Effects of pH, ionic strength, and solutes on DNA adsorption by andosols

The adsorption of DNA by two andosols was investigated as function of solution pH, ionic strength in solution and some solutes, so as to understand the behavior of extracellular DNA molecules in two andosols. DNA adsorptions greatly decreased by increasing pH of suspensions in a pH range of 3.0–9.0. The adsorption of DNA molecules by both andosols was not affected by ionic strength from 0.1 to 0.5 mol L−1 NaCl. However, the DNA adsorption increased proportionally by increasing Mg2+ concentration in the suspension. Addition of phosphate decreased DNA adsorption, indicating competition between DNA molecules and phosphate ion in the adsorption by andosols. These results suggest that there are several DNA adsorption mechanisms in soil.