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RESEARCH PROFILES Pesticides in cigarette smoke With the help of a relatively uncommon technique called electron monochromator-MS (EM-MS), researchers have detected three nitro pesticides—flumetralin, pendimethalin, and trifluralin—in cigarette smoke for the first time. The results, which were reported in the May 15 issue of Analytical Chemistry (pp 3227–3233) by Kent J. Voorhees, A. John Dane, and colleagues at the Colorado School of Mines, suggest that ~10% of pesticide residues on tobacco survive the combustion process. Pendimethalin and trifluralin are considered “possible human carcinogens” by the U.S. Environmental Protection Agency (EPA), and all three pesticides are suspected endocrine-disrupting compounds (EDCs). Flumetralin has been banned for use on tobacco in the European Union. Pesticide residues on tobacco are not federally regulated in the U.S. because tobacco is not consumed as a food. EPA approves which pesticides can be used, but it does not set tolerances for pesticides on tobacco. It took quite a bit of detective work to identify the three pesticides. “Basically, we got into the area of pesticides by accident because we weren’t looking for them. We were trying to identify unknown peaks, which we thought were some kind of NPAH [nitro-polycyclic aromatic hydrocarbon],” says Voorhees. The project started out with the goal of determining which NPAHs are formed during combustion of cigarettes. The researchers analyzed smoke from several tobacco samples, including 3 pure-tobacco-type cigarettes, a reference cigarette, and 11 commercial cigarettes. Several major brands and varieties were tested. Because of the complexity of cigarette smoke, a rigorous cleanup procedure had to be performed. The samples were then analyzed by GC/EM-MS. EM-MS allows the user to control how much electron energy is involved in the ionization process, and it alleviates some of the problems associated
with negative-ion chemical then on, the project shifted ionization, says Voorhees. from looking at NPAHs to The technique is particularlooking for other nitroly useful for analyzing eleccontaining pesticides, says trophilic compounds, such Dane. as NPAHs, he says. Thanks to a 2003 U.S. Initially, the researchers General Accounting Office monitored the m/z 46 ion, report that listed the top which is unique for NO–2, 26 pesticides used in tobacco farming, the researchers in negative-ion mode. Alhad some idea what to though they could identify Three endocrine-disruptexpect. They decided to 7 NPAHs on the basis of ing pesticides have been monitor 2 other dinitroanimatched retention times, 5 found in cigarette smoke line pesticide molecular chromatographic peaks did for the first time. weights—m/z 281 for not match any of the 58 pendimethalin and m/z 335 for triflustandards tested. ralin. The retention times matched 2 of Then Dane made an important the unknown m/z 46 peaks, indicating observation. He was conducting tubethe presence of the 2 pesticides. furnace combustion experiments to deWhether the pesticides detected in termine how NPAHs form relative to cigarette smoke pose a health risk is temperature. He knew that unsubstitutunclear because the reported levels ed PAHs increase in concentration with temperature. But whenever he was moni- are low compared with those used in toxicological tests. In addition, no longtoring the unknown peaks, he observed term studies have been performed, says just the opposite. As the temperature Voorhees. Cigarette smoke is known to increased, the concentration decreased. “It implied to me that they were already contain >4700 compounds. The synergism of these pesticides with those other present in the tobacco itself,” says compounds is completely unknown, he Dane. adds. Sure enough, when he performed an Some researchers in the field believe extraction, Dane observed a very large that air is an important source of EDCs quantity of one of the unknown comthat should not be overlooked. “Hupounds relative to what he saw in the mans and wildlife are certainly exposed tobacco smoke. The unknown peak in to EDCs from the air,” says Andreas the extract chromatogram was about Gerecke, who is leading a project at an order of magnitude bigger than the Empa-Materials Science & Technology same peak in the tobacco-smoke chromatogram. At that point, “I was actually (Switzerland) to identify EDCs in diesel exhaust and outdoor air. Most of the able to start using the full capabilities of work on EDCs, however, has focused the [GC/EM-MS] instrument,” says on drinking-water and wastewater treatDane. ment, biosolids, and cattle feedlot operThe molecular weight of the unations, says Brian Gullett of EPA’s known compound was determined in National Risk Management Research negative-ion, full-scan mode, and MS Laboratory. “While certain well-known fragmentation data were obtained in EDCs are emitted into the air (chloripositive-ion, full-scan mode. When the researchers combined both sets of infor- nated dioxins and furans) from combustion, very little is known about other mation, they got a match. A database search selected the pesticide flumetralin. airborne EDCs from combustion processes,” he says. a The compound’s identity was further —Britt Erickson confirmed by exact mass analysis. From J U N E 1 , 2 0 0 6 / A N A LY T I C A L C H E M I S T R Y
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