The effect of low-temperature biochar and its non-pyrolyzed composted biosolids source on the geochemical fractionation of Pb and Cd in calcareous river sediments

Single extraction and sequential extraction assays were used to compare the effect of low-temperature biochar and its non-pyrolyzed composted biosolids on Pb and Cd mobility in the buffered conditions of calcareous river sediments. Results showed that amendment reduced the mobility of both metals, though under higher pH conditions, the effect of the non-pyrolyzed composted biosolids on the mobility of Pb was more apparent. On the other hand, the low temperature biochar had a more significant effect on the mobility of both metals under low pH conditions. The single extraction scheme used to simulate varying physicochemical conditions confirmed that amendment decreased Pb mobility up to 49% and Cd up to 96%. Sequential extraction assays confirmed a shift in predominant metal-fraction associations; from potentially mobile fractions to the more immobile ferromanganese oxide and organic matter fractions. These results highlighted the significant impact biochar amendment can have on metal mobility even when temporarily buffered by the physicochemical conditions in the calcareous substrates.