Influence of pH on Cadmium and Zinc Concentrations of Cucumber Grown in Sewage Sludge

Parthenocarpic cucumber ( Cucumis sativus L. ‘La Reine’) plants were grown in the greenhouse in containers filled with equal parts by volume of peatmoss and vermiculite blended with 0%, 25%, or 50% by volume compost made from ferric-chloride-precipitated, lime-stabilized, digested sewage sludge composted with wood-chips and amended with various rates of sulfur. The Cd concentration of leaf and fruit samples from plants grown in media amended with 25% or 50% compost and S at 0, 10, 20, or 40 g·liter –1 was unaffected by changes in pH from 7.2 to 3.4. However, Zn concentration in fruit samples from plants grown in media amended with 25% compost and S at 40 g·liter –1 increased relative to other rates of S, whereas Zn concentration of leaf tissue was unaffected by rate of S application. Yield of fruit was not significantly affected by any of the treatments. Cucumber plants can be grown successfully in media amended with as much as 50% composted sewage sludge low in heavy metal content and over a wide range of pH values without the accumulation of fruit Cd levels hazardous to human health.