For conventional plastics and the same plastics amended with
additives that were supposed to enhance biodegradability, almost
no biodegradation was observed after nearly two years of incubation
in soil (Fig. 1). The highest observed conversion during soil
incubation was 1.0 0.1% (PP þ 2% additive). For all other plastics
amended with additives, the final cumulative biodegradation
ranged between 0.9 and 1%. These values were less than that
measured for the negative control (PP) which reached a final cumulative
conversion of 1.3 0.7%. Although they were not significantly
different. SEM images did not reveal qualitative changes in
the appearance of PP or PP þ 2% additive after the 2 year incubation
period (Fig. 2E and F).