It’s no secret that humans have had a tremendous impact on the planet, both good and bad. From architectural wonders like the Great Pyramid of Giza to the mysterious beauty of the Mona Lisa to ecological disasters like Chernobyl, humans have put their fingerprints on the planet for good or ill. As environmental consultants, we are generally in a position where we are looking for a specific release or use of hazardous materials that can be traced back to a single source, such as a dry cleaner that improperly disposed of chlorinated solvents or insulating materials containing asbestos that were installed to keep pipes from bursting. In these scenarios, the source of the hazard can generally be located and remediated or mitigated, and the risk to human health or safety can be reduced. But, what about when the source of the contamination is civilization? How do you remove the risk from contact with the byproducts of modern life?
While this may sound dramatic, it is unfortunately a fact of life. In urban areas, background contamination is almost always present, and we are all the source. Polycyclic aromatic hydrocarbons, or PAHs, are naturally occurring chemicals, which are extremely carcinogenic. These chemicals are present in many substances including coal, gasoline, wood, tobacco and many others. These chemicals are often formed and released through combustion. They can even be formed by cooking meat at high temperatures. Do you like your steak well done? Well, those beautiful grill marks contain PAHs. Based on the EPA screening levels for initial assessment, exposure to benzo(a)pyrene in soil at a concentration of 0.11 parts per million over a lifetime increases a person’s risk of cancer by 1 in 100,000.
PAHs are so prevalent in urban areas that a specific equation was developed to determine when remediation is necessary. This equation weighs specific PAH constituents based on toxicity and produces a unitless number. If this number is greater than 1, remediation must occur. Less than 1 is considered urban background. Benzo(a)pyrene is given a 1 to 1 ratio in this equation. If you consider that an initial screening level of 0.11 ppm would be considered contaminated, you could encounter a situation where you have benzo(a)pyrene contamination nine times what would be considered contaminated by the initial EPA screening levels and it would just be considered urban background. In reality, benzo(a)pyrene rarely appears in soils as the sole PAH constituent, so the actual amount of urban background is somewhat less than nine times the initial screening level. Also, initial screening levels are incredibly conservative, so don’t worry, you can still overcook your steaks, even if some people find it sacrilegious!
Contaminants aren’t just PAHs either. We have assessed fields that have been fallow for decades and we still find traces of pesticides such as endrin, which was banned in the United States in 1991. Chloroform and bromodichloromethane are extremely prevalent in soil gas due to the use of chlorine in municipal drinking water sources. Arsenic can be naturally occurring but can also accumulate in soils due to the use of phosphate fertilizers. In Shelby County, the background concentrations for arsenic in soils are generally considered to be 10 ppm. For reference, the initial screening level for arsenic in soil is 0.68 ppm. That means that background arsenic in Memphis can be over 14 times the initial EPA screening level.
Urban contamination is a fact of life. Does this mean that we are all in constant contact with toxic levels of contamination in our day-to-day lives? Technically yes, depending on the definition of toxic levels of contamination. While this may seem bleak, the initial screening levels are extremely conservative and we still live relatively considerably longer lives than our ancestors. The potential for exposure does not always mean actual exposure, and something higher than initial EPA screening levels isn’t a guarantee that you will experience a negative health effect. The takeaway in all of this is that we must protect our wilderness areas. While humans are robust and capable of significant amounts of exposure, other species such as birds and insects are not. We need to protect these pristine locations if only to remember that there was a time before modern civilization.
Organizations like the Sierra Club and the Natural Resources Defense Council work hard to protect our natural resources and wildlife from human impact. Check them out to learn how you can be part of their effort.