FACTORS INFLUENCING HEAVY-METAL DISTRIBUTION IN 6 OKLAHOMA BENCHMARK SOILS

Six contrasting benchmark Oklahoma soils underlain by sedimentary rock were selected and sampled by horizon to parent material or a 2-m dept h. Total Co, Cu, Ni, Pb, and Zn concentrations by horizon in total soi l and clay fractions were determined by x-ray fluorescence. Total conc entration of heavy metals in these soils is dependent on clay content. There are fivefold more Cu, twofold more Zn and Ni, and 1.5-fold more Co and Pb in the clay fraction than in the total soil. The clay fract ion of surface horizons contains a greater concentration of Cu, Zn, an d Co than subsoil horizons due to biogeochemical cycling of these micr onutrients from the subsoil to the surface during melanization. Biogeo chemical cycling reduces the total amount of heavy metal loss from sur face to subsoil horizons by clay translocation but doesn't offset the illuviation of total heavy metals sorbed to clay. Higher levels of tot al heavy metals in each profile for each element are found in the B ho rizons than the A horizons (77% of the samples). Characterization of s oil for total heavy metal content should include a sample from the B h orizon especially in soil with higher clay content in the B than the A horizon. Soil parent material discontinuities cause changes in concen tration of several heavy metals within two of the six soil profiles. I dentification of soil parent material discontinuities is not a consist ent factor causing change in heavy metal concentration within the soil s studied.