Vessel Pollution: Two Main Causes And Their Impact

Marine pollution is a growing problem, with the ocean being flooded by two main types of pollution: chemicals and trash. While most of the pollution comes from land-based sources, the maritime industry, including the construction, repair, and scrapping of vessels, is the most likely source of vessel-based pollution. The two most common causes of vessel-sourced pollution are oil spills and the discharge of waste. Oil spills can occur due to accidents at sea or operational discharges such as reballasting and tank cleaning, while waste discharge includes sewage, ballast water, and cargo residues, which can introduce invasive species and pollutants into marine environments.

Two common causes of vessel-sourced pollution

Oil spills from accidents at sea

One of the most well-known oil spills occurred in 1989, when the Exxon Valdez oil spill in Alaska resulted in a massive environmental disaster. The incident highlighted the challenges and limitations of oil spill cleanup efforts, as the high-pressure, hot-water hoses used to clean up beaches caused more damage than the oil alone. This spill also led to the Oil Pollution Act of 1990, which established that those responsible for oil spills can be held accountable for the costs of cleanup and restoration.

Another notable incident took place in 1979 in the Bay of Campeche in the Gulf of Mexico. An oil well operated by the Mexican petroleum company Pemex collapsed, resulting in the discharge of around 140 million gallons of oil into the sea over ten months. The oil slick covered an area of around 1100 square miles, threatening marine life and nesting sites for sea turtles.

In 1983, two separate accidents occurred, both involving oil tankers. The first incident happened in August when the Spanish tanker Castillo de Bellver caught fire about 70 miles northwest of Cape Town, South Africa. The tanker was carrying 250,000 tons of light crude oil, and the burning vessel eventually broke in half, with the stern sinking and releasing 110,000 tons of oil into the water. The second accident occurred in the Persian Gulf during the Iran-Iraq war, when an oil tanker collided with the Nowruz Field platform. This resulted in approximately 80 million gallons of oil flowing into the Persian Gulf for seven months before the spill could be controlled.

More recently, in 2010, the Deepwater Horizon oil rig explosion caused 779,000 tons of crude oil to spill into the sea, impacting the coastlines of Cuba, Florida, Louisiana, and Mississippi. This disaster led to increased awareness of the toxic compounds in oil and their severe health effects on marine life, including heart damage, stunted growth, and immune system problems.

International operational discharges

Marine pollution from vessels is a pressing issue, with international trade and commerce heavily reliant on shipping. While land-based sources are the primary contributors to marine pollution, pollution from vessels is a significant concern, leading to the development of international agreements and regulations to address this issue.

One notable agreement is the International Convention for the Prevention of Pollution from Ships (MARPOL), which includes six technical Annexes with regulations aimed at preventing and minimising pollution from ships, both accidental and operational. The United States, for instance, passed the Act to Prevent Pollution from Ships (APPS) in 1980 to implement the provisions of MARPOL.

MARPOL's Annexes cover various aspects of pollution control. Annex I, which is mandatory for all signatory nations, addresses the prevention of pollution by oil from operational measures and accidental discharges. It mandates that new oil tankers have double hulls, and existing tankers were required to follow a phase-in schedule to retrofit double hulls. This annex also details the discharge criteria and measures for controlling pollution by noxious liquid substances carried in bulk.

Annex II, also mandatory, focuses on the control of pollution by noxious liquid substances (NLS) in bulk. It specifies the conditions under which certain residues can be discharged into reception facilities. Annex III, which is optional, provides general requirements for issuing detailed standards on packing, marking, labelling, documentation, stowage, quantity limitations, exceptions, and notifications for harmful substances.

Annex IV, another optional annex, addresses the prevention of pollution by sewage from ships. It prohibits the discharge of sewage into the sea, except when the ship has an approved sewage treatment plant or is discharging treated sewage at a specified distance from the nearest land. The Baltic Sea area is currently the only Special Area designated under Annex IV, with stricter discharge requirements.

Annex V, also optional, outlines regulations for the prevention of pollution by garbage from ships, specifying the types of garbage, distance from land, and manner in which it can be disposed of. Notably, it imposes a complete ban on the disposal of plastics into the sea.

In addition to MARPOL, other international agreements contribute to the prevention of vessel-sourced pollution. For example, the 2001 International Convention on the Control of Harmful Anti-Fouling Systems on Ships aims to align with international standards by prohibiting the use of organotin, a chemical used to inhibit the growth of marine organisms on vessel hulls.

While these international agreements provide a framework for addressing vessel-sourced pollution, effective implementation and enforcement are crucial to ensure compliance and minimise the environmental impact of international operational discharges.

Noise pollution

While most marine pollution comes from land-based sources, the maritime industry is the most likely source of ocean pollution. The construction, repair, and scrapping of vessels, as well as the transportation of cargo and other materials across the ocean, contribute to this.

One of the two common causes of vessel-sourced pollution is oil spills and discharges. The 1978 Amoco Cadiz oil spill, for instance, saw approximately 223,000 tons of oil spilled, ruining over 100 miles of the Brittany coast in France. While this incident was caused by an accident at sea, vessel-source pollution also includes international operational discharges, such as reballasting, tank cleaning, and the direct discharge of waste into the oceans. These operational discharges constitute approximately 80% of the world's vessel-source oil pollution. Other sources of oil pollution include leaking pipelines, engine oil disposed of down sewers, and ballast water from oil tanks on return ships.

The second common cause of vessel-sourced pollution is noise. Ships create noise pollution that disturbs natural wildlife, with the highest concentrations occurring in shipping lanes, port areas, and densely trafficked ocean routes. Older and larger vessels emit significant low-frequency noise (10 to 500 Hz) caused by engine vibrations, propeller cavitation, and hull turbulence. This form of pollution is referred to as underwater noise pollution and is unevenly distributed across marine environments.

To prevent or minimize vessel-sourced pollution, the international community has cooperated to develop laws and agreements, such as the International Convention for the Prevention of Pollution from Ships (MARPOL) and its six annexes, which include regulations for the control of pollution by noxious liquid substances and the prevention of pollution by harmful substances carried by sea and sewage from ships. The US has also implemented the Annex VI Marine Pollution Act of 2008, which aligns with international standards related to anti-fouling systems by prohibiting the use of organotin, a chemical used to inhibit the growth of marine organisms on vessel hulls.

Ballast water discharge

Ballast water is a mandatory component of ships, providing stability and manoeuvrability during journeys. It is often taken on in coastal waters when ships discharge wastewater or unload cargo, and it is then discharged at the next port of call when more cargo is loaded. Ballast water is typically stored in a ballast tank when the cargo hold is empty or not fully filled. It can also be used to adjust a ship's buoyancy, with additional weight causing the ship to sink lower below the surface water level.

To address the environmental impact of ballast water discharge, the International Maritime Organization (IMO) adopted the "International Convention for the Control and Management of Ships' Ballast Water and Sediments" in 2004. This convention aims to control the environmental damage caused by ballast water by requiring all ships to implement a "Ballast Water Management Plan". This includes keeping a ballast water record book and carrying out ballast water management procedures to a given standard.

The US has also taken steps to regulate ballast water discharges, with the Environmental Protection Agency (EPA) and the US Coast Guard regulating the concentration of living organisms discharged in ballast water under the authority of the Clean Water Act. In 2013, the EPA published its latest Vessel General Permit, setting numeric ballast water discharge limits for commercial vessels 79 feet (24 m) in length or greater. Similarly, Australia has implemented ballast water management requirements, with vessels required to meet the regulation D-2 discharge standard of the International Convention for the Control and Management of Ships' Ballast Water and Sediments.

Sewage discharge

To address this issue, several international agreements and regulations have been put in place. The International Convention for the Prevention of Pollution from Ships (MARPOL) and its Annexes, including Annex IV, provide a framework for controlling and preventing pollution by sewage from ships. Annex IV sets out regulations regarding the discharge of sewage into the sea, including requirements for ships' equipment and systems for sewage control, the provision of port reception facilities, and survey and certification.

In the United States, Section 312 of the Clean Water Act regulates sewage discharges from vessels. The Act is jointly implemented by the Environmental Protection Agency (EPA) and the Coast Guard. The EPA establishes no-discharge zones and regulates the equipment used to treat or hold sewage, such as marine sanitation devices (MSDs). These devices use maceration, disinfection, or holding tanks to treat or store sewage effluent.

It is important to note that not all marine sanitation devices require the use of chemicals, but those that do typically rely on chlorine to treat sewage. Proper maintenance of these systems is essential, and regular checks are recommended to ensure effective treatment. By complying with international regulations and utilizing approved treatment methods, the impact of sewage discharge from vessels on marine environments can be mitigated.

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