Page 7: Guidelines for Canadian Drinking Water Quality: Guideline Technical Document – Vinyl Chloride
Part II. Science and Technical Considerations (continued)
The U.S. Environmental Protection Agency (EPA) currently has three approved analytical methods (Method 502.2 Revision 2.1, Method 524.2 Revision 4.1 and Method 524.3 Version 1.0) for the analysis of vinyl chloride in drinking water (U.S. EPA, 2003, 2009a). These methods are general methods for the identification and measurement of purgeable volatile organic compounds (VOCs). The methods use purge and trap procedures, followed by a capillary gas chromatography (GC) column to separate the analytes. After an elution from the GC column, the analytes are identified by different detection techniques.
Method 502.2 Revision 2.1 uses a purge and trap capillary GC column equipped with photoionization detectors (PID) and electrolytic conductivity detectors (ELCD) in series. The method's MDL will vary depending on the GC column used and ranges from 0.02 to 0.04 µg/L for the PID and from 0.01 to 0.18 µg/L for the ELCD.
Method 524.2 Revision 4.1 uses a capillary GC column interfaced with a mass spectrometer (MS). The method has MDL values between 0.04-0.17 µg/L, depending on the GC column and the interface used between the GC and MS (U.S. EPA, 1995).
Method 524.3 version 1.0, approved in 2009, uses the GC-MS technique and has a detection limit of 0.029 µg/L for vinyl chloride. The advantages of the method include an optimization of the purge and trap parameters, an option for use of selected ion monitoring (SIM) and the use of solid acid preservatives (U.S. EPA, 2009a).
Two Standard Methods can also be used for the analysis of vinyl chloride in drinking water (APHA et al., 2005). These methods, SM 6200B and SM 6200C, are based on purge and trap capillary GC followed by MS detector or PID and ELCD in series, respectively. Method SM 6200B has an MDL of 0.12 µg/L, and SM 6200C has an MDL of 0.025 µg/L. The minimum quantitation levels, defined as the lowest level that can be quantified accurately using these methods, are 0.48 µg/L and 0.1 µg/L for methods SM 6200B and SM 6200C, respectively.
A recent study investigating the factors affecting the leaching of vinyl chloride from PVC and CPVC piping used in drinking water applications reported an MDL of 0.0045 µg/L using GC-MS in SIM mode (Richardson and Edwards, 2009).
However, the practical quantitation level (PQL) for U.S. EPA-approved methods is 2 µg/L and is based on the capability of laboratories to measure vinyl chloride within reasonable limits of precision and accuracy at the time of regulation. Current PQL assessments are based on two approaches: (1) the lowest value for which 75% of laboratories can quantitate within prescribed accuracy limits based on actual performance data, if the data is sufficient; or (2) multiplying the upper levels of the MDLs to account for the variability inherent to test methods and instruments used for analyses, when data is insufficient. In establishing the PQL, the U.S. EPA considers and prefers the laboratory performance data for methods approved at the time of the review over the MDL approach (U.S. EPA, 2009d).
In the second 6-year review of existing National Primary Drinking Water Regulations, the U.S. EPA determined that there was insufficient proficiency testing data to derive PQLs (U.S. EPA 2009d). Therefore, the U.S. EPA used two other sources to derive an estimated quantitation level (EQL): a minimum reporting level (MRL) approach and an MDL multiplier approach based on the approved analytical methods. The EQL is an estimate of the possible lower bound for a PQL. It is based on statistical analysis of proficiency test results for a method or the MRL from the dataset. The MRLs represent laboratory analytical limits for a large pool of laboratories in the U.S. Using the MRLs of more than 139,000 records collected from 1998 to 2005, the U.S. EPA established an EQL of 0.5 µg/L for vinyl chloride, reporting that a high percentage of the samples achieved a MRL of 0.5 µg/L.
Applying a multiplier of 10 to the upper bounds of the MDL for each of the two approved analytical methods (502.2 and 524.2), resulted in a possible PQL range of 1.7 to 1.8 µg/L. These values were slightly below the current PQL of 2 µg/L (U.S. EPA, 2009d). Ultimately, the U.S. EPA chose not to modify the existing PQL, because the data could not support the adoption of a lower value (U.S. EPA, 2009d).
There is no equivalent centralised program for the collection and rigorous statistical analysis of analytical data in Canada. As such, establishing a PQL for Canadian laboratories is not possible.
Vinyl chloride is typically found in groundwater in the vicinity of landfills and where there have been spills of vinyl chloride or chlorinated precursor compounds. As such, it is important to characterize these groundwater sources in order to select the appropriate treatment for removal of vinyl chloride. The selection of an appropriate treatment process will depend on many factors, including the characteristics of the raw water supply and the source and concentration of vinyl chloride.
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