Environmental Engineering Reference
In-Depth Information
The photodegradation of fishing gear (Al-Oufi et al., 2004; Meenakumari
and Radhalakshmi, 1995, 1988), polyethylene netting and twine
(Meenakumari and Ravindran, 1985a, b), and nylon monofilament
(Meenakumari and Radhalakshmi, 1988; Thomas and Hridayanathana,
2006) in beach environments have been reported. Mechanistically and
kinetically, the weathering of plastics exposed in the supra-littoral zone
is very similar to that on land. These mechanisms and factors affecting
degradation on land are well known (Andrady, 1996; Andrady et al., 2009;
Hamid, 2000).
10.2.2 Surface Water Zone
Weathering rates for plastic waste floating in surface waters of the ocean are
markedly lower compared to that exposed on beaches or on land (Andrady
and Pegram, 1989b, 1990b, 1993). There are several reasons responsible for
this retardation in degradation in water.
1. 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.
2. The surface of the plastic in seawater is readily fouled by a variety of
marine species. This thick opaque foulant layer shields the plastic from
solar UV-B radiation and retards oxidation.
3. Oxidation rates depend on the availability of oxygen in the
environment. Unlike in air (~20% O 2 ), seawater has a much lower
concentration of oxygen (6.6 mg/l at 25°C).
10.2.3 Deep Water and Sediment Zones
Beyond the photic zone, photodegradtion is much slower; the cold, anoxic
deep-water environment is not conducive to oxidative degradation of
plastics.Thesameistrueofthemarine sediment whereplasticsarebelieved
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).
Search WWH ::




Custom Search