Marine pollution refers to the introduction of harmful substances or energy—such as noise, heat, or light—into the ocean environment by human activities. According to the United Nations Convention on the Law of the Sea (UNCLOS), it is defined as the direct or indirect human introduction of materials that result in deleterious effects on living resources, hazards to human health, and impairment of water quality. Approximately 80% of marine pollution originates from land-based sources, reaching the ocean through rivers, sewage systems, and atmospheric deposition.
Primary Sources and Classification
The pollutants entering the marine ecosystem are categorized based on their origin and physical properties.
- Land-Based Sources: This accounts for the majority of the pollution load, including untreated municipal sewage, industrial effluents, and agricultural runoff containing pesticides and fertilizers.
- Atmospheric Inputs: Gaseous pollutants and dust particles, such as nitrogen from fossil fuel combustion and heavy metals like mercury, settle on the ocean surface through precipitation.
- Maritime Activities: Pollution arising from shipping (ballast water discharge), oil spills from tankers, and offshore drilling operations.
- Deep-Sea Mining: A burgeoning concern involving the extraction of polymetallic nodules, which causes sediment plumes and noise pollution in the benthic zone.
Major Pollutants and Their Impact
The following table summarizes the key pollutants and their ecological consequences:
| Pollutant Type | Primary Source | Impact on Marine Ecosystem |
| Nutrients (Nitrogen/Phosphate) | Fertilizers, Sewage | Causes Eutrophication and “Dead Zones” (Hypoxia). |
| Marine Plastics | Urban waste, Fishing nets | Ingestion by marine life; Microplastics enter the food chain via biomagnification. |
| Petroleum (Oil) | Tanker spills, Runoff | Coats bird feathers/mammal fur; blocks sunlight for marine plants. |
| Persistent Organic Pollutants (POPs) | Pesticides, Industrial chemicals | Causes reproductive failure and endocrine disruption in marine mammals. |
| Heavy Metals (Mercury, Lead) | Mining, Coal burning | Leading to toxicity; e.g., Minamata disease from mercury-tainted fish. |
| Acoustic Pollution | Sonar, Shipping, Seismic surveys | Disrupts communication and navigation for cetaceans (whales/dolphins). |
Critical Phenomena in Marine Pollution
Eutrophication and Dead Zones
Excessive nutrient loading (nitrogen and phosphorus) triggers Algal Blooms. As these blooms die and decompose, bacteria consume the dissolved oxygen, leading to Hypoxia (low oxygen). This creates “Dead Zones” where most marine life cannot survive. Notable examples include the Gulf of Mexico and the Baltic Sea.
Marine Plastic and Microplastics
It is estimated that 75–199 million tonnes of plastic currently reside in the oceans. Over time, plastic breaks down into microplastics (particles < 5mm). These are consumed by zooplankton and fish, eventually reaching humans through the food chain (Biomagnification).
Thermal and Light Pollution
Power plants often discharge warm water into coastal areas, reducing oxygen solubility and causing thermal shock to sensitive species like corals. Additionally, Artificial Light at Night (ALAN) disrupts the migratory patterns of sea turtles and the circadian rhythms of various marine organisms.
Global Legal Frameworks and Initiatives
International cooperation is governed by several treaties and specialized agencies.
- UNCLOS (1982): Often called the “Constitution for the Oceans,” it sets the legal framework for all maritime activities and mandates states to protect the marine environment.
- MARPOL Convention (1973/78): The main international convention aimed at preventing pollution from ships, whether operational or accidental (Oil, Chemicals, Sewage, Garbage).
- London Convention (1972): Specifically regulates the dumping of wastes at sea to prevent marine pollution.
- Global Plastic Treaty (INC-5): Ongoing negotiations (as of 2024-2025) to create a legally binding instrument to end plastic pollution globally.
- UN Decade of Ocean Science (2021–2030): Theme “The science we need for the ocean we want,” focusing on reversing the decline in ocean health.
India’s Status and Regulatory Measures
India has a vast coastline of 7,516.6 km, making marine pollution a significant national concern.
- Coastal Regulation Zone (CRZ) Notification: Issued under the Environment (Protection) Act, 1986, to regulate industrial and developmental activities in coastal areas.
- National Maritime Day (April 5): The 2026 theme is “Maritime India — Empowering Progress,” emphasizing sustainable growth in the blue economy.
- Swachh Sagar, Surakshit Sagar Campaign: A massive coastal cleanup initiative launched to remove tons of marine litter.
- Deep Ocean Mission: While focusing on exploration, it includes components for ocean climate change advisory services and biodiversity conservation.
Important Facts and Trivia for Prelims
- Great Pacific Garbage Patch: A collection of marine debris in the North Pacific Ocean, held together by the North Pacific Subtropical Gyre. It is twice the size of Texas.
- Blue Flag Certification: An international eco-label awarded to beaches that meet high environmental and safety standards. India currently has several certified beaches (e.g., Shivrajpur, Ghoghla).
- Sentinel Species: Marine organisms like oysters and mussels are used as bio-indicators to monitor heavy metal levels in coastal waters.
- ITLOS Ruling 2024: The International Tribunal for the Law of the Sea recently ruled that Greenhouse Gases (GHGs) constitute marine pollution, expanding the scope of UNCLOS obligations.