Heavy metals in sewage sludge utilized in agriculture.

To evaluate the fertilizing and polluting potential of sewage sludge and to establish whether the latter limits the former or not, sludge must be characterized, application rates chosen, and sludge effects monitored. This work emphasizes that chemical analysis aimed at total metal quantification cannot by itself ensure reliable answers about the agricultural value of sludge. The EEC directives about heavy metals in sewage sludge provide the total content limitation of each element without taking into consideration the respective fractions of metals present in their free state constituting the chemical state most directly related to sanitary risk. To evaluate the role of the Environmental Impact Assessment (EIA) in a such disposal system, a scheme is proposed.