Soil bugs munch on plastics

Friday, July 27th, 2018

ETH ZURICH

Plastics...soils... what does one have to do with the other? It has been widely publicized that plastic waste is one of the most pressing issues facing our environment. Misinformation about recycling, littering and numerous other misdeeds have resulted in an insurmountable problem with plastic wastes becoming so large that they have created a "plastic-island" in the Pacific Ocean and are washing up on beaches throughout the Caribbean. However, science has found what may be part of a solution to our problem with "soil-bugs" or microbes that can digest plastic! Learn more about this fantastic discovery in this excerpt by Eurekalert!

Our world is drowning in a flood of plastic. Eight million tons of plastic end up in the oceans every year. Agricultural soils are also threatened by plastic pollution. Farmers around the world apply enormous amounts of polyethylene (PE) mulch films onto soils to combat weeds, increase soil temperature and keep the soil moist, thereby increasing overall crop yields.

After harvest, it often is impossible for farmers to re-collect the entire films, particularly when films are only a few micrometers thin. Film debris then makes its way into the soil and accumulates in the soil over time, because PE does not biodegrade. Film residues in soils decrease soil fertility, interfere with water transport and diminish crop growth.

Soil microbes mineralise films composed of alternative polymer

Researchers at ETH Zurich and the Swiss Federal Institute of Aquatic Science and Technology (Eawag) have now shown in an interdisciplinary study that there is reason to be hopeful. In their recent study, they demonstrate that soil microbes degrade films composed of the alternative polymer poly(butylene adipate-co-terephthalate) (PBAT). Their work has just been published in the journal Science Advances.

In the research project coordinated by Michael Sander, Kristopher McNeill and Hans-Peter Kohler, former ETH doctoral student Michael Zumstein succeeded in demonstrating that soil microorganisms metabolically utilised the carbon in the PBAT polymer both for energy production and also to build up microbial biomass.

"This research directly demonstrates, for the first time, that soil microorganisms mineralise PBAT films in soils and transfer carbon from the polymer into their biomass," says Michael Sander, Senior Scientist in the Environmental Chemistry Group in the Department of Environmental Systems Science at ETH Zurich.

Like PE, PBAT is a petroleum-based polymer that is used to make various products, including mulch films. Because PBAT was already classified as biodegradable in compost, the ETH and Eawag researchers aimed at assessing whether PBAT also biodegrades in agricultural soils. By comparison, PE does not biodegrade in compost or in soil.

Find out more about soil microbes and the ways that they are working in our environment here.