Kiera Jefferson
Ships have played a major role in the development of the world economy, with the vast majority of international trade and commerce being accomplished through shipping. However, the environmental impact of the shipping industry is significant, contributing to air pollution as well as water pollution, as well as oil pollution. Cruise ships, in particular, have been identified as a source of significant pollution in oceanic and marine areas, releasing large amounts of sewage, wastewater, and carbon emissions. Oil spills, collisions, and the improper disposal of plastic waste are also major contributors to marine pollution. To address these issues, international agreements such as the International Convention for the Prevention of Pollution from Ships (MARPOL) have been negotiated to prevent or minimize pollution from vessels.
| Characteristics | Values |
|---|---|
| Oil spills | Oil spills are the most commonly known form of environmental pollution by ships. |
| Air pollution | Ships are responsible for more than 18% of nitrogen oxides pollution, 3% of greenhouse gas emissions, and emit other air pollutants such as sulphur oxides and particulate matter. |
| Water pollution | Ships discharge wastewater, sewage, and ballast water containing harmful chemicals, metals, minerals, bacteria, and algae into the ocean, adversely affecting marine life and the ecosystem. |
| Solid waste | Cruise ships generate about 8 tons of solid waste during a one-week cruise, contributing 24% of solid waste generated by vessels worldwide. |
| Plastic pollution | Shipping is a key contributor to plastic pollution in the oceans, including macroplastics, mesoplastics, microplastics, and nanoplastics. |
| Ship strikes | Ship collisions can result in injuries and deaths of marine life, such as the North Atlantic right whale. |
| International efforts | International agreements such as MARPOL and the Law of the Sea Convention aim to prevent pollution from ships and balance the rights of coastal states with international shipping duties. |
| Scrubber systems | Some ships use scrubber systems to address air pollution, but these can increase water pollution if the wash water is not properly treated and disposed of. |
| Fuel consumption | Cruise ships burn large amounts of heavy fuel oil, contributing to marine pollution through oil spills and emissions of dangerous levels of sulfur and heavy metals. |
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What You'll Learn
Oil spills
The cleanup and restoration processes following oil spills are crucial but can be costly and time-consuming. Various methods and tools are used for cleanup, including skimmers (boats that scoop up oil), sorbents (large sponges), chemical dispersants, in situ burning of freshly spilled oil, washing oil off beaches, vacuum trucks, and shovels or road equipment. Restoration projects, such as building marshland or protecting bird nesting habitats, are implemented to actively enhance the environment and accelerate the recovery of different species and habitats.
International agreements, such as the International Convention for the Prevention of Pollution from Ships (MARPOL), have been established to address concerns about marine pollution from ships. These agreements aim to prevent pollution by oil, noxious liquid substances, harmful substances, sewage, garbage, and air pollution from ships. Additionally, specific legislation, like the Coast Guard Authorization Act of 2010 in the United States, has been enacted to align with international standards and prohibit the use of harmful chemicals in marine vessels.
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Air pollution
Commercial ships burn fuel for energy and emit several types of air pollution as by-products. These ship-source pollutants are linked to climate change and public health impacts. Greenhouse gases (GHG), nitrogen oxides (NOx), sulphur oxides (SOx), and particulate matter are among the most common types of air pollution caused by ships.
A medium-sized cruise ship uses about 150 tonnes of fuel daily, emitting as much particulate matter as one million cars. A luxury cruise ship releases ten times more carbon emissions than all of Europe's cars. The shipping industry's contribution to air pollution is significant, with container ships emitting about 1 billion metric tons of carbon dioxide into the air annually, accounting for about 3% of all greenhouse gas emissions.
The impact of shipping on air quality is particularly notable in port cities, where millions of residents are exposed to additional pollution. For example, in 2021, 430 million people lived near major Chinese port cities like Shanghai and Shenzhen. The high-sulphur content of heavy fuel oil used by ships contributes to the pollution problem, with sulphur dioxide (SO2) emissions from international shipping estimated at 1.7 million tonnes per year in European seas.
The health impacts of ship emissions are significant. Tiny airborne particles from ship emissions can enter the lungs, pass through tissues, and enter the bloodstream, triggering inflammations that can lead to heart and lung failures. According to the World Health Organization, poor air quality is linked to asthma, respiratory and cardiovascular disease, and premature death. It is estimated that air pollution from international shipping accounts for approximately 400,000 premature deaths per year worldwide, costing society more than €58 billion annually.
To mitigate the impact of shipping on air quality, various measures can be implemented. Using low-sulphur fuels is one of the easiest ways to reduce ships' impact on air quality. Low-sulphur fuels can reduce other pollutant emissions, such as black carbon, and make engines run smoother and more efficiently. Another option is to install scrubbers, which can cut SO2 emissions by 99% and reduce other polluting particles. Additionally, speed reduction can effectively reduce fuel consumption and, consequently, air pollutants.
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Grey and blackwater discharge
Greywater is wastewater from sinks, showers, dishwashers, and laundries. It contains fats, oils, harmful chemicals, bleaches, and germs that can be harmful to human health. Greywater can turn septic in less than 24 hours if left untreated. While greywater discharge from vessels is a comparatively low contributor to overall water quality in the aquatic environment, it is still an important source of pollution in localised areas.
Greywater carries numerous particles that can be harmful to marine life, including bacteria, pathogens, pharmaceuticals, personal care products, per- and polyfluoroalkyl chemicals, and other toxic chemicals. A 2021 Ocean Conservancy report found high levels of bacteria, solids, nutrients, and metals in ship greywater, with contaminants present in numbers comparable to raw sewage.
Cruise ships generate particularly large amounts of greywater. A large cruise ship releases around one million gallons of greywater during a single week’s voyage. Many cruise ships treat their wastewater on board (through incineration, pulping, or grinding) before discharging it overboard. However, the treatment plants may not effectively remove harmful contaminants, and the high concentration of greywater in oceanic waters can have a potent adverse effect on the marine environment.
Blackwater is sewage water, comprising waste from toilets and medical dispensaries. Like greywater, untreated blackwater contains high concentrations of nitrates, phosphates, and organic matter that can contaminate water bodies. Blackwater is rich in bacteria and algae, which can adversely affect oceanic life forms and the entire marine ecosystem.
To address the issue of grey and blackwater discharge, the Code of Practice for Vessel and Facility Management sets out mandatory requirements for vessel operators to manage wastewater while travelling in state waters. The EPA encourages vessel operators to implement onboard wastewater management systems to reduce environmental and public health risks.
International conventions such as MARPOL Annex IV aim to prevent pollution from sewage at sea, providing guidelines for the treatment and discharge of sewage waste. However, there is currently no internationally enforced requirement regulating the discharge of greywater, and organisations are calling for more stringent guidance in forthcoming MARPOL revisions.
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Solid waste
Food waste is a significant component of solid waste from cruise ships, with an estimated 30% of food disposed of as "fish food". This waste is ground up and mixed with water until it is liquified, and then pumped out of the ship while at sea. However, the food served on cruise ships often contains pesticides, antibiotics, and hormones that are not natural for marine life. As a result, the liquified food waste can accumulate contaminants in animals at the bottom of the food chain, impacting predators and other wildlife.
Cruise ships also generate solid waste in the form of sewage or "black water", which includes human waste, chemicals, pharmaceuticals, bacteria, viruses, and heavy metals. While modern cruise ships have advanced sewage treatment plants, the high volume of sewage generated can still lead to pollution and oxygen depletion in the oceans. Additionally, some cruise ships have been caught illegally dumping sewage and other solid waste into the ocean, further contributing to marine pollution.
Recyclable materials, such as plastics, paper, glass, and metals, are typically collected and stored onboard cruise ships and then offloaded at ports for proper disposal. However, there have been instances where companies have discharged plastic waste into the sea, either accidentally or intentionally, violating international regulations. This plastic pollution can have significant environmental and ecological impacts, with over 5 trillion plastic particles floating on the ocean's surface by 2014.
Overall, solid waste from ships, especially cruise ships, is a major contributor to ocean pollution, and proper waste management and disposal are crucial to minimize environmental impacts.
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Collisions with marine life
Marine life collisions with ships are a significant concern, with evidence that more species are at risk of collision, especially in coastal areas frequented by smaller vessels. Between 1890 and 2018, the number of globally registered large commercial vessels increased from 11,108 to over 94,000, and this increase in commercial vessels coincided with a rise in fatal ship strikes on large whales.
The greatest danger to the North Atlantic right whale is injury from ship strikes. Between 1970 and 1999, 35.5% of recorded deaths were attributed to collisions, and from 2004 to 2006, the average number of mortalities and serious injuries caused by ship strikes increased to 2.6 per year. In 2017, an unprecedented mortality event occurred, resulting in the deaths of 17 North Atlantic right whales caused primarily by ship strikes and entanglement in fishing gear. To reduce these collisions, the United States' National Marine Fisheries Service (NMFS) and National Oceanic and Atmospheric Administration (NOAA) introduced vessel speed restrictions in 2008, which expired in 2013. However, these restrictions did not prevent the mortality event in 2017.
Whales, dolphins, sea turtles, and other marine species are at risk of collision with ships. The 'bow null' effect created by large ships masks engine noise, leaving whales and sea turtles unaware of approaching vessels. Blunt trauma from vessel hull strikes can result in bruising, broken bones, or death, while propeller strikes can cause deep cuts in the tissue of these animals, leading to severe scarring or death if major arteries or the spinal cord are severed. Beached whales or sea turtles with large wounds, missing fins, or other missing body parts are evidence of deadly encounters with ships.
To address this issue, NOAA Fisheries has adopted seasonal speed restrictions in certain areas to reduce the threat of ship collisions with endangered North Atlantic right whales. Additionally, they have established Dynamic Management Areas, where mariners are asked to reduce speed or avoid the area altogether when right whale groups are sighted. Whale Alert, a smartphone app, also helps track and share real-time whale sightings to prevent collisions.
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Frequently asked questions
Oil spills are the most commonly known form of ocean pollution caused by ships.
Oil spills can be caused by ship collisions, fires, groundings, or faulty engine systems and improper repair work.
Ships also contribute to plastic pollution, sewage pollution, chemical pollution, and air pollution.
Ships burn fuel for energy and emit greenhouse gases, nitrogen oxides, sulphur oxides, and particulate matter as by-products.
International agreements such as the International Convention for the Prevention of Pollution from Ships (MARPOL) and its six annexes have been put in place to prevent and minimize pollution from vessels.
