Mobile Air Monitoring on the Gulf Coast: TAGA Buses

How EPA Analyzed the Data

Use of the TAGA mobile laboratory allows us to perform real-time (second-by-second) monitoring of the air up and down the coastal areas nearest to the spill and pick up any early indication of these chemicals in on-shore air.

EPA's general approach to evaluating any TAGA mobile lab detections of chemicals such as EGBE (also known as 2-butoxyethanol) and dipropylene glycol mono butyl ether is to compare the second-by-second TAGA air measurements to low health-based screening concentrations. This comparison allows us to identify measurements that we will closely evaluate.

When the measured concentrations are below the screening level, we conclude that the chemical is not present at levels that warrant further attention.

If the measured concentration is above the health-based screening level, we would investigate further. We would look at how high the concentration is above the screening level and for how long the concentration is above the screening level. We also would examine information for that pollutant, and the situations in which it might cause health problems. In addition, we would look at information about the winds in the area to understand whether the air monitored originated in the Gulf or from somewhere on shore. Based on this further investigation, we would determine whether follow-up actions would be needed. Possible follow-up actions include conducting additional monitoring to better assess the source of the pollutant, or to track the pollutant concentration over time. We might also collect air samples using other methods to assess the potential for human exposures that may be a health concern. If there is cause for immediate concern, we will work with state and local officials to determine necessary steps to protect the public health and work with the news media to notify the public.

Screening Levels

The very low screening levels we used for screening the TAGA second-by-second measurements are the EPA inhalation reference concentrations (RfC). An RfC is an air concentration a person can breathe continuously over a lifetime without an appreciable risk of health problems. EPA develops RfCs based on toxicity information about a chemical. RfCs are peer-reviewed by experts inside and outside the EPA. The lifetime RfCs are used in this analysis of second-by-second data simply to provide a very low screening level to target measurements for a closer look. In any closer look, EPA will analyze the longer data record using health based concentrations relevant to time periods over which people might be exposed.

For more information on RfCs see www.epa.gov/iris/help_ques.htm#rfd.

EGBE

For EGBE, EPA compared the instantaneous TAGA mobile lab measurements to the EPA's inhalation reference concentration (RfC) of 330 parts per billion (ppb). The highest TAGA lab's second-by-second EGBE measurement to date is well below 330 ppb.

Dipropylene Glycol Mono Butyl Ether

There is limited toxicity information available for dipropylene glycol mono butyl ether, and there is no RfC. However, the compound is one of the class of compounds known as glycol ethers, which have similarities in chemical structure. In the absence of a specific RfC, we used the RfC for the most toxic glycol ether for which we have such a value. This allows us to identify a low screening level, which is our purpose here. This is 7 ppb, the reference concentration for ethylene glycol monomethyl ether. The current highest second-by-second concentration of dipropylene glycol mono butyl ether is well below 7 ppb.

For More Information:

For more information on the EGBE RfC see www.epa.gov/ncea/iris/subst/0500.htm#refinhal

For more information on the ethylene glycol monomethyl ether RfC, see www.epa.gov/iris/subst/0640.htm#refinhal