The second and more likely explanation is that the bioavailability of larger PEG molecules was lower in the soil than the sediment. Limited bioavailability in soils may have resulted from both spatial separation between the PEG molecules and the cells and, in case of close contact, slow uptake into the cell of soil microorganisms. The soil incubations were static (i.e., non-stirred) and conducted under unsaturated conditions (i.e., 50% of the soil WHC)likely resulting in low rates at which spatial separation between PEGs and cells were overcome.