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Role of biochar as a bioamendment to reduce heavy metals translocation into Zea mays plants

TitleRole of biochar as a bioamendment to reduce heavy metals translocation into Zea mays plants
Publication TypeMiscellaneous
Year of Publication2015
AuthorsBandara, Tharanga, Yathavakulasingam Thushyanthy, and Vithanage Meththika

Biochar is considered as a promising material that can be used as a cost-effective soil amendment to immobilize heavy metals in contaminated soils. Shooting range soil is reported as highly contaminated soil with heavy metals specifically by Pb and Cu due to the bullets and bullet fragments. In this study, woody biochar (BC), prepared by slow pyrolysis of Gliricidia sepium biomass (BM) at 300 and 500 °C with a holding time of 3 h and waste byproduct of same BM from a bioenergy industry (BC700), were examined as potential bioamendments on heavy metal immobilization in shooting range soils in Sri Lanka. A pot experiment was conducted with maize (Zea mays) plants by adding BC at three different percentages as 1, 2.5 and 5% (w/w). Soil without amendments served as the control where all treatments were triplicated and arranged in completely randomized design (CRD). Sequential extraction method was conducted to determine the geochemical partitioning of heavy metals in mineral and organic phases including bioavailability of Pb and Cu. After six weeks, maize plants were harvested and the total content of Pb and Cu in shoots and roots were analyzed by atomic absorption spectrometry after digestion with 5 ml of concentrated HNO3 acid in microwave digester system. The initial soil pH was 5.78 (1:5 soil–water) and a relatively low electrical conductivity value was observed (0.028 dS/cm). The contamination levels of Pb and Cu in the soil were 20843 and 1861 mg/kg, respectively. Maize grown in control soil showed the least biomass production compared to the BC amended soils whereas the highest biomass production was observed in plants which were grown in 5% BC700 which was 7 fold higher than the control. The highest accumulated concentration of Pb and Cu were found in roots in the control soil and were 11948 and 339 mg/kg respectively. The lowest accumulated concentrations of Pb and Cu were observed in shoots that were grown in 5% BC700 amended soil and it was respectively 62 and 90% reduction compared to the control. The pH values of all the treatments were laid between 5.78-7.08. Although there was no any significant difference throughout the treatments soil, pH has showed a slight increase with the application of biochar from higher pyrolysis temperature and with the increase of the application rate. The highest extractable concentration of Pb and Cu were observed in the control soil whereas the highest reduction percentage was recorded in 5% BC700 treatment for Pb and Cu (65 and 84%) respectively compared to the control. Results suggested that the addition of 5% BC which is a waste byproduct of the bioenergy industry, has the capability of immobilizing heavy metals and thus reducing the phyto-toxicity in shooting range soil. As the plant factor is higher than translocation factor for maize, it may be used as a phytostabilizer