Degraded plastics debris

L. M. Stevens, Marine Plastic Debris Fouling and Degradation, unpublished M.Sc Thesis, The University of Auckland, Auckland, New Zealand, 1992. 

Beyond the photic zone, photodegradtion is much slower the cold, anoxic deepwater environment is not conducive to oxidative degradation of plastics. The same is true of the marine sediment where plastics are believed to ultimately accumulate. While, the occurrence of plastics debris in the sediment has been demonstrated, interaction of such debris with bottom-dwelling organisms is not well understood at the present time (Watters et al., 2010). 

Stevens LM. Marine plastic debris fouling and degradation [Unpublished MSc Thesis]. University of Auckland 1992. p 110. 

Zbyszewski M, Corcoran PL, Hoddn A. Comparison of the distribution and degradation of plastic debris along shorelines of the Great Lakes, North America. J Great Lakes Res 2014 40 (2) 288-299. 

Table 6. Effect of degraded plastics mulch debris on yields [36]...

Finally the growth of vegetables in fields to which particulate degraded polyethylene containing transition metal compounds has been added has been studied in Taiwan for five years. Table 17.17 follows the yields of lettuce with and without plastic debris over this period. Again, no increase in the concentration of heavy metals was observed in the plants. 

Compared with tar, which has a relatively short lifetime in the marine environment, the residence times of plastic, glass and non-corrodible metallic debris are indefinite. Most plastic articles are fabricated from polyethylene, polystyrene or polyvinyl chloride. With molecular weights ranging to over 500,000, the only chemical reactivity of these polymers is derived from any residual unsaturation and, therefore, they are essentially inert chemically and photochemically. Further, since indigenous microflora lack the enzyme systems necessary to degrade most of these polymers, articles manufactured from them are highly resistant or virtually immune to biodegradation. That is, the properties that render plastics so durable... 

In conclusion, a solution to waste treatment by self-degradation of plastics has not been favored at least for the packaging industry. However, it has been successfully implemented for selected controlled-life plastics in agriculture (mulching). It is also a possible solution for marine debris, plastics in release control of fertilizers and pesticizers, biomedical applications, and diapers. Converting to polymers which are soluble in selected solvents may also permit some special treatment. 

The plastics floating in seawater precludes heat build-up and consequent increase in sample temperatures. The plastic remains at the lower seawater temperatures slowing down degradation relative to debris exposed on beaches. 

Cooper DA, Corcoran PL. Effects of mechanical and chemical processes on the degradation of plastic beach debris on the island of Kauai, Hawaii. Mar Pollut Bull 2010 60 (5) 650-654. 

As a moulding material, PVC was considered as an alternative to ABS for telephone housings and its applications included selector mechanism bank separators (Fig. 8.14). In selector mechanism bank separators it suffered from ageing, plasticiser migration and, with particular relevance to the selector application, was chemically degraded by the zinc content of finely divided brass or nickel silver wear debris. The problem was minimised by attention to material grade since the mechanism was found to relate to the lubricant and stabiliser contents of the plastic. 

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