Somewhat eerily, plastic waste pollution is affecting the environment in far more ways than expected, a new study shows.
Over the last 70 years or so, plastic waste has become a ubiquitous presence. It is found everywhere on earth, invading ecosystems on land, in freshwaters, and in the ocean.
Now, apparently, these ecosystems are adapting and developing enzymes that can degrade plastics.
Scientists at Sweden's Chalmers University of Technology say they have found "multiple lines of evidence" that the number of such enzymes is on the rise, correlataing with increasing rates of plastic pollution.
They said the past decades have provided sufficient time, from an evolutionary standpoint, for various microbes to respond to plastic compounds.
The researchers recently published their findings in the scientific journal mBIO.
They analysed samples of environmental DNA from hundreds of locations around the world, using computer models to search for microbial enzymes with plastic-degrading potential, which was then cross-referenced with the official numbers for plastic waste pollution across countries and oceans.
They said they found strong correlation between the global microbiome's plastic-degrading potential and measurements of plastic pollution – "a significant demonstration of how the environment is responding to the pressures we are placing on it," said Aleksej Zelezniak, associate professor in systems biology at Chalmers.
In other words, the quantity and diversity of plastic-degrading enzymes is increasing, in direct response to local levels of plastic pollution.
The variation found between the land and ocean samples both in number and type of plastic particles, as well as plastic-degrading enzymes, was striking, researchers said.
The samples taked from land, for example, contained relatively high levels of phthalate-based plastic additive compounds. These compounds are known to be particularly susceptible to leaking during production, disposal, and recycling.
They said this correlated with finding a greater number of enzymes able to degrade these compounds in these land samples, indicating a connection between the two.
Something similar turned up in the ocean samples: the greater the depth, the higher the quantity of plastic-degrading enzymes in a sample.
The dataset looked at 67 locations from 8 oceans, at 3 different depths, and researchers said this was a consistent finding, indicating a connection with the higher level of microplastics that have been repeatedly observed at deeper levels in the ocean.
"Currently, very little is known about these plastic-degrading enzymes, and we did not expect to find such a large number of them across so many different microbes and environmental habitats," said Jan Zrimec, one of the authors and a researcher at the National Institute of Biology in Slovenia. "This is a surprising discovery that really illustrates the scale of the issue."
Even more notable: nearly 60 percent of the identified plastic-degrading enzymes did not map to any known enzyme classes, suggesting that the team had uncovered novel plastic-degrading enzymes.
The researchers believe that their results could potentially be used to discover and adapt enzymes for novel recycling processes.
"The next step would be to test the most promising enzyme candidates in the lab to closely investigate their properties and the rate of plastic degradation they can achieve. From there you could engineer microbial communities with targeted degrading functions for specific polymer types," said Zelezniak.