After the biomineralization studies, the amounts of 14C-remnant, 14C-extractable and 14C-non-extractable residues were determined in soil subsamples of each flask. The 14C-extractable residues were determined basically according to Andréa et al. (2001), by extraction of (3 ×) 3 g soil subsamples of each flask with 15 mL of H3PO4 0.35 mol L-1 by microwave-assisted solvent extraction (MASE) in microwave commercial apparatus at 800 W of power output in 5 cycles of 30 sec each. The 14C-remnant and 14C-non-extractable residues were determined also by combustion of (3 ×) 0.5 g soil samples of each flask, respectively before the extraction and after drying of the extraction solvent. The radiocarbon amounts were determined by LSC of 1.0 mL aliquots of the soil extracts and the total trap from combustions.