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EPA Response to BP Spill in the Gulf of Mexico

Polycyclic Aromatic Hydrocarbons on the Gulf Coastline

In response to the BP oil spill, EPA monitored air, water, sediment, and waste generated by the cleanup operations. Ongoing response and restoration efforts are posted to RestoreTheGulf.gov.

While emergency response data collection has ended, results continue to be available on this site. Any new data will continue to be posted to this site, and data will continue to be available here for the foreseeable future.

Much of the content of this site continues to be available for historical and information purposes, but we are no longer updating these pages on a regular basis.

Polycyclic Aromatic Hydrocarbons (PAHs) are a group of semi-volatile organic compounds (SVOCs) that are present in crude oil that has spent time in the ocean and eventually reaches shore and can be formed when oil is burned.

The oil that has reached the shore is commonly called ‘weathered oil’. PAHs present in the weathered oil evaporate slowly over a period of weeks or months.

PAHs come from other sources as well. They are formed during the incomplete burning of gas, coal, garbage, or other organic substances and from motor vehicle exhaust.

In air sampling for PAHs on shore in the Gulf region, EPA is focusing on the following compounds:

  • benzo(a)pyrene,
  • benzo(a)anthracene,
  • benzo(b)fluoranthene,
  • benzo(k) fluoranthene,
  • chrysene,
  • dibenz(a,h)anthracene,
  • indeno(1,2,3-cd)pyrene, and
  • naphthalene.

EPA is focusing on these pollutants because they are present in weathered oil and are also released from burning oil, and, at elevated concentrations, could potentially cause health problems, including long-term health effects such as cancer.

The monitors cannot determine where the PAHs originate. Therefore PAH levels in the air around the monitors could be coming from the oil, or from other sources.

Analyzing Air Samples for PAHs

EPA is analyzing air samples for semi-volatile organic compounds (SVOCs) – specifically, for pollutants known as polycyclic aromatic hydrocarbon chemicals (PAHs). EPA is sampling for these pollutants because they are present in oil and because, at elevated concentrations, they may cause health problems.

To evaluate the PAHs EPA scientists compare air sampling results to health-based screening concentrations (also called “screening levels”) in the Gulf region. These screening levels were developed from health effects information about each PAH, including information regarding exposure levels that might pose an increased risk of cancer. At this time, EPA is using health-protective screening levels that assume a person is breathing a pollutant continuously (24 hours a day, seven days a week) for as long as one year. EPA will re-evaluate this time-period if needed.

Screening Levels for One-Year Average Exposure to Polycyclic Aromatic Compounds (PAHs) Commonly Found in Crude Oil

Contaminant concentration, 1-year average. Measured in nanograms /cubic meter (ng/m3)

Health Concern?


Benzo(a)pyrene: 640 ng/m3 and below **

Low concern for increased risk of health problems for measurements in this range.

Public: No action suggested. EPA will continue to evaluate sample results.

Benzo(a)anthracene: 6,400 ng/m3 and below

Benzo(b) fluoranthene: 6,400 ng/m3 and below

Benzo(k) fluoranthene: 6,400 ng/m3 and below

Chrysene: 64,000 ng/m3 and below

Dibenz(a,h) anthracene: 580 ng/m3 and below

Indeno(1,2,3-c,d) pyrene: 6,400 ng/m3 and below

Naphthalene: 30,000 ng/m3 and below

Benzo(a)pyrene: Above 640 ng/m3 **

Level of health concern depends on how much above these levels the measurement is and for how long. Concentrations slightly above these levels for short durations do not generally pose health concerns. There may be some health concern if people are exposed to these levels continuously for a year or more.

Public: No immediate action suggested. EPA will continue to monitor the levels closely. Additional investigation may be needed, e.g., reviewing information about the detected chemical, and where the higher concentrations may be coming from. Additional monitoring may be needed.

Benzo(a)anthracene: Above 6,400 ng/m3

Benzo(b) fluoranthene: Above 6,400 ng/m3

Benzo(k) fluoranthene: Above 6,400 ng/m3

Chrysene: Above 64,000 ng/m3

Dibenz(a,h) anthracene: Above 580 ng/m3

Indeno(1,2,3-c,d) pyrene: Above 6,400 ng/m3

Naphthalene: Above 30,000 ng/m3

If air pollution reaches levels requiring immediate action, you will be notified via local news media.

How EPA is using sampling data and screening levels for the PAHs

Monitoring staff are taking air samples at several locations along the Gulf coast. The air quality samples are collected in canisters, which are shipped to a laboratory for analysis. The daily results shown in the table are the average 24-hour concentration for each day.

EPA will compare individual measurements as well as long-term averages (i.e. levels averaged over many days) to the screening level. Since the screening levels are based on exposure lasting for many months, this average is more appropriate for evaluating the potential risk to health than any single measurement.

Results that are below the health-based screening level generally indicate a low potential for health concerns. In addition, a single daily reading that is higher than the screening level does not indicate a health problem will occur.

However, if a measured concentration is above the health-based screening level, EPA will investigate further. EPA would look at how high the concentration is above the screening level, how long the concentration stays above the screening level, and the impact of the concentration on the running average concentration over many days. EPA will also look at how these measurements compare to measurements in the region prior to the spill. EPA would also look at information for that chemical, and the situations in which it might cause health problems. After this further investigation, EPA would determine whether follow-up actions are needed. Possible follow-up actions include conducting additional monitoring to better identify the source of the pollutant, or to track the pollutant concentration over time. If there is cause for immediate concern, EPA will work with state and local officials to notify people in the area through local news media.

Additional information

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