Analysis of Drinking Waters for a Suite of Pesticides using GC with dual ECD (US EPA Method 508.1) after SPE Concentration

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1 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 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 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 C 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.

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 Atrazine (with metabolites) Chlordane-alpha/gamma ,4 -DDT Dieldrin Endrin HCH-gamma (Lindane) * Heptachlor * Heptachlor epoxide * Hexachlorobenzene * Hexachlorocyclopentadiene Methoxychlor Metolachlor Cis/trans-Permethrin Simazine SGT-HEM RPD 34 Toxaphene Trifluralin *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

3 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 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

4 Table 3. Lab Fortified Blank, Four Runs Run 1 Run 2 Run 3 Run 4 %RSD 2,4'-DDD ,4'-DDE ,4'-DDT ,4'-DDD ,4'-DDE ,4'-DDT Aldrin alpha-bhc beta-bhc Chlordene Chlorothalonil Chlorpyrifos cis-chlordane cis-nonachlor DCPA Decachlorobiphenyl (Surrogate) delta-bhc Dieldrin Endosulfan I Endosulfan II Endosulfan sulfate Endrin Endrin aldehyde Endrin ketone Etridiazole gamma-bhc (Lindane) Heptachlor Heptachlor epoxide Hexachlorobenzene Hexachlorocyclopentadiene Methoxychlor P a ge 4

5 Table 3. Lab Fortified Blank, Four Runs (Continued) Run 1 Run 2 Run 3 Run 4 %RSD Mirex Oxychlordane Permethrins (cis & trans) Propachlor Tetrachloro-m-xylene (Surrogate) Total DDT trans-chlordane trans-nonachlor Trifluralin Table 4. Relative Percent Differences Between Duplicates LFB LFB Dup RPD 2,4'-DDD ,4'-DDE ,4'-DDT ,4'-DDD ,4'-DDE ,4'-DDT Aldrin alpha-bhc beta-bhc Chlordene Chlorothalonil Chlorpyrifos cis-chlordane cis-nonachlor DCPA Decachlorobiphenyl (Surrogate) delta-bhc Dieldrin Endosulfan I P a ge 5

6 Almond Milk Table 4. Relative Percent Differences Between Duplicates (Continued) LFB LFB Dup RPD Endosulfan II Endosulfan sulfate Endrin Endrin aldehyde Endrin ketone Etridiazole gamma-bhc (Lindane) Heptachlor Heptachlor epoxide Hexachlorobenzene Hexachlorocyclopentadiene Methoxychlor Mirex Oxychlordane Permethrins (cis & trans) Propachlor Tetrachloro-m-xylene (Surrogate) Total DDT trans-chlordane trans-nonachlor Trifluralin References: 1. US EPA, accessed on September 28, Guidelines for Drinking Water Quality, World health Organization (2011) Fourth Edition, bitstream/10665/44584/1/ _eng.pdf, accessed on September 29, European Water Directive, accessed September 29, AN _01 16 Northwestern Drive, Salem, NH USA Tel: (603) Support-Service@horizontechinc.com