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The Chemistry and Fertility of Soils under Tropical Weeds 145
R OH
Hydroxyls CEC
-
R O
R C O
O H
Carboxylics
R C O
O -
Increasing pH
Fig. 8.7. The development of negative charges of organic matter origin with hydroxylic and
carboxylic functional groups (Salam, 2017).
The decrease in soil pH may reverse the process. The decrease in soil pH may
dissolve the heavy metal precipitates, decrease the soil CEC and release the
adsorbed heavy metal cations. Likewise, the presence of organic acids may
dissolve heavy metal precipitates, desorb the adsorbed heavy metals, and solubilize
the heavy metals to stay in soil solution in the forms of metal complexes or metal
chelates. Therefore, any natural or anthropogenic agents and processes that may
change the soil pH, the concentration of organic acids, and the activities of soil
enzymes may change the chemical processes and the concentration of heavy metal
in soil solution.
Abdul Kadir Salam and Nanik Sriyani – 2019
