Plastics are everywhere, and the ocean is no exception: 11 million metric tons of plastics enter the ocean each year, where they are dispersed widely, reaching the deepest trenches and most remote islands of the Arctic.
We have long known that marine animals can mistake plastic bags and other plastic contaminants for food. To date, all families of marine mammals and seabirds, as well as all seven species of sea turtles, have been documented ingesting plastics—almost 1,300 species in total.
We also know that eating plastics can be fatal for wildlife. When ingested, macroplastics — plastics larger than five millimeters in any direction — can block or puncture an animal’s organs or cause lethal torsion in the digestive tract, also known as torsion.
But understanding the relationship between ingestion of these large plastics and animal deaths has long been a challenge. In an effort to investigate this connection, our team at the nonprofit Ocean Conservancy collaborated with experts from the University of Toronto, the Federal University of Alagoas, and the University of Tasmania to answer a seemingly simple question: How much ingested plastic is too much?
This question led us to undertake an ambitious effort to compile more than 10,000 animal autopsies—called necropsies—in which both the cause of death and data on plastic ingestion were known. These necropsies had been reported in peer-reviewed literature, in stranding network databases (collections of information on stranded marine fauna), and in two original data sets.
What we found
Our data set included 31 species of mammals, 57 species of seabirds, and all seven species of sea turtles. We then modeled the relationship between plastics in the digestive tract and the probability of death for each group, looking at both the total number of plastic pieces and the volume of the plastics.
Our findings are alarming.
First, we found that plastic consumption was common among all types of animals: almost half of sea turtles, more than a third of seabirds and one in eight marine mammals had plastic in their stomachs. In the case of sea turtles that ingested plastic, approximately five percent died directly as a result, a worrying figure considering that five of the seven sea turtle species are already endangered.
Second, we found that the lethal dose was much smaller than we had initially assumed, especially for small seabirds.
For example, if an Atlantic puffin consumes plastic the size of three sugar cubes, it has a 90 percent chance of dying.
Also read: 80% of marine litter is plastic, especially bags and bottles
A loggerhead sea turtle that ingests a little more than two plastic baseballs has the same chance. And for a harbor porpoise, consuming the equivalent of a plastic soccer ball is fatal 90 percent of the time.
Third, we discovered that not all plastics cause the same damage. When modeling lethal ingestion thresholds, we looked at both the number of plastic pieces and the volume of plastic, and found that the type of plastic is actually very important, as each type affects the gastrointestinal tract differently.
For seabirds, rubber materials such as balloons were the most lethal; consuming just six pea-sized fragments could be fatal. For marine mammals, lost fishing gear — also known as ghost gear — posed the biggest risk: Just 28 tennis ball-sized pieces could kill a sperm whale.
Almost half of the individual animals in our data set that had ingested plastics were on the International Union for Conservation of Nature’s red list, that is, endangered, vulnerable, threatened or critically endangered.
Protect marine life from plastics
The most effective way to protect marine wildlife is to reduce the amount of plastic that enters the ocean in the first place. By identifying which plastics are the most deadly to key ocean species, we can help guide specific actions, such as banning some of the most dangerous items, such as balloons, fishing lines and plastic bags.
Last year, Florida banned the intentional release of balloons, which has important implications for the protection of seabirds and manatees, which were also highly represented in our data set.
The research also demonstrates the potentially significant impact of removing plastics from coastlines, waterways and the ocean through cleanups and other removal efforts.
By modeling lethal doses, making our data open access for anyone to search, and generating this new framework to guide risk assessment efforts, we hope our findings will inform the continued development and implementation of solutions that protect vulnerable ocean species from the dangers of marine plastics.
About the authors:
Britta Baechler is Associate Professor, Department of Physical and Environmental Sciences, University of Toronto; Erin Murphy is Associate Professor, Center for the Study of Biodiversity Outcomes, Arizona State University.
This text was originally published on The Conversation.
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