Plastics used in the marine environment

 The annual global demand for plastics has consistently increased over the recent years and presently stands at about 245 million tonnes. Being a versatile, light weight, strong and potentially transparent material, plastics are ideally suited for a variety of applications. Their low cost, excellent oxygen/moisture barrier properties, bio-inertness and light weight make them excellent packaging materials. Conventional materials such as glass, metal and paper are being replaced by cost effective plastic packaging of equivalent or superior design. Nearly a third of the plastic resin production is therefore converted into consumer packaging material that include disposable single-use items commonly encountered in beach debris. (How much of the 75–80 million tonnes of packaging plastics used globally each year ends up in the oceans, has not been reliably estimated. Several broad classes of plastics are used in packaging: Polyethyelene (PE), Polypropylene (PP), Polystyrene (PS), Poly(ethylene terephthalate) (PET); and Poly(vinyl chloride) (PVC). Their high-volume usage is reflected in their production and consequently these in particular have high likelihood of ending up in the ocean environment. Extensive fishing, recreational and maritime uses of the ocean, as well as changing demographics favoring immigration to coastal regions, will increase the future influx of plastics waste into the oceans. Land-based sources including beach littler contributes about 80% of the plastic debris. The entire global fishing fleet now uses plastic gear and some gear is invariably lost or even discarded carelessly at sea during use. Polyolefins (PE and PP), as well as nylons are primarily used in fishing gear applications. About 18% of the marine plastic debris found in the ocean environment is attributed to the fishing industry. Aquaculture can also be a significant contributor of plastics debris in the oceans. The rest is derived largely from land-based sources including beach litter. Virgin resin pellets, a common component of debris, enter the oceans routinely via incidental losses during ocean transport or through run-off from processing facilities. Quantifying floating plastic debris (generally using surfacewater collection of debris with neuston nets) seriously underestimates the amounts of plastics in the ocean as those in the sediment andmid-water are excluded by the technique. The visibility of debris as flotsam requires plastics to be positively buoyant in sea water (specific gravity of sea water is 1.025). However, only a few of the plastics typically used in the marine environment has a specific gravity lower than that of seawater. (The specific gravities given are for the virgin resins; plastics in products are often mixed with fillers and other additives that may alter their specific gravity.) Denser varieties of plastics such as nylons tend to submerge in the water column and even reach the coastal sediment.

1.2. Microplastics in the oceans

A recent significant finding is that minute fragments of plastic debris, termed microplastics, occur in oceans worldwide)  including even in Antarctica . Microplastics, a form of man-made litter, have been accumulating in the oceans for at least over the last four decades. Sampled from surface waters or from beach sand this fraction of litter includes virgin resin pellets, compounded masterbatch pellets and smaller fragments of plastics derived from the larger plastic debris .The term ‘microplastcs’ and ‘microlitter’ has been defined differently by various researchers. Gregory and Andrady (2003) defined microlitter as the barely visible particles that pass through a 500 lm sieve but retained by a 67 lm sieve (0.06–0.5 mm in diameter) while particles larger than this were called mesolitter. Others , including a recent workshop on the topic defined the microparticles as being in the size range stained by lipophilic dyes. Digestion of the sample with hot dilute mineral acid can be used to remove the biomass impurities as the treatment will not have any impact on the microplastics fraction. Microplastics suspensions might be identified using optical microscopy, electron microscopy, Raman spectroscopy and FTIR spectroscopy. A schematic of this suggested sampling approach designed to isolate microplastics. As a prelude to discussing the mechanisms responsible for generation of microplastics, understanding the light-induced degradation and biodegradation of plastics in the marine environment is important.

Extracted from: https://www.sciencedirect.com/science/article/pii/S0025326X11003055