Adsorption of PEGs to soil particles may have further lowered bioavailability. Conversely, sediment incubations were fully water-saturated and continuously stirred and therefore likely resulted in high transfer rates of PEG molecules to cell surfaces (and less adsorption of PEGs due to competitive displacement from particle surfaces by water). Furthermore, it is possible that differences in the cell wall architecture and membrane rigidities between soil and sediment microorganisms resulted in a more stringent MW-cutoff for microbial uptake in soils. Further work is needed to elucidate uptake mechanisms, including diffusion of sufficiently low MW PEGs across membranes, potential partial uptake of larger PEG molecules into microbial cells with one chain end to then undergo intracellular exolytic processing -followed by continuous gradual uptake and processing of the remainder of the PEG chain, and endocytosis. Differences in the uptake pathways may control the MW at which PEG molecules undergo fast intracellular processing.