The mSPLP (E9003) method…

The mSPLP (E9003) method does not seem to be calibrated to produce accurate readings for fine grained soils, in particular clays. The mSPLP calls for a 0.5 µm filter to remove solids from the filtrate prior to analysis, but this filter does not seem to remove fine soil particles resulting in artificially high metal concentrations due to suspended and/or dissolved metals.

Based on discussions with various environmental laboratories, I understand that the mSPLP still possesses some analytical limitations for metals which may affect accuracy and reliability of sample results. Laboratories have observed that clayey soils seem to create mSPLP analysis concentrations higher than bulk analysis would anticipate. Possible attributable causes are:
- Finer textured soils (particularly clay) can pass through (or be dissolved by) the 0.45 µm filter and bias towards higher concentrations of metals.
- The leaching is done by an unbuffered solution. The pH of submitted soils can have a large effect on the amount of metals which will be leached into solution.
- The natural state of the metals (e.g. oxidation state) can also have large effects on the bulk vs leachate analysis.

Has there been any additional investigation into these concerns?