Comparative strategies for litter abatement

The predicted growth rate of plastics production in the US (Fig. 12.1) tracked the actual values remarkably well over the 20 years since the predictions were published, with the exception of the last four years when growth dropped to an average of 3% due to the US recession. Data on the accumulation of litter are not available. 

The assumptions behind this model are as follows. (1) The production of plastics in 1970 in the United States was 19 600 million pounds. (2) The production of plastics will increase annually by 6%. (3) The proportion of plastics production which will be used in packaging applications will be constant at 20% per annum. (4) Two per cent of plastics packaging will become litter. 

In view of these complexities, an exact measure of the rate and extent of biodegradation of polymeric materials like plastics is difficult to define. The following definitions are proposed [20]. 

By using repetitive transfer to minimal media in which the only carbon source is degraded polymer, it was possible to isolate bacteria which are capable of attacking degraded polyethylene and polypropylene [23]. 

A further conclusion of this work is that those bacteria which have been demonstrated to attack plastic residues are of relatively common varieties which would be expected to be widely distributed in soils in most terrestrial environments. No fungi capable of utilizing the polymers were isolated by this technique. Furthermore, none of the fungi isolated from the soil were capable of utilizing these polymers as the sole source of carbon. 

---