Unquestionably, plastic pollution is a global scourge. Thanks to an over-reliance and overuse of single-use plastics, a poor recycling infrastructure, not enough industry or governmental momentum into switching over to something more sustainable and, perhaps, an imprecise understanding of how to handle the problem, the oceans are home to hardy plastics, from the macro to the micro.
It’s unclear at present what effect microplastics are having on marine life – and us, seeing as we often eat marine life – but it’s quite clear to see what happens when wildlife suspects larger pieces are made of food and tries to eat them. A heartbreaking new paper in Scientific Reports attempted to quantify how deadly plastic ingestion like this is for sea turtles, and they found that all it takes sometimes is one single piece.
Making such a calculation is a grim and difficult endeavor. Each sea turtle will be different from the last, with some able to handle more plastic than others. The amount that each sea turtle ingests will also vary wildly depending on the availability of plastic in the area.
In order to get the best estimate they could, two datasets were considered: one featuring necropsies of 246 sea turtles, and another featuring 706 of them included in a national strandings database. This revealed that, on average, a juvenile sea turtle that has eaten 14 pieces of visible plastic has a 50 percent chance of dying as a result.
The study, led by the Commonwealth Scientific and Industrial Research Organization (CSIRO) and the University of the Sunshine Coast, points out early on that sea turtles were among the first organisms observed to be eating plastic. One paper, dating back to 1982, describes how plastic bags were found in the intestinal tracts of leatherback marine turtles.
Indeed, the plastic pollution problems has been known about for at least half a century, but despite this, it’s only got far worse. We know that there’s a lot more plastic in the ocean than ever before, and we know animals eat it, but specific details about how much is being eaten and what effects this has on wildlife has proved harder to pin down.
It’s not easy to tell whether plastic is being ingested by such creatures intentionally or accidentally. There’s some evidence suggesting that plastic that physically resembles turtle’s food is taken up at a higher rate, but either way, it can cause a range of issues. Sometimes, it’s just excreted harmlessly, but in many others, the turtles’ guts are perforated to lethal effect.
This study marks the first time a numeric relationship between plastic ingestion and lethality has been made. It seems that, if 226 plastic items are consumed, death is certain.
Their results also confirm that eating a low number of plastic pieces may not kill many sea turtles, but it still can kill some through gut impacts or perforations. It could only take one single piece for a sea turtle to perish. In fact, the team places such odds of mortality for a sole segment of plastic being ingested at 22 percent.
Sea turtles are particularly vulnerable to this cause of death. They have a complicated gastro-intestinal tract that allows plastic to get trapped in its nooks and crannies more easily, and they are also unable to regurgitate, meaning that what goes into their throats stays in their throats.
Fortunately, this model has quite broad applications, and its technique could at least be applied to other wildlife. Around 700 species, from seabirds to fish, interact with a wide range of our trash in some way or another. This study, then, provides a starting point to calculate just how deadly some of those interactions are.