Marine pollutant is one of the more misunderstood terms in dangerous goods, because it is not a hazard class. It is a property that a substance can have in addition to whatever else it is, and it triggers its own marking and documentation.
The treaty basis is MARPOL Annex III, which governs harmful substances carried by sea in packaged form. The IMDG Code implements it.
How a substance becomes a marine pollutant
Through aquatic toxicity, assessed against criteria aligned with the Globally Harmonized System. In broad terms a substance qualifies where it is acutely toxic to aquatic life, or chronically toxic combined with poor degradability or a tendency to bioaccumulate.
The practical consequence is that many perfectly ordinary products qualify. Detergents and surfactants, many paints and coatings, pesticides and herbicides, some cosmetics, certain metal compounds, and a long list of industrial chemicals. Shippers who would never describe their product as hazardous are frequently shipping marine pollutants.
Two different situations
- The substance is already dangerous goods. A flammable liquid that is also aquatically toxic ships under its own class and UN number, Class 3, and additionally carries the marine pollutant mark and the annotation on the declaration. The class does not change.
- The substance is only environmentally hazardous. It has no other hazard. Then it is classified as Class 9 under one of two entries:
- UN 3077, environmentally hazardous substance, solid, n.o.s.
- UN 3082, environmentally hazardous substance, liquid, n.o.s.
UN 3077 and 3082 are among the most frequently used entries in the whole code, precisely because so many products are toxic to aquatic life and nothing else.
The technical name is not optional
Both are n.o.s. entries, meaning not otherwise specified. For any n.o.s. entry the technical name of the substance must appear in brackets after the proper shipping name:
UN 3082, Environmentally hazardous substance, liquid, n.o.s. (contains xylene), 9, III, Marine Pollutant
Not a brand name, not "chemical mixture". The technical name is what lets an emergency responder know what has been released and what lets the vessel planner apply segregation groups. A declaration without it is rejected, and correctly so. See the dangerous goods declaration.
The mark
The marine pollutant mark is a fish and tree symbol, black on a white or contrasting background, bordered. It goes on packages and, where the quantity requires it, on the container itself alongside the other placards.
It is a mark, not a hazard label. It sits in addition to the class label, never instead of it. A Class 3 marine pollutant carries both the flammable liquid label and the marine pollutant mark.
Quantity thresholds and exemptions
Some relief exists for small quantities. Single packagings and inner packagings of limited size containing marine pollutants may be exempt from certain provisions, and the specific thresholds are set in the code. But the relief is narrower than people assume, and it does not remove the substance from the code entirely.
The other thing to know is that marine pollutant status is a sea and inland waterway concept. By air, aquatic toxicity alone does not make something dangerous goods, so a product that is a marine pollutant by sea may be entirely unregulated by air. That asymmetry catches shippers who switch mode without re-checking classification.
Practical steps
- Read section 12 of the safety data sheet, ecological information, alongside section 14. Section 14 should state marine pollutant status, but section 12 is where the underlying toxicity data lives.
- Ask the manufacturer directly if section 14 is silent. Many older safety data sheets predate the current criteria.
- Get the technical name for the declaration, in writing, before you book.
- Re-check when you change mode. Unregulated by air does not mean unregulated by sea.
- Do not rely on the product being ordinary. Detergent is the textbook example of an everyday marine pollutant.
General guidance. Marine pollutant status is determined by the substance own aquatic toxicity data against the criteria in the IMDG Code in force. Work from the safety data sheet and the code, not from product familiarity.
