Since their invention roughly 75 years ago, plastics have become increasingly prevalent in the consumer marketplace. Today, we use and dispose of plastics on a daily basis, in products like bottled water and grocery bags. Plastics now represent a significant portion of the solid waste we generate.

Unfortunately, plastic wastes are polluting our oceans. And it is thought that the majority of plastic that ends up there is originating on land. Plastic debris entering the ocean from coastlines can have dangerous effects on the oceans themselves, their wildlife, and even humans. Over time, plastics degrade into small pieces that are easy for small animals to ingest. This decay process also makes it difficult to pinpoint pollution sources after plastics enter the ocean.

The best strategy to mitigate the harmful effects we're seeing is simply to reduce the input of plastics into the ocean. However, only recently have scientists been able to figure out where all of it's coming from. Today, they've released a new estimate of the input of plastics from populations living within 50 km of coastlines worldwide.

These scientists identified three categories that can help provide information about plastics polluting the oceans: (1) the mass of waste generated per capita annually; (2) the percentage of waste that is plastic; and (3) the percentage of plastic waste that has the potential to enter the ocean as debris.

Scientists estimate that 2.5 billion metric tons (MT) of solid waste was generated in 2010 in 192 coastal countries, which collectively account for 93 percent of the global population. Approximately 11 percent of this waste is plastic (275 billion MT). In order to estimate coastal plastic debris, scientists assumed that plastic waste roughly tracked with plastic resin production; they then scaled their results for the population living within 50 km of the coast.

The final result? They estimate that 99.5 million MT of plastic waste was generated in coastal regions in 2010 and that 4.8 to 12.7 million MT entered the ocean in 2010. That's 1.7 to 4.6 percent of the total plastic waste generated by the countries.

This estimate is at least one order of magnitude greater than any that had previously been reported. It's also likely to be low, as it only represents plastics that are buoyant in seawater, which accounts for only about half of plastic production in North America and two-thirds of plastic in the US waste stream.

However, this estimate is a good start to understanding how much plastic waste is infiltrating the oceans and affecting marine life today. And, in the process of their study, the authors have developed a model that can help us assess strategies intended to reduce plastic waste input into the oceans.

Science, 2015. DOI: 10.1126/science.1260352 (About DOIs).