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. The EPA has taken the discussion and simplified it so that Permit Writers no longer need to request digestion procedures in order to use the best possible digestion. The term “best” is subjective to the individual nature of environmental samples and how well samples were taken to digestive completion. The 2012/2016 Method Update Rule has put forth a footnote to explain the current requirements on how a “Total” or “Total Recoverable” sample will be digested, below is the verbiage as 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.
The above digestion requirements were listed in both the 2012 and 2016 Method Update Rules. The rules 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 results as “Total Metal.”