When we choose an analytical method that is a published US EPA, ASTM, or alternative test procedure that may even be codified in the Code of Federal Regulations, we expect to be taking the right approach for our monitoring and environmental measurements. After all, the US EPA, ASTM, Standard Methods, or other organizations that develop and publish methods – the experts, have given their seal of approval. During the method validation steps, the full scope and application of the procedure are to be defined, along with development of key quality control metrics and ruggedness
testing. Unfortunately, there are several notable weaknesses in these published methods, and users need to be aware of those. Let’s look at some specific examples where we have identified issues or have observed indications of potential bias.
- Numerous interferences that can result in positive and negative bias have been identified with Free, Weak Acid Dissociable (WAD) and Total Cyanide analyses. A large number of published and codified US EPA, ASTM and other organizations’ methods and standards are available. Selecting the best method of choice requires knowledge of the source water, soil, sediment, or other sample matrix to identify method shortcomings.
US EPA Method 901.1, Gamma Emitting Radionuclides in Drinking Water. This method codified for use under the Safe Drinking Water Act in 40 CFR Part 141 is often employed by laboratories for non-potable water as well as solid matrices such as soils and sediments. The perceived advantage of this method is minimal sample preparation allowing direct gamma counting of a sample aliquot. Unfortunately, laboratories have also extended the list of analytes beyond those six included in the cross-check study. If measuring Ra-226, Pb-210, Po-210, or other radionuclide not listed in Method 901.1, another approach should be considered. There are known weaknesses with this method for Ra-226 and Pb-210 and other analytes that we can describe, and the US EPA describes this method for qualitative and confirmatory analysis indicating deficiency for critical quantitative use.
- US EPA Method SW-846 3060A, Alkaline Digestion for Hexavalent Chromium. This digestion step developed for soils, sludges, sediments and similar waste materials is designed to solubilize all forms of Cr(VI) and to prevent oxidation or reduction of either chromium form, Cr(III) and Cr(VI), during the procedure. As an SW-846 method, it is routinely a required step for waste characterization and, therefore, regulatory determination of materials under the Resource Conservation and Recovery Act (RCRA). However, Environmental Standards has been working on a study that indicates the method may be flawed when its use is extended beyond typical environmental matrices. In this case, the method has been applied to measure Cr(VI) in slag generated during the steelmaking process. Our study indicates the likelihood for oxidation of resident Cr(III) within the slag during this digestion step.
One approach for reducing the approval of new methods that may be unsuitable or flawed is to submit comments when the US EPA or other organizations first publish the draft methods and standards. With respect to US EPA methods, these are to follow a defined path from concept to verification, to draft and final version. The draft and final versions are to be published in the Federal Register
and allow public comment. Environmental Standards follows these publications, and in the past 5 years, has provided comments and several draft methods including draft US EPA Methods 8327
, and 325b
. Yet, as identified above, method problems may not be identified until they go into regular use. If you are experiencing environmental data madness, give us a call and we can help vet the issues.