Thursday, February 21, 2013

What are PAHs?

PAHs, or Polycyclic Aromatic Hydrocarbons, consist of hundreds of separate chemicals that occur together as mixtures.  PAHs are naturally occurring and are concentrated by the burning of fossil fuels and the incomplete burning of carbon-containing materials (such as wood, tobacco, and coal).  PAHs are also a wide and varied group of compounds whose sources include tire particles, leaking motor oil, vehicle exhaust, crumbling asphalt, atmospheric deposition, coal gasification, and parking lot sealants, as well as sources inside the home (such as tobacco smoke, wood fire smoke, grilling or charring meat). PAHs are also commonly found in particulate matter of air pollution and tend to adhere to surfaces, attaching readily to sediment particles and leading to elevated concentrations in sediments. PAHs have complex chemical structures, so they do not break down easily and are persistent in the environment.

Why should we be concerned about PAHs?
Some PAHs are known to be toxic to aquatic animals and humans. Generally, higher molecular weight PAHs tend to be more stable, persist in the environment longer, are less water soluble, and are more toxic. Exposure to UV light can increase toxicity of PAH compounds and increase toxicity to some aquatic species. (Garrett 2004) Scientific studies have documented detrimental impacts from PAHs on aquatic organisms. Examples include: 
• In Austin, Texas biological studies revealed a loss of species and decreased number of organisms in streams with PAHs present (Van Metre 2005)
• In Puget Sound, Washington’s Ambient Monitoring Program (WA DFW) found PAHs were associated with:
– Liver lesions and tumors in fish,
– Liver problems leading to reproductive impairment,
– Malformations in fish embryos and embryonic cardiac dysfunction,
– Reduction in aquatic plants (eelgrass) that provide fish habitat.

The most significant effect of PAH toxicity to humans is cancer. Increased incidences of lung, skin, and bladder cancers are associated with occupational exposure to PAHs (USDHHS 2009). Other non-cancer effects are not well understood, though they may include adverse effects on reproduction, development, and immunity. PAHs generally have a low degree of acute toxicity to humans, meaning harmful effects through a single or short-term exposure are minimal. Mammals absorb PAHs through inhalation, contact with skin, and ingestion (EPA Ecological Toxicity). Recent research by USGS raises concerns about exposure of children through inhalation and ingestion of house dust contaminated by PAHs that have abraded from nearby parking lots sealed with coal tar sealant (Mahler 2010).

Effective April 1, 2011, The Town of Boone requires permits for the application of pavement or asphalt sealants within the corporate limits of the Town of Boone and within the Town of Boone’s Extra Territorial Jurisdiction. (ETJ).   No person may apply a pavement or asphalt sealant to parking lots or driveways without a permit because the sealants contain toxins especially dangerous for aquatic life.   For the most recent fact sheet from NC State University on PAHs click on this website

No comments:

Post a Comment