CADMIUM, LEAD, ZINC, COPPER, AND NICKEL IN AGRICULTURAL SOILS OF THE UNITED-STATES-OF-AMERICA

Three thousand forty-five surface soil samples from 307 different soil series were analyzed for Pb, Cd, Zn, Cu, Ni, cation exchange capacity (CEC), organic C, and pH in the course of a study of trace element uptake by major agricultural crops. The soil data from this study are summarized here statistically and in map form to show their interactions and generalized geographic distribution patterns. Amounts of all rive metal elements are generally low in the Southeast. A regional high of about 15 mg/kg Pb covers the Mississipi, Ohio, and Missouri River valleys. Higher values for other elements are generally concentrated in the West and in the lower Mississippi River Valley. Maximum Cd levels were found in soils of the coast ranges of central and southern California. Copper levels are noticeably higher in organic soil areas of Florida, Oregon, and the Great Lakes. Nickel and Cu concentrations are high in serpentine soil areas of California. Nickel levels are also somewhat higher in the glaciated areas of the northern great plains and in northern Maine. For the entire dataset, the values of the minimum-maximum, 5th, 50th, and 95th percentiles are as follows: (mg/kg dry soil) Cd, <0.005 to 2.0, 0.036, 0.20, 0.78; Pb, 0.5 to 135, 4.0, 11, 23; Zn, 1.5 to 264, 8.0, 53, 126; Cu, 0.3 to 495, 3.8, 18.5, 95; Ni, 0.7 to 269, 4.1, 18.2, 57; pH (pH units) 3.9-8.9, 4.7, 6.1, 8.1; CEC (cmol/kg) 0.6 to 204, 2.4, 14.0, 135; and organic C % 0.09 to 63, 0.36, 1.05, 33.3. Metal levels generally increased with increasing clay concentration.