There’s as much as 100 times less plastic floating on surface of the world’s oceans than would be expected given the mushrooming use of the material in recent decades, a new study has found.
But what’s happened to the missing material is not at all clear — it could be ingested by sea creatures, quickly disintegrated into microscopic particles, washed ashore or attach to other objects and sink, according to researchers at the University of Western Australia’s Oceans Institute.
The July 1 study, by scientists at UWA and universities in Saudi Arabia and Spain, used data collected on the Spanish government’s Malaspina 2010 expedition and found that plastic debris was widespread, contaminating 88 percent of water samples.
Malaspina, which involved 250 researchers and two research ships looking at the impact of climate change on the ocean, collected more than 3,000 water samples at 141 points around the world between December 2010 and July 2011.
“A conservative first-order estimate of the floating plastic released into the open ocean from the 1970s (106 tons) is 100-fold larger than our estimate of the current load of plastic stored in the ocean,” the UWA report said. “Our study reports an important gap in the size distribution of floating plastic debris as well as a global surface load of plastic well below that expected from production and input rates.”
UWA said in a news release that the biggest gap was in particles smaller than 1 millimeter in diameter, and said that an “unknown mechanism” is removing smaller particles at a faster rate than larger particles.
The study estimated there are between 7,000 and 35,000 tons of plastic floating on the ocean surface now.
While it admits that measuring plastic in the ocean is a complex task, the study said that the amount of plastic on the surface has not kept pace with the rapid increase in plastic production in recent decades.
In the 1970s, for example, it said the U.S. National Academy of Sciences estimated that 45,000 tons of plastics washed into the oceans each year, and it noted that since then, global plastic production has increased five-fold to 265 million tons a year.
“Historical time series of surface plastic concentration in fixed ocean regions show no significant increasing trend since the 1980s, despite an increase in production and disposal,” the study said.
The researchers did not offer any firm suggestions on what would happen to the missing plastic, but said that it was unlikely that more of it would be washing ashore. They said there could be mechanisms to accelerate the breakdown into smaller particles, it could be devoured by marine animals or attach to objects like barnacles, a process called biofouling.
It said that five ocean gyres had the bulk of the plastic. The North Pacific gyre had the most, about 33 percent of the total, because of its size and its proximity to the sea coasts of East Asia, which includes one-third of the world’s coastal populations.
“Because plastic inputs into the ocean will probably continue, and even increase, resolving the ultimate pathways and fate of these debris is a matter of urgency,” the study said.