Poly Aromatic Hydrocarbons (PAHs) in the Environment
3/15/2021
The reasons for remediation activities across the country are as varied and diverse as there are environmental projects. Yet, if we were to take these activities and roll them up into a single category, we would see a common thread. That is, years ago, environmental rules and regulations did not exist. And that resulted in waterways and lands in every state being used as dumping grounds: no matter what the environmental and health consequences might have been. After all, since there were no regulations to require proper disposal of hazardous materials, it was, simply, a very cost-effective method to get rid of unwanted chemicals in the most expediate manner. And that resulted in hazardous materials being dumped into nearby rivers, lakes and open fields. Many of the materials that have been discarded, persist today, being resistant to the typical modes of degradation, including rain, snow, temperature extremes as well as biodegradation. As a result, they remain a health threat to all forms of life due to their persistent toxic characteristics.
One class of materials – polycyclic aromatic compounds, or PAHs – has become major contaminants-of-concern for which many remediation projects have been authorized. And while PAHs are somewhat susceptible to photodecomposition under sunlight and react with other pollutants such as ozone and nitrogen oxides, the result is the formation of complex and even more potent toxic compounds.
PAHs in the soils have become a potential human health risk within the food chain. For instance, vegetables cultivated on wastewater-contaminated soils may take up these pollutants in sufficient quantities. Numerous studies have demonstrated that vegetables have accumulated high concentrations of PAHs that originated from PAH-contaminated soils. Additionally, other pathways, including inhalation and dermal contact, also contribute to the human exposure to environmental carcinogenic PAHs.
PAHs are a class of chemicals that are found in coal, crude oil, and gasoline. They also are produced when wood, garbage, and tobacco are burned. PAHs can bind to or form small particles in the air. High-temperature cooking will form PAHs in meat and in other foods. One specific PAH is Naphthalene and is produced commercially in the United States to make other chemicals.
PAHs can also be the biproduct of naturally occurring events. For example, volcanic eruptions and forest–prairie fires, but largely from the incomplete burning of some organic substances during anthropogenic (i.e. man-made) combustion processes, such as vehicular emissions, wood smoke, coke and asphalt production, and waste incineration.
As its name suggests – polycyclic – contain two or more fused aromatic rings: molecular structures that are typically classified as mutagens and carcinogens. While there are more than 100 different PAHs identified within the environment, there are 16 specific PAHs have been identified as prominent exposure risks and since the 1970’s, have been listed as priority pollutants by the United States Environmental Protection Agency (US EPA). These priority PAHs include naphthalene, acenaphthylene, acenaphthene, fluorene, anthracene, phenanthrene, fluoranthene, pyrene, chrysene, benz[a]anthracene, benzo[b]fluoranthene, benzo[k]fluoranthene, benzo[a]pyrene (B[a]P), indeno[1,2,3-cd]pyrene, benzo[g,h,i]perylene, and dibenz[a,h]anthracene.
Among these priority PAHs, B[a]P, a known human carcinogen, is commonly used as an indicator for other PAH exposures, since PAHs mostly occur as a group rather than a singular pollutant. Therefore, by identifying B[a]P, it can be an indication that other PAHs are present. Below is an illustration of the 16 PAHs classified as priority pollutants. As one can see, PAHS are large molecules that contain multiple 6-sided, double-bonded rings (aka benzene rings), known as aromatic compounds.
A problem when measuring airborne PAH concentrations is that the vapor pressure of these materials is very low so it is very unlikely that they would become airborne. Therefore, real-time monitoring with a photoionization detector (PID) or with traditional industrial hygiene sample collection, would result in non-detectable concentrations. Even though these compounds – in general – can be ionized by a PID (detected) should they vaporize. Nevertheless, while a PID or sample collection methods may not detect PAHs via an airborne assessment, they may be present in significant quantities in the soils. Thus, in order to determine the presence of PAHs, it would be necessary to collect soil samples for laboratory analysis.
Should PAHs become airborne, it would most likely occur due to attaching to soil particulate as it is resuspended due to forceful winds or aggressive soil disturbances. Through extrapolation of PAH soil concentration data, it is possible to determine how much soil would be necessary to become airborne, thereby creating an inhalation hazard due to resuspended PAHs. As an example, a recent environmental study in New Jersey (February 2020)1 indicates that the collective of the 16 priority PAH pollutants has an approximate soil concentration of 2.8 mg per kilogram of soil. Using the coal tar pitch PEL of 0.2 mg/m3, it would require a suspension of 71.43 grams of soil per cubic meter of air to meet the occupational health limit: an airborne concentration that, under normal conditions, would not be feasible. Therefore, respiratory protection would typically not be necessary (unless an industrial hygiene assessment determines such PPE is warranted).
PAHs can penetrate our skin and become a systemic health concern, targeting such internal organs as the kidneys and liver. Therefore, appropriate protection from potential contact exposures is necessary and should include such PPE as gloves, such as nitrile. Nitrile is considered a general use glove when handling solvents, oils and greases while providing excellent dexterity; a necessary attribute when handling tools such as scoops and needing to log information. However, they do tend to tear easily and therefore, having an ample replacement supply is crucial. Eye protection (i.e. safety glasses), long sleeve shirts (in the summer, short sleeves with a minimum 4-inch sleeve is appropriate) and long pants are also necessary. Based on IH assessment, disposable coveralls with booties may also be necessary as well as having a supply of water to wash exposed skin surfaces.
1-(https://www.state.nj.us/dep/dsr/publications/PAHs_NJ_Soils.pdf)
If you’re always trying to be normal you will never know how amazing you can be
Maya Angelou