Question on Incremental Sampling Methodologies

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One of the main tenants of the Incremental Sampling Methodologies approach is the analysis of a larger analytical subsample. For organic analysis, this doesn't seem to be a problem, but it is for metals. The digestion blocks that are the norm in environmental labs basically fix the analytical sample at 1 or maybe 2 grams. In fact, the official digestion methods are only validated for these small sample sizes. Is pulverization the only way to really get around the limitation on the analytical subsample size?

Experts Response:
You are correct that using large subsamples is a common part of Incremental Sampling Methodology (ISM). For organics using 10-30 g is already the norm so this isn't really a change for organic extractions. As you point out most metals digestion methods are optimized for 1-2 g aliquots. There are two common ways to address this limitation.

What is the difference between total metals vs. dissolved metals analysis and what form the metal is being analyzed

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Can you explain the difference between total metals versus dissolved metals analysis and what form of the metal is being analyzed?

Expert Repsonse: 

Total metals analysis for water samples include the metals content both dissolved in the water and present in the particulates in the water. Typically a dissolved metals analysis of a water sample is performed by removing the particulates with a filter, then analyzing the filtered water for metals. The most common filters used for this purpose have a 0.45 um pore size.

Total metals analysis results should always be greater than or equal to dissolved metals analysis results, because dissolved metals is a subset of total metals. Dissolved metals are generally considered more mobile and biologically available. Thus, the dissolved metals results are useful for risk assessment and fate & transport studies.

The specific metal species (or form) present in the dissolved fraction is highly dependent on the metal of interest. Most of the dissolved species are solvated metal cations such as Na(I) or Cr(VI). Some metals species are present as oxy anions such as arsenite.  

Water solubility of the elemental metals (i.e. neutral valence state) is generally quite low. For example this website states elemental mercury [Hg(0)] has a water solubility limit of 56 ug/L at 25C (http://www.inchem.org/documents/cicads/cicads/cicad50.htm#2.1).

Most regulations use total metals results because it is often considered more conservative and protective, however, depending on the purpose of the regulation it might be based on dissolved or total metal concentrations.

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Potassium permanganate to oxidize phenol from landfill leachate as treatment process

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We would like to use potassium permanganate (KMnO4) to oxidize phenol from landfill leachate as a treatment process (i.e. reduce phenol below POTW required limits) prior to sending leachate to a local POTW. However, we are not sure what could potentially be formed when the KMnO4 oxidizes the phenol and how these subsequent formation products should then be removed. 

Expert Response: 

The reaction product of phenol and permanganate will be 1,4-benzoquinone. It is not regulated, and I suspect that it will be degraded in a biological treatment system. Since your treated leachate is going to a POTW, this should be sufficient to eliminate both the phenol and the by-product.

Ask the Expert Question: 

We also would need to know what potassium permanganate (KMnO4) would do to ammonia, cyanide, hydrogen sulfide and dissolved metals which are also present in the leachate at lesser concentrations than the phenol. 

Expert Response: 

Regarding the reaction of permanganate with the other constituents, I would expect ammonia to be oxidized to nitrate, cyanide to carbon dioxide and nitrate, and sulfide to sulfate. 

With the metals it would depend on the specific metals and their oxidation states.  For example, the leachate probably contains some dissolved ferrous iron because the landfill will be a reducing environment. The reaction with permanganate will convert this ferrous iron to ferric iron, and that would almost certainly result in a ferric oxide precipitate. These constituents are likely to react with permanganate more quickly than phenol, so you will have to add sufficient permanganate to oxidize these before you will get thorough oxidation of the phenol.