The Argument on “Total” Metals

by | Mar 25, 2021 | Reports

Lab worker working samples

Why is there still an argument about which digestion method should be reported as “total” metals?

When you’re looking at an old QAPP, permit or analytical report, you might have noticed that there were different listings for how the metals were to be identified and reported out.  This was based upon what digestive method was designated at the project’s setup.  There was either a  Total Recoverable (TR) designation or a Total (T) designation.  While the two titles may sound similar, the acids used in each digestion may or may not have delivered a true “total” recovery from the sample based upon the matrix of said sample.

Total vs. Total Recoverable digestion has been the focus of many arguments over the years, with each camp claiming applicability of its selected digestion procedure to a non-filtered sampled aliquot.  When I say “camp,” I mean people developed preferences for the digestive procedure that they believed fit their sample matrix or they developed data baselines that they did not want to move away from with a new digestion procedure.

The EPA was probably tired of the amount of correspondence that they received on this issue and by legal action took it out of the hands of the many different players involved.  With guidance from the 2012 Method Update Rule (MUR), the permit writers no longer needed to request digestion procedures in order to use the “best” possible digestion.  The digestive methods for both TR and T were/are going to be reported as “Total Metals.” 

What the 2019 Method Update Rule Says

Starting with the 2012 Method Update Rule (MUR)  and continuing on with the most recent 2019 MUR, the EPA language contains a footnote (4)  to explain the current requirements on how a “Total” or “Total Recoverable” sample will be digested and reported, below is the verbiage as it relates to ICP/ICP-MS requirements:

For the determination of total metals (which are equivalent to total recoverable metals) the sample is not filtered before processing. A digestion procedure is required to solubilize analytes in suspended material and to break down organic-metal complexes (to convert the analyte to a detectable form for colorimetric analysis). The approved total recoverable digestion is described as Method 200.2 in Supplement I of “Methods for the Determination of Metals in Environmental Samples” EPA/600R- 94/111, May, 1994, and is reproduced in EPA Methods 200.7, 200.8, and 200.9 from the same Supplement. For analyses using inductively coupled plasma-atomic emission spectrometry (ICP-AES), the direct current plasma (DCP) technique or EPA spectrochemical techniques (platform furnace AA, ICP-AES, and ICP-MS) use EPA Method 200.2 or an approved alternate procedure (e.g., CEM microwave digestion, which may be used with certain analytes as indicated in Table IB); the total recoverable digestion procedures in EPA Methods 200.7, 200.8, and 200.9 may be used for those respective methods. Regardless of the digestion procedure, the results of the analysis after digestion procedure are reported as “total” metals.”

To be clear the above digestion requirements listed in the 2019 MUR supersede older EPA rules and digestion procedures and as such will be SVL’s default digestion (EPA 200.2). SVL upon request will use alternative digestive methods but will still report out our results as “Total Metals.”  You can visit the EPA’s site at: https://www.epa.gov/cwa-methods/methods-update-rule-2019.

We know change is difficult and recognize that our reporting format may no longer match what you have always been used to.  Please, contact your Project Manager and let them walk you through our report format and why we report your analyses in the manner that we do.

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