The effect of sludges from two Adelaide sewage treatment plants on the growth of and heavy metal concentrations in lettuce

Abstract

In a glasshouse experiment, lettuce was grown on a market garden soil near Adelaide, South Australia, to investigate how yields and foliar concentrations of Cd, Cu, Ni, Mn, Pb, and Zn are affected by applications of sewage sludges of different origin. One sludge came from a modern treatment plant and the other from an abandoned treatment farm now within the Adelaide suburban area. Heat sterilization of one of the sludges decreased the uptake of Cd, Cu, and Zn, and especially of Ni and Mn. Fertilizing with sludges alone gave poor yields thus indicating the need for supplementary nutrients. High rates of sludge application gave marked increases in some metal concentrations in the lettuce. The ease with which metals in the sludges could be absorbed by lettuce decreased in the following order: Cd > Zn > Ni > Cu >> Pb. The effect of pot size is discussed. Monitoring of produce may be required if sludge is used at high rates in intensive crop production on a similar soil.