Three Avena fatua (wild oat) populations resistant to imazamethabenz, flamprop, and fenoxaprop-P were identified from the northwest agricultural region of Manitoba, Canada. These populations were identified after producer reports of failure of imazamethabenz to provide satisfactory control in the field. Although these A. fatua populations had previously been exposed to other herbicides, primarily ACCase inhibitors, imazamethabenz had never before been applied. In growth room experiments, resistant (R) plants were 7.2 and 8.7 times more resistant to imazamethabenz and flamprop, respectively, than susceptible (S) plants, as measured by the ratio of dosages required to inhibit shoot dry matter accumulation by 50% (GR50 R/S). The three populations did not differ significantly (P < 0.05) in levels of resistance to imazamethabenz. Similarly, the populations did not differ in levels of resistance to flamprop. The populations differed in their response to fenoxaprop-P; levels of resistance for two populations were 2.0-fold, while the remaining population was 2.9-fold. An experiment conducted in 1995 in one of the infested fields confirmed multiple herbicide resistance, with A. fatua panicle numbers in August being 36, 128, and 44% of untreated controls at recommended dosages of imazamethabenz, flamprop, and fenoxaprop-P, respectively. Three additional populations of A. fatua with multiple herbicide resistance from other areas of Manitoba were identified in a 1996 field experiment. For the six A. fatua populations in the 1996 experiment with multiple herbicide resistance, panicle numbers expressed as a percentage of the untreated controls varied from 44 to 77% for imazamethabenz, 57 to 83% for flamprop, and 43 to 88% for fenoxaprop-P (commercially recommended dosage of each herbicide). Multiple herbicide resistance in A. fatua is not rare; screening of A. fatua seed samples from across Manitoba and Saskatchewan has identified a number of additional R populations. The evolution of herbicide resistance in the absence of direct selection is a very serious development as producers with multiple herbicide resistance in A. fatua are left with a very limited number of herbicide options for selective control in crops commonly grown in western Canada.

The organotins, mainly the trialkyltins and triphenyltins, have a widespread application as fungicides, anti-fouling coatings for porous and non-porous surfaces, herbicides, insecticides, and generic biocides. Traditional environmental monitoring methods can only give limited speciation of the organometallics. The speciation of a wide variety of alkyl-and aryl-tin isomers using liquid chromatography coupled with mass spectrometry under positive-ionization conditions is reported. Detection of the organotins was enhanced by the use of acetic acid in the methanol mobile phase. There were unexpected high-mass ions with multiple tin-isotope patterns present in many of the spectra. These high-mass species were possibly attributable to tin polymers, whose presence has been observed by others using X-ray methods.The use of alkyl-and aryl-tins in the environment has increased dramatically over the last few decades. The US Environmental Protection Agency (U.S. EPA), through the Office of Research and Development (ORD) and its analytical methods development program at the Environmental Monitoring Systems Laboratory at Las Vegas (EMSL-LV) is conducting a program to understand the properties of organometallics, including organotin compounds. The objective is to provide effective monitoring, measurement, or speciation methods. Prevailing methodology only analyzes the total amount of tin. It is important to be able to differentiate the differing organic functional groups, as they can impart various levels of toxicity to different organisms.' The ability to monitor and speciate the organotins at low levels has become a serious environmental need., The organotins, mainly the trialkyltins and triphenyltins, are widely applied as fungicides, anti-fouling coatings for porous and non-porous surfaces, herbicides, insecticides, and generic biocides.' The di-and mono-organotin compounds are mainly used in non-pesticidal industrial applications, for example as stabilizers for polyvinyl chloride and as precursors for forming SnO, films on glass and homogeneous catalyst^.^ It is estimated that the world-wide pesticidal use of the triorganotin compounds is 8000 metric tons, and is exceeded by the non-pesticidal applications of the di-and mono-organotins, at 27 000 metric tons annually. Traditional environmental monitoring methods (e.g., derivatization with gas chromatography/flame photometry4 and hydride formation with atomic absorption spectrometry') can only give limited speciation of the organometallics. Other researchers have used liquid chromatography/ionspray mass spectrometry (LC/IS-MS) to characterize the alkyl-and aryl-tin species6 and to quantify tributyltin in a sediment reference materiaL7 Our research efforts have concentrated on the speciation of a wide variety of alkyl-and aryl-tin congeners (Table 1) by liquid chromatography coupled to electrospray mass spectrometry (LC/ES-MS) under positive-ionization conditions. *Author to whom correspondence should be addressed. EXPERIMENTALElectrospray mass spectrometry. A Vestec (Hous...

SummaryThe objective of this research was to evaluate, in the laboratory, the potential of gas chromatography/ion mobility spectrometry (GC/IMS) for monitoring vinyl chloride and other organic compounds in air samples in the field. It was determined that GC/IMS has the potential to directly detect vinyl chloride in air at the 2 ppbv level, and when concentrated on an adsorbent trap from a 1 L sample of air, detection could be lowered to the 0.02 ppbv level. From a comparative investigation of 18 EPA priority pollutants and 34 common vapor-phase organic compounds, many compounds were found to provide a more sensitive response in IMS than vinyl chloride, indicating that GC/IMS would he broadly applicable to the direct detection of vapor-phase organics in air.Operating parameters including drift gas, spectrometer temperature, and sample-inlet position were evaluated and discussed with respect to sensitivity and resolution. High temperature dramatically increased sensitivity to vinyl chloride. Vinyl chloride was shown to produce both negative and positive ion mobility spectra, with the negative-mode spectra resulting from electron-capture dissociation of the vinyl chloride. The limit of detection for vinyl chloride was found to be 7 pg/s. Limits of detection for 18 EPA priority pollutants were determined and compared to vinyl chloride. The responses of 34 other vapor-phase organic compounds were also compared to that of vinyl chloride. Non-selective, positive-ion detection of 30 of the 34 compounds was demonstrated along with selective, electron-capture-type detection of 29 of them. Chloride-specific and bromide-specific detection illustrated the advantages of selected-ion monitoring in IMS.

Seven laboratories participated in an interlaboratory evaluation of a liquid chromatography / mass spectrometry (LC/MS) method for the analysis of 10 chlorinated phenoxy acid herbicides. The focus of this evaluation was to test the intercomparability of LC/MS data obtained from two types of LC/MS interfaces [i.e., thermospray (TS) and particle beam (PB)]. Eight simulated sample extracts were sent to each laboratory for LC/MS analysis. There were statistically significant differences between interfaces in the quantitative data for all analytes except 2-(2,4,5-trichlorophenoxy)propanoic acid (silvex). Particle beam exhibited a high positive bias and a low relative standard deviation at the highest sample extract concentration range, 500 pg/mL, while TS showed a low bias and a low relative standard deviation at the lowest sample extract concentration range, 5 pg/mL. Another factor of this study was to look for any performance differences between interfaces of the same type, but differing manufacturers. A statistical difference was observed, between PB interfaces, for 2-(l-methylpropyl)-4,6-dinitrophenol (dinoseb).

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