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Marine litter issues, impacts and actions

A study that will contribute to developing a marine litter strategy for Scotland’s seas in light of the Marine (Scotland) Act 2010.


2 Review of the Types, Sources and Distribution of Marine Litter

2.1 Types of marine litter

The majority of marine litter consists of synthetic materials such as plastic, metal, glass and rubber. Internationally 84.1% of the total marine litter found within the coastal area (in 76 countries) could be separated into ten key items including smoking materials, food and beverage containers and other various types of packaging, which by material mainly consist of plastic (Ocean Conservancy, 2008).

2.2 Type by material

Marine litter comprises of various material types, but can be classified into several distinct categories, split by main point source and material (Fanshawe & Everard, 2002; Sheavly & Register, 2007; Cheshire et al., 2009; MCS, 2009; Galgani et al., 2010):

  • General grouped materials
    • Plastics
    • Glass
    • Rubber
    • Metal
    • Timber
    • Paper & cardboard
    • Textiles

2.2.1 Plastics

Plastics cover a wide range of synthetic polymeric materials (such as polypropylene, polyethylene, polyvinyl chloride, polystyrene, nylon, and polycarbonate) (National Research Council, 1994 in OSB, 2008). Plastics can include moulded, soft, foam, fisheries related equipment (nets, ropes, buoys, monofilament line, light sticks), smoking related items (cigarette butts, lighters, and cigar tips), microplastic particles, beverage bottles, bags, food wrappers, bottle caps, and toys ( UNEP, 2005b).

Plastics as a result of their buoyancy accumulate on the sea surface and are often washed ashore (Thompson et al., 2009). Plastics comprise 50-80% of marine litter; stranded on beaches, floating on the ocean surface and on the seabed (Gregory & Ryan, 1997; Derraik, 2002; Barnes, 2005; Morishige et al., 2007; in Barnes et al. 2009).

In addition, most polymers are highly persistent in the marine environment, degrading by photo-catalysis when exposed to UV radiation. The lifetime of plastics is estimated between 100-1000 years depending on the properties of the polymer and the environment it is exposed to; with increasing depth, oxygen concentrations and temperatures are low and light is absent, which further increase their lifetime (Galgani et al., 2010).

In a local context, beach surveys across the UK suggest that plastic as a proportion of marine litter is slowly increasing, from 55% in 1994 to 64% in 2010. An indication of the extent of plastic in our seas is via the use of ecological indicators: Gannets collect the majority of their nest material at sea, and recent surveys have found over 90% of the 30,000 gannet nests on Grassholm Island off the coast of Wales contain plastic ( MCS, 2009).

2.2.2 Other synthetic materials

Other synthetic materials are similar to plastic in that they are used in a wide range of products, are often cheap to produce and lightweight and thus are common marine litter items. These include glass such as light globes, fluorescent globes and bottles; rubber including tyres, balloons and gloves; and metal including drink cans, aerosol cans, foil wrappers and disposable barbeques. These items can undergo fragmentation over long time periods and often do not completely biodegrade ( OSB, 2008).

2.2.3 Semi-degradable

Processed timber such as pallets, crates and particle board, and paper and cardboard items such as cartons, cups and bags, also contribute to marine litter but is found in much smaller quantities than synthetic materials. This maybe due to a shorter residence time in the marine environment as they are relatively quick to bio- and photo-degrade, thus their accumulative impact on the environment, society and economy may be much less (Velander & Mocogni, 1998; UNEP, 2005b; Galgani et al., 2010).

2.2.4 Textiles

Textiles also constitute as marine litter including clothing, shoes, and furnishings. The specific impacts of these items are unknown, but are generally considered of lesser importance than other synthetic materials (Velander & Mocogni, 1998; UNEP, 2005b; Galgani et al., 2010).

2.3 Type by function

Products are made with specific materials based on their function and durability requirements, thus separating as type by function often enables easier identification of the source. The choice of material and applied usage is also a key factor in their residence time in the marine environment.

  • Specific type by source
    • Sewage Related Debris
    • Derelict Fishing Gear
    • Beverage/food packaging
    • Household items
    • Manufacturing and transportation-related wastes
    • Smoking-related wastes

2.3.1 Sewage Related Debris

Sewage related debris ( SRD) is discharged to the marine environment directly through domestic outfalls and combined sewer overflows ( CSOs) or indirectly via rivers or other water courses. It has been suggested that sewage can amalgamate into mats with the potential to travel large distances depending on prevailing winds, thus outfalls do not need to be in close proximity to the sink to have added to it (Smith, 1993 in Velander & Mocogni, 1998).

SRD includes cotton bud sticks, nappies, tampons, condoms, human waste (faeces) and sanitary products and at the time of the last survey constitutes 20.5% of coastal marine litter in Scotland based on the number of items found ( MCS, 2011).

2.3.2 Derelict Fishing Gear

Derelict fishing gear ( DFG) refers to nets, lines, bait boxes, floats, creels, and other recreational or commercial fishing equipment that has been lost, abandoned, or discarded in the marine environment. Modern gear is generally made of synthetic materials and metal and can persist for a very long time within the marine environment (Velander & Mocogni, 1998). At the time of survey, DFG makes up 8.9% of coastal marine litter in Scotland ( MCS, 2011).

2.3.3 Other

Other groupings by function include:

  • Beverage/food packaging such as bottles, cans, lids, food wrappers and containers and disposable cups, plates, straws and utensils
  • Household items such as clothing, furniture, appliances, light bulbs and computers
  • Manufacturing and transportation-related wastes such as shipping containers and their contents, resin pellets, barrels, drums, shipping pallets, plastic sheeting and strapping bands
  • Smoking-related wastes such as cigarette filters, packaging, cigar tips and disposable lighters

2.4 Lifecycle of marine litter

Marine litter originates from different sources, circulates through various pathways and eventually accumulates in litter sinks (figure 2.1). Data can aid in the quantification of these different factors and the transformations that occur through the process (Fanshawe & Everard, 2002). Evaluating this lifecycle of marine litter (spatial, temporal) is an essential part of any remediation and prevention technique and is fundamental prior to implementation, to allow for the identification and quantification of response variables and a review of the effectiveness of any management interventions (Cheshire et al., 2009).

Marine litter is in dynamic flux between the land and ocean interface, with several types and states of material (Cheshire et al., 2009).Flux rates between different sources and sinks can be measured directly (observation of amounts of material being transported) or indirectly (inferences based on changes in the amounts of litter in each pool over time). This can aid long-term management strategies, with better control of input sources leading to a reduced influx rate and accumulation in the system (Cheshire et al., 2009).

Figure 2‑1 The sources, pathways and sinks for marine litter

Figure 2 1 The sources, pathways and sinks for marine litter. Sources include wind-blown litter (curved arrows), water-borne litter (grey arrows), vertical movement of litter through the water column (including suspension and seabed - sinks; stippled arrows), and ingestion by marine organisms (black arrows). Sinks include shallow coastal areas (1), continental shelf (2) and open ocean (3); 2 & 3 include litter suspended in the water column. (Taken from Ryan et al., 2009)

2.5 Sources

The sources of marine litter are diffuse including offshore, coastal, riverine and land-based. However the ability to identify a particular source from an individual litter item is difficult, depending on the state of the litter item (weathering) or the possibility of multiple sources. A number of initiatives and studies have looked at the differing proportions of litter from each of these sources and their results show that the greatest proportion is from land based sources. At the global scale it has been reported that up to 80% is derived from land based sources (Faris and Hart, 1994). In the UK approximately 47% was from land based sources, 17% from fishing and shipping and a further 37% is non sourced ( MCS, 2011). At the Scotland level source information shows 37.5% was public, 8.9% fishing, 20.5% SRD, 1.7% shipping, 1.6% fly tipped, 0.2% medical and 29.6% non-sourced (figure 2-2). A distinction also exists between accidental and deliberate waste disposal, though with the exception of fly tipping this is often impossible to distinguish.

Figure 2‑2 Litter by source on Scottish beaches

Figure 2 2 Litter by source on Scottish beaches ( MCS, 2009)

Sources can be categorised in a number of different ways. This report has used the Marine Conservation Society approach: public; fishing; sewage related debris; shipping; fly tipped; medical and non sourced. Details of each are given below and sub-categorized where necessary.

2.5.1 Public

'Public' is a diffuse source of marine litter, encompassing many sub-source types such as beach users (point source) and riverine and urban runoff (diffuse source). Litter in this category includes food and drink cartons and packaging and smoking related waste.

2.5.1.1 Recreational & leisure usage

Litter sourced from recreational and leisure usage usually involves the inappropriate disposal of litter from the public either accidental or deliberate, of which constitutes a large proportion of beach litter ( MCS, 2009).

Beach users and recreational tourists are a key source of litter accounting 37% of all beach litter in 2010 ( MCS, 2011). This is despite laws such as the Environmental Protection Act (1990) prohibiting the dropping of litter in a public place which includes beaches (Hall, 2000). For some litter types however, it is difficult to distinguish direct origin (beach or boat user) (Hall, 2000; MCS, 2009).

Recreational boat owners and operators can also discharge waste into the riverine, estuarine, coastal and marine environment. Litter items can include food containers, plastic bottles and recreational fishing gear (Sheavly, 2005; Mouat et al., 2010).

2.5.2 Fishing

Marine litter associated with commercial marine fisheries and coastal aquaculture includes nets, ropes, buoys and cages. The release of these items into the marine environment result from the snagging of gear on bottom topographical features, accidental loss, deliberate dumping and the failure to remove these items (Mouat et al., 2010).

Litter arising from the fish farming and aquaculture industry, has been under the direct control of individual managers with some fish farmers have admitting to littering however these quantities are seen as relatively small compared to other sources.

Marine, coastal and riverine recreational fishing activities generate small localised areas of marine litter accumulation through the incorrect disposal of fishing lines, tackle and waste items used by anglers (Katsanevakis & Katsarou, 2004). In popular fishing areas high levels of waste can be left.

2.5.3 Sewage related debris

The discharge of untreated sewage due to ineffective waste treatment facilities and combined sewer overflows (storm events), results in an influx of SRD (cotton bud sticks, nappies, condoms, sanitary products) into coastal waters (Hall, 2000; Allsopp et al., 2006; Mouat et al., 2010).

A study (Hall, 2000) found in comparison to some European countries (e.g. Denmark) the UK has a large percentage (25%) of coastal outfalls that do not have preliminary treatment or screens to remove large items. This does not take in to account recent investment in the network but nonetheless a large number of combined sewer overflows do still exist. SRD represented 20.5% of litter in the MCS Beach watch weekend 2010 ( MCS, 2009); nearly three times higher than the UK average of 7.3%. It is often found to be the most offensive litter type and poses some public health and safety risk.

2.5.4 Shipping and offshore industries

Marine litter can be released into the marine environment by shipping vessels including cargo, bulk carrier, military, surveillance, research, passenger ships and non-commercial vessels, either accidentally (inappropriate storage) or deliberately. The contents of approximately 10,000 cargo containers are lost worldwide each year (Podsada, 2001 in Mouat et al., 2010). A recent example of this was the MSC Napoli which was beached off the Devon coast after a structural failure; over 100 containers were lost.

The release of marine litter can occur from offshore oil and gas activities, either accidentally or deliberate. Items can include safety equipment (gloves, hardhats) and waste generated from exploration and resource extraction. (Fanshawe & Everard, 2002; Mouat et al., 2010)

2.5.5 Fly tipped

Fly-tipping is defined as the ' illegal deposit of waste onto land that has no license to accept it' (Scottish Flytipping Forum, 2010). The Dumb Dumpers campaign is administered on behalf of the Scottish Flytipping Forum by Keep Scotland Beautiful, and aims to prevent fly-tipping. According to guidance from Scottish Flytipping Forum (2010) although reasons behind fly-tipping are complex, they mainly result from ignorance of the proper management facilities and avoidance of waste management charges and can be linked to antisocial behaviour.

Disposal costs (skips, landfill tax) may discourage the proper disposal of waste, although a study found no empirical evidence that fly-tipping had increased after the introduction of landfill tax apart from some isolated cases (Scottish Executive, 2001). This maybe due to limited baseline data stemming from an absence of standardised recording procedures.

Coastal and terrestrial fly-tipped items are subject to transportation by the wind and rivers distributing them into the marine environment.

2.5.6 Other Sources

There are a variety of other sources most notably land based which contribute to the marine litter problem.

2.5.6.1 Wind blown

Windblown litter is a diffuse source, with many sources of origin and is more of a pathway than a direct source, assisting the distribution of land-based litter to the ocean. Light-weight items such as plastic bags and plastic film (agricultural) are often the most common windblown litter items.

2.5.6.2 Riverine

Litter derived from riverine inputs can have a different relative composition (proportion of litter types) to other marine litter in situ. This is mainly due to a greater influence of SRD and fly-tipped source items in rivers (Williams & Simmons, 1997). Localised areas (sinks) along beaches near estuaries and river outflows, can therefore are largely different composition of marine litter to other coastal areas. This has implications for litter sampling strategies in that they should address all potential sources rather than limited to recreational and marine sources (Williams et al., 2002).

2.5.6.3 Municipal waste management

Poor waste management practices can be a major source of litter, enabling the transportation of litter into the marine environment through a variety of pathways (wind, riverine). Thus marine litter can originate from landlocked areas and is not necessarily derived in-situ or in close proximity to the sink. In addition, a number of derelict, former waste sites exist on or near the coast, either managed privately or by Local Authorities. An example of this is Nigg Bay, Aberdeen where the coast is eroding and leaching waste out into the coastal environment. Much of the waste at this particular site is landfill material and road materials such as tarmac. These sites cause problems as in many cases those individuals / companies / regional councils responsible for managing the sites are no longer in existence.

2.5.6.4 Industry

Small plastic resin pellets used as the feedstock for plastic production are an example of industrial discharges. The proliferation of these litter items have been recorded in monitoring surveys and usually enter the marine environment through accidental loss during transport and poor disposal techniques (Mouat et al., 2010).

2.5.6.5 Other

Agricultural waste such as silage wrap can enter the marine environment by wind blown and riverine processes. Derelict coastal developments and infrastructure such as piers and derelict vessels also provide a source of marine litter, usually proliferated through wave induced erosion. Marine litter can also originate from military activities such as munitions (Fanshawe & Everard, 2002; Mouat et al., 2010).

2.6 Pathways

Litter suspended in the water column has the ability to circulate between sources and sinks, using pathways (Cheshire et al., 2009). Tidal currents, surface winds and oceanic currents (Fanshawe & Everard, 2002) can influence the distribution, accumulation and end sink of marine litter items depending on their density and longevity.

2.6.1 Oceanic circulation

Ocean and surface winds can influence the drift of litter items suspended in the water column and are instrumental in the distribution of global marine litter. For example, plastic tags and bottles of Canadian origin have been recorded along the coasts of the UK; acting as indicators of large scale oceanic transport systems (Fanshawe & Everard, 2002).

2.6.2 Coastal circulation

The spatial/ temporal distribution and rates of accumulation and fragmentation of beach cast marine litter is also dependant on local coastal geomorphological processes. Research by HR Wallingford (1997) illustrated that the Scottish coastline can be divided into 11 major sediment cells. A sediment cell is defined as "a length of coastline which is relatively self-contained as far as the movement of sand and shingle is concerned and where interruption of such movement should not have a significant effect upon adjacent sediment cells" ( HR Wallingford, 1997).

It has been suggested that litter from land-based sources and oceanic sources depending on local currents, could circulate within these cells (Fanshawe & Everard, 2002). Thus these cells could provide logical geographical boundaries or coastal catchments, in which management plans for beach cast and coastal litter could be implemented ( MAFF, 1995). This may be preferential to litter management within political boundaries only (Fanshawe & Everard, 2002). Indeed this could also provide boundaries in which flux rates between land-based sources and coastal cell catchments can be quantified with only a slight influence from other marine sources.

2.7 Sinks

Litter sinks in the marine environment include the seafloor across coastal shallow waters and deep sea, as well as suspended in the water column (Fanshawe & Everard, 2002; Galgani et al., 2010).Depending on the relative isolation of a beach, the sink may only be temporary if regular beach cleaning occurs, but can be quickly replenished from offshore deposits (Williams et al., 1993).

2.7.1 Water column

The water column is a temporary sink for marine litter, although this is dependent on coastal currents and the buoyancy of individual litter items. Plastic density varies, with some items denser than seawater. This leads to stratification in the water column of litter of a similar density (floating, mid-water, bottom load). Surveying techniques therefore need to take this distribution of litter into consideration, as most studies to date have only focussed on floating debris (Galgani et al., 2010).

It is also possible to make predictions of the source and future drift of suspended litter, using spatial data on potential sources such as shipping traffic and prevalent currents. This can be useful for assessing the overall impacts on certain ecosystems and infrastructure in the predicted area of deposition (Galgani et al., 2010).

2.7.2 Shallow coastal areas

Shallow coastal areas (<40m depth) can act as litter sinks, due to their inherent geomorphological features and hydrodynamics. Marine litter is generally much greater in shallow coastal areas than the continental shelf and deep seafloor (Katsanevakis, 2008).

The influence of hydrodynamics on coastal bays can contribute to litter accumulation rates as well as land-based source inputs. Sheltered coastlines have greater litter accumulation rates whereas open coastlines which experience intensive wave action, have lower rates due to wave-induced cleaning of the seabed (Hess et al., 1999; Katsanevakis & Katsarou, 2004; Galgani et al., 2010).

It has been suggested for shallow coastal areas, fishing activities significantly contribute to the density of seabed marine litter; with anchored vessels and the location of ports significantly influencing the distribution and pattern of marine litter on the seabed (Katsanevakis & Katsarou, 2004).

A study by Velander & Mocogni (1998), whilst now outdated due to network improvements, offers an example of the various influences on marine litter in coastal environments. The accumulation of litter on Cramond beach was, at the time of study due to a combination of factors:

  • Proximity of sources
    • Proximity to an urban centre (Edinburgh) which increases the likelihood of litter from public (recreational & leisure usage) sources
    • Proximity of sewage outflow pipes (Cramond Island sewage outflow pipe) and villages / towns where raw/poorly treated sewage is discharged, increasing the likelihood of SRD.
    • Proximity to rivers (the mouth of the Almond River) which increases the likelihood of riverine sources of litter and industrial effluent
    • Proximity to ports, fishing and shipping routes for example a large number of commercial and pleasure vessels use the Firth of Forth, which increases the likelihood of litter by accidental or illegal dumping from these vessels
  • Local pathways
    • A prevailing current near the sink such as the prevailing current which flows into the Cramond beach causeway resulting in the accumulation of litter
  • Position of sink
    • Local hydrodynamics of the area such as intrinsic problems with the flow of estuarine waters and the accumulation of litter in estuaries (Firth of Forth Estuary)

2.7.3 Deep seabed

The majority of macro-debris eventually settles to the seabed, of which plastics, as they are elsewhere, are dominant. Litter aggregation on the seabed is localised, dependant on nearby source inputs and seabed topography (Galgani et al., 2000). The seabed topography of Scottish waters ranges from the continental shelf sea areas (<250m) to the deep ocean regions (>2000m).

The continental shelf is marked by features such as banks and deep channels with a dramatic continental slope of the west coast. The variation in the seabed can be illustrated by Figure 2-3. Local circulation patterns and hydraulic force from rivers can transport plastics away from the coast into deeper waters, accumulating in areas of low circulation and high sediment accumulation, such as coastal canyons (Galgani et al., 1996; Hess et al., 1999; Stefatos et al., 1999; Katsanevakis and Katsarou, 2004). The deep seabed is a stable habitat, which influences material decomposition rates, thus increasing the residence time of benthic marine litter in the sink.

There is limited data on the abundance and distribution of meso- and micro-litter items on both the continental shelf and deep ocean (Galgani et al., 2000).

Figure 2‑3 Bathymetry, seabed topography and geographical features of the seas around Scotland

Figure 2 3 Bathymetry, seabed topography and geographical features of the seas around Scotland (taken from Baxter et al., 2008)

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