Researchers identify new nitrated PAH compounds from combustion that are hundreds of times more mutagenic than parent PAHs
A team led by researchers at Oregon State University has discovered novel nitrated polycyclic aromatic hydrocarbon (NPAH) compounds produced by combustion sources or formed in the atmosphere that are hundreds of times more mutagenic than their parent PAHs, which are known carcinogens. The findings were published in the ACS journal Environmental Science and Technology.
These new compounds were not previously known to exist, and raise additional concerns about the health impacts of heavily-polluted urban air or dietary exposure. It has not yet been determined in what level the new compounds might be present, and no health standards now exist for them.
PAHs form naturally as the result of almost any type of combustion, from a wood stove to an automobile engine, cigarette or a coal-fired power plant. Many PAHs, such as benzopyrene, are known to be carcinogenic, are believed to be more of a health concern that has been appreciated in the past, and are the subject of extensive research.
PAHs can become even more of a problem when they chemically interact with nitrogen to become “nitrated,” or NPAHs; the newly-discovered compounds are NPAHs that were unknown to this point.
The compounds were identified in laboratory experiments that mimic the type of conditions which might be found from the combustion and exhaust in cars and trucks, or the grilling of meat over a flame.
The researchers worked with five higher molecular weight PAHs, including benzo[a]pyrene-d12 (BaP-d12), benzo[k]- fluoranthene-d12 (BkF-d12), benzo[ghi]perylene-d12 (BghiP-d12), dibenzo[a,i]pyrene-d14 (DaiP-d14), and dibenzo[a,l]pyrene (DalP) because of their mutagenicity and the lack of data on their formation of NPAH products during heterogeneous reactions.
Some of the compounds that we’ve discovered are far more mutagenic than we previously understood, and may exist in the environment as a result of heavy air pollution from vehicles or some types of food preparation. We don’t know at this point what levels may be present, and will explore that in continued research.—Dr. Staci Simonich
This study found that the direct mutagenicity of the NPAHs with one nitrogen group can increase 6 to 432 times more than the parent compound. NPAHs based on two nitrogen groups can be 272 to 467 times more mutagenic.
For technical reasons based on how the mutagenic assays are conducted, the researchers said these numbers may actually understate the increase in toxicity.
The discoveries are an outgrowth of research on PAHs that was done by Simonich at the Beijing Summer Olympic Games in 2008, when extensive studies of urban air quality were conducted, in part, based on concerns about impacts on athletes and visitors to the games.
Beijing, like some other cities in Asia, has significant problems with air quality, and may be 10-50 times more polluted than some major urban areas in the US with air concerns, such as the Los Angeles basin.
An agency of the World Health Organization announced last fall that it now considers outdoor air pollution, especially particulate matter, to be carcinogenic, and cause other health problems as well. PAHs are one of the types of pollutants found on particulate matter in air pollution that are of special concern.
Concerns about the heavy levels of air pollution from some Asian cities are sufficient that Simonich is doing monitoring on Oregon’s Mount Bachelor, a 9,065-foot mountain in the central Oregon Cascade Range. Researchers want to determine what levels of air pollution may be found there after traveling thousands of miles across the Pacific Ocean.
This work was supported by the National Institute of Environmental Health Sciences and the National Science Foundation. It is also an outgrowth of the Superfund Research Program at OSU, funded by the NIEHS, that focuses efforts on PAH pollution. Researchers from the OSU College of Science, the University of California-Riverside, Texas A&M University, and Peking University collaborated on the study.
Narumol Jariyasopit, Melissa McIntosh, Kathryn Zimmermann, Janet Arey, Roger Atkinson, Paul Ha-Yeon Cheong, Rich G. Carter, Tian-Wei Yu, Roderick H. Dashwood, and Staci L. Massey Simonich (2013) “Novel Nitro-PAH Formation from Heterogeneous Reactions of PAHs with NO2, NO3/N2O5, and OH Radicals: Prediction, Laboratory Studies, and Mutagenicity,” Environmental Science & Technology doi: 10.1021/es4043808