The International Convention for the Prevention of Pollution from Ships (MARPOL) is the most important international regulation for preventing pollution of the marine environment by oil tankers due to accidental or operational causes. MARPOL was adopted by IMO in 1973, which incorporated much of provisions of OILPOL 1954 and its amendments into Annex I.  Annex I made several improvement in OILPOL. It suggested requirements for regular monitoring of oil discharges into sea water, and made Governments responsible to provide shore reception and treatment facilities at oil terminals and ports. Other five annexes of MARPOL cover chemicals, harmful substance packages, sewage, garbage, and air pollution in their respective spheres.

Annex I of the Convention contains most important regulations for preventing pollution by oil from shipping vessels. As MARPOL 73 was under the process of implementation, a series of tanker accidents occurred in 1976-77, leading to the formulation of the 1978 MARPOL Protocol that fully absorbed the 1973 Convention. The combined version, referred to as (MARPOL 73/78), was finally implemented in October 1983. In 1997, a new Protocol was adopted by IMO to amend and add a new Annex VI in the Convention, which was finally implemented in May 2005. In July 2011, IMO introduced new amendments to Annex V that prohibits the discharge of all garbage into the sea, except as provided otherwise, under specific circumstances. IMO also included new measures in Annex VI to significantly reduce the greenhouse gas emission from merchant ships. The amended version of Annex V and VI will come into force from January 01, 2013. At present, 136 nations representing 98% of global shipping tonnage are signatories to the MARPOL Convention.

Annexes of MARPOL Convention:

Annex I  Regulations for the Prevention of Pollution by Oil (entered into force 2 October 1983)

Covers prevention of pollution by oil from operational measures as well as from accidental discharges; the 1992 amendments to Annex I made it mandatory for new oil tankers to have double hulls and brought in a phase-in schedule for existing tankers to fit double hulls, which was subsequently revised in 2001 and 2003.

Annex II  Regulations for the Control of  Pollution by Noxious Liquid Substances in Bulk  (entered into force 2 October 1983)

Details the discharge criteria and measures for the control of pollution by noxious liquid substances carried in bulk; some 250 substances were evaluated and included in the list appended to the Convention; the discharge of their residues is allowed only to reception facilities until certain concentrations and conditions (which vary with the category of substances) are complied with.

In any case, no discharge of residues containing noxious substances is permitted within 12 nautical miles of the nearest land.

Annex III Prevention of Pollution by Harmful Substances Carried by Sea in Packaged Form (entered into force 1 July 1992)

Contains general requirements for the issuing of detailed standards on packing, marking, labeling, documentation, stowage, quantity limitations, exceptions and notifications.

For the purpose of this Annex, “harmful substances” are those substances which are identified as marine pollutants in the International Maritime Dangerous Goods Code (IMDG Code) or which meet the criteria in the Appendix of Annex III.

Annex IV Prevention of Pollution by Sewage from Ships  (entered into force 27 September 2003)

Contains requirements to control pollution of the sea by sewage; the discharge of sewage into the sea is prohibited, except when the ship has in operation an approved sewage treatment plant or when the ship is discharging comminuted and disinfected sewage using an approved system at a distance of more than three nautical miles from the nearest land; sewage which is not comminuted or disinfected has to be discharged at a distance of more than 12 nautical miles from the nearest land.

In July 2011, IMO adopted the most recent amendments to MARPOL Annex IV which are expected to enter into force on 1 January 2013. The amendments introduce the Baltic Sea as a special area under Annex IV and add new discharge requirements for passenger ships while in a special area.

Annex V Prevention of Pollution by Garbage from Ships (entered into force 31 December 1988)

Deals with different types of garbage and specifies the distances from land and the manner in which they may be disposed of; the most important feature of the Annex is the complete ban imposed on the disposal into the sea of all forms of plastics.

In July 2011, IMO adopted extensive amendments to Annex V which are expected to enter into force on 1 January 2013. The revised Annex V prohibits the discharge of all garbage into the sea, except as provided otherwise, under specific circumstances.

Annex VI Prevention of  Air Pollution from Ships (entered into force 19 May 2005)

Sets limits on sulphur oxide and nitrogen oxide emissions from ship exhausts and prohibits deliberate emissions of ozone depleting substances; designated emission control areas set more stringent standards for SOx, NOx and particulate matter.