CALTEST INFORMATIONAL BULLETIN
Caltest Rationale for Pyrethroid Analysis by EPA method 8270 modified GCMS.
Written by Peter Halpin - Summer, 2005.
INTRODUCTION
This presentation gives a summary of a practical adaptation to an existing well-developed EPA method in response to a new need for pyrethroid pesticide environmental monitoring data.
EPA method 8270 Gas Chromatography with Mass Spectrometer (GC/MS) is modified by using Selected Ion Monitoring narrow range scanning to achieve the detection levels required with the high confidence of analyte identification that is the hallmark of GC/MS as a technique. This approach is important because of its relevance to the needs of the current environmental monitoring community, and because of its potentially wide application (the equipment we used is installed in thousands of environmental labs across the country).
RATIONALE
Pyrethroid pesticides appear to be a significant source of sediment toxicity in urban and agriculturally dominated streams. Interest in pyrethroid pesticides has increased sharply as the usage has increased (partly due to urban bans on Diazinon and Chlorpyrifos) and new research has shown acute sediment toxicity at much lower pyrethroid concentrations than previously understood. Current research in California agricultural stream sediments and urban creek sediments indicate pyrethroid related acute sediment toxicity to arthropods. The San Francisco Bay Regional Water Quality Control Board staff report on pesticide related toxicity (referenced in the article) states the expectation that this toxicity will be widely observed in urban creeks subject to pesticide run-off.
Up until two years ago, there was no commercial demand for environmental monitoring analysis of pyrethroids. Now, analysis of these compounds is being required by the California Central Valley Regional Water Quality Control Board in stormwater and agricultural run-off, and sediments in creeks receiving stormwater inputs from both agricultural sites and residential areas.
We researched which methods others had employed in the analysis of pyrethroids. We then took the existing, promulgated, very common and well understood method EPA method 8270, and adapted it to the selected ion-monitoring manner of operation. This approach saves labor intensive extract clean-up steps; analyst data work-up time, covers more compounds, and has a higher confidence in analyte identification than the GC ECD alternative.
The method we describe is conceptually based on the work already done by the USGS and the California Department of Food and Agriculture. USGS published their method in 2001 but did not focus on pyrethroids exclusively or as extensively. The California Department of Food and Agriculture lab uses the same approach but does not cover the same extensive analyte list and does not meet the same reporting levels.
REFERENCE METHODS
Our reference methods are:
- USGS (USGS Water Resources Investigations Report 01-4098, 2001 Methods of Analysis by the U.S. Geological Survey National Water Quality Laboratory – Determination of Moderate-Use Pesticides and Selected Degradates in Water by C-18 Solid Phase Extraction and Gas Chromatography/Mass Spectrometry)
- The California Department of Food and Agriculture (Determination of Pyrethroids in Sediment Water EMON-SM-52-7 2003)
- The EPA’s test manual, SW-846,Test Methods for Evaluating Solid Waste, Physical/Chemical Methods, Method 8270 Semivolatile Organic Compounds by Gas Chromatography/Mass Spectrometry (GC/MS).
The importance of this application of the 8270 method for the listed analytes of interest is the achievement of reporting levels required to measure near, or lower than acute toxicity criteria. Without this modified method, analytical choices are limited to the published GC-ECD analyses with extensive clean-ups, very time consuming analyst confirmation of analyte (comparison of 2 nd dissimilar column data for each chromatographic peak at target retention times), and less than optimal sensitivity; or very expensive High Resolution GC/MS. GC/ECD costs and the GC/MS Selected Ion Monitoring method described are in the $350 - $400 range. High Resolution GC/MS analyses are usually in the $1,000 to $1,600 range.
We used the most common GC/MS in the market, the Agilent 5973 quadrapole, purchased in 1997. The availability of its use is far greater than the alternative of High Resolution GC/MS or LC/MS-MS which are limited to a small number of research and special function labs. The method described here is based on a very common, well understood EPA method, and yet reaches the sensitivity levels required in sediments at a low cost. It also allows analysis of any of the pyrethroids, where GC/ECD is limited to those that are halogenated.
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