The Earth's oceans have become a giant dumpsite for wastes. Plastic products such as toys, shopping bags, fishing nets and bottles are the top pollutants in the ocean today.

To determine the amount of plastic littering in the ocean, environmental scientist Marcus Eriksen, from Five Gyres Institute in Los Angeles, and colleagues made 24 sea expeditions over a course of six years visiting the Mediterranean Sea, the Bay of Bengal and Australia as well as all of the five subtropical gyres, large systems of rotating ocean currents that play a crucial role in creating concentrations of marine debris known as garbage patches.

During these expeditions, Eriksen's team collected water samples so they can estimate the amount of microplastics, or plastic fragments that are smaller than 4.75 millimeters. They also conducted visual surveys and used the data to simulate the distribution and quantity of plastic in the ocean using an ocean model.

The researchers found that the ocean currently holds about 5.3 trillion plastic pieces weighing about 269,000 tons, which is equivalent to the weight of 570 Boeing 747s that are fully loaded.

"There's much more plastic pollution out there than recent estimates suggest," Eriksen said. "It's everything you can imagine made of plastic. It's like Walmart or Target set afloat."

Eriksen and colleagues also discovered that microplastics make up more than 90 percent of the buoyant waste. Eriksen said that these are particles from larger items that were reduced to smaller pieces because of sunlight, waves and being nibbled by marine animals such as sharks and fishes.

"Based on our model results, we estimate that at least 5.25 trillion plastic particles weighing 268,940 tons are currently floating at sea," the researchers wrote in their study published in the journal PLOS ONE on Dec. 10. "The vast majority of these plastics were small fragments."

Plastic pollution in the ocean raises concern because the hazardous waste also accumulates toxins that are present in the water and these harmful substances could be transferred to the animals that eat them.

Plastic wastes also kill a number of seabirds and marine animals. Fragments of plastic objects, for instance, could get lodged in the throats and digestive tracts of animals that ate them. Plastic fishing nets could also entangle sea turtles and dolphins.

Eriksen said that a solution to this problem is the adoption of improved waste-management practices on land. He also promoted the use of alternatives to plastic products especially plastic bags.

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