Oceans, caught between devil and the deep blue sea… (Pun intended!) – VI

During a voyage, dead ahead, through roaring sea and the pitch-black night, a captain sees the light on a collision course with his ship.

Reaching for the radio, he conveys his message: “Change your course ten degrees east.”

“Change yours ten degrees west,” comes the reply.

The captain responds, “I’m a navy captain! Change your course, sir!”

“I’m a seaman second class,” the next reply comes back. “Change your course, sir.”

The captain is furious. “I’m a battleship! I’m not changing course!”

The man replies, “I’m in a lighthouse. Your call sir…” (!!)


Nature guides us to be on correct course with warnings such as – Excessive rains, extreme summers, droughts, severe winters and so on – from time to time.  However, out of our arrogance like a battleship, we disregard these and abuse the planet in response.  

As seen in earlier articles oceans offer humanity endless services starting from acting as oxygen pump to controlling the atmosphere to providing us psychological solace and encouragement.  However, we don’t even bat an eye before throwing our trash into oceans.  Pathways of pollution into the seas almost every time originate from human activities on land. 

Pollutants entering oceans

As you can see from above pie-chart, the primary pollutant in the ocean is human sewage. Human sewage mainly consists of excrement from toilet-flushing; wastewater from bathing, laundry, and dish-washing; and animal and vegetable matter from food preparation that is disposed of through an in-sink garbage disposal. Because coasts are densely populated, a massive amount of sewage reaching seas and oceans is of particular concern.  Various constituents the wastewater contains, harm the ecosystems and pose significant threats to the food chain and ultimately to public health in general.

Sewage originates primarily from domestic, commercial, and industrial sources. In many developed countries, they typically deliver the wastes either to on-site septic systems or centralized sewage treatment facilities. In both methods, they treat sewage before discharging to surface-water bodies, usually a stream, river, or coastal outlets.  Although sewage treatment facilities are designed to accommodate and process sewage from their service areas; partly treated or even untreated sewage is often discharged directly into the oceans, especially in the developing countries. Among other reasons for not treating the wastewater are – old or malfunctioning effluent treatment plants and infrastructure.  Also, events of heavy rainfalls or storms, etc. overwhelm the systems, since they are used for combined sewers and storm-water drains (known as combined sewer overflows). In developing countries with no on-site or centralized sanitation facilities, no opportunity exists for any treatment, and human wastes go directly into surface waters, finally ending into coastal oceans.

In urban India, around 400 million people live in coastal cities. Only about 30% of the sewage generated from this population is treated through treatment plants before let it flow into the oceans.  The rest 70% is randomly dumped in lakes, wells, rivers, and seas.  Therefore according to the analysis of various data sources, almost three-fourths of country’s water bodies are polluted. India’s urban areas generate approximately 62,000 million liters of sewage every day.  However treatment capacity across India is only 23,277 million liters per day (MLD).  In other words, it also means 63% of the sewage generated in urban India is released without any treatment on it. 

India also has an enormous amount of free-flowing dust and / or flying trash, oil spills and other contaminants on the roads run down with rain waters into rivers, finally ending into oceans.  There are no statistics available for this kind of sewage flowing utterly untreated into ocean waters.  

Another source of ocean pollution by sewage-related waste is the disposal of sludge, a semisolid by-product of the sewage treatment process, often called sewage-sludge. Historically, sludge in developed nations was always disposed of in coastal waters. New York’s twenty sewage treatment plants, for example, once disposed of their sludge offshore in a region known as the New York Bight. Although today’s environmental regulations in the United States prohibit this practice, sewage sludge is still disposed at sea in many countries.

Sewage contains very high quantities of nutrients, primarily nitrogen and phosphorous. Under natural conditions, low concentrations of these nutrients limit the productivity of aquatic ecosystems. Sewage promotes the excess growth of marine primary producers — plants, algae, and cyanobacteria — in a process known as eutrophication. Many harmful algal blooms are linked to increasing quantities of nitrogen and phosphorus in coastal areas, mainly from nutrient-rich wastewater and agricultural runoff. These two nutrients are necessary for life, and in proper amounts, they help plants grow faster. But in areas with limited water flows, the waters can suffer from over-enrichment (eutrophication), which triggers the oxygen depletion that leads to algal blooms.  Among the most visible signs of the pollution problem are out-of-control blooms of algae that blanket coastal areas. Although algal blooms are a naturally occurring phenomenon, the frequency and severity of harmful algal blooms (HABs) have increased in the past three decades. 


Some algae become harmful by their biomass. Growing to nearly a million cells per milliliter of seawater, algal blooms covering broad areas of surface water can block sunlight and air from reaching the life below. The problems become worse when the algae die: they sink to bottom waters where bacteria digest them, consuming more oxygen in the process. Eventually, the bacteria-laden waters become so depleted of oxygen (a condition known as hypoxia) that they suffocate marine animals to death. 

Another problem is with pathogens, antibiotics, and hormones.  Livestock and humans excrete these through urine and faces. Significant sources of sewage containing these compounds are hospitals, intensively managed farms, and slaughterhouses. Once in the water, antibiotics can inhibit the growth of bacteria that play an essential role in removing nitrogen from water. Also once these contaminants collect in zooplankton, larvae, and small fish (often by direct consumption), they work their way up the food chain and cause problems in the fish, marine mammals, and people who eat them.

Out of pollutants entering seas, human sewage has the most significant contribution and plays a vital role in environmental damage.  When will we understand caution warnings being offered by nature again and again?


  1. Water Encyclopaedia
  2. ENVIS Centre on Hygiene, Sanitation, Sewage Treatment Systems, and Technology; Sponsored by Ministry of Environment, Forests & Climate Change, Govt of India
  3. Safeguarding the Health of Oceans by Anne Platt Mcginn, Editor – Jane A. Peterson, Worldwatch Paper 145, March 1999


Milind Joshi


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