Fig. 7. Cadmium concentration in leaves of romaine lettuce grown on unlimed (pH 5.6) Christiana fine sandy loam (fine, kaolinitic, mesic Typic Paleudults) amended with 0, 56, 112, and 224 Mg ha^–1 of heat-treated biosolids in 1976 (mean for six crop years) analyzed by linear regression standard error, or plateau regression 95% confidence intervals. Biosolids contained 13.4 mg Cd kg^–1, 1330 mg Zn kg^–1, and 83 g Fe kg^–1 dry weight.