Marine litter poses a vast and growing threat to the marine and coastal environment.
It is found in all sea and ocean areas of the world .– not only in densely populated regions but also in remote places far away from any obvious source. Marine litter travels over long distances with ocean currents and winds and is found everywhere in the marine and coastal environment, from the poles to the equator, from continental coastlines to small remote islands. Marine litter originates from many sources and causes a wide spectrum of environmental, economic, safety, health and cultural impacts. The very slow rate of degradation of most marine litter items, mainly plastics, together with the continuously growing quantity of the litter and debris disposed, is leading to a gradual increase in marine litter found at sea and on the shores.
It is estimated that about 6.4 million tons of marine litter are disposed in the oceans and seas each year. According to other estimates and calculations, some 8 million items of marine litter are dumped in oceans and seas every day, approximately 5 million of which (solid waste) are thrown overboard or lost from ships. Furthermore, it has been estimated that over 13,000 pieces of plastic litter are floating on every square kilometre of ocean today.
Marine litter could, for example, be waste from landfills (waste dumps) on land. It could be galley waste and cargo room waste from commercial shipping. It could be domestic waste, including waste from beachgoers. It could be nets and fish boxes from fishing vessels. It could be waste from industrial production or distribution. It could be medical waste, and sewage-related waste from bathrooms. However, the main sources can be grouped as follows:
| Main sea – based sources of marine litter | Main land – based sources of marine litter |
|---|---|
- Merchant shipping, ferries and cruise liners; - Fishing vessels; - Military fleets and research vessels; - Pleasure craft; - Offshore oil and gas platforms; and - Aquaculture installations. | - Municipal landfills (waste dumps) located on the coast; - Riverine transport of waste from landfills, etc., along rivers and other inland waterways; - Discharges of untreated municipal sewage and storm water (including occasional overflows); - Industrial facilities (solid waste from landfills, and untreated waste water); and - Tourism (recreational visitors to the coast). |
As we discussed above there are many sources of marine pollution. But in this paper we will discuss only the three of it. They are the pollution of the marine environment by plastic, marine debris and antifouling paint.
The pollution of the marine environment by plastic and marine debris
Plastics are synthetic organic polymers, and though they have only existed for just over a century, by 1988 in the United States alone, 30 million tons of plastic were produced annually. The versatility of these materials has lead to a great increase in their use over the past three decades, and they have rapidly moved into all aspects of everyday life . Plastics are lightweight, strong, durable and cheap. Characteristics that make them suitable for the manufacture of a very wide range of products. These same properties happen to be the reasons why plastics are a serious hazard to the environment. Since they are also buoyant, an increasing load of plastic debris is being dispersed over long distances, and when they finally settle in sediments they may persist for centuries.
The literature on marine debris leaves no doubt that plastics make-up most of the marine litter worldwide (Table 1). Though the methods were not assessed to ensure that the results were comparable, Table 1 clearly indicates the predominance of plastics amongst the marine litter, and its proportion consistently varies between 60% and 80% of the total marine debris (Gregory and Ryan, 1997).
Horsman (1982) estimated that merchant ships dump 639,000 plastic containers each day around the world, and ships are therefore, a major source of plastic debris (Shaw, 1977; Shaw and Mapes, 1979). Recreational fishing and boats are also responsible for dumping a considerable amount of marine debris, and according to the US Coast Guard they dispose approximately 52% of all rubbish dumped in US waters (UNESCO, 1994). Plastic materials also end up in the marine environment when accidentally lost, carelessly handled or left behind by beachgoers. They also reach the sea as litter carried by rivers and municipal drainage systems. There are major inputs of plastic litter from land-based sources in densely populated or industrialized areas, most in the form of packaging.
A study done on 1033 birds collected off the coast of North Carolina in the USA found that individuals from 55% of the species recorded had plastic particles in their guts (Moser and Lee, 1992). The authors obtained evidence that some seabirds select specific plastic shapes and colors, mistaking them for potential prey items. Shaw and Day (1994) came to the same conclusions, as they studied the presence of floating plastic particles of different forms, colors and sizes in the North Pacific, finding that many are significantly under-represented. Carpenter et al. (1972) examined various species of fish with plastic debris in their guts and found that only white plastic spherules had been ingested, indicating that they feed selectively. A similar pattern of selective ingestion of white plastic debris was found for loggerhead sea turtles (Caretta caretta) in the Central Mediterranean (Gramentz, 1988). Among seabirds, the ingestion of plastics is directly correlated to foraging strategies.
Ryan (1988) performed an experiment with domestic chickens (Gallus domesticus) to establish the potential effects of ingested plastic particles on seabirds. They were fed with polyethylene pellets and the results indicated that ingested plastics reduce meal size by reducing the storage volume of the stomach and the feeding stimulus. He concluded that seabirds with large plastic loads have reduced food consumption, which limits their ability to lay down fat deposits, thus reducing fitness. Other harmful effects from the ingestion of plastics include blockage of gastric enzyme secretion, diminished feeding stimulus, lowered steroid hormone levels, delayed ovulation and reproductive failure
Marine debris, consisting of derelict fishing nets, buoys, and ropes, wash up on shores, become entangled in reefs, and endanger threatened species and habitats. Entanglement in plastic debris, especially in discarded fishing gear, is a very serious threat to marine animals. According to Schrey and Vauk (1987) entanglement accounts for 13–29% of the observed mortality of gannets (Sula bassana) at Helgoland, German Bight. Entanglement also affects the survival of the endangered sea turtles (Carr, 1987), but it is a particular problem for marine mammals, such as fur seals, which are both curious and playful (Mattlin and Cawthorn, 1986).
Young fur seals are attracted to floating debris and dive and roll about in it (Mattlin and Cawthorn, 1986). They will approach objects in the water and often poke their heads into loops and holes (Fowler, 1987; Laist, 1987). Though the plastic loops can easily slip onto their necks, the lie of the long guard hairs prevents the strapping from slipping off (Mattlin and Cawthorn, 1986). Many seal pups grow into the plastic collars, and in time as it tightens, the plastic severs the seal’s arteries or strangles it (Weisskopf, 1988). Ironically, once the entangled seal dies and decomposes, the plastic band is free to be picked up by another victim (DOC, 1990; Mattlin and Cawthorn, 1986), as some plastic articles may take 500 years to decompose (Gorman, 1993; UNESCO, 1994).
Once an animal is entangled, it may drown, have its ability to catch food or to avoid predators impaired, orOnce an animal is entangled, it may drown, have its ability to catch food or to avoid predators impaired, or incur wounds from abrasive or cutting action of attached debris (Laist, 1987, 1997; Jones, 1995). According to Feldkamp et al. (1989) entanglement can greatly reduce fitness, as it leads to a significant increase in energetic costs of travel. For the northern fur seals (Callorhinus ursinus), for instance, they stated that net fragments over 200 g could result in 4-fold increase in the demand of food consumption to maintain body condition.
Lost or abandoned fishing nets pose a particular great risk (Jones, 1995). These ‘‘ghost nets’’ continue to catch animals even if they sink or are lost on the seabed (Laist, 1987). In 1978, 99 dead seabirds and over 200 dead salmon were counted during the retrieval of a 1500 m ghost net south of the Aleutian Islands (DeGange and Newby, 1980). In a survey done in 1983/84 off the coast of Japan, it was estimated that 533 fur seals were entangled and drowned in nets lost in the area (Laist, 1987).Whales are also victims, as ‘‘they sometimes lunge for schools of fish and surface with netting caught in their mouths or wrapped around their heads and tails’’ (Weisskopf, 1988).
Studies (Gregory, 1996; Zitko and Hanlon, 1991) have drawn attention to an inconspicuous and previously overlooked form of plastics pollution: small fragments of plastic (usually up to 0.5 mm across) derived from hand cleaners, cosmetic preparations and airblast cleaning media. The environmental impact of these particles, as well as similar sized flakes from degradation of larger plastic litter. There are many possible impacts of these persistent particles on the environment (Zitko and Hanlon, 1991). For instance, heavy metals or other contaminants could be transferred to filter feeding organisms and other invertebrates, ultimately reaching higher trophic levels (Gregory, 1996).
The pollution of the marine environment by antifouling paint particle
Antifouling paints are applied to the hulls of boats and to many static structures that are submerged, including pontoons, piers, aquaculture nets, buoys, pipelines and drilling platforms, to prevent the growth of fouling organisms (Voulvoulis et al., 2002; Konstantinou and Albanis, 2004; Chambers et al., 2006; Almeida et al., 2007). Accumulations of slime, algae and animals increase the frictional resistance of a boat moving through water, resulting in lower speeds, greater fuel consumption and poorer manoeuvrability. Fouling on many static structures may compromise safety by reducing stability and concealing structural defects.
With the phasing out and ultimate ban on triorganotin (e.g. tributyltin, TBT) formulations, most contemporary marine antifouling paints contain a Cu(I)-based biocidal pigment (e.g. cuprous oxide or, less commonly, cuprous thiocyanate). Zinc oxide is sometimes used as the principal, albeit relatively weak, biocidal pigment, but is more generally used in combination with Cu(I) as a booster, increasing the toxicity of the latter by 200-fold, and/or to impart flexibility and facilitate the erosion process of the coating (Watermann et al., 2005). Because some diatoms and algae are resistant to inorganic Cu and Zn, the antifouling properties of contemporary formulations are further enhanced by the addition of one or more secondary or booster co-biocides. These include zinc and copper pyrithione, Irgarol 1051, chlorothalonil, TCMS pyridine, Sea-nine 211, ziram, zineb, dichlofluanid and diuron.
Since antifouling is effected by the slow, controlled leaching of biocides from the painted surface, elevated environmental concentrations of these chemicals are most significant in semi-enclosed marine systems, such as harbours, marinas and estuaries, where the transport, berthing or docking of vessels is important. The aqueous concentrations and environmental effects of these chemicals in situ or under controlled laboratory conditions are, therefore, well documented. Less well studied, however, are the distributions, characteristics and effects of discarded antifouling paint particles (APP) and their residual biocides in the marine environment (Champ, 2003). APP are generated during boat maintenance and cleaning (the latter is undertaken both out of water and in water), flake off poorly maintained structures and abandoned boats, and are shed during the impaction or grounding of boats.
Although the chemical makeup, including biocidal composition, of spent antifouling particulates is similar to that of the corresponding freshly painted formulation, the environmental impactsof the two forms of application are likely to be very different. For instance, the transport or location of APP is not coupled with that of an artificial structure, and generation of APP by flaking, defoliation, sanding or blasting ensures exposure of a greater surface area of chemical constituents, including those in historical coatings, once in the aqueous medium. Given these characteristics, it is predicted that APP provide significant, localised sources of contemporary and historical biocides to interstitial environments and, during subsequent resuspension or dredging of sediment, to the overlying water column, and that APP and component biocides may be processed and accumulated by benthic epifaunal and infaunal invertebrates.
Large quantities of APP are generated in boatyards and shipyards during the repair, maintenance and cleaning of vessel hulls. The size of particulates produced depends on the method of paint removal (e.g. scraping, stripping, sanding, hydroblasting, sand-blasting, soda-blasting) and can range a few microns in diameter to several cm in length . In many countries, particles and slurries generated from the maintenance of naval and commercial ships during dry docking is collected and treated at facilities on site and/or disposed of as hazardous waste.
Concentrations of biocides and metals in different antifouling formulations vary considerably (Sandberg et al., 2007); consequently, spent APP arising from a single facility or location are highly heterogeneous in their chemical makeup.
Measurements of contemporary composites collected from a variety of locations within the EU indicate dry weight Cu and Zn concentrations of up to about 35% and 15%, respectively (equivalent to Cu2O and ZnO contents of about 40% and 20%, respectively), and a ratio of Cu to Zn of around 2–3:1. Fig. 6 shows the elemental concentrations of a paint composite collected from a recreational boatyard in Plymouth. Aside from Cu and Zn, the majority of the composite consists of relatively inert elemental constituents of the polymeric matrix. Of environmental significance, however, are significant quantities of other trace metals, such as Ba, Cd, Cr, Ni, Pb and Sn.
A direct consequence of the presence of APP in sediment arising from boat maintenance or ship groundings is an increase in levels of biocides and trace metals, often to concentrations in excess of quality guidelines, in the benthic and intertidal environments.
Given the design and function of antifouling paint, contamination of sediment by discarded APP is predicted to result in elevated concentrations of trace metals, in highly bioavailable ionic and hydrophobic forms, in poorly circulating interstitial waters. Inter stitial trace metal levels are likely to be offset to some extent by subsequent interactions with ambient sediment, including precipitation of sparingly soluble species and adsorption of metals to oxides and organic matter of the sediment surface. Subsequent, physical disturbance of the bed, via dredging or during storms, for example, will result in the transient elevation of trace metal concentrations in the overlying water column through both the injection of metal-rich interstitial waters and desorption of loosely held cations from resuspended particulates.
Antifouling paint particles (APP) are abundant in the benthic environment in the vicinity of boat repair facilities, abandoned structures and grounded ships. Although their more general distribution in marine systems has not been systematically addressed, fine particles generated by sanding or blasting of boat hulls or that are produced gradually through erosion are predicted to be transported widely. Some of the effects of APP are similar to those arising from in life applications of antifouling paint. However, an extensive knowledge of biocide behaviour on painted surfaces is not sufficient for predictive or management purposes regarding APP because of the different and, in some cases, poorly defined properties and pathways of biocides in particulate form. Differences relate to transportation in the aqueous medium, leaching rate, transfer to additional substrates, persistence, and interactions with and processing by invertebrates.
Regardless of the outcomes of such investigations, greater caution needs to be exercised by boaters and boatyards during the removal and disposal of APP, and more awareness or stricter enforcement of relevant codes of practice or legislation is required.
REFERENCES
A. Turner, 2010. Marine pollution from antifouling paint particles. Marine Pollution Bulletin 60, 159–171
D.D. Ofiara, J.J. Seneca, 2006. Biological effects and subsequent economic effects and losses from marine pollution and degradations in marine environments: Implications from the literature. Marine Pollution Bulletin 52, 844–864
J.G.B. Derraik, 2002. The pollution of the marine environment by plastic debris: a review. Marine Pollution Bulletin 44, 842–852
L.S. Fendall, M.A. Sewell , 2009. Contributing to marine pollution by washing your face: Microplastics in facial cleansers. Marine Pollution Bulletin 58, 1225–1228
T.H. Mace, 2012. At-sea detection of marine debris: Overview of technologies, processes, issues, and options. Marine Pollution Bulletin 65, 23–27
UNEP 2005: Marine Litter, an analytical overview.
