Environmental Engineering Reference
In-Depth Information
are gaining importance. The fragments of these materials are very easy to biodegrade
by microorganisms.
The rate of polymer degradation differs in the ocean environment compared to
on land. The photo-oxidative degradation, because of UV radiation, on loating
or submerged plastics in the sea is very slow when compared to biodegradation of
plastics on land. Petroleum-based polymers such as poly(e-caprolactone) (PCL) and
polybutylene succinate (PBS) and starch blended polymers produced from biomass
such as polylactic acid (PLA) and polyhydroxybutyrate (PHB) are biodegradable.
The order of degradation is PHB = PCL > PBS > PLA [16].
Plastics widely used in the marine environment include: PE, PS, PET, PP and PVC.
Polyoleins (PP and PE) and Nylons when exposed to the marine environment undergo
photo-oxidation irst by the UV-B radiation from sunlight. Once the degradation
is initiated then they undergo thermal oxidation for some time. As long as oxygen
is available to the material it undergoes autocatalytic degradation. During these
processes the MW of the material reduces and oxygen rich functional groups are
generated. Hydrolytic degradation (reaction with water) is not signiicant in the
seawater. Degradation processes in the marine environment, even in the benthic
sediments are several orders of magnitude slower than degradation by light induced
oxidative degradation. The amount of dissolved oxygen is less in sea water because
of the presence of salt. Shah and co-workers have reported a list of microorganisms,
which degrade different types of plastics [17]. Guo and co-workers have reported
the biodegradation rates of different plastics [18].
1.6 Plastics and Leachants which cause Toxicity
Plastics are considered to be biochemically inert [19]. However, plasticisers are often
added to plastics during production to impart special properties or to improve its
stability by providing resistance to heat, oxidative damage and microbial degradation.
Additives are also added to improve the workability of the plastic. The stabilisers
and chemicals used in the production of plastics are highly toxic, and not only affect
ground water, the environment, the air we breathe but they also leach into packed
foods, bottled water, even into our skin and into the organisms that ingest plastics.
The most dangerous toxicants which cause health effects include: bisphenol A (BPA),
dioxins and phthalates.
Phthalates are toxic chemicals that are known to leach out from PVC, which can
cause serious health problems. Phthalates are reported to be carcinogenic, and linked
to allergies and asthma [20]. They can also cause damage to the liver, kidneys and
heart as well. It can cause serious problems in children. PVC is the major contributor
