MARPOL

MARPOL (short for "marine pollution") is the principal international treaty governing pollution from ships. It was adopted under the auspices of the International Maritime Organization (IMO) on 2 November 1973 and substantially modified by the 1978 Protocol, which merged with the parent convention before it had entered into force. The combined instrument, commonly cited as MARPOL 73/78, entered into force on 2 October 1983. A further 1997 Protocol added rules on air pollution.

The convention is structured around six technical Annexes, each addressing a different pollution source:

• Annex I – oil and oily wastes
• Annex II – noxious liquid substances carried in bulk (chemicals)
• Annex III – harmful substances carried in packaged form
• Annex IV – sewage from ships
• Annex V – garbage, including the 2018 amendments tightening plastic-waste rules
• Annex VI – air pollution, including SOx, NOx and, since the 2020 "IMO 2020" rule, a 0.50% global cap on the sulphur content of marine fuel oil

Annexes I and II are mandatory for all parties; the others are optional, though they have been very widely adopted. MARPOL relies on flag-state enforcement supplemented by port-state control: ships must carry certificates such as the IOPP (International Oil Pollution Prevention) certificate, and port authorities may inspect and detain non-compliant vessels.

The treaty also designates Special Areas and Emission Control Areas (ECAs) — for example the Baltic Sea, the North Sea, and the North American ECA — where stricter discharge or emission limits apply. MARPOL is frequently invoked in IMO Marine Environment Protection Committee (MEPC) negotiations and is a touchstone reference in debates over shipping decarbonisation, plastic pollution, and Arctic shipping governance.