Dec. 20, 2001 A study from the Johns Hopkins Bloomberg School of Public Health says that very high exposure to a gasoline additive, methyl tert-butyl ether (MTBE), can trigger a false positive reading on some breath-alcohol analyzers used by law enforcement officers to determine legal intoxication. MTBE is used to oxygenate gasoline and in some areas is required by law to reduce emissions. The findings appear in the December 2001 issue of Forensic Science International. “Human exposure to MTBE has become widespread. Under unique circumstances, exposures can be quite high. Because MTBE readily partitions from the blood into the breath, there is the potential for interference on breath alcohol analyzers,” says Timothy J. Buckley, assistant professor at the Johns Hopkins Bloomberg School of Public Health. “We studied this and our results showed that MTBE does present a positive interference on the older type analyzers. Workers like gas station attendants and auto mechanics may receive sufficient levels of MTBE to trigger a .10 reading on certain breath-alcohol analyzers, which is one legal standard for intoxication, but only in combination with drinking alcohol. MTBE exposure on its own is not enough to trigger a false positive reading of .10,” explains Dr. Buckley.
New Jersey state officials first raised the question of whether MTBE exposure could interfere with breath-alcohol analyzer when they were challenged in a court case in 1995. Dr. Buckley and his colleagues compared the Breathalyzer™ with the Alcotest™ detector. Both breath-alcohol analyzers are commonly used by police officers in United States. The Breathalyzer™ was developed in the 1950s and uses a visible light detector to determine the presence of alcohol in the breath, while the newer Alcotest™ uses electrochemical and infrared absorption sensors to detect alcohol levels. Various breath mixtures of MTBE and MTBE mixed with alcohol were simulated in a laboratory and run through both machines.
According to the study’s results, MTBE presented a positive interference on the older Breathalyzer™. However, even for the most extreme exposures, this interference would not be sufficiently high enough to register a false positive unless it occurred in addition to alcohol consumption. Alcohol mixed with a modest dose of MTBE, similar to the exposure received from the refueling of a car, was not sufficient to create a false positive reading. Only high exposure to MTBE coupled with alcohol was able to create a false positive reading of legal intoxication.
The researchers were unable to create a false positive reading with the newer more advanced Alcotest™. This instrument successfully identified the interference invalidating the test.
“The Breathalyzer™ may not be accurate under the most extreme conditions. Occupational exposure to MTBE would need to be considered in any case where this older breath-alcohol analyzer is used to determine legal intoxication especially now that many states are lowering the standard for intoxication to .08 blood alcohol level. We need to anticipate both the socio-legal and public health implications associated with the introduction of new chemicals into consumer products where there is potential for such widespread human exposure,” adds Dr. Buckley.
Timothy J. Buckley, Joachim D. Pleil, James R. Bowyer, J. Michael Davis are the authors of “Evaluation of methyl tert-butyl ether (MTBE) as an interference on commercial breath-alcohol analyzers” published in Forensic Science International.
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