Marine litter is a clearly visible problem along the Baltic Sea coastline, but it also accumulates out at sea and occurs in many different types and size classes. The smallest microlitter particles are invisible to the human eye, but reach the marine food web when animals ingest them. Larger pieces of marine litter deteriorate habitat quality and can cause direct harm to animals when they become entangled or ingest the litter. Plastic materials are a special concern due to their risks to the environment and very low degradation below the photic zone in the water column, resulting in high persistence of plastic litter especially at the seafloor. Around 70% of the litter items recorded in the Baltic Sea are derived from human usage of plastic materials. The regional goal agreed in HELCOM is to reduce the amount of marine litter significantly by 2025 and prevent harm from litter in the coastal and marine environment.
Litter in the sea can affect human activities and have socio-economic impacts, due to the cost of removal, or negative effects on tourism and recreation, for example. It may also damage fishing gear or present a risk to navigational safety. Marine litter also has various effects on marine life, either directly or by affecting the quality of the habitat by effects on physical structure or local biogeochemistry.
Artificial, polymer materials, more commonly known as plastics, are of special concern due to their longevity, and because they may provide a pathway for the transport of harmful chemicals into the food web. Litter has been observed to cause harm to animals, via ingestion clogging the digestive tract or causing contamination. Additionally, marine litter is known to damage, alter or degrade habitats and to be a possible vector for the transfer of alien species, leading to effects on biodiversity. The risks associated with microlitter for marine animals is presently under extensive study, including evaluation of potential effects on nutrition and food webs.
During the last few years HELCOM has worked and made progress on the development of core indicators for assessing marine litter. These indicators are not yet operational, although an assessment approach is underway for beach litter, litter on the seafloor and microlitter in the water column (HELCOM 2016a–c).
Marine litter on the beach
Marine litter is often left by people on beaches, or it may end up at the shoreline after transportation from other points of discharge. Updated data for the Baltic Sea region is currently available covering the time period either 2012 to 2016 or 2014 to 2016 for eight countries, and gives an indication of the spatial distribution of marine beach litter along the Baltic Sea coastlines (Figure 4.3.1).
Plastic is clearly the most common litter material, followed by paper, processed wood, metal and ceramics (Figure 4.3.2). The amount of litter items on the beach are highest during spring for most types of litter materials for the Baltic Sea, although there are differences between countries. Most of the litter items are found in the western Baltic Sea and in the Northern Baltic Proper, whilst wooden litter items are recorded mostly in the central and northern parts of the Baltic Sea. The spatial differences are influenced by local human activities but also by the level of beach cleaning in between monitoring events. In addition, the shape of the coastline and the direction of water currents appear to play an important role in determining where litter accumulates.
The available data is not yet sufficient to evaluate the trend in beach litter over time for all basins. It is anticipated that the longest available data series will be used for further analysis and baseline determination.
Litter on the seafloor
Litter that has entered the marine environment can be transported long distances by water currents, and can accumulate on the seafloor far away from its original source. Hence, all types of sources can contribute to seafloor litter, but items associated with maritime activities, such as lost and discarded fishing gear are a major component of seafloor litter. Abandoned, lost, or discarded, fishing gear is termed ’ghost nets’ and pose a threat to marine life since they continue fishing not only fish, but also birds and marine mammals and can be considered as posing an especially large risk to marine life. Experiments have shown that the catching efficiency of lost gillnets amounts to approximately 20% of the initial catch rates after three months, and around 6% after 27 months (WWF Poland 2011).
Seafloor litter can be monitored alongside fish, using trawling surveys. The Baltic International Trawl Survey (BITS), coordinated by the international council for exploration of the sea (ICES), has been going on for several years but data on litter on the seafloor has been collected systematically only since 2015. The trawl survey covers areas from the Northern Baltic proper and south, but there is no Baltic-wide trawl survey and shallow water areas are not covered.
The term microlitter is used for litter particles smaller than 5 mm, but they can also be much smaller (GESAMP 2015). Some studies have focussed on particle sizes as low as 20 or even 10 µm. It includes both synthetic and non-synthetic particles (such as plastic, cellulose, cotton, wool, rubber, metal, glass, combustion particles). The particles can be from primary sources, or derived from the breakdown of larger litter items (so called secondary particles). Microlitter may be found in all parts of the environment; on the water surface, within the water column, on the sea floor and shore, as well as inside marine organisms. Also particles with low density (such as many common plastic types) can reach the sea floor by being incorporated in marine snow, attached to detritus falling from the surface to the deeper water. Most of the environmental harm of microlitter has been associated with microplastics. Ingestion of microplastics by a variety of animals has been shown in laboratory and field studies.
Although the proportion of microlitter of different materials has not been assessed in the Baltic Sea, it is likely that plastic polymers form the majority of microlitter particles, like they do for larger marine litter, but other components may also be important (Magnusson et al. 2016). Information on impacts of microlitter and microplastics on marine food webs is constantly growing.
Impacts and recovery
Many marine litter items, and their negative impacts, accumulate in the environment due to the slow degradation time. Additionally, the degradation process will make the nature of the problem change over time from macro to microlitter. Global estimates have indicated that 275 million metric tons of plastic waste was generated in 192 coastal countries in 2010, with 4.8 to 12.7 million metric tons entering the ocean (Jambeck et al. 2015), and the world annual plastic production is increasing. Most plastics are used in packaging or in the building industry and are discarded within a year of their production.
Political will and a robust regulatory framework are key factors in reducing marine litter. With increasing awareness, efforts are also increasing to change production and consumption patterns with the aim of stopping waste becoming litter. In addition, regulatory frameworks and actions to improve waste and wastewater management are important. A large number of measures have been undertaken by HELCOM over recent years, which directly or indirectly can be expected to have resulted in reducing amounts of marine litter. Among them, the 2013 HELCOM Ministerial Declaration (HELCOM 2013a) made a commitment to achieve a significant quantitative reduction of marine litter by 2025 (compared to 2015) and to prevent harm to the coastal and marine environment. Such an aim is intended to be achieved via the implementation of land-based measures, sea-based measures and educational and outreach actions defined as part of the HELCOM Action Plan on Marine Litter (HELCOM 2015b).