmful substances. Particulate filters should be installed in exhaust systems to capture PAHs and other particulate matter before they are released into the atmosphere. We should use scrubbers and electrostatic precipitators in industrial settings to remove PAHs and other pollutants from exhaust gases.

Adopt Cleaner Industrial Processes

We must optimize industrial processes to minimize the formation of PAHs. For example, in the steel industry, using electric arc furnaces instead of traditional coke ovens can reduce PAH emissions. We should use alternative materials that produce fewer PAHs when processed. For example, in the production of aluminum, using prebaked anodes instead of Søderberg anodes can reduce PAH emissions.

Regulate and Monitor Emissions

Implementation and enforcement of stringent regulations on PAH emissions from industrial processes, transportation, and residential heating should be done. We should ensure continuous monitoring systems to track PAH emissions and ensure compliance with regulatory standards.

Promote Public Awareness and Education

We must educate the public about the sources and health effects of PAHs and encourage behaviors that reduce PAH production, such as using cleaner fuels and properly maintaining combustion appliances. We can provide training for workers in industries that produce PAHs to adopt best practices for minimizing emissions.

Reduce Biomass Burning

We can promote cleaner cooking methods and stoves in regions that rely on biomass for cooking. Improved cookstoves and solar cookers can significantly reduce PAH emissions. We can also implement sustainable forest management practices to reduce uncontrolled biomass burning and forest fires, which are significant sources of PAHs.

Implement Urban Planning Measures

Incorporation of green infrastructure in urban planning to absorb and filter pollutants, including PAHs, from the air. Also we should implement traffic management measures to reduce vehicle emissions, such as promoting public transportation, carpooling, and non-motorized transport (biking, walking).

Conclusion

PAHs have widespread and multifaceted effects on general health, largely mediated through mechanisms involving oxidative stress, inflammation, DNA damage, and disruption of normal cellular functions. Understanding these mechanisms is crucial for developing strategies to mitigate PAH exposure and reduce their adverse health impacts. Preventing the production of PAHs requires a multifaceted approach involving technological advancements, regulatory measures, public awareness, and changes in behavior. By implementing these strategies, it is possible to significantly reduce PAH emissions and their associated health and environmental impacts.

References

References are available in hardcopy of the website “Periobasics: A Textbook of Periodontics and Implantology”.