The “Breakdown” of Endrin and DDT for Non-Environmental Chemists

As the title makes clear, this post is aimed more at non-environmental laboratory personnel who are not familiar with US EPA methods.  If you are one of those environmental lab gurus who shudders at the sound of a “pesticide degradation check”, this is probably stuff you already know.

Anyways, for the rest of you, you may have noticed that a lot of chromatography consumable manufacturers, like Restek, like to give you performance specs for endrin and DDT breakdown in marketing literature, application notes, etc.  Some of you may wonder what this means or why it matters to you.

Endrin

Endrin

To start off, endrin and DDT are two chlorinated pesticides, whose usage has been banned or regulated in many countries, along with several other chlorinated pesticides.  These pesticides largely came into use after WWII and became widely used due to their effectiveness as insecticides.  Most of you are probably aware of DDT and its historical use in fighting malaria carrying mosquitos.  Several of these pesticides have persisted in the environment for long periods of time without degrading.  They also are not easily broken down by biological systems, causing a buildup in fat cells that can be passed through the food chain.  Rachel Carson released her famous environmental science treatise “Silent Spring” in 1962, which specifically focused on the dangers of pesticide accumulation in the environment, with many references to DDT.  The book helped to spawn a large scale environmental movement and changed the way we think of chemicals and the environment forever.  Eventually, growing environmental concerns would lead to the creation of the US Environmental Protection Agency (EPA) and result in greater legislation and regulation over chemicals in the environment.

4,4'-DDT

4,4′-DDT

This brings us back to endrin and DDT, which would be phased out of use, along with other chlorinated pesticides.  Even though not in use today in the US, these chemicals still persist in the environment.  The US EPA has developed analytical methods to analyze for a multitude of environmental contaminants from chlorinated pesticides to disinfection by-products.  These analytical methods are designated by number codes, such as 8081B, 8270D, 525.2, 608, etc.  One specific EPA method for analyzing for chlorinated pesticides by gas chromatography is 8081 (8081B, being the most current revision).  The method outlines requirements for looking at samples by GC, using dual columns with electron capture detection.  EPA methods are often explicit in many quality control requirements, such as how many points the calibration curve must be, how often a calibration check must be run, requirements for blanks, matrix spikes, etc.

One of the specific requirements of EPA method 8081 is a pesticide degradation (breakdown) check prior to running samples and at least every 12 hours during a sequence of samples.  This check involves injecting a mid-level standard containing only endrin and DDT and calculating what is known as the “breakdown” percentage.  DDT degrades to form DDE (dehydrochlorination) and DDD (dechlorination) and endrin degrades to form endrin aldehyde and endrin ketone (epoxide group in endrin is opened to form either aldehyde or ketone).  These reactions can easily occur at high temperatures, like those found in the inlet, as the compounds interact with a variety of surfaces and matrix components.  Breakdown percentage is calculated as follows (area refers to peak area):

Breakdown_EquationEPA method 8081B requires each breakdown percentage to be below 15% to continue with the analysis of actual samples.

This pesticide degradation check is used as an indicator of instrument cleanliness/inertness.  The goal of any chromatographic method should be to detect only what is found in the initial sample that is injected into the instrument (easier said than done!).  As the instrument gets dirty from sample matrix or if you do not use quality inert consumables (liners, columns, press-tights, etc), breakdown of these very sensitive pesticides will occur in the GC system.  This can compromise the analysis, as products are being formed within the instrument rather than actually coming from the sample.  The breakdown products for endrin and DDT are also compounds of interest in method 8081, since breakdown occurs naturally in the environment, as well.  Some of the breakdown products are more toxic than the parent products to biological systems.

These particular pesticides were chosen because they are extremely sensitive to chemical change within a hot injector and require very inert conditions to perform well.  The performance of these pesticides has implications beyond that for themselves and their breakdown products.  Poor performance (aka high breakdown) for these pesticides is a likely indication that there will be similar issues with other sensitive analytes as well.  Even if you don’t work in an environmental lab and perform this degradation test, the breakdown numbers can still be meaningful.  Inert liner deactivations like the Restek Premium deactivation involve complex chemistry to combat analyte interaction and breakdown in the inlet.  While you may never personally analyze endrin or DDT, the low breakdown percentages that you see in product literature are indicative of a quality deactivation that will work well for a large number of sensitive analytes at trace levels.

Link to US EPA Method 8081B: 

http://www3.epa.gov/epawaste/hazard/testmethods/sw846/pdfs/8081b.pdf

One Response to “The “Breakdown” of Endrin and DDT for Non-Environmental Chemists”

  1. BOC Sciences says:

    More chemical suppliers should act like Restek in providing the performance specs for endrin and DDT breakdown in marketing literature, and application notes to remind people of being more environment friendly.

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