Recently, the Joint Expert Group on the Science OF Marine Pollution (GESAMP) released a new survey report on the sources OF marine litter (SEA-BASED SOURCES OF MARINE LITTER GESAMP No.108, 2021). The report provides an overview of the various sources of marine debris, particularly plastic waste, and their impact on the environment, assesses the availability of available data, highlights the urgency of reducing marine debris, and outlines some ongoing initiatives and recommendations. This report not only provides suggestions for future academic research, but also helps people to have a deeper understanding of the harms caused by marine environmental pollution, and also has certain guiding significance for our marine production practice activities.
1. Research background
Any persistent, manufactured or processed solid materials discarded, disposed of or abandoned by human activities in the marine and coastal environments are all referred to as marine debris. Since the 70s of the 20th century, people have paid more and more attention to the negative impact of human production and life on the marine environment, and marine debris has been recognized as a threat to marine health. Especially since the commercialization of plastics in the 50s of the 20th century, the threat to ocean health has been exacerbated by the manufacture, use and disposal of plastic products around the world. Over the past decade, there has been a growing understanding of the levels, sources, negative impacts, and measures to reduce marine debris and microplastics in the world’s oceans. However, the amount of marine litter, especially plastic waste, continues to increase, with harmful impacts on biodiversity, ecosystems, fisheries, animal welfare, maritime transport and maritime safety. GESAMP Working Group 43 was formally established in April 2019 in accordance with the agreement in principle reached at the 45th Annual Meeting of GESAMP. Its overall goal is to conduct a survey and analysis of the sources of marine litter, especially from shipping and fisheries, to gain a broader understanding of the relative proportions of different sources, to analyze the use and management of plastics in both industries, and the scope and extent of the impact of marine litter sources. Ultimately, these new understandings about the sources of marine litter can be used by international organizations to intervene on the sources of marine debris based on established priority guidance.
2. Classification of marine plastic waste sources
It is generally believed that most of the plastic waste entering the ocean comes from land (some say up to 80%). At the same time, marine debris also has ocean-based activities. Additionally, some forms of marine debris may not only be a significant source of plastic waste, but may have a greater impact on marine biota and habitats than others. In GESAMP’s report on the sources of marine debris, the following five main sources are focused:
fishery
According to the Food and Agriculture Organization of the United Nations (FAO), the number of fishing vessels worldwide was estimated at 4.566 million in 2018, and global fish production peaked at 179 million tons, of which 54% of the production came from capture fisheries and 46% from aquaculture. About 87% of the total production is used for human consumption. Among all manual operations, commercial activities, and recreational fishing engaged by humans, those abandoned, lost, or otherwise discarded fishing gear (ALDFG) are the main source of marine debris. This includes various metal materials such as nets, ropes, hooks, buoy sinkers and anchors. Occasional, periodic, or extensive loss of gear can occur due to a variety of reasons, including inclement weather, normal wear and tear, wild sea creatures straying or biting, and underwater obstacles. In a 2019 tracking report, it was pointed out that about 5.7% of fishing nets, 8.6% of fishing nets, and 29% of rope lines are lost in the world’s oceans every year.
aquaculture
As of 2016, 202 countries around the world are engaged in aquaculture, with nearly 600 aquatic species for human consumption (FAO 2018). Generally speaking, aquaculture systems include nets such as ropes, buoys, and mesh bags. Plastics used in aquaculture include polyester, polyethylene, polypropylene, polyethylene chloride, and expanded polystyrene. It is generally believed that the main causes of marine litter generated by aquaculture operations are normal wear and tear of plastic nets, destruction of aquaculture equipment, extreme weather effects, and improper waste management by operators. Unfortunately, to date, no region in the world has systematically monitored plastic waste generated by aquaculture operations at the regional or national level. An assessment of aquaculture operations in the EEA in 2016 showed that approximately 3,000 tonnes to 41,000 tonnes of aquaculture-related equipment and waste were generated annually and that the total amount of this waste could be present in the EEA’s marine environment was between 95,000 and 655,000 tonnes.
Shipping and shipping
International maritime trade is closely related to global economic development, and global maritime trade has increased by an average of 20% over the past half century (1970-2017). According to statistics for the first half of 2020, the total number of ships registered under the IMO in the world is about 53,000. The increase in merchant shipping capacity has led to congestion on regular shipping routes, while also increasing the impact of navigation accidents and accidents on the marine environment. Plastic waste is a major source of solid waste generated by ships; More and more scrapped ships also produce solid waste such as fibers, solid foams and polyvinyl chloride; Cleaning of ship hulls, ship coatings, and wastewater systems are also accompanied by the generation of microplastics. Although the MARPOL Convention and environmental regulations of various countries are becoming stricter in the management of preventing ships from polluting the marine environment, it is still not ruled out that ships may intentionally or unintentionally discharge plastics in their operations. Although there are few detailed studies that can quantify the amount and type of plastic waste discarded during transportation on ships, the annual loss of cargo accounts for 0.001-2% of the total cargo; The operating waste generated per person per day is 0.01 cubic meters to 0.1 cubic meters, and the plastic and domestic waste is 0.003 cubic meters to 0.015 cubic meters. The cost of reducing pollutants from ships is considerable, with an estimated total value of approximately US$279 million in annual waste loss to shipping in the APEC region.
Marine waste dumping and other substances
Of the waste that can be disposed of at sea, the dredged material is by far the most in terms of volume and tonnage. In the past few decades, countries have adopted laws and regulations to prevent, reduce and control the pollution of the marine environment by dumping, in accordance with the provisions of the United Nations Convention on the Law of the Sea and the London Convention, but the statistics on the amount of plastic or other waste contained in dumped waste are very limited. Due to the lack of routine monitoring, there is a general lack of quantitative data on the large amount of marine debris and microplastics that may be contained in many dumps, including dredged material.
Other marine pollutants
Due to the limited information available, it is very difficult for the Working Group to gather information on other types of marine pollution sources and the quantification of microplastics. But there is evidence that the use of microplastics in offshore oil and gas activities may be very high, and most estimates may underestimate the actual level of plastic emissions. The loss of shark nets is also a source of marine pollution, with 65%-70% of weather balloons deployed globally ending up in the ocean and eventually becoming a burden on global marine debris. Artificial coral reefs containing plastics, especially PVC or rubber components, are degrading toxic chemicals, breaking down into microplastics and spreading into the surrounding environment. The amount and frequency of waste left over from spacecraft recycling, as well as single-use plastics used in scientific research, have not been recorded or reported by national research projects.
3. Solutions to reduce marine debris
Given the diversity of marine pollutant sources, marine debris reduction efforts require a broad range of actions and approaches to conduct research on the sources, volumes, impacts, and solutions of marine debris to generate the necessary evidence to inform management and policy implementation at all levels. Specifically,
First, the supervision of fishery management departments should be improved, technological innovation should be carried out in the design and operation of fishing gear, and port reception facilities should be increased to prevent and reduce the loss and discarding of fishing gear.
Secondly, the shipping industry should continue to optimize the standardized management of ship waste disposal, scientifically record the quantity, classification, time and location of garbage disposal, and improve the convenience of shore-based receiving facilities.
Finally, all stakeholders, including governments, NGOs, communities, industry, and academia, are called upon to conduct effective environmental education and raise awareness to build consensus to achieve the vision of reducing marine debris pollution.
