Samples of low density polyethylene previously subjected to physicochemical treatments-thermal treatment (TT) at 105 and 150 degreesC or accelerated aging treatment (AAT)-were subjected to biodegradation by a consortium of four fungi during 9 months. Morphological, structural, and surface changes and mineralization were evaluated. TT samples showed decreases in the onset melting temperature (T-o), melting point (T-m), relative crystallinity (Phi), and mean crystallite size (L-110). The degradation products in all treated samples were carbonyl and double bonds groups. The biological treatment (BT) affected the properties of all treated samples. T-o at 3 months decreased with respect to sample at 0 months; the changes were higher in TT samples; the samples then remained without significant changes. Increases in Phi were observed in TT samples within a 3-month BT, after which reductions occurred. After a 9-month BT, increases in L-110 were registered in all samples (up to 2.6 nm). The highest mineralization value (3.26%) was obtained with the AAT. The reported changes suggested that the fungi mainly digest the amorphous phase of polyethylene in the first stage of the experiment, but later they also digest small crystals. Superficial growth of microorganisms occurred, and penetration of hyphae was observed in most oxidized samples. (C) 2004 Wiley Periodicals, Inc.