Kinetics of Cu and Zn desorption from spiked soils at different DOM concentrations ([Ca] = 3 mM, pH 5.5): (A) Cu with the Matapeake soil; (B) Cu with the Codorus soil; and (C) Zn with the Matapeake soil. Soil particle concentration m = 46.9 g L−1. Flow rate Q= 1 mL min−1. Solid lines are model calculations