It is likely that the added organic matter played a
role in the formation of organic matter–Fe(III)–arsenic association, leading to partial re-immobilisation of
the liberated As at the latter stage of the experiment. Zn showed a consistent trend where it was initially
released with reductive dissolution of Fe and Mn compounds and then re-immobilised, possibly through
hydrolysis to form insoluble zinc hydroxide. In spite of abundant presence, release of Pb was limited due
to its low solubility under less acidic conditions. It appears that anaerobic environment stabilized the
soil-borne Cr by forming insoluble Cr(OH)3.