CALTEST INFORMATIONAL BULLETIN
Written by Richard L. Heines † , Peter W. Halpin † June 2006
ABSTRACT
An existing, commonly used EPA Gas Chromatography Mass Spectrometry (GC/MS electron ionization) method (EPA 8270) was modified by using a narrow range selected ion scan instead of the traditional full scan to yield the necessary sensitivity to analyze the pyrethroids at environmentally relevant levels of low ng/L in water and sub ug/kg in sediment. This analytical approach does not routinely need the multiple extract clean up procedures of ECD analysis, and provides the benefits of analyte confirmation by the mass spectra of the compounds of interest.
INTRODUCTION
Pyrethroid pesticides appear to be a significant source of sediment toxicity in urban and agriculturally dominated streams[1,2]. The toxicity appears to be widespread in the Sacramento and San Francisco California Bay areas[3], and occurs at very low concentrations.
Recent sediment toxicity studies indicate thresholds of acute toxicity to arthropods at low (2-10) ug/kg (part per billion) levels. [ 1]. Generally speaking the analysis of pyrethroid pesticides has been limited to reporting levels that are higher than the concentrations of interest for these analytes. Environmentally relevant reporting limits would ideally be in the low ng/L (part per trillion) range for water for most pyrethroids[4]. Sediment reporting levels should start at 1 ug/kg dry weight, and lower if possible with a target of one tenth the LC-50 (The concentration that causes mortality in 50% of the test organisms). Currently there are no regulatory approved methods. The draft EPA HPLC method 1660 reporting levels are in the low part per billion range in water, and therefore not sensitive enough to provide environmentally relevant reporting levels. The GC ECD (electron capture detector) method has been successfully used for the halogenated pyrethroids. However, for confirmation of analyte identity and handling matrix affects a mass spectrometer method is preferred when adequate sensitivity can be achieved.
This modified GCMS method is useful for all the pyrethroids of current interest in California monitoring programs and meets the concentration related monitoring goals[5] for 9 of 10 pyrethroids in water, and all ten in sediment. The described GCMS SIM method is more sensitive than the EPA draft HPLC method, has equivalent or lower reporting limits than the existing GC/ECD method in use, and includes a wider analyte list than is possible with GC/ECD. Additionally, the GCMS method provides three dimensional data compared to two dimensional GC data.
The analytes of interest at this point seem to be represented by the following list:
Bifenthrin, Cyfluthrin, Cyhalothrin, Cypermethrin, Esfenvalerate/Fenvalerate, Fluvalinate, Fenpropathrin, Permethrin, Resmethrin, Tralomethrin/Deltamethrin [ 5,6,7,8]. Those listed together (separated only by a ‘/’) are unable to be separated by current GC/ECD (Gas Chromatography with Electron Capture Detector) or GC/MS analysis.
Many argue that the primary data collection efforts for pyrethroids should be in the sediment matrix due to the high affinity of these compounds for solids, and the observed acute toxicity in sediments.
For uniformity of application in a potentially regulatory context, we run the EPA 8270 GC/MS method exactly like all other EPA methods used for environmental compliance, the primary difference being the mode of data acquisition is narrow-range scan instead of full scan. In full scan mode, the mass spectrometer is constantly scanning the range of 50 to 550 amu. In the selected ion mode the mass spectrometer is only scanning for the predetermined three most abundant ions per analyte. Scanning for fewer ions provides much greater equivalent sensitivity compared to full range data acquisition.
In the EPA 8270 [9] modified GC/MS-SIM method the mass spectrometer uses electron ionization and data is collected in the selected ion mode, using a narrow range scan for the three most abundant ions per analyte. Analyte identification is based on chromatographic relative retention time, accompanied by measurement of the most abundant ion, in the proper ratio to the second most abundant ion, and with the presence of a third characteristic ion.
INSTRUMENTATION AND PROCEDURE
Analysis of the final extracts was performed on a Agilent 6890 GC with a model 5973 mass spectrometer manufactured in 1997. An model 7673A autosampler is used to inject 2-ul. The GC is equipped with a silico-steel split/splitless injection port and a J&W DB-5MS 30 meter capillary column with a 250 um diameter and a film thickness of 0.25um. Helium is used as the carrier gas. The isomers are summed and quantified as ‘total’. Some of the target analytes have up to 4 diasteromers. An experienced mass spectromter analyst opens each sample data file and reviews each analyte to assure proper identification and integration. Analytes eluted from the capillary column are introduced into the mass spectrometer. Identification of target analytes is accomplished by comparing their selective mass ion ratios with the selective mass ion ratios of authentic standards. Quantitation is accomplished by comparing the response of a major (quantitation) ion relative to an internal standard using a five-point calibration curve. Second Source calibration check standards are employed. Batch QC is EPA style of Method Blank, Laboratory Control Standard, Matrix Spike and Matrix Spike duplicate for each and every batch of samples, with a maximum batch size of 20 samples. Internal standard is added to the sample extract at the instrument. Instrument tune is checked every 12 hours. Control limits are established based on lab in-house data. Extraction surrogates are reported, but data is not normalized to that recovery.
EXTRACTION
For water, a one-Liter sample collected in glass with Teflon-lined lid. The entire sample is poured into a Teflon 2-liter separatory funnel. To try to recover all analyte possible from the sample container walls 60ml. of Methylene chloride is added to the empty sample container, the lid screwed on tightly, and the sample bottle shaken with the solvent for approximately 30 seconds. The sample bottle solvent rinse is added to the separatory funnel with the sample. The water sample is extracted three times with 60 ml. of methylene chloride and shaken ten minutes each time on an auto-shaker. The combined solvents from the bottle rinse and all three extractions are then concentrated to 1mL final volume. Currently this is done with macro and micro Kaderna-Danish apparatus followed by a nitrogen blowdown to final volume. Pyrethroids have a strong affinity for solids, and rapidly adsorb to sediment particles. Any pre-filtering prior extraction may cause a reduction in total pyrethroids measured due to loss of analyte adsorbed to particles filtered out. Because of this, environmental water analyses for pyrethroids is often based on ‘whole water’, that is water with all sediments/suspended solids included. Alternatively solids and filtered water fractions can be collected. When whole water samples are analyzed by liquid-liquid extraction, results will include pyrethroids bound to the solids as well as any dissolved fraction present.
Sediment is collected into a glass jar with Teflon lined lid. At the lab, the sample is homogenized with a stainless steel spatula. A 30g +/- 0.1 g portion is placed in a 250 ml wide mouth jar. Sodium sulfate is added and mixed with the sample until the sample has no free liquid and is a sandy texture. The sample and sodium sulfate mix is then spiked with 200 ul of surrogate solution. The extraction procedure consists of adding 100ml of a 1:1 mix of methylene chloride and acetone and sonicating in a chilled sonic bath. The extraction process is carried out three times sequentially. After each extraction, the supernatant solvent is poured off through a pre-washed filter paper containing roasted sodium sulfate to remove moisture. All extraction solvent is concentrated to a final volume of 2ml using macro and micro Kaderna-Danish and nitrogen blow down. Separate from the extraction process, an aliquot of the sediment is analyzed for percent moisture in order to convert results to dry weight.
HOLD TIMES
USGS [11] and California Dept of Food and Agriculture [12] hold time studies in water indicate hold times as short as 3 days to 13 days depending on the analyte. Such short hold times require coordination with the lab to extract the samples in time. Spiked sediment samples have shown reproducible recoveries after several months frozen.
The importance of the 8270 GC/MS-narrow range scan method is the economical achievement of reporting limits low enough to be relevant for 9 of 10 pyrethroids with water quality goals; and for monitoring at the toxicity ranges demonstrated in sediments in recent studies. This technique also provides the ability to identify the analyte with confidence even in complex matrixes. In the case of the non-halogenated pyrethroids, traditional GC/ECD is not suitable, but the GC/MS is. This method can be valuable for routine monitoring. For even lower level work related to researching sub-lethal affects, other techniques, or more sensitive mass spectrometers will likely be required.
ACKNOWLEDGMENT
Caltest staff acknowledges the work of the USGS and the California Department of Food and Agriculture for their development of the GCMS narrow range scan selected ion monitoring approach.
REFERENCES
- Amweg E, Weston DP, Ureda NM. 2005: Use and Toxicity of Pyrethroid Pesticides in the Central Valley, California, USA, Environ Toxicol Chem ; Vol. 24 (4);966-972
- Weston DP, You JC, Lydy M.J. 2004. Distribution and toxicity of sediment-associated pesticides in agriculture-dominated water bodies of California's Central Valley. Environ Sci Technol 38(10):2752-2759.
- Johnson B. 2005. Diazinon and Pesticide Related Toxicity in Bay Area Urban Creeks, Water Quality Attainment Strategy and Total Maximum Daily Load (TMDL), Proposed Basin Plan Amendment and Staff Report, August 2005. San Francisco Bay Regional Water Quality Control Board, Oakland, CA.
- Goh KS , Newhart KL.2005. Pyrethroids: Use, Physico-Chemical Properties and Aquatic Toxicity. Pyrethroid Method Development Project, California Department of Pesticide Regulation, Environmental Monitoring Branch, 1001 I Street, Sacramento, California 95812,
- Marshack J. 2003. A Compilation of Water Quality Goals. California Central Valley Water Quality Control Board, 11020 Sun Center Drive #200 Rancho Cordova , CA 95670 ,
- Kelley, K. 2003. Monitoring Surface Waters and Sediments of the Salinas and San Joaquin River Basins for Synthetic Pyrethroid Pesticides . Study 219. California Department of Pesticide Regulation, Environmental Monitoring Branch, 1001 I Street, Sacramento, California 95812
- Starner, K. 2004. A Preliminary Assessment of Pyrethroid Contamination of Surface Waters and Bed Sediments in High Pyrethroid-Use Regions of California. Study 224. California Department of Pesticide Regulation, Environmental Monitoring Branch, 1001 I Street, Sacramento, California 95812
- Moran K. 2005. Pesticides in Urban Surface Water, Urban Pesticides Use Trends Annual Report. San Francisco Estuary Project, Oakland, CA
- U.S. EPA. 2005. SW-846 Manual, Test Methods for Evaluating Solid Waste, Physical/Chemical Methods. U.S. Government Printing Office, Superintendent of Documents, Washington, DC 20402.
- You J, Weston D, Lydy M.J. 2004. A Sonication Extraction Method for the Analysis of Pyrethroid, Organophosphate, and Organochlorine Pesticides from Sediment by Gas Chomatography with Electron-Capture Detection. Arch Environ Contam Toxicol 47, 141-147
- Sandstrom MW, Stroppel ME., Foreman WT, Schroeder MP. 2002. Methods of Analysis by the U.S. Geological Survey National Water Quality Laboratory-Determination of Moderate-Use Pesticides and Selected Degredates in Water by C-18 Solid Phase Extraction and Gas Chromatography/Mass Spectrometry. Water Resources Investigations Report 01-4098, U.S. Geological Survey Method O-2002-01, USGS Denver, Colorado.
- White J, Feng H, Cooper C, Rivera L, Jackson T. 2003. Determination of Pyrethroids in Sediment Water. EMON-SM-52-7. California Dept. of Food and Agriculture, Center for Analytical Chemistry, Environmental Monitoring Section, Sacramento, CA
Table I: Pyrethroid Calibration, Method Detection Limits, Reporting Limits and Hold Time for Aqueous Samples
|
CAS# |
Lowest Calibration Standard
(PPM) |
Aqueous MDL (ug/L)
(PPB) |
Aqueous Report Limit (ug/L)
(PPB) |
USGS & CA Dept. of Ag Aqueous Extraction Hold Times (Days) |
|
Bifenthrin |
82657-04-3 |
0.002 |
0.005 |
0.005 |
13 |
|
Cyfluthrin |
68359-37-5 |
0.01 |
0.004 |
0.01 |
13 |
|
Cyhalothrin |
68085-85-8 |
0.002 |
0.004 |
0.005 |
3 |
|
Cypermethrin |
52315-07-8 |
0.005 |
0.003 |
0.005 |
13 |
|
Fenvalerate/
Esfenvalerate |
51630-58-1 |
0.005 |
0.004 |
0.005 |
13 |
|
Fluvalinate |
69409-94-5 |
0.002 |
0.003 |
0.005 |
|
|
Fenpropathrin |
39515-41-8 |
0.01 |
0.003 |
0.01 |
|
|
Permethrin |
52645-53-1 |
0.002 |
0.003 |
0.005 |
3 |
|
Resmethrin |
10453-86-8 |
0.002 |
0.006 |
0.01 |
|
|
Deltamethrin/
Tralomethrin |
66841-25-6 |
0.005 |
0.003 |
0.005 |
|
|
2-Fluorobiphenyl (SS) |
321-60-8 |
NA |
NA |
NA |
NA |
|
p-Terphenyl-d14 (SS) |
1718-51-0 |
NA |
NA |
NA |
NA |
|
|
Table II: Pyrethroid Calibration, Method Detection Limits, and Reporting Limits for Sediment Samples
|
CAS# |
Lowest Calibration Standard (mg/L) |
Sediment MDL ug/Kg (PPB) |
Sediment Report Limit ug/Kg (PPB) |
|
Bifenthrin |
82657-04-3 |
0.002 |
0.09 |
0.33 |
|
Cyfluthrin |
68359-37-5 |
0.01 |
0.09 |
0.33 |
|
Cyhalothrin |
68085-85-8 |
0.002 |
0.05 |
0.33 |
|
Cypermethrin |
52315-07-8 |
0.005 |
0.07 |
0.33 |
|
Fenvalerate/
Esfenvalerate |
51630-58-1 |
0.005 |
0.08 |
0.33 |
|
Fluvalinate |
69409-94-5 |
0.002 |
0.05 |
0.33 |
|
Fenpropathrin |
39515-41-8 |
0.01 |
0.09 |
0.33 |
|
Permethrin |
52645-53-1 |
0.002 |
0.04 |
0.33 |
|
Resmethrin |
10453-86-8 |
0.002 |
0.11 |
0.33 |
|
Deltamethrin/
Tralomethrin |
66841-25-6 |
0.005 |
0.05 |
0.33 |
|
2-Fluorobiphenyl(SS) |
321-60-8 |
NA |
NA |
NA |
|
p-Terphenyl-d14(SS) |
1718-51-0 |
NA |
NA |
NA |
|
