ABSTRACT
This chapter presents the newly available long-term field data in terms of their implications on land application of sludges. In the early days of land application studies, several researchers hypothesized that organically complexed metals in soils were less available to plants than uncomplexed metals. Depending on the way sludges are applied, plants often respond to Cd and Zn introduced into soils in a different manner. When sludge applications were terminated, soil microbial activity would reduce organic matter levels of the sludge-amended soils resulting in a higher availability of sludge-borne metals. Crops grown on a soil which received annual sludge applications exhibited a slight but significant increase in Cd and Zn concentrations of plant tissues. Even for soils that received repeated heavy sludge applications and for plants that were known to accumulate metals, there was little indication that the availability of sludge-borne heavy metals would rise upon termination of sludge applications.
