EFFECTS OF REPEATED SEWAGE-SLUDGE APPLICATIONS ON PLANT ACCUMULATION OF HEAVY-METALS

This study evaluated plant absorption of heavy metals from various sewage sludge treatments. Three anaerobically digested municipal sludges (Chicago, Salt Lake City, and Idaho Falls) were added to field plots of the calcareous Millville soil (Typic Haploxeroll) and planted to 'Larker' spring barley (Hordeum vulgare L.) and Swiss chard (Beta vulgaris, L. var. 'Cicla'). Each sludge was added yearly at 20 Mg ha(-1) for 5 years; the Chicago sludge was also added once (the first year) at 100 Mg ha(-1), and also at 40 Mg ha(-1) the first and third years. Increased sludge additions increased metal concentrations in barley and Swiss chard. The first year, adding 21.2 kg Cd ha(-1) in 100 Mg ha(-1) of Chicago sludge increased plant Cd concentrations about six-fold (from 0.11 to 0.64 mg kg(-1) in grain and from 0.7 to 4.4 mg kg(-1) in Swiss chard). In subsequent years the increase in Cd was smaller. The relatively small Cd additions in 20 Mg ha(-1) of Salt Lake and Idaho Falls sludges did not increase Cd in barley grain. Concentrations of Zn, Cu, and Ni did not increase as greatly as Cd following sludge addition. Although only a few individual barley grain samples exceeded the recommended maximum of 0.5 mg Cd kg(-1) for feeds, most of the barley leaf and Swiss chard samples were much higher in Cd than the 0.5 mg kg(-1) level. The Zn, Cu, and Ni levels in the crops were below suggested threshold values.