2.1
This section explores what is currently known regarding the drivers of marine litter in Scotland. This includes the current understanding of the key sources and pathways from which litter enters the marine environment, referring to evidence from the wider UK and globally where needed. The pressures of such sources on the distribution and composition of marine litter across Scotland’s marine environment are then discussed.
Drivers of marine litter
2.2
Plastic is now the most prolific form of litter detected across marine environments globally and can form up to 95% of litter found on beaches, the sea surface and the seafloor.[2] Across the North-East Atlantic, plastic items represented 94% of litter found on beaches in the latest ‘OSPAR Quality Status Report 2023’ at the OSPAR Maritime Area Scale.[3]
2.3
Plastic litter is primarily classified by size and is categorised into macroplastics and microplastics, the latter of which is broken down into primary and secondary microplastics – these are defined in Table 1. Nanoplastics, plastic particles less than 1000 nm in size, have only recently been a focus of scientific research and data surrounding the impacts of nanoparticles is not conclusive.[4] Given this, potential sources of nanoplastics have not been considered here.
Table 1. Classifications of plastic litter in the marine environment
Type |
Definition |
Microplastics
(<5 mm in size) |
Primary microplastics: intentionally manufactured plastic particles, e.g. virgin plastic pellets or ‘nurdles’, microbeads in personal care products.
Secondary microplastics: formed from the fragmentation of macroplastics through weathering (abrasion, degradation with UV light) or through product use, such as fibres from textiles and plastic particles from marine paints, tyre and brake debris.[4],[5] |
Macroplastics
(> 5 mm in size) |
Larger plastic items, largely visible to the human eye, such as plastic packaging (e.g. bottles, caps, bags), fishing nets, shipping debris and sewage-related debris (e.g. sanitary products and wet wipes). |
2.4
The proliferation of plastic within the marine environment is linked to the rapid increase in the production and utilisation of plastic over the last half a century, with global production increasing from ~5 million tonnes (MT) in 1950 to 30 MT in 1988 and was reported to be 390.7 MT in 2021.[6],[4] The utilisation of plastic across many sectors (e.g., healthcare, agriculture, textiles, fishing and aquaculture) has been driven by its inherent properties of being lightweight, cheap to produce, durable, corrosion and flame-resistant, and versatile.5 For Europe, over 57.2 MT of plastic was produced in 2021 with packaging forming the largest end-use market for plastic, comprising 39.1% of plastic products. More than 87% of plastics produced in Europe were formed from fossil-based plastic as opposed to recycled or bio-based plastics.[6]
2.5
These same properties facilitate the longevity and dispersal of macro and- microplastics litter once in the marine environment and further degradation of macroplastics to secondary microplastics. Plastic items have now been reported across the most remote marine environments, with forms of plastic pollution being detected in the surface waters of the Antarctic Peninsula,[7] Arctic[8] and ingested by deep-sea organisms.[9]
2.6
Empirical estimates of the abundance, trends and fate of marine litter are lacking. This is due to many complex factors affecting the distribution of marine litter (discussed below); a lack of quantitative data, particularly for regions less accessible such as the high seas and deep seas, and a lack of standardised methods used to report on marine litter.[10] Evidence suggests that the seafloor acts as the largest sink for litter entering the marine environment,[11],[12],[2] with as much as 94% of all plastic litter residing on the seafloor, equating to 25.3 to 65 million tonnes.[13],[11] For the North Sea, marine litter is abundant across the seafloor and up to 80% comprises plastic litter.[14]
2.7
Based on the global production and mismanagement of plastic waste, “business as usual” scenarios estimate that between 10.5 and 28 million metric tonnes (MMT) of plastic litter could enter the marine environment by 2025, up from 4.8-12.7 MMT estimated in 2010.[15]
Pathways and sources of marine litter
2.8
When considering the pathways in which litter enters the marine environment, it is generally classified as coming from either land- or marine-derived (or commonly referred to as land or marine-based) litter depending on where it entered the sea.[16] For this report, land-derived litter explicitly refers to the input of litter items that entered the marine environment from activities or sources on land. Marine-derived litter refers to marine litter items that originated from activities at sea.
2.9
It is widely report that as much as 80% of all marine litter is land-derived;[5],[17] however, very few quantitative estimates exist within the scientific literature for determining the exact contribution of land- and marine-derived litter.[17] This is partly due to difficulties in attributing litter items to the activity of origin following degradation, alongside the high spatial variability in the abundance and composition of marine litter (as discussed below). Current figures suggest that the prevalence of land- and marine-derived litter is dependent on the sea region assessed and analytical methodology used. Estimates for land-derived inputs across Europe range from 50%-84%, while at-sea sources can contribute 16%-50%.[18]
2.10
Land-derived plastic litter can be directly discarded into the ocean and coastal environments or transported to the marine environment via inland waterways, rainwater runoff, wind and wastewater outflows.[19],[16] Evidence suggests that the effects of climate change and increasing extreme weather events, such as increased rainfall, flooding[20] and stronger winds[21] have an influence on the deposition, abundance and movement of plastic waste across riverine/oceanic boundaries.
2.11
One of the most cited studies quantifying land-derived marine litter estimated that 4.8 to 12.7 MT of macroplastic is derived from mismanaged waste (littered or inadequately disposed waste)[i] produced by coastal populations (defined as within 50 km distance of a coastline).[16] This equated to between 15% and 40% of littered waste entering the sea. For in-land pathways, it is estimated that 75,000 to 1.1 MT of plastic waste can enter via rivers annually; however, this is likely to vary depending on the catchment characteristics and flow rate of a river.[33]
2.12
Based on these estimates of ‘marine leakage’, a more recent study quantified the input of macro- and microplastics into the Scottish Atlantic Coast and North Sea Coast using simple oceanographic patterns. Estimates suggests that more than 60% of marine plastics, in some cases more than 90%, was attributed to littering by the public and was entering the marine environment through rivers.[22] This equates to ~1000 tonnes (T) of macro plastic each year.
2.13
Across the OSPAR Maritime Area, single-use plastics (e.g. plastic bags, cigarette filters, cotton bud and balloons) represented 26% of litter observed with an abundance of 45 items/100 m – greater than maritime-related plastic items (21%). For regions relevant to the UK, the Greater North Sea and the Celtic Seas single-use plastic items represented 37 items/100 m in each area.[23]
2.14
In Scotland, to better understand the movement of litter from land to sea via rivers, Keep Scotland Beautiful’s ‘Upstream Battle’ citizen science programme has surveyed sites along the River Tay and the River Clyde and their tributaries to assess common litter items that may be contributing to marine litter. Not surprisingly, highest recorded items comprised plastic (34.5% of items for the Tay and 41.7% for the Clyde) with top littered items including cigarettes, snack packets and plastic pieces.[24],[25]
2.15
The Marine Conservation Society (MCS) in 2009 reported that 37.5% of marine litter in Scotland originated from the public, whilst litter originating from fly-tipped waste comprised 1.6%.[26],[27] The current contribution of fly-tipped waste to marine litter is largely unknown. Based on the most recently reported estimate, using data collected in 2012, Zero Waste Scotland estimated that at least 26,000 T of waste is illegally flytipped each year.[28] More recent estimates and trends regarding flytipping have not been confidently assessed due to changes in reporting systems in Scotland. [29]
2.16
The contribution of the different sources of marine litter across Scotland’s coastal environment are highly variable and can be influenced by several factors, including coast type, catchment area population size, coastal currents and wind exposure.[30] For example, up to 93% of plastic from land-derived sources on the west coast originated from the Clyde catchment area. For the east coast, approximately 46% of plastic entering the sea from land originated from the Forth catchment. Around 40 T (eight million pieces) of macroplastic litter enters Scottish seas annually from remote sources.[31]
2.17
Comparisons between mainland and island regions report that, by count, the greatest contributor to island litter was marine-derived litter (48%), in contrast to land-derived litter for the mainland (47%). Fishing nets were the biggest sub-source of litter by count, with 19% comprising of fishing nets (0-50 cm).[32] Similar studies also report a greater influence of fishing-derived litter across more remote beaches across the Scottish continental shelf than mainland beaches.[33],[34] For the Orkney Islands, across 35 survey sites 47% of beach macro-debris was attributed to the fishing sector, while less than 10% was attributed to leisure and tourism-related activities.[35]
2.18
The most commonly detected litter items on Scottish OSPAR beaches between 2020 and 2022 were land-derived and included sanitary items, plastic pieces (2.5-50 cm), packets, cotton bud sticks, caps/lids and cutlery/trays/straws (see section 8).[36] Similarly, the largest source of litter items reported in the latest GES assessment for beach litter (2008 to 2015) were land-derived across the Marine Strategy Framework sub-regions Greater North Sea and Celtic Seas. The most commonly found litter items were made of plastic, specifically polystyrene fragments, followed by food and drinks packaging, sewage-related debris (SRD); however, this was followed by smaller fishing-related litter.[37]
2.19
SRD results from the discharging of raw sewage and storm water, either directly into the ocean or via rivers waters. The most recent assessment of UK beach litter reported that SRD was a top ten litter item across Scottish beaches, whereas this is not the case for beaches in England, Wales and Northern Ireland, indicating that SRD is a particular issue for Scotland.[37] Outside of GES, SRD is also routinely recorded during beach clean surveys across Scotland.[33],[38],[39]
Microplastics
2.20
Globally, microplastics are increasingly being detected in the marine environment,[40],[41],[78] alongside the growing public awareness[42] of their prevalence and potential ecological impacts (see section 3). Despite this, the major sources of microplastics, composition and distribution in the marine environment remain understudied.[43] Estimates of microplastics in the ocean range from thousands to hundreds of thousands of particles per km2[44],[2] and can be readily transported from surface waters, where they first float, through the water column to the deep ocean, washed up on beaches and in sea ice.[2]
2.21
For Scotland, the only statutory monitoring and assessment of microplastics was delivered through the SMA2020, which surveyed microplastics in surface waters of Scotland’s Marine Regions (SMRs) and Offshore Marine Regions (OMRs)[ii] from 2013/14 to 2019/20 (see Figure 4).[45] Results showed that microplastics (defined as particles sized < 5 mm in their longest dimension) are present in the surface waters of all marine regions sampled. Microplastic concentrations ranged from 0 to 91,128 particles per km2 with hotspots in the Clyde SMR (0 to 77,168 particles per km2), particularly at the head of Loch Long Forth, and Tay (0 to 83,729 particles per km2) and the Solway (607 to 91,128 particles per km2).[46]
2.22
Fragmented plastics, microplastic particles or fibres formed from the breakdown of larger plastic items, accounted for almost 50% of the microplastics recovered in the SMA2020. The second most abundant form of plastic was microbeads originating from personal care products.[47]
2.23
The input of microplastics into the aquatic environment can be influenced by several factors, these include land-use (e.g. application of sludge[47] and proximity to waste water treatment plants)[48] proximity to urbanised regions[49] and marine activities, such as proximity to fishing grounds.[50],[51] However, evidence also suggests that factors such as population density[52], or geographic remoteness[53] are not always accurate predictors of microplastic abundance as plastic particles can be transported away from input sources via oceanic currents. This is likely the case for low microplastic abundance in the Solent estuary[54] and high microplastic abundance in intertidal sediments around Orkney[55] and in the Argyll SMR.[50]
2.24
Modelling of oceanographic currents with the microplastic estimates from the SMA2020 estimated that between 124 to 127 T of microplastics enter the Atlantic coast regions and North Sea coast annually, compared to 477 T and 582 T of macroplastics, respectively. As much as 77% to 98% of microplastics enter these coastal waters from land-derived sources.[23] Land-derived microplastics can enter the marine environment through less obvious routes, such as microplastics bypassing wastewater treatment plants, through storm drains and through the air.[56] Estimating microplastic flux from Scottish rivers based on catchment population size and microplastic abundances from 13 rivers worldwide suggests that riverine inputs to sea are 22% (by mass) of macroplastics.[32]
Most influential land-derived sources of microplastics
2.25
Using evidence of the potentially most prevalent sources of marine litter across the EU, ESS collated the current understanding of such sources at a Scottish level. The composition, inputs and major sources of marine litter across Scotland were also explored.
Surface water run off: tyre wear
2.26
A review for the EU Commission in 2018 examined the main sources of secondary microplastics (released through ‘wear and tear’ or accidental spills, not intentionally added microplastics e.g. microbeads) into the aquatic environment from EU28 Member States, Norway and Switzerland. Modelled pathways of microplastics into surface waters identified that particles released from tyre abrasion is the largest source of microplastics entering the aquatic environment, it is estimated that 503,586 T of microplastics per year are generated from the wear of automotive tyres.[57] An IUCN report that modelled releases of primary microplastics into the oceans, using empirical data on the consumption and use of tyre and loss through use, also identified tyre particles as the largest source of primary microplastics for Europe.[44]
2.27
A literature review of the quantifications of the major sources of marine microplastics within the OSPAR Maritime Area also indicates that tyre abrasion has the capacity to input the greatest amount of microplastics into the water environment; however, this was one of the most understudied sources within the scientific literature.[58]
2.28
Tyre tread particle emissions across seven European countries ranged from 0.52 to 1.5 kg per capita per year with the UK at 0.98 kg per capita per year.[59] However, no dedicated study has examined the pathway of tyre and road debris entering the aquatic environment or quantified this as a potential route for microplastics in marine litter in Scotland.
Treated waste water: microplastics
2.29
The same review for the EU Commission reported the second largest source of microplastics is from the washing of textiles due to the more clearly defined pathways from source to surface waters and waste water treatment works (WWTWs).[58] An OSPAR assessment also reported microbeads from personal care products emitted from treatment of domestic wastewater as the next most influential source of marine litter.[59]
2.30
For treated sewage, effluent released from WWTWs has been shown to be a potential route for microplastics entering freshwater environments, typically rivers, or directly into the marine environment.[60] WWTWs receive wastewater influent from domestic, industrial and surface water run-off. These can contain microplastics, such as microplastics intentionally added to cosmetics and industrial scrubbers, or secondary microfibres released from the washing of textiles.[57] WWTWs are primarily designed to remove biochemical oxygen demand, suspended solids and ammonia from wastewater, not microplastics.[61] Moreover, microplastic removal efficacy is dependent upon the treatment facility and the physiochemical properties of plastics, which affect their ability to be removed from wastewater.
2.31
Evidence indicates that primary and secondary treatment processing are largely effective at removing microplastics from treated wastewater with removal efficiencies of 95-99%[62],[63],[64] and ~100% removal performance for WWTWs activated sludge plants that have tertiary treatments.[65] However, evidence for the efficiency of microbead removal during tertiary treatment is less conclusive.[66] Despite this, it has been suggested that due to the large volumes of effluents being discharged from WWTWs, they are still a potentially significant source of microplastics into the aquatic environment.[67] For example, a secondary WWTW on the River Clyde, Glasgow, produces an average 260,954m3 of treated wastewater from a population of approximately 650,000 people. Despite a microplastic removal rate of 98.4%, based on three years of average daily flow rate data, it was estimated that over 65 million microplastic particles were still released in the final WWTW effluent every day.[49]
2.32
A study examining microplastics in the intertidal sediments across Scapa Flow, Orkney found microfibres were generally more abundant than plastic particles. As well as hydrographic conditions, the authors stated that high microfibre abundance at Congesquoy was highly likely to be linked to its proximity to the wastewater treatment plant at Bu Point, which according to Scottish Water discharges 750m3 into the Bay of Ireland daily.[56] Elsewhere in the UK, for the Solent estuary, the most commonly detected microplastics were from sewage and wastewater including fibres from textiles and rounded pellets most likely from cleaning and cosmetic products, alongside pre-production pellets that were also visible on the river bank.[55]
2.33
Microbeads from personal care products were the most detected primary microplastic across the SMRs surface waters sampled between 2014 and 2020. Despite a ban in Scotland in 2018 of microbeads being intentionally added to rinse-off cosmetic products, it is likely that these products remain in the environment from prior releases.[47]
Plastic pellet loss
2.34
The third largest source identified in the EU Commission review was plastic pellets, powders and flakes (hereafter referred to as pellets) although there is greater uncertainty surrounding the total amount entering the aquatic environment due to greater opportunities for capture prior to reaching a WWTW, alongside the variability in treatment processes/efficacies across WWTWs.[58] The OSPAR assessment also reports primary microplastics from industry (pre-production pellets) as #one of the largest sources of microplastic emissions across the OSPAR catchment area.[59]
2.35
Plastic pellets, commonly termed ‘nurdles’, are small 2-5 mm plastic particles used primarily within the polymeric plastic production industry.[68] Throughout the plastic production supply-chain, pellets can be lost due to spillages whenever they are handled, such as filling and emptying, storage, loading for transport and shipping. This is often referred to as ‘pellet loss’ and can lead to pellets being released into the environment, either through indirect or direct routes. Pellet loss can also occur from the mismanagement of plastic pellets, such as insufficient clean-up after a spill.[69]
2.36
An Impact Assessment accompanying an EU Commission provision to prevent plastic pellet loss estimated that between 52,140 and 184,290 T of pellets are unintentionally released into the EU environment annually. This comprises 0.08 to 0.28% of total pellets volumes in the EU. Logistics (transport, intermediate storage and handling during these operations) attributed the largest pellet loss (27,870 to 111,480 T), followed by converters (15,600 to 46,800 T), producers (7222 to 21,665 T) and recyclers (1448 to 4345 T).[70]
2.37
Very few studies have attempted to quantify pellet loss into the aquatic environment, despite being identified as a key source of marine pollution since the 1980’s.[71] Robust estimates come from the river Rhine, where spherules (pellets) comprised 60% of plastic particles within the river and were linked to different industries.[72] For the river Danube, during heavy rainfall researchers estimated 693 to 138,219 pellets per 1000 m3 within the Danube Alluvial Zone National Park that is adjacent to a plastic manufacturing site.[73]
2.38
To date there is no study that has directly measured pellet loss from UK industries. Eunomia conducted a study on behalf of Fidra to estimate total pellets lost from the UK plastics industry using estimates of pellet loss from two published reports, alongside an unsourced estimate from a UK processor. Based on this, Eunomia estimated that 48 to 480 T of pellets are lost at plastic processors annually each year in the UK, while 32 to 320 T are lost during transport and 25 to 250 T are lost at UK plastics producers.[74] This totals an estimated annual loss of 105 to 1,054 T pellets in the UK.
2.39
Eunomia estimated pellet loss throughout the supply chain for Scotland. This estimate assumed that 15%[iii] of the UK plastics industry is located in Scotland, alongside correspondence with an unnamed Scottish plastics producer, and estimates that 15.8 to 158.1 T of pellets could be lost annually from Scottish industries.[76] The Eunomia report acknowledges the limited number of studies available to estimate pellet loss in the UK but highlights their usefulness in helping to inform a true rate of loss.[75]
2.40
A study carried out in 2004 reported that plastic pellets were detected on the majority of beaches within the Firth of Forth but were not quantified as they were “too numerous to count”.[76] Polypropylene pellets were reported in the surface water assessment carried out as part of the SMA2020, with an average abundance of 203 particles per km2 across the whole study area.[69]
2.41
Fidra’s ‘Great Nurdle Hunt’, a citizen science programme gathering data on nurdle pollution across beaches, has reported pellets across the majority of Scotland’s coastlines with hotspots detected across the east coast with frequent occurrences of 101 to 1000 and >1000 nurdles recorded.[77] North Queensferry, a beach located ~12 miles from Ineos Polymers across the Firth of Forth Special Site of Scientific Interest (SSSI), has received media attention for its level of pellet pollution.[78],[79]
Marine-derived sources of litter
2.42
Global estimates suggest that marine-derived litter sources input 0.54 to 5.01 MT of litter into the marine environment every year,[19] with the mid-point for plastic litter inputs as 1.75 MT per year.[13] This comprises a much smaller proportion of marine litter compared to land-derived inputs. The major sources of marine-derived litter are from commercial fishing, aquaculture, recreational fishing and shipping containers.[80],[5]
2.43
Very few estimates exist for the exact contribution of litter from commercial and recreational fishing. The extent of waste generated by such activities is dependent on the scale of such activities and regulatory action.[81] For example, estimates for the seafood industry (comprising commercial fishing, aquaculture and in this instance recreational boating) ranged from 9% in the Mediterranean Sea and Baltic Sea to 42% in the Black Sea.[19] As a proportion of marine-derived litter, the overall estimate is that 22% originated from the fishing sector, whilst 13% originates from the shipping sector.[19]
2.44
Plastic use is widespread in aquaculture for parts of cages, nets and mesh for cages, harvest bins and packaging for feed. Across the European Economic Area (EEA), between 3,000 and 41,000 T of waste is produced from the fishery and aquaculture industries, ~72% of this is likely to be plastic waste.[82] From this, it was estimated that 15% of the total plastic waste is lost to the marine environment likely through mismanagement of waste[120] or after extreme weather.[19] Based on this figure, the total plastic waste emitted into the sea each year from fishing and aquaculture gear can range between 9,888 and 22,685 T.[120]
2.45
Across the OSPAR regions, the highest percentage of maritime-related plastic items as a proportion of items classified in each region was observed in the Greater North Sea (25%), indicating that marine-derived litter is a regular source of litter in this region.[24] As highlighted in Section 6.8, the prevalence of fishing-derived litter on Scottish beaches varies substantially and potentially has a greater influence on more remote beaches in the Highlands and Islands regions. Given this, while there are other sources of marine-derived litter recognised globally (such as shipping, marine coating and paints)[83],[84],[85] only commercial, recreational fishing and aquaculture are considered further in this section.
2.46
KIMO UK’s ‘Fishing for Litter’ scheme in Scotland, which implements OSPAR recommendation 2010/19[86], has recorded over 2000 T of retrieved fishing gear from 2005 to 2021 but this retrieval may only comprise a small proportion of fishing-derived litter.[87] One study combining simple oceanographic circulation parameters with empirical estimates of beach litter for the Scottish Atlantic Coast and North Sea Coast reported that fishing releases ~20 T (four million pieces) of marine litter a year, accounting for ~2% of all marine litter in Scotland.[32] A more recent study estimates this to be much higher with 234 T to 614 T of small fishing-related litter entering the sea annually from demersal fishing along the Scottish Atlantic coast.[88]
2.47
Scotland is the world’s third largest producer of farmed salmon with a significant number of salmon farms on the west coast, in addition to farms for other types of fish and bivalves.[89] Aquaculture has expanded significantly – between 2009 and 2019, global aquaculture production increased by 64% and is projected to double by 2050. Marine litter from aquaculture is expected to increase as a result.[90],[84] No studies on the contribution of Scottish aquaculture to marine litter have been identified.
2.48
Understanding the origins and main pathways of fishing-derived litter, particularly fragments of fishing ropes and nets, ending up on Scottish beaches is inherently difficult. A study examining patterns of fishing debris across UK beaches found that the occurrence of fishing-based litter was most likely explained by a beach’s proximity to fishing ports and fishing grounds.[91]
2.49
Globally, there are various routes in which fishing gear can enter the marine environment and it is generally considered under the classification of abandoned, lost or discarded fishing gear (ALDFG). This could be through fishers losing or abandoning gear when it makes contact with another object (e.g. a vessel), gear conflict (e.g. passive gear is unintentionally towed by a trawl), malfunction of tracking systems, damage through snagging on submerged objects or by marine organisms, loss from bad weather or quick discarding of gear in areas where fishing is illegal.[92],[93] Across the west coast of Scotland, the majority of small fishing sourced beach litter composed of short pieces of net, rope and twine that had been cut and was suggested to be from the mending of nets on board vessels that are then unintentionally lost due to poor waste management on board.[90]
2.50
A study in 2013 conducted by Marine Scotland (now Marine Directorate) aimed to assess the extent of, and possible scenarios resulting in, gear conflict in Scottish inshore waters. Gear conflict was reported to be most prevalent within 3 nautical miles across the South West (Boan, Campeltown and Ayr) and the North West (Kinlochbervie, Lochinver, Ullapool, Portee, Mallaig) regions. Static gear operators (67% of nephrop creelers and 63% using other creels) reported that deliberate intent from other operators was perceived to be the main cause of gear conflict; however, several potential causes of gear conflict were also declared.[94]
2.51One difficulty in quantifying the amount of commercial and recreational fishing gear that may contribute to marine litter is a lack of regular data collection on how much fishing gear is sold, in-use and ultimately lost through ALDFG.[95],[58] A UK-wide gear inventory, carried out by UK devolved governments, industry and stakeholders, estimated that approximately 60,000 T of commercial fishing gear is in use across the UK, and 62,000 T of aquaculture gear. For both fishing and aquaculture gear, the greatest weight of material in use is in Scotland (35,000 T and 44,000 T respectively).[96] Another study estimated that between ~480 and ~1000 T of fishing and aquaculture gear is used in Scotland.[97] This is estimated to generate 5 to 110 T of microplastics from fishing net gear in the sea per year.[98]
2.52
The prevalence of ALDFG and the potential impact of ghost gear[iv] and its wider ecological impacts (see section 3) is recognised by the OSPAR action to tackle this source of marine litter.[99] Gear is now lasting longer once lost or discarded as it is largely produced from synthetic fibres, such as nylon and polyethylene as opposed to historically being composed from natural materials, such as cotton or hemp and therefore needs to be better mitigated.[100]
2.53
In summary, the largest constituent of marine litter, both globally and at a UK-Scotland-level, is land-derived litter. Within this, mismanaged waste, particularly public littering is the greatest contributor transported via inland waterways or deposited directly into the coastal environment. For Scotland, the prevalence of marine- and land-derived litter can be influenced by the type of coastal environment, wind exposure, currents and location. For example, several studies show that fishing-derived litter is a greater pressure across the Highland and Islands coastal regions.
2.54
Microplastics have been reported in surface waters throughout Scotland but attributing microplastics to source is inherently difficult. In the EU, the three greatest sources of microplastics into the marine environment are: tyre wear, treated waste water effluent and plastic pellet (including powders and flakes) loss.
2.55
Fishing-derived litter (originating from recreational, commercial and aquaculture) is the greatest contributor to marine-derived litter across Scotland; however, estimates quantifying its proportion of marine litter in Scotland vary. Fishing-derived marine litter can be a result of gear being abandoned, lost or discarded but there is currently a lack of understanding regarding the major causes of this form of marine litter in Scotland. This is partly due to a lack of regular data collection on how much fishing gear is sold, in-use and ultimately lost through ALDFG.
[i]This study defined inadequately disposed litter as litter that is not formally managed and includes disposal in dumps or open, uncontrolled landfills, where it is not fully contained.
[ii] The 11 Scottish Marine Regions and 10 Offshore Marine Regions represent geographical split of the Scottish Economic Exclusive Zone (0-200 nautical miles), as depicted in The Scottish Marine Regions Order 2015.
[iii] The British Plastics Federation’s current estimate of plastic processed in the UK is 3.5 MT, 1.4 MT lower than the estimate used in the study and state that only 8% of the plastic industry is based in Scotland
[iv] Lost or abandoned gear that continues to ‘fish’ once lost, such as entanglement with marine mammals and habitats, like rocky structures.
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[5] Li, W. C., TSE, H. F. and Fok, L. “Plastic waste in the marine environment: A review of sources, occurrence and effects.” Science of the Total Environment, 566, (2016): 333-349. doi:10.1016/j.scitotenv.2016.05.084
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[9] Taylor, M. L., Gwinnett, C., Robinson, L.F. and Woodall, L. C. “Plastic microfibre ingestion by deep-sea organisms.” Scientific Reports, 6, (2016): 33997. doi:10.1038/srep33997
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[11] Pham, C.K., Ramirez-Llodra, E., Alt, C.H.S., Amaro, T., Bergmann, M., Canals, M., Company, J.B., Davies, J., Duineveld, G., Galgani, F., Howell, K.L., Huvenna, V. A.I., Isidro, E., Jones, D., O.B., Lastras, G., Morato, T., Gomes-Pereira, J.N., Purser, A., Stewart, H., Tojeira, I., Tabau, X., Van Rooij, D. and Tyler, P.A. “Marine Litter Distribution and Density in European Seas, from the Shelves to Deep Basins.” PLoS One, 9, no.4 (2014): e95839. doi:10.1371/journal.pone.0095839
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