An issue that has resurfaced recently is the reporting of non-target compounds. Each of the U.S. EPA approved methods has a list (or lists) of target compounds which are within the scope of the method. The compounds which are actually reported will vary from lab to lab and from project to project - a well-designed project will specify exactly which target compounds should be included in each method. Gas chromatography - mass spectroscopy (GC-MS) methods have the option of looking at non-target peaks and making tentative identifications by comparison with library mass spectra. These tentatively-identified compounds (TICs) are typically reported with an estimated concentration, since the TICs were not used in calibration. The U.S. EPA Contract Lab Program (CLP) requires the reporting of up to 20 TICs per sample. Some laboratories have fixed prices for reporting the largest ten or twenty non-target compounds. 

Reporting TICs for non-GC-MS methods is less routine, since tentative identifications usually cannot be made without re-analysis using a standard of the suspected compound. However, the number of non-target peaks can be reported for chromatographic methods. 

The reporting of non-target compounds is not required by the California Environmental Laboratory Accreditation Program (ELAP). Since the reporting of non-target compounds is not required by method, and not required as part of lab certification, the user of data should be aware. A lab which discovers an unexpected peak during analysis may report verbally or in writing to the client, but will often follow the client's request. Commercial labs have been caught in ethical dilemmas when significant non-target compounds appear but were not part of the client's request.  

The history of site investigations has revealed examples of unconventional contaminants that are not target compounds in the usual test methods: methyl-tetrahydrothiophenes from refinery alkylation sludge (McColl site), lewisite, an extremely toxic chemical agent buried with kits used for military training, 1,4-dioxane, a commonly used solvent (can be measured by Method 8260 or 8270, but with method modifications), glycol ethers, and methyl-tert-butyl ether (MTBE). 

Methyl-tert-butyl ether (MTBE), which we discussed in an earlier column, is an example of a non-target compound for EPA Method 8260, which is a popular method for volatile organics. The occurrence of MTBE has motivated Regional Water Quality Control Boards to require MTBE monitoring to be included in leaking underground fuel tank (LUFT) investigations and most laboratories now include MTBE as a target compound in GC-MS as well as GC-FID/PID methods for petroleum contamination. There is a body of data on groundwater contamination, including data used in the Lawrence Livermore National Laboratory "Plumathon" study, which does not include MTBE because it was not a target compound, although it may have been present at detectable concentrations in some samples. 

The lessons for lab clients: know what you are asking for, and whether the lab will be reporting non-target compounds. For regulators: require the reporting of TICs if a site is uncharacterized and there is a reasonable probability of contamination with unconventional pollutants. 

The laboratory ethical dilemma for reporting non-target compounds is yet to be resolved. ELAP and the National Environmental Laboratory Accreditation Conference have encountered the issue, and future quality standards may help create more consistency in reporting unexpected pollutants. 

Bart Simmons, Ph.d., is the Chief of the Hazardous Material Laboratory, Department of Toxic Substances Control, Berkeley, CA.