Redistribution of zinc from sewage sludge applied to a range of contrasting soils

An incubation study has been performed to investigate the rates of redistribution of 65Zn from spiked sewage sludge into different soil fractions. The labeled zinc in soils amended with sludge was fractionated by operationally defined procedures at three different times (1, 7 and 30 days after incubation) into exchangeable, organically bound, amorphous iron oxide-bound, crystalline iron oxide-bound and residual fractions. The rates of redistribution of zinc from sewage sludge mainly depended on soil pH. In acid soils, most of the sludge-derived zinc (70-80%) went to the exchangeable pools, and was retained in this form at high concentration for at least a month. The effect of the time during digestion of the incorporation of a 65Zn spike into sludge was also studied. Although the results were significantly effected by spike timing, the effects of the latter on subsequent zinc fractionation results were minor compared with the effect of soil pH.