MARPOL ANNEXES: PROTECTING OUR OCEANS
The Six Annexes Every Seafarer Should Know
The ocean is the foundation of global maritime trade, but every voyage also carries the responsibility to protect the marine environment. Ships generate different forms of pollution—from oil and chemicals to sewage, garbage, and atmospheric emissions. To control these risks, the International Maritime Organization (IMO) developed MARPOL 73/78, the principal international convention for preventing pollution from ships.
MARPOL is built around six technical annexes, with each annex addressing a specific category of ship-generated pollution. Together, they establish requirements covering shipboard equipment, cargo handling, discharge procedures, record keeping, fuel use, and operational practices.
For seafarers, MARPOL is more than a regulatory framework. It is part of everyday shipboard responsibility. Understanding these six annexes helps crews make safe decisions, maintain proper records, and prevent pollution before it occurs.
What Is MARPOL 73/78?
MARPOL stands for the International Convention for the Prevention of Pollution from Ships. The convention was adopted to minimize pollution from ships caused by both routine operations and accidental incidents.
The framework addresses six major pollution categories:
- Annex I – Oil Pollution
- Annex II – Noxious Liquid Substances in Bulk
- Annex III – Harmful Substances Carried in Packaged Form
- Annex IV – Sewage
- Annex V – Garbage
- Annex VI – Air Pollution
Each annex contains specific requirements that apply according to the vessel, cargo, equipment, operating area, and circumstances.
ANNEX I – PREVENTION OF POLLUTION BY OIL
Oil pollution is one of the most serious environmental risks associated with shipping. MARPOL Annex I establishes regulations designed to prevent accidental and operational oil pollution.
It covers oil tankers as well as other ships that carry or generate oil residues.
Shipboard systems and procedures may include:
- Oily Water Separators (OWS)
- Oil discharge monitoring and control systems
- Sludge handling arrangements
- Oil Record Book
- Slop tanks and associated piping
- Shipboard Oil Pollution Emergency Plans
The Oil Record Book (ORB) is particularly important because it records prescribed oil-related operations onboard. Accurate entries provide evidence that operations have been conducted in accordance with applicable requirements.
The principle is straightforward: oil must be contained, processed, recorded, and disposed of through approved procedures rather than released illegally into the sea.
ANNEX II – NOXIOUS LIQUID SUBSTANCES IN BULK
Chemical and product tankers may carry liquid substances that can be harmful to marine ecosystems.
MARPOL Annex II regulates the discharge of noxious liquid substances carried in bulk and categorizes substances according to the hazards they present to the marine environment and human health.
Cargo residues and tank washings must be handled according to applicable procedures and the requirements for the particular cargo.
This makes proper cargo planning and tank-cleaning procedures extremely important.
Officers and crew must understand:
- Cargo classification
- Cargo handling procedures
- Tank cleaning requirements
- Cargo residue management
- Discharge restrictions
- Cargo documentation
A small operational mistake involving a hazardous chemical can have consequences far beyond the ship itself.
ANNEX III – HARMFUL SUBSTANCES IN PACKAGED FORM
Unlike Annex II, which deals with harmful liquid substances carried in bulk, Annex III focuses on harmful substances transported in packaged form.
These may include dangerous goods carried in:
- Drums
- Containers
- Packages
- Portable tanks
- Other approved transport units
Proper marking, labelling, packaging, documentation, and handling are essential.
This annex works closely with the international requirements governing the transport of dangerous goods by sea.
For seafarers, correct identification is critical. Knowing what is inside a package—and understanding its hazards—helps the crew respond appropriately during loading, stowage, transportation, and emergencies.
ANNEX IV – PREVENTION OF POLLUTION BY SEWAGE
Ships generate sewage through normal accommodation and operational activities. If discharged improperly, untreated sewage can affect marine ecosystems and coastal waters.
MARPOL Annex IV regulates the discharge of sewage from ships and establishes requirements for approved sewage treatment systems and other arrangements.
Depending on the vessel and operating circumstances, sewage may be managed through:
- Approved sewage treatment plants
- Holding tanks
- Approved discharge arrangements
Crew members must understand the ship's sewage system, operating procedures, maintenance requirements, and applicable discharge restrictions.
Good sewage management is an essential part of maintaining hygiene onboard while protecting surrounding waters.
ANNEX V – PREVENTION OF POLLUTION BY GARBAGE
Garbage is one of the most visible forms of ship-generated pollution.
MARPOL Annex V regulates the disposal of garbage from ships and places particular restrictions on the discharge of plastics into the sea.
Shipboard garbage may include:
- Plastics
- Food waste
- Domestic waste
- Cooking oil
- Operational waste
- Cargo residues
- Incinerator ash
Proper segregation, storage, processing, and disposal are therefore essential.
Ships maintain appropriate garbage management procedures and, where applicable, Garbage Record Books to document relevant operations.
The message is simple:
What is generated onboard must be managed onboard.
ANNEX VI – PREVENTION OF AIR POLLUTION
Modern shipping is increasingly focused not only on protecting the ocean but also on protecting the atmosphere.
MARPOL Annex VI addresses air pollution from ships, including emissions such as:
- SOx – Sulphur Oxides
- NOx – Nitrogen Oxides
- Particulate matter
- Certain ozone-depleting substances
The global sulphur limit for marine fuel was reduced to 0.50% m/m in 2020, while stricter limits apply in designated Emission Control Areas.
Ships may use compliant low-sulphur fuels, alternative fuels, or approved exhaust gas cleaning systems to meet applicable requirements.
Annex VI also incorporates energy-efficiency and greenhouse-gas-related measures, including EEXI and CII, making it a major part of the industry's transition toward cleaner shipping.
Why MARPOL Matters to Every Seafarer
MARPOL compliance is not the responsibility of the Master or Chief Engineer alone. Every crew member contributes to pollution prevention.
A successful environmental management culture requires:
- Correct waste segregation
- Accurate record keeping
- Proper equipment operation
- Safe cargo handling
- Compliance with discharge procedures
- Regular maintenance
- Effective communication
- Immediate reporting of pollution risks
A minor shortcut onboard can potentially become a major environmental incident.
MARPOL and Port State Control
MARPOL compliance is also closely connected to inspections by Flag States and Port State Control authorities.
During inspections, authorities may examine areas such as:
- Oil Record Books
- Garbage Record Books
- Bunker delivery documentation
- Oily Water Separator operation
- Sewage treatment systems
- Garbage management
- Fuel changeover procedures
- Engine emission compliance
- Pollution emergency plans
Incomplete records, incorrect procedures, or malfunctioning pollution-prevention equipment can lead to deficiencies and potentially serious consequences for the vessel and company.
Therefore, good MARPOL compliance means being prepared every day—not only when an inspection is expected.
The Golden Rule of MARPOL
The six annexes may cover different pollution sources, but they share one fundamental principle:
PREVENT POLLUTION BEFORE IT HAPPENS.
Technology can help, regulations can establish standards, and inspections can enforce compliance—but the final line of defence is the people operating the ship.
Every engineer maintaining an OWS, every deck officer monitoring cargo operations, every crew member segregating garbage, and every officer maintaining accurate records contributes to protecting the marine environment.
Looking Toward Cleaner Shipping
MARPOL continues to evolve as the maritime industry faces new environmental challenges. Ships are becoming more energy efficient, alternative fuels are gaining attention, waste-management systems are improving, and digital technologies are helping crews monitor environmental performance.
The future of shipping will depend on combining regulatory compliance, technological innovation, and responsible human behaviour.
For today's seafarer, understanding MARPOL is therefore not simply about passing an examination. It is about understanding the environmental responsibility that comes with operating a vessel.
Conclusion
MARPOL 73/78 provides the international framework for preventing different forms of ship-generated pollution. Its six annexes cover oil, noxious liquid substances, harmful packaged substances, sewage, garbage, and air pollution.
Each annex addresses a different risk, but all six serve one common objective: keeping shipping efficient while protecting the marine environment.
The ocean connects the world. Protecting it is a responsibility shared by every vessel, every company, and every seafarer.
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