Characterization of Cadmium and Zinc in Four Soils Treated with Sewage Sludge

Abstract

AbstractCadmium and Zn were characterized in soils treated with 100 Mg ha−1 of an anaerobically digested sewage sludge from Chicago, IL. The four soils included a Chalmers silt loam (Typic Haplaquolls) (Indiana), Celina loam (Aquic Hapludalfs) (Michigan), Celina silt loam (Aquic Hapludalfs) (Ohio), and a Piano silt loam (Typic Aquidolls) (Wisconsin). The single application of sludge supplied 19 kg Cd ha−1 and 340 kg Zn ha−1. Four or five crops of barley (Hordeum vulgare L.) had been grown on each site prior to soil sampling. Soil solutions obtained by a centrifugation method contained Zn in the range of 1.4 to 10.5 µmol L−1 while Cd ranged from 18 to 135 nmol L−1. The addition of sludge increased the concentration of both metals in the soil solutions of all four soils. Evaluation of soil solution data with the computer program GEOCHEM showed that > 85% of the total soluble Cd and > 91% of the total soluble Zn existed as the free metal ion. Sludge addition increased the amount of Cd and Zn extracted by DTP A and 4 M HNO3. The relative increases in soil solution and extractable Cd and Zn were different in each of the four soils even though the same sludge was applied at the same rate. Diffusion coefficients measured with a cation exchange resin paper method (De), ranged from 1.8 × 10−11 to 1.7 × 10−9 cm2 s−1 for Zn and from 5.2 × 10−11 to 3.2 × 1O−10 cm2 s−1 for Cd. The application of sludge had little or no effect on the magnitude of De for either Cd or Zn as measured by the resin paper method, but the diffusion coefficients for Zn were inversely related to soil pH. Increases in the flux of Cd and Zn to plant roots in sludge‐treated soils will be a reflection of changes in soluble and extractable Cd and Zn.