Analysis of Drinking Waters for a Suite of Pesticides using GC with dual ECD (US EPA Method 508.1) after SPE Concentration Eric Scott and Keith Ewing, Kentucky Department for Environmental Protection, Frankfort, KY USA Key Words Pesticides, Drinking Water, EPA Method 508.1, SPE, Solid Phase Extraction, SPE-DEX 4790, Horizon Technology Inc. Introduction Pesticides, including insecticides, herbicides and fungicides are used extensively to increase agricultural yields. The total world usage of pesticides in 2007 was approximately 5.2 billion pounds with the US consuming approximately 22% of the total. 1 The wide use of pesticides yields concern that drinking water sources will become contaminated, exposing the population to hazardous substances that may cause cancer. Several pesticides have regulated maximum contaminant levels (MCL) in drinking water and several more are on the draft Candidate Contaminant List (CCL-4), including metolachlor and permethrin, which may bring their regulation in the future, depending upon how frequently they are found to occur in drinking water sources. US EPA Method 508.1 is a sensitive method to detect chlorinated pesticides in drinking water using solid phase extraction (SPE) and Gas Chromatography (GC) coupled with ECD detection. Method 508 includes twenty nine chlorinated pesticides, three herbicides and four organohalides that can be determined in drinking water in any stage of treatment, and groundwater. Table 1 shows compounds from method 508 that have regulated maximum contaminant levels in the US and limits that the World Health Organization (WHO) specifies. 2 In Europe, the European Directive handles pesticides in a different way. 3 Each pesticide is limited to a maximum concentration of 0.1 µg/l and the sum of the pesticides present must not exceed 0.5 µg/l. In the case of aldrin, dieldrin, heptachlor and heptachlor epoxide the parametric value is 0.030 µg/l. EPA Method 508 is a good method for measurement of regulated levels and for screening of other pesticides that may be present. This work will demonstrate the performance of method 508 using solid phase extraction using an automated system. Experimental One liter of water is passed through the SPE disk, retaining the analytes. The sample bottle is automatically rinsed and the analytes eluted from the disk into a collection vessel. Shown: SPE-DEX 4790 Extractor from Horizon Technology SPE-DEX 4790 Disk Extraction system (Horizon Technology) equipped with Atlantic C18 47- mm SPE disks. Ethyl acetate and methylene chloride are elution solvents. Drying is performed with DryDisk membrane drying in a DryVap Evaporation system (Horizon Technology). The method for extraction using the SPE-DEX 4790 is shown in Table 2.
Table 1: Regulated Pesticides in Drinking Water Analyte CAS Registry Number Maximum Contaminant Level US (µg/l) Maximum Contaminant Level WHO (µg/l) Alachlor 15972-60-8 2 20 Atrazine 1912-24-9 3 100 (with metabolites) Chlordane-alpha/gamma 5103-71-9 5103-74-2 2 0.2 4,4 -DDT 50-29-3 1 Dieldrin 60-57-1 0.03 Endrin 72-20-8 2 HCH-gamma (Lindane) 58-89-9 0.2 * Heptachlor 76-44-8 0.4 * Heptachlor epoxide 1024-57-3 2 * Hexachlorobenzene 118-74-1 1 * Hexachlorocyclopentadiene 77-47-4 50 Methoxychlor 72-43-5 40 10 Metolachlor 51218-45-2 10 Cis/trans-Permethrin 54774-45-7 51877-74-8 Simazine 122-34-9 4 2 SGT-HEM RPD 34 Toxaphene 8001-35-2 3 Trifluralin 1582-09-8 20 *Removed because occurrence was below the level of concern. 20 Results and Discussion Drinking water samples from the county are obtained using usual tap collection procedures. Table 3 lists the compounds and recoveries from Lab-fortified blank samples and duplicates, fortified at 100 µg/l. The recoveries are excellent and the precision between runs is very good. Table 4 shows the Lab Fortified Blank and Lab-fortified Blank duplicate. The agreement is well within the 20% relative percent difference limit specified in the method. P a ge 2
Conclusion Solid phase extraction has become well established and most of the US EPA drinking water methods include SPE as the primary extraction technique or as an alternative. This work demonstrates the good performance of automated SPE for a wide suite of chlorinated pesticides, herbicides and organic compounds. Recoveries are good and agreement between duplicates is well within the method requirements of 20%. In addition to good reproducibility, automation of the technique requires less attention than a manual extraction technique. Table 2. Program for Automated Pesticide Extraction using the SPE-DEX 4790 Step Solvent Soak Time Dry Time Prewet 1 1:1 Ethyl Acetate/DCM 1:00 min 30 sec Prewet 2 Methanol 1:00 min 0 sec Prewet 3 Reagent Water 5 sec 0 sec Prewet 4 Reagent Water 5 sec 0 sec Sample Process Air Dry 4:00 min Rinse 1 Ethyl Acetate 1:30 min 30 sec Rinse 2 DCM 1:30 min 30 sec Rinse 3 1:1 Ethyl Acetate/DCM 1:30 min 30 sec Rinse 4 1:1 Ethyl Acetate/DCM 1:30 min 1:00 min Table 2. GC Conditions (Model 6890 GC, Agilent) Column Injector Temperature Temperature Dual Column Analysis DB-5 and a DB-1701 0.53 mm ID x 30 m Cool On-Column Injection; 60 o C 60 o C 260 o C; Linear over 35 minutes Program Detector Dual ECD System; Detector Temp 285 o P a ge 3
Table 3. Lab Fortified Blank, Four Runs Run 1 Run 2 Run 3 Run 4 %RSD 2,4'-DDD 102 96 118 99.5 9.4 2,4'-DDE 94 85 116 89.5 14.3 2,4'-DDT 97.5 105 118 107 7.9 4,4'-DDD 112 101 120 108 7.2 4,4'-DDE 104 94 116 107 8.6 4,4'-DDT 104 89 79 91.5 11.3 Aldrin 84 82.5 102 77 12.6 alpha-bhc 92 98.5 92 104 6.0 beta-bhc 91 92.5 86.5 89 2.9 Chlordene 91.5 82.5 86 76.5 7.5 Chlorothalonil ----------- 107 106 96.3 5.7 Chlorpyrifos 133 106 118 107 10.8 cis-chlordane 106 86 120 95.5 14.3 cis-nonachlor 97.5 96 118 113 10.4 DCPA 111 106 124 105 7.8 Decachlorobiphenyl (Surrogate) 82.5 76 94.5 96 11.0 delta-bhc 95 100 97.5 99 2.2 Dieldrin 113 104 122 109 6.8 Endosulfan I 108 104 127 111 9.0 Endosulfan II 105 102 120 112 7.3 Endosulfan sulfate 118 94.5 82.5 89 16.1 Endrin 110 108 126 108 7.7 Endrin aldehyde 27.9 62 69 55 33.6 Endrin ketone 103 102 119 112 7.4 Etridiazole 103 100 81 88.5 11.0 gamma-bhc (Lindane) 95.5 98.5 93.5 104 4.7 Heptachlor 94.5 92 102 92 5.0 Heptachlor epoxide 104 97 85 93 8.4 Hexachlorobenzene 95.5 87.5 84 77.5 8.7 Hexachlorocyclopentadiene 73.9 65.3 62.6 81.3 12.0 Methoxychlor 99.5 99 113 98.5 6.8 P a ge 4
Table 3. Lab Fortified Blank, Four Runs (Continued) Run 1 Run 2 Run 3 Run 4 %RSD Mirex 85 74.5 108 87.5 15.8 Oxychlordane 97 87.5 79 84.5 8.7 Permethrins (cis & trans) 105 92.2 118 83.5 15.1 Propachlor 111 95 86 90.2 11.4 Tetrachloro-m-xylene (Surrogate) 81 76.5 71.5 60.5 12.2 Total DDT 102 95 111 101 6.5 trans-chlordane 114 92.5 110 101 9.2 trans-nonachlor 104 90 113 104 9.2 Trifluralin 112 102 95.5 85.2 11.4 Table 4. Relative Percent Differences Between Duplicates LFB LFB Dup RPD 2,4'-DDD 102 102 0 2,4'-DDE 94 96.5 2.6 2,4'-DDT 97.5 98 0.5 4,4'-DDD 112 111 0.9 4,4'-DDE 104 103 1.0 4,4'-DDT 104 102 1.9 Aldrin 84 85 1.2 alpha-bhc 92 90 2.2 beta-bhc 91 91 0 Chlordene 91.5 94 2.7 Chlorothalonil 107 94 12.9 Chlorpyrifos 133 128 3.8 cis-chlordane 106 105 0.9 cis-nonachlor 97.5 100 2.5 DCPA 111 108 2.7 Decachlorobiphenyl (Surrogate) 82.5 77.5 6.3 delta-bhc 95 94 1.1 Dieldrin 113 112 0.9 Endosulfan I 108 108 0 P a ge 5
Almond Milk Table 4. Relative Percent Differences Between Duplicates (Continued) LFB LFB Dup RPD Endosulfan II 105 104 1.0 Endosulfan sulfate 118 115 2.6 Endrin 110 108 1.8 Endrin aldehyde 62 55.5 11.1 Endrin ketone 103 103 0 Etridiazole 103 99 4.0 gamma-bhc (Lindane) 95.5 93.5 2.1 Heptachlor 94.5 93.5 1.1 Heptachlor epoxide 104 104 0 Hexachlorobenzene 95.5 93.5 2.1 Hexachlorocyclopentadiene 73.9 70 5.4 Methoxychlor 99.5 97.5 2.0 Mirex 85 87 2.3 Oxychlordane 97 99 2.0 Permethrins (cis & trans) 105 104 1.0 Propachlor 111 109 1.8 Tetrachloro-m-xylene (Surrogate) 81 80 1.2 Total DDT 102 102 0 trans-chlordane 114 112 1.8 trans-nonachlor 104 102 1.9 Trifluralin 112 113 0.9 References: 1. US EPA, http://www.epa.gov/pesticides/pestsales/07pestsales/usage2007.htm, accessed on September 28, 2015. 2. Guidelines for Drinking Water Quality, World health Organization (2011) Fourth Edition, http://apps.who.int/iris/ bitstream/10665/44584/1/9789241548151_eng.pdf, accessed on September 29, 2015. 3. European Water Directive, http://eur-lex.europa.eu/legal-content/en/txt/pdf/?uri=celex:31998l0083&from=en, accessed September 29, 2015. www.horizontechinc.com AN1031602_01 16 Northwestern Drive, Salem, NH 03079 USA Tel: (603) 893-3663 Email: Support-Service@horizontechinc.com