The present work investigates the behaviour of heavy metals accumulating in soils treated with urban sludge with respect to untreated soils. Metal sorption during transport in the soils was evaluated by means of breakthrough curves obtained via the soil column leaching test and the results of laboratory experiments were compared with those of field experiments carried out on the same soil treated in situ with urban sludge. Soil column leaching tests show that the amount of heavy metals retained in the soil increases when the soil is treated with sludge both in situ and in laboratory; the order of selectivity (Pb > Cu > Zn > Ni) remains similar for the two types of matrix. Experiments carried out both with soils treated with sludge in laboratory and in situ show a good agreement between the two sets of data as far as retention capacity is concerned; conversely, an increase in the soil resistance to pH change following acid input is observed when sludge treatments are carried out in situ.

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