Plastic waste is present in all the world’s ocean basins, including around remote islands, the poles and in the deep seas. Accumulating in the natural environment, plastics will only decompose over hundreds or even thousands of years.

A majority of marine plastic waste  originates from land-based sources and is transported to the ocean through rivers, with the remaining share of debris coming from fishing activities, natural disasters and other sources. Marine debris encompasses large objects, microplastics and nanoplastics, which entangles or is ingested by species who live in them. Microplastics may travel up the food chain and pose potential risks to human health once ingested. Marine litter also leads to a range of socioeconomic impacts to tourism, fishing and aquaculture, and shipping.

- Plastic waste prevention

Plastics waste can be prevented by leveraging incentives along the value chain, as well as by addressing negative externalities associated with plastics production upstream, and plastics waste generation and littering downstream.

Policy interventions to foster plastic waste prevention include the introduction of price signals (e.g. through taxes on disposable plastic goods or deposit-refund schemes for reusable packaging), product bans for particularly harmful products which are prone to leakage but unlikely to be collected and recycled (e.g. microbeads), product durability standards and consumer education campaigns.

- Waste management

Improvement of waste management systems can help ensure adequate end-of-life treatment of plastic waste. It is estimated that between 14 to 18% of waste plastics generated globally are collected for recycling and 24% is incinerated. The remainder is disposed of in landfills, via open burning or uncontrolled dumping, or released to the wider environment.

Improving water quality from source-to-sea requires managing both point and diffuse sources of pollution. One of the main policy challenges facing OECD countries is the effective management of diffuse sources of nutrient pollution, which are caused by activities that have no specific point of discharge, and are often linked to agricultural and urban pollution via overland flow to surface waters.

Unless attention is turned to these diffuse sources, further deterioration of water quality and the ocean can be expected as human populations grow, industrial and agricultural production intensifies, and climate change causes significant alteration to the hydrological cycle.

Globally, one of the most prevalent water quality challenges is eutrophication; a form of water pollution caused by excess use of nutrients (nitrogen and phosphorous). Eutrophication can trigger toxic algal blooms and cause “dead zones” (oxygen depletion) in the ocean and coastal waters leading to significant loss of marine biodiversity. Excessive nitrogen in the environment also contributes to climate change, depletion of the ozone layer, air pollution, nitrate toxicity in groundwater and drinking water, loss of biodiversity and deterioration of soil quality.

Global shipping is responsible for approximately 30% of total global nitrogen oxide (NOx) emissions. These emissions have been  linked to thousands of premature deaths in coastal areas. Ships account for approximately 2.5% of total global greenhouse gas (GHG) emissions. Other environmental impacts from shipping include biodiversity impacts related to ballast water and the effect of noise pollution on ocean wildlife. Global policy efforts have recently focused on sulphur and GHG emissions from ships and ballast water management, but efforts could be intensified with respect to NOx and particulate matter (PM) emissions.

 The International Transport Forum (ITF) at the OECD has conducted various studies that aim to provide policymakers with tools to reduce air emissions from shipping.

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Decarbonising Maritime Transport: Pathways to zero-carbon shipping by 2035 examines what would be needed to achieve zero CO2 emissions from international maritime transport by 2035. It assesses measures that can reduce shipping emissions effectively and describes possible decarbonisation pathways that use different combinations of these measures. In addition, it reviews under which conditions these measures could be implemented and presents concrete policy recommendations.