How does sonication affect the mineral and organic constituents of soil aggregates?--A review

Application of ultrasound to disperse soil aggregates has been critical in enabling researchers to separate and analyze aggregate building blocks that include organic and mineral particles as well as mineral associated organic matter. But the forces generated in the process may also alter the dispersion products and, thus, potentially interfere with the interpretation of experimental results. This review summarizes present knowledge on experimental conditions that may lead to physical damage and chemical modifications of aggregate building blocks. The energy level at which physical disintegration of organic particles could be detected was as low as 60 J mL-¹. Physical damage of sand- and silt-sized mineral particles was observed to commence at energy levels exceeding 700 J cm-³. No evidence was found for the disintegration of particles within the clay-size fraction of soils even though studies analyzing pure minerals such as kaolinite revealed particle breakage after application of energy amounts > 12,000 J cm-³. Here we outline a strategy to minimize artifacts such as physical damage of mineral or organic particles resulting from ultrasonication by adopting a stepwise dispersion protocol involving successively higher energy levels, accompanied by a sequential separation of organic and mineral compounds.