I D E N T I F I C A T I O N O F R E S I D U A L P E S T I C I D E S IN WATER BY GC/QPMS T A K E S H I M U R A T A and SEJI T A K A H A S H I
Analytical Applications Department, Shimadzu Corporation 1 Nishinokyo-Kuwabaracho Nakagyo-ku, Kyoto, 604, Japan
(Received March 1991) Abstract. The extensive use of the broad range of pesticides employed to maintain golf courses has prompted serious environmental concerns in Japan since courses tend to be located in mountainous regions, often in close proximity to virgin water sources. Since older empirical methods are not appropriate for substance identification and determination of substance concentrations on the ppb order, gas chromatographyquadrupole mass spectrometry ( G C / Q P M S ) can be employed. A simple extraction of 500 ml of drainage pond water gives a sample which allows identification of pesticides with quantitation on the ppb order using selected ion monitoring (SIM). A sample of drainage pond water from a golf course revealed fenitrothion, funitrothion, chlorothalonil and isoprothiolane in concentrations of 120.1, 20.7, 45.6 and 130.5 ppb, respectively.
Introduction
Pesticides, the general term for substances used to kill noxious or otherwise unwanted insects, weeds, fungi, bacteriae, etc., have become invaluable in increasing crop yields and reducing labour in modern agriculture. In Japan, for example, the labour expended in weeding rice paddies has been reduced by an estimated one-fiftieth (1/50) since the introduction of contact and pre-emergence herbicides. In spite of their utility, threats to the environment and to animal and human health have engendered strict control of pesticide use in more developed nations. Recent media coverage in Japant~ has inflamed a growing public concern over the toxicities and quantities of pesticides employed on golf courses throughout the nation, and promises to push the issue into the political arena since so many varied interests are involved. A single golf course may use four or five specific compounds out of a choice of 100 or so commercially available pesticides depending upon the local flora and fauna to be controlled. Since golf courses are often built in pristine highlands, the potential for contamination of streams and rivers at their sources is great. Past practices at selfregulation of the kinds and amounts of substances that could by employed to 'safe' levels was limited to simple empirical evidence gathered by observing how, for example, varieties of goldfish, crustaceans and plant life, fared in and around golf course drainage ponds built specifically for this purpose. The need to carefully monitor the escape of pesticides into virgin water sources prompted us to examine the applicability of G C / Q P M S to the identification and quantitation of traces of these substances in drainage ponds on golf courses and further downstream. Attention was focused on the use of an easy and reproducible extraction of these substances from water samples. Standards were used to determine the suitability Environmental Monitoring and Assessment 19: 55-62, 1991. 9 1991 Kluwer Academic Publishers. Printed in the Netherlands.
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of electron impact ionization (EI), mass chromatography (MC) for positive identification, and selected ion monitoring (SIM) for trace quantitation.
Experimental Dimpylate (Diazinon), Simazin (CAT), Chlorothalonil (TNP), Chloropyrifos, Captan, Fenitrothion (Sumithion, MEP), Isoprothiolane, and Promicide were purchased from Wako Pure Chemicals, Japan, and were used as received. Guaranteed Purity grade n-Hexane and Acetone (Wako) were used without further purification. Each pond and river water sample (500 ml) was extracted with a mixture of n-hexane and acetone (10 ml/25 ml), X 2) in a separatory funnel with shaking (30 min). The combined extracts were evaporated to dryness under a stream of N2. The residue was taken up in 500 #1 of acetone from which 1,2 or 5 #1 aliquots were injected for selected ion monitoring. Concentration to 1/100 volume gave samples for mass chromatography. Chromatographic separations were performed on DB-17 chemically bonded (50% phenylmethyl) fused silica capillary columns (30 m • 0.3 m m I.D.). Injector temperatures were 300~ and column temperatures were programmed from 60~ to 300~ at 15~ Mass chromatography (MC) and selected ion monitoring (SIM) were performed on a QPI000EX and a QP2000A (both Shimadzu Corp.). Mass spectra were recorded at an ionization energy of 70eV, ion source temperature of 250~ and trap current of 60 #A.
Results and Discussion E I MASS SPECTRA OF STANDARDS
Table I lists ten of the pesticides most often employed on golf courses and their specific use. Figures 1 and 2 are the EI mass spectra of compounds 1 to 8 from Table I. Note that in the spectra of compounds 4 and 5 no molecular ion was apparent. This is probably due to TABLE I Typical pesticides for golf courses. No.
MW
Empirical Formula
Common and/or Trade Name
Usage
1 2 3 4 5 6 7 8 9 10
304 201 264 394 299 277 290 323 255 278
C12H21 N 2 03
Diazinon (Dimpylate) Simazin (CAT) Chlorothalonil (TPN) Chloropyrifos Captan Sumithion (MEP) Isoprothiolane Flutranil Promicide Funitrothion (MPP)
Insectcide Herbicide Bactericide I nsectcide Fungicide Insecticide Bactericide Insectcide Herbicide Insectcide
P C 7 Hi2 N 5 C1 C 8 N 2 CI4 C 9 H H N 03 S P C13 C 9 H 8 N 02 S CI 3 C 9 Ht2 N 05 S P C~2 HI8 04 $2 Ct7 Hi6 F 3 N 02 Ci2 Hi2 N O CI2 C~0 H~5 03 S2 P
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Fig. 3. Total ion chromatogramof pesticidemixture(1 - 5). 1. Diazinon 2. Simazin(CAT) 3. Chlorothalonil (TPN) 4. Chloropyrifos5. Captan. the unstable nature of these compounds in this ionization mode. Normally, the presence of a molecular ion is desirable for both MC and SIM. When no molecular ion is detected, a characteristic fragment ion can be selected, preferably from the higher mass range where the ion is less likely to be interfered with. For substances 4 and 5, m / z 314 and m / z 151, respectively, are suitable choices. IDENTIFICATION BY MASS CHROMATOGRAPHY A mixture of standard compounds 1 through 5 (see Table I) was prepared to afford component concentrations of 1.0, 5.0, 0.25, 1.0 and 1.0 ppm, respectively. Figure 3 is the total ion chromatogram of the mixture. The quality of the separation and the high sensitivity displayed indicate the potential of this analytical method to the detection and identification of these substances in trace quantities, even when a sample might contain ten or more substances of interest. Figure 4 is the total ion chromatogram (TIC) of an extract of a water sample obtained from a drainage pond on golf course 'A'. Compounds 3, 6, 7, and 10 (see Table I) were detected along with several hydrocarbons, the ubiquitous plasticizers Dibutyl Phthalate (DBP) and Dioctyl Phthalate (DOP), and the isoprenoid Squalene. Figure 5 shows the corresponding mass chromatograms using the molecular ions of compounds 3, 6, 7, and 10, common fragment ions ( m / z 67, m / z 71, m / z 85, and m / z 125) for the H C ' s (including squalene), and the common fragment ion m / z 149 for DBP and DOP. The presence and amounts of the plasticizers, which are often found in the plastic caps and cap liners of solvent reagent bottles, could be accounted for if they were contaminants of the solvents used in the extraction. This was confirmed by running blank samples. Their presence in an environmental sample, however, cannot be ruled out since the dialkyl
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