Sewage sludge is frequently used as a soil fertilizer although it may contain elevated concentrations of priority pollutants including di-(2-ethylhexyl)phthalate (DEHP). In the present study, the kinetics of microbial 14{sup left}DEHPmineralization was studied in laboratory microcosms with sewage sludge and agricultural soil. A biphasic model with two independent kinetic expressions was used to fit the mineralization data. The initial mineralization activity was described well byfirst-order kinetics (r{sup}2 > 0.97), whereas mineralization in long-term incubations (>40 days) was described better by fractional power kinetics (r{sup}2 > 0.95). The mineralization activity was much lower in the late phase presumably due to a declinein the bioavailability of DEHP caused by diffusion-limited desorption. The initial DEHP mineralization rate in sludge-amended soil varied between 3.7 and 20.3 ng of DEHP (g dw){sup}-1 d{sup}-1 depending on incubation conditions. Aerobic DEHPmineralization was 4-5 times faster than anaerobic mineralization. DEHP mineralization in sludge-amended soil was much more temperature sensitive than was DEHP mineralization in soil without sludge. Indigenous microorganisms in the sewage sludge appearedto dominate DEHP degradation in sludge-amended soil. It was estimated that >41 of the DEHP in sludge-amended soil will have escaped mineralization after 1 year. In the absence of oxygen, >68 of the DEHP will not be mineralized within 1 year.Collectively, the data suggest that a significant fraction of the DEHP in sludge-amended soils may escape mineralization under in situ conditions.
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