Chemical fractionation and heavy metal accumulation in maize (Zea mays) grown on CCA contaminated soil amended with rubber processing sludge manure

Arsenic, Chromium and Copper are common soil toxicants. Compost prepared from rubber processing sludge (organic waste) was used as soil amendment to increase chromated-copper-arsenate contaminated soil fertility and provide humus materials to the soil. Zea mays (maize) plant had been used to accumulate some amounts of heavy metals in their shoots when grown on soils contaminated with heavy metals. This property was exploited in this investigation. A pot experiment was set up containing 2000g of CCA contaminated soil. The CCA contaminated soil samples in the pots were amended with rubber processing sludge to different %age levels (2%, 5%, 10% and 20 %.). This was thoroughly mixed, watered and left for a period of two weeks to acclimatize. A control was set up using CCA contaminated soil without amendment. The total concentration of Cr, Cu and As in the CCA contaminated soil was established as 265.84±33.6mg/kg,155.82±12.98mg/kg and 32.09±48mg/kg respectively. A six step sequential extraction scheme was used to partition these metals among six operationally defined fractions, (F1) water soluble, (F2) exchangeable; (F3) carbonate bound (F4) Fe-Mn oxide bound, (F5) organic bound and (F6) residual. The sums of these metal fractions (F1 + F2 + F3 + F4 + F5 + F6) in mg/kg were: As (31.05±1.35), Cr (251.51±6.61), and Cu (151.68±1.38). The mobility factor for the metals were calculated as As (60%), Cr (19%), and Cu (8%). This mobility factor (Mf) revealed that arsenic with a total concentration of 32.09mg/kg which is the lowest has the highest Mf value (60). This makes it to be highly labile and consequently more dangerous than the other two metals Cr with an Mf19 and Cu with an Mf value of 8.The uptake of the metals As, Cr and Cu by the plants in both the control pots and pots with amendment were established. The use of rubber processing sludge amendment especially at 20% level raised the pH level of the soil sample from 6.20 to 6.99. A near neutral pH could result in the largest diverse bacteria population. This bounds the metals in the pots with amendments resulting in lower uptake by plants while there is higher uptake in the control pots resulting in the plants dying before the 20 days experimental duration. © Research India Publications.