METALS IN URBAN GARDENS - EFFECT OF LIME AND SLUDGE

Cd and Zn concentrations in vegetables raised in a community garden on a low-pH, urban soil (Udorthent) with no history of dumping or other contamination were higher than those from another community garden loc ated on a reclaimed landfill where digested sewage sludge had been app lied, and where total soil Cd, Cu, Pb, Zn, and soil pH were higher. Ve getables from the latter site in turn had higher levels of Cd and Zn t han those raised on a low-metal, neutral-pH, urban garden site. Split plots with and without added Lime were established on the low-pH site. Beet (Beta vulgaris, L.), lettuce (Lactuca sativa,L.), radish (Raphan us sativus, L.), and Swiss chard (Beta vulgaris, L., var. cicla) had l ower Cd and Zn concentrations in limed than unlimed plots, while veget able Cu and Pb concentrations were not affected by Liming. After four years of liming, Cd and Zn in vegetables reached background levels, an d there was no observable difference between limed and unlimed plots, Cd and Zn in Swiss chard, lettuce, and beet leaves showed highly signi ficant inverse correlations with son pH (.64* < r(2) < .96**) in lime d and unlimed plots. These results indicate that total soil Cd and Zn may be less important than soil pH in determining vegetable metal avai lability. Beet and radish root had lower concentrations of Cd, Cu, and Zn than did leaves of the Same species, while beet roots had higher p h levels than beet leaves. Among the four metals studied, only Cd and Zn in vegetables correlated closely (r(2) = .85*), indicating a commo n mode of uptake.