FACTS ABOUT PAHS

In many countries, including the USA and the European Union, Polycyclic Aromatic Hydrocarbons are classified as priority pollutants. Sixteen specific PAHs have been identified as being of significant concern for both environmental and human health. People are typically exposed to a mixture of PAHs rather than individual compounds. These mixtures can be found in numerous everyday sources. PAHs are pervasive in the environment, and exposure to these substances can occur in various settings, including homes, outdoor spaces, and workplaces. In the United States, PAHs have been detected in some drinking water supplies, with background levels ranging from 4 to 24 nanograms per liter (ng/L).

These compounds are formed through the incomplete combustion of various organic materials, including coal, oil, gas, wood, and even everyday substances like tobacco and charbroiled meat. Comprising over 100 different types, PAHs are typically found in complex mixtures, such as those present in combustion byproducts like soot. While they are predominantly natural in origin, individual PAHs can also be synthesized for research purposes. However, these manufactured compounds do not replicate the intricate mixtures found in natural combustion products.

In their pure form, PAHs are often observed as colorless, white, or pale yellow-green solids. Some may even emit a faint, pleasant odor. Their applications are diverse, ranging from medicinal uses to the manufacturing of dyes, plastics, and pesticides. Certain PAHs are integral components of asphalt, playing a vital role in road construction.

PAHs are not confined to specific industrial applications; they are ubiquitous in the environment, found in air, water, and soil. They may be present in the air, attached to dust particles, or exist as solids in soil or sediment. Their widespread presence in substances such as crude oil, coal tar pitch, creosote, and roofing tar further underscores their environmental significance.

The study of PAHs has practical implications for understanding their impact on the environment and human health. As the exploration of PAHs continues, their complex nature and varied applications present both opportunities and challenges, making them a compelling subject in the field of environmental science. Their story is a testament to the intricate relationship between human activity, chemical innovation, and the natural world.

PAHs in the environment

Primarily, PAHs are released into the air from natural sources such as volcanoes and forest fires, as well as human activities like residential wood burning and vehicular exhaust. These airborne PAHs can travel vast distances, existing as vapors or adhering to small solid particles, before returning to the earth through rainfall or particle settling. In addition to air, PAHs can also contaminate surface water. This can occur through discharges from industrial facilities and wastewater treatment plants. If improperly stored, they may escape from containers at hazardous waste sites, leading to soil contamination.

The behavior of PAHs in the environment is influenced by specific properties, such as their solubility in water and volatility. Generally, PAHs are not highly soluble in water, which affects how they move and where they accumulate. While some PAHs may evaporate into the atmosphere from surface waters, the majority tend to adhere to solid particles, eventually settling at the bottoms of rivers or lakes. In the realm of soil, PAHs are more likely to cling tightly to particles, limiting their mobility. However, certain PAHs have been known to contaminate underground water sources, posing potential risks to both the environment and human health.

PAH Exposure in People

Exposure to PAHs is a multifaceted issue that can occur through various means, reflecting the widespread presence of these chemicals in our daily lives.

  • 1. Breathing Air Containing PAHs: Individuals may be exposed to PAHs through the air they breathe. This can include: Emissions from cars, trucks, and other vehicles contain PAHs, contributing to air pollution, smoking or being around smokers can lead to inhalation of PAHs present in tobacco smoke, burning wood in fireplaces, stoves, or open fires releases PAHs into the air as well as the heating and application of asphalt on roads can release fumes containing PAHs.
  • 2. Dietary Exposure: Cooking methods that char or grill meats can create PAHs, leading to ingestion through consumption also PAH particles can settle on food from the air, leading to unintentional ingestion. Once PAHs enter a person's body, they undergo a transformation. The body metabolizes these chemicals into breakdown products known as metabolites. These metabolites are then excreted from the body through urine and feces. The pathways of PAH exposure highlight the complex relationship between human activities, environmental factors, and individual behaviors. Understanding these exposure routes is vital for assessing risks and implementing measures to minimize potential health impacts. The presence of PAHs in various aspects of daily life underscores the importance of continued research, public awareness, and responsible practices to mitigate exposure and safeguard public health

Federal Regulations

The U.S. Environmental Protection Agency (EPA) has provided guidelines to protect individuals from potential health effects of PAHs. Suggested daily intake limits for specific PAHs include:

  • Anthracene: 0.3 milligrams (mg)
  • Acenaphthene: 0.06 mg
  • Fluoranthene: 0.04 mg
  • Fluorene: 0.04 mg
  • Pyrene: 0.03 mg all per kilogram (kg) of body weight.

The presence of PAHs in various aspects of daily life underscores the importance of understanding their sources, exposure pathways, and potential health impacts. Federal regulations and guidelines aim to mitigate risks, but continued vigilance, research, and public awareness are essential to ensure safety and minimize exposure to these complex chemical compounds.

How PAHs Affect People’s Health

CDC Investigation: A significant study led by the Centers for Disease Control and Prevention (CDC) delved into the presence of Polycyclic Aromatic Hydrocarbons (PAHs) within the U.S. population. During the years 2003–2004, scientists analyzed ten different PAH metabolites in the urine samples of 2,504 individuals, aged six and older. These participants were part of the broader National Health and Nutrition Examination Survey (NHANES). The findings of the study were revealing, as PAHs were detected in the majority of the participants.

Long-term Exposure and the Risk of Cancer

Chronic Contact with PAHs: Research into the long-term effects of exposure to PAHs has revealed concerning links to cancer. Individuals who have been exposed to mixtures containing PAHs, either through breathing or skin contact over extended periods, may be at risk of developing cancer. The impact of exposure to PAHs is not straightforward. It is influenced by a myriad of factors, including the dosage, duration of exposure, method of contact, personal attributes, lifestyle habits, and even the presence of other chemicals. This complexity necessitates a nuanced approach to understanding and mitigating the risks associated with PAHs.

Polycyclic Aromatic Hydrocarbons in Breast Milk of Nursing Mothers: Correlates with Household Fuel and Cooking Methods Used in Uganda, East Africa

A research project in Uganda examined the presence of Polycyclic Aromatic Hydrocarbons (PAHs) in the breast milk of 60 nursing mothers, with a particular focus on how household fuels and cooking techniques affected these levels. The study found that PAHs with 2–3 rings were more prevalent, and that 33% of the variation in PAH concentrations could be attributed to the fuel type and cooking methods used. Specifically, charcoal was associated with higher PAH levels than firewood, and the levels increased depending on the cooking method, in the sequence of boiling, grilling, and deep-frying. While the study determined that the associated health risks to infants were within acceptable limits, it underscored the necessity for additional research to confirm these findings.

https://www.cdc.gov/biomonitoring/PAHs_FactSheet.html

https://wwwn.cdc.gov/TSP/PHS/PHS.aspx?phsid=120&toxid=25

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Ssepuya, F., Odongo, S., Bandowe, B. A. M., Abayi, J. J. M., Olisah, C., Matovu, H., ... & Ssebugere, P. (2022). Polycyclic aromatic hydrocarbons in breast milk of nursing mothers: Correlates with household fuel and cooking methods used in Uganda, East Africa. Science of The Total Environment, 842, 156892.

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WHY IS A BIOSENSOR FOR PHENANTHRENE DETECTION IN WATER IMPORTANT?

In a series of studies conducted across different regions, the presence and potential environmental impact of Polycyclic Aromatic Hydrocarbons (PAHs), with a particular focus on phenanthrene, have been brought to light.

In Malaysia, research into the ecological effects of PAH contamination in aquatic ecosystems has uncovered alarming findings. Phenanthrene, one of the PAHs, was found to have harmful effects on the African catfish (Clarias gariepinus), including triggering oxidative stress and negatively impacting the immune system.

Meanwhile, in Tehran, Iran's capital, an investigation into urban runoff revealed significant concentrations of phenanthrene. The study found that the average PAH level in the city's most polluted drainage system was about 9.4 µg/l, with concentrations ranging from zero to a peak of 15.1 µg/l. Intriguingly, the rainy season saw a spike in phenanthrene levels, as rainwater washed the pollutant from the streets. Furthermore, the central drainage channel, which handles runoff from the heavily trafficked city center, recorded higher phenanthrene levels compared to other channels.

In another comprehensive analysis, the concentrations of six specific PAHs, including phenanthrene, were examined in water, Catfish, and Tilapia. Phenanthrene emerged as the second most prevalent PAH, with a concentration of 0.083 mg/L in water. The study also emphasized that the levels of PAHs were consistent across both water and fish, hinting at a shared source of contamination. These findings collectively underscore the importance of monitoring phenanthrene and other PAHs in the environment. As urbanization and pollution continue to rise, the levels of these potentially harmful compounds are likely to increase, posing a growing threat to both aquatic ecosystems and human health.

A biosensor specifically designed to detect phenanthrene would offer a precise and efficient method for regular monitoring. This could be vital for both early detection of contamination and ongoing water quality management. With increasing awareness of the environmental and health impacts of PAHs, there may be regulatory requirements to monitor and control phenanthrene in water. A biosensor for phenanthrene would facilitate compliance with such regulations.

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Karami, A., Romano, N., Hamzah, H., Simpson, S. L., & Yap, C. K. (2016). Acute phenanthrene toxicity to juvenile diploid and triploid African catfish (Clarias gariepinus): molecular, biochemical, and histopathological alterations.

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