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EPA Response to BP Spill in the Gulf of Mexico

Volatile Organic Compounds (VOCs) 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.

EPA is analyzing air samples for volatile organic compounds (VOCs) – including specifically, benzene, ethylbenzene, toluene, and xylene. EPA is sampling for these pollutants because they are present in oil and because, at elevated concentrations, they may cause health problems, including cancer.

These chemicals are also emitted by many other sources, such as motor vehicles, industries, and paints or solvents. The monitors cannot determine where the VOCs originate. Therefore VOC levels in the air around the monitors could be coming from the oil spill or from other sources.

To evaluate the VOCs EPA scientists compare air sampling results to health-based screening concentrations (also called “screening levels”) in the Gulf region. These screening levels are developed from health effects information about each VOC, including information regarding exposure levels that might pose an increased risk of health problems. 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.

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

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 average (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.  But also screening the individual measurements allows EPA to closely track the results.

Results that are below the health-based screening level generally indicate a low potential for health concerns for exposures up to a year.  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 from the Agency for Toxic Substances and Disease Registry


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

Health Concern?


Benzene:  20 µg/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.

Toluene:  5000 µg/m3 and below

Ethylbenzene:  3000 µg/m3 and below

Xylene: 3000 µg/m3 and below

Benzene:  Above 20 µg/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.

Toluene:  Above 5000 µg/m3

Ethylbenzene:  Above 3000 µg/m3

Xylene:  Above 3000 µg/m3

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

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