Dumping Oil and Hazardous Waste at Sea

In one line

MU's 2026 second question asks what dumping oil and hazardous waste into the sea does to marine biodiversity and coastal ecosystems, and a good answer gives the mechanism of harm, the ecosystems affected, and the instrument that governs each.

In exam wording: the discharge of oil and hazardous wastes into the sea harms marine biodiversity and coastal ecosystems through acute toxicity, physical smothering and coating, chronic sublethal effects, bioaccumulation and biomagnification through the food chain, oxygen depletion, and the physical destruction of habitat; the governing instruments are Part XII of the United Nations Convention on the Law of the Sea 1982, MARPOL 73/78 for operational discharges from ships, the London Convention 1972 and its 1996 Protocol for deliberate disposal, the Basel Convention 1989 for the transboundary movement of hazardous waste, and the Civil Liability and Fund Conventions for compensation.

The mechanisms of harm

One: acute toxicity. The lighter aromatic fractions of crude oil are acutely toxic, and they are the fractions that dissolve. Larvae and eggs, which float at the surface, are killed at concentrations far below those that harm adults. A single spill during a spawning season can remove a year class.

Two: coating and smothering. Oil coats feathers and fur, destroying insulation and buoyancy, so birds and mammals die of cold or drown. On a shore it smothers the intertidal community, and on a reef it kills the coral polyps.

Three: chronic sublethal effects. Below the concentration that kills, hydrocarbons impair reproduction, growth, immunity and behaviour. These effects are invisible in a survey that counts corpses, which is why the damage from a spill is routinely underestimated.

Four: bioaccumulation and biomagnification. Persistent substances, especially mercury and persistent organic pollutants, are taken up faster than they are excreted, and their concentration rises at each step of the food chain. Top predators, and the people who eat them, receive the highest dose. Minamata is the historical example and it gave its name to a convention.

Five: oxygen depletion. Organic waste and nutrient loading feed algal blooms; the bloom dies; its decomposition consumes the oxygen; and the water becomes hypoxic or anoxic. Nothing that cannot swim away survives.

Six: physical destruction. Dumped solids smother the benthos. Dredged spoil buries a seabed community. Sunken vessels and structures alter the substrate.

The ecosystems, and why the coastal ones suffer most

Mangroves. Oil penetrates the sediment and persists for years because the anaerobic mud does not degrade it. Mangroves are nurseries, so the loss propagates through the fishery for a decade.

Coral reefs. Coral is sensitive to both oil and to sediment. A reef is the most species-rich marine ecosystem and it recovers over decades if at all. The South China Sea award of 2016 found severe and in places permanent harm to the coral reef ecosystem from island-building, and held China to have violated articles 192 and 194 of the Law of the Sea Convention.