Causes & effects of ocean pollution

on August 22, 2017

Pollution entering our oceans from both man-made and natural activities is affecting marine ecosystems throughout the world. And the danger isn't just to marine animals: most of the pollutants that enter the ocean come from the land, according to the National Oceanographic and Atmospheric Administration. Animals often eat these pollutants which, means humans will as well.

Scientists have estimated that up to 100,000,000 metric tons of plastic trash are in the world’s oceans. There are many causes of ocean pollution. Here are some of the biggest culprits:


Runoff from the land comes from both urban and agricultural areas. Often referred to as non-point source pollution, runoff can originate from sources such as cars and trucks, septic tanks, farms, and timber harvesting operations. Chemicals that end up on roads and highways flow over and under the ground with rainwater, as do pesticides; fertilizers; and carbon-, nitrogen-, and phosphorous-rich particulates, eventually reaching the ocean. Inland mining can cause an influx of mineral and soil deposits. These travel through rivers and estuaries, making soil a real threat to marine ecosystems. Runoff can even smother marine plants and coral reefs.

Anything from litter and debris to dust can make it into the ocean by way of the wind. This causes objects such as plastic to be suspended in the water and never decompose.

Intentional discharge

Toxic waste, including mercury, released by manufacturing plants enters the sea and the food chain, making its way up to larger species consumed by humans. Agricultural toxins can be direct biological hazards and raise ocean temperatures, which can be deadly for some animals and plants.

Discharge of plastic is another problem. Scientists have estimated that up to 100,000,000 metric tons of plastic trash, which doesn't degrade easily, are in the world’s oceans. Discarded fishing nets and other plastics can entangle wildlife, potentially restricting their movement, injuring, or even starving them. Dolphins, turtles, crabs, crocodiles, sharks, and sea birds are especially vulnerable.

Sewage passed directly into the ocean, including human waste and mining materials, is a problem as well.

Atmospheric pollutants

Various types of pollutants can get in the water through rain. A particular menace is carbon dioxide, which has built up with climate change. The oceans are absorbing the excess and becoming more acidic. This has been particularly troublesome for calcium carbonate structures such as corals, which cannot regenerate or regrow. About one million species depend on thriving coral habitats. In addition, the excess CO2 can dissolve the shells of various marine animals.

Oil spills

Ships and platforms release large amounts of oil every year. However, oil isn’t the only pollutant that comes from ships, which may also discharge fuel, plastic, and human waste. Crude oil is difficult to clean up. It's also toxic, suffocating, and devastating to marine life. Crates lost during storms, accidents, and other emergencies pollute the ocean as well.

Ships also cause noise pollution, disrupting the balance of life for marine animals such as dolphins and whales that use echolocation.

Deep-sea mining

The ocean floor is a valuable source of gold, silver, copper, and zinc, but mining under the sea is a major source of pollution. Sulfide deposits created when these substances are drilled can have environmental impacts that aren’t fully understood. Material leaks and corrosion of equipment only exacerbate the problem.

Effects of pollutants in the ocean

The overabundance of pollution has a variety of consequences. One is excess nitrogen and phosphorous. Although plants require these to grow, too high a concentration can cause algal blooms, in which algae overrun the ecosystem. Once these organisms start to sink and decompose, oxygen is depleted and the area becomes a dead zone because marine life cannot survive in that environment. Fish and other forms of life that can swim away leave; other species that cannot move die off.

Debris in the water, whether chemically harmful or not, can be hazardous. It can kill all kinds of marine life. Discarded metal cans and plastic, broken glass, fishing gear, and parts of ships can harm people who come into contact with them. Beaches can become littered with trash that came from thousands of miles away, affecting human health and recreation. If there is enough debris in the water, it can even make it dangerous for ships to navigate.

Once the smallest organisms consume pollutants, their predators consume them. Plastics, garbage, heavy metals, and chemicals make their way up the food chain, ultimately accumulating in seafood that people catch and eat. Coastal pollution contaminates mussels and other shellfish that the seafood industries rely on.

Other specific effects of ocean pollution on sea life include:

  • Oil covering the feathers of birds and the gills of fish
  • Skin and eye irritation and lung and liver problems from oil deposits and byproducts
  • Reproductive system failure from exposure to poisonous industrial and agricultural chemicals
  • Consumption of toxic substances stored in the fatty tissues of fish

Despite the detrimental effects of pollution, the problem persists. About eight million metric tons of plastic end up in the oceans every year, according to EcoWatch, while other studies estimate that as many as 12.7 million metric tons may have washed into the ocean in 2010.

Improved infrastructure can limit the amount of pollution. Much of the plastic that gets washed into oceans is from countries with large populations and poor waste management. Nations are also beginning to issue regulations to limit ocean pollution. The degree of success has been variable, and we must do more to reverse the current trends.

Sources: Conserve Energy Future,, NOAA, EcoWatch