Why coal tar can cause cancer?

The carcinogenic mechanism of coal tar primarily involves the presence of a complex mixture of polycyclic aromatic hydrocarbons (PAHs).

PAHs are organic compounds composed of multiple aromatic rings, and many of them are known to be carcinogenic. When coal tar is applied to the skin or when individuals are exposed to it occupationally or environmentally, the PAHs within the coal tar can be absorbed into the body.Research from Health and Safety Executive indicates that the polycyclic aromatic hydrocarbons (PAHs) present in coal tar pose a serious health threat to workers, and long-term exposure significantly increases the risk of developing cancer.

Why coal tar can cause cancer
Why coal tar can cause cancer

Once inside the body, PAHs can undergo metabolic transformation in the liver. This process can convert PAHs into reactive intermediates that have the potential to bind to DNA. This binding can result in the formation of DNA adducts, which are chemical modifications to the DNA molecule. If not repaired, these adducts can lead to errors during DNA replication, potentially causing mutations in critical genes that regulate cell growth and division.

Mutations in tumor suppressor genes, for example, can disable their normal function, which is to prevent the formation of tumors. Additionally, mutations in proto-oncogenes, which are genes that regulate cell growth, can convert them into oncogenes, promoting uncontrolled cell growth and division.

The ultimate outcome of these genetic alterations can be the development of cancer. The specific type of cancer that may result from coal tar exposure can vary depending on the tissues that are most affected by the PAHs. For example, skin exposure to coal tar is associated with an increased risk of skin cancer, while inhalation of coal tar particles can increase the risk of lung cancer.

Coal tar is also used in some medical treatments for conditions like psoriasis and eczema due to its anti-inflammatory and keratolytic properties. However, the benefits of such treatments must be weighed against the potential risks of exposure to carcinogenic compounds. Regulatory agencies and healthcare professionals carefully consider the balance of risks and benefits when prescribing or recommending treatments involving coal tar.

The primary cancers linked to coal tar exposure

Coal tar, which contains high levels of polycyclic aromatic hydrocarbons (PAHs), has been associated with an increased risk of several types of cancer. The primary cancers linked to coal tar exposure include:

  1. Skin Cancer: Prolonged skin contact with coal tar, such as in the case of workers in the roofing industry or those using coal tar-based skin treatments, has been associated with an increased risk of skin cancer, including squamous cell carcinoma and basal cell carcinoma.
  2. Lung Cancer: Inhalation of airborne PAHs from coal tar, particularly in occupations like road construction, roofing, and coal gasification, has been linked to an increased risk of developing lung cancer.
  3. Bladder Cancer: Some studies have suggested a potential increased risk of bladder cancer among workers exposed to coal tar, although the evidence is not as strong as for skin and lung cancer.
  4. Scrotal Cancer: Historical data has shown a high incidence of scrotal cancer in chimney sweeps, who were exposed to soot and coal tar due to their occupation, which involved climbing into chimneys and coming into direct contact with the tar deposits.

Occupational exposure

Occupational exposure to coal tar can occur in a variety of industries and job roles where workers may come into contact with coal tar products or during the production and use of coal tar itself. Here are some of the professions and industries where such exposure is more likely:

The primary cancers linked to coal tar exposure
The primary cancers linked to coal tar exposure
  1. Coal Gasification and Coke Production Workers: In the past, coal gasification plants produced gas for heating and lighting from coal, and the byproduct was coal tar. Workers in these facilities, as well as those in coke oven plants where coal is heated to produce coke, could be exposed to coal tar.
  2. Road Construction and Maintenance Workers: Coal tar has been used historically as a binder in asphalt for road paving due to its waterproofing and binding properties. Workers involved in the construction, repair, and maintenance of roads where coal tar-based pavements are used may be exposed to coal tar.
  3. Roofing Industry Professionals: Coal tar pitch was traditionally used in roofing materials, especially for waterproofing flat roofs. Roofers who work with coal tar-based products can be exposed to coal tar during the application and repair of such roofs.
  4. Wood Preservation Workers: Coal tar creosote, which is a wood preservative, is used to treat wood to protect it from moisture and decay. Workers in木材 preservation facilities where creosote is used may be exposed to coal tar.
  5. Railroad Workers: Coal tar-based products have been used for treating wooden railway ties (sleepers) to extend their lifespan. Workers involved in the maintenance and replacement of railway ties could be exposed to coal tar.
  6. Utility Workers: In some cases, utility workers may come into contact with coal tar when working with or near older infrastructure that may have used coal tar for sealing or insulating purposes.
  7. Chemical and Pharmaceutical Industries: Coal tar is used in the production of various chemicals and pharmaceuticals, such as dyes, pharmaceutical intermediates, and pesticides. Workers in these industries may be exposed to coal tar during the manufacturing process.
  8. Research and Development Scientists: Scientists and researchers studying the properties of coal tar or developing new applications for coal tar byproducts may be exposed in laboratory settings.

How to reduce the hazards?

Occupational workers can mitigate the health risks associated with coal tar exposure by implementing a combination of engineering controls, administrative measures, and personal protective equipment (PPE). Here are some strategies to reduce the hazards:

How to reduce the hazards
How to reduce the hazards
  1. Engineering Controls: These are measures designed to remove or reduce the hazard at its source. They include:
    • Local Exhaust Ventilation: Installing ventilation systems to remove airborne contaminants and minimize inhalation exposure.
    • Enclosure: Using physical barriers or enclosures around processes that generate coal tar fumes or dust to contain them and prevent their spread.
    • Substitution: Where possible, replacing hazardous materials with less toxic alternatives.
  2. Administrative Controls: These are policies and work practices that aim to reduce exposure. They include:
    • Training: Providing comprehensive training to workers on the hazards of coal tar, including proper handling, storage, and disposal procedures.
    • Work Practices: Implementing safe work practices, such as wetting down work areas to reduce dust and using low-vapor pressure materials to minimize the release of volatile compounds.
    • Rotation: Limiting the duration and frequency of workers’ exposure by rotating tasks or job roles to reduce overall exposure levels.
  3. Personal Protective Equipment (PPE): This includes wearing specialized clothing and equipment to prevent contact with coal tar. PPE may include:
    • Respiratory Protection: Wearing appropriate respiratory protection, such as NIOSH-approved powered air-purifying respirators (PAPRs) or supplied-air respirators, when engineering controls are not sufficient to reduce inhalation exposure.
    • Skin Protection: Wearing impermeable gloves, aprons, and boots to prevent skin contact with coal tar.
    • Eye Protection: Using safety goggles or face shields to protect against splashes or dust that could irritate the eyes.
    • Clothing: Wearing protective clothing that covers the body and is made of materials that resist penetration by coal tar.
  4. Hygiene Practices: Implementing good hygiene practices to minimize the potential for taking contaminants home or into community environments:
    • Change Rooms: Providing separate change rooms for street clothes and work clothes to prevent contamination of personal clothing.
    • Showers: Encouraging workers to shower at the end of their shift to remove any contaminants before changing into street clothes.
    • Laundry Facilities: Providing facilities for the proper cleaning and storage of work clothing and PPE.
  5. Medical Monitoring: Regular health check-ups for workers who are regularly exposed to coal tar to monitor for any signs of health issues related to exposure.
  6. Regulatory Compliance: Ensuring that all processes and practices align with local, state, and federal regulations regarding the handling and exposure to coal tar.

By implementing these strategies, employers can create a safer work environment and reduce the potential health risks associated with coal tar exposure for their employees.

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