in Fig. 4a–c. The obtained results indicated that
organic matters had important role in controlling the release of
metals. Because on heating, H2O2 dissociate to hydroxyl radicals
(OH−) that could attack proteins, carbohydrates and polyunsaturated
fatty acids present in the biological samples. Hence, it
improved the efficiency of the extraction of metals from BIOs. It
was reported that oxidation of BIOs with high organic matter is
usually incomplete with only HNO3 and, traditionally, the use of
a strongly oxidizing acid such as HClO4 is necessary; presently
we found that H2O2 combined with HNO3 yielded clear solutions
and improved recovery, is also consistent with other study