Environmental Risk of Polymer and their Degradation Products

Polymer-based materials are found everywhere in the environment, but their impacts are yet to be fully understood. The degradation of different polymer types has been extensively investigated under specific laboratory conditions. However, only limited data are available on their degradation under environmentally relevant conditions, where a number of processes are assessed at once. This thesis therefore describes a series of outdoor aquatic microcosm studies and laboratory experiments to investigate the degradation of a case study polymer (natural rubber latex), to characterise the formation of degradation products, and to assess the effects these may have on aquatic organisms.
The outdoor microcosm studies showed that the exclusion of light and material thickness had a greater influence on degradation rate than media pH and sample movement. Analysis of the degradation solutions demonstrated that when the latex polymer degraded, there was an increase in the formation of microscopic latex particles; zinc (used to speed up the rate of curing processes) migrated from the latex polymer into the test solutions; and a mixture of dissolved substances that are potentially oxidised latex oligomers with additives residues were formed. Further analyses also showed that the atmosphere is a receiving environmental compartment for polymer degradates though the identification of a range of volatile substances produced during the degradation process.
Laboratory experiments were then conducted to investigate the direct toxicity of the formed degradate mixtures, using two freshwater organisms with different life cycle traits, the water column crustacean Daphnia magna and the sediment-dwelling larvae of Chironomus riparius. The results suggest that, to the organisms tested, there is limited environmental risk associated with latex degradation products.
Overall, environments receiving polymer debris are potentially exposed to a mixture of compounds that include the parent polymer, fragmented particles, leached additives, and subsequent degradation products; however at environmentally relevant concentrations this latex degradates pose little risk.