A. and Vozzella, M. E. 2001. Adsorption of nucleic acid constituent uracil on copper(II)-loaded, solid peat and soil-derived humic acids. Can. J. Soil Sci. 81: 309-316. Humic acids (HA) in compost, peats and soils sorb organic compounds selectively. This paper investigates the micro-and macroscopic properties of solid HAs isolated from a German peat (GHA) and a New Hampshire soil (NHA) using tightly bound copper(II) and nucleic acid constituent uracil adsorption as analytical probes. Isotherm measurements at 5.0-35.0°C show that tightly bound Cu(II) decreases the amount of uracil adsorbed by GHA at mM or lower uracil concentrations whereas previous work revealed the opposite effect for bound Hg(II). Site capacity comparisons are consistent with lower coordination numbers for HA-bound Hg(II) than for HA-bound Cu(II). Low coordination numbers leave Hg(II) sites open for uracil binding. Enthalpy and entropy changes for uracil adsorption on GHA, NHA, their Cu(II) and Hg(II)-loaded forms and on compost-derived HA are linearly correlated, indicating that HAs are free energy buffers. Water and bound metals evidently play major roles in HA-solute interactions and in HA aggregation/disaggregation.