Saturday, April 24, 2010

Hydrogen peroxide is not a good reagent for the removal of soil organic matter

Organic matter (OM) is the most important cementing agent of soil particles. Soils containing high amount of OM (like the limestone soil from Leyte in the picture below) generally have good aggregation (i.e. the sand, silt and clay particles are glued together by the OM). Removal of OM using chemical reagents is thus an important pretreatment in textural or particle size analysis as well as in the evaluation of soil mineralogy, cation exchange capacity, and surface area.
Soil in Leyte having a dark surface horizon due to OM 
Hydrogen peroxide (H2O2) which was first used in 1923 by G.W. Robinson to destroy soil organic matter, is the most widely used chemical reagent for removing OM in soil laboratories worldwide. However, there have been some scientific reports indicating that it may not be a good reagent for that purpose due to some unwanted effects on the mineral soil particles. In the Philippines, it is not also easy to procure large volumes of hydrogen peroxide since it requires clearance from the Philippine National Police.
Robert Mikutta and colleagues from the Institute of Soil Science and Plant Nutrition of the University of Halle-Wittenberg, Germany in a study published in the Soil Science Society of American Journal, Vol. 69 (2005), compared the performance of the three most accepted reagents for OM removal: hydrogen peroxide, sodium hypochlorite (NaOCl), and disodium peroxodisulfate (Na2S2O8).
The old soil mineralogy lab at the Univ Halle-Wittenberg
They found that: 1) removal of OM from soil is mostly incomplete with efficiency of removal varying with reaction conditions and sample properties; 2) sodium hypochlorite and disodium peroxodisulfate are generally more effective in removing OM compared with hydrogen peroxide; 3) alkaline conditions and additives favoring dispersion and/or decomposition of OM such as sodium pyrophosphate, are crucial for OM removal; and 4) OM removal can be little in soils containing high amounts of clay-sized minerals like Fe oxides, poorly crystalline Fe and Al phases, and expanding clay types.
The authors also found that the use of hydrogen peroxide to remove OM should be avoided for the determination of mineral particle properties since the treatment may promote organic-assisted dissolution of poorly crystalline minerals at low pH, disintegration of expandable clay minerals, and transformation of vermiculite into mica-like products due to ammonium (NH4+) fixation.
Clay collection for mineralogical analysis 
They concluded that sodium hypochlorite and disodium peroxodisulfate are less harmful for soil minerals than hydrogen peroxide; prolonged heating to 40 degrees Celsius during any pretreatment may transform poorly crystalline minerals into more crystalline ones; and sodium hypochlorite can be used at 25 degrees Celsius and can thus prevent heat-induced soil mineral changes.
Simply put: sodium hypochlorite is better than hydrogen peroxide in removing OM from soil samples.

Reference

Mikutta R, Kleber M, Kaiser K and Jahn R. 2005. Organic matter removal from soil using hydrogen peroxide, sodium hypochlorite, and disodium peroxodisulfate. Soil Science Society of America Journal 69: 120-135.

4 comments:

wahanahilab said...

yes i like your blog

10001110101 said...

Thanks for the summary! I've been researching this exact topic and even found Mikutta's paper, but this really sums it up nicely. I've been looking for new methods of organic matter removal that don't involve intense heating, because I've read that heat can fuse certain clay particles and interfere with the particle size analyses I perform. Anyway, keep it up!

Victor B. Asio said...

To 10001110101, thanks a lot for your kind comment.I appreciate that.

Anonymous said...

dear sir,

i would like to ask if hydrometer method is ok for textural analysis. we used this method to all types of soil but we didnt destroy organic matter content using those chemicals you mentioned. we just used some kind of dispersing agent such as calgon solution and disperse the soil using dispersing instrument. did we get the right textural class of the soil? is our method ok?