University of Bayreuth researchers find plastics biodegrading in soil boost CO2 emissions

In Germany, biodegradable microplastic particles in soils can lead to an increased rise in CO₂ emissions to the Earth’s atmosphere. This is shown by an interdisciplinary study published in “Applied Soil Ecology” by the Collaborative Research Centre 1357 “Microplastics” at the University of Bayreuth. In this study, experts in soil ecology and ecological microbiology compare the effects of a conventional and a biodegradable plastic in different soils in a systematic way for the first time. The consequences for the microbial biomass in the soils, especially on bacteria and fungi, are also analyzed.

The Bayreuth scientists selected two plastics for their study: LDPE (low-density polyethylene) is a conventional, non-biodegradable plastic that has been used in the chemical industry for decades. PBAT (polybutylene adipate terephthalate), on the other hand, is a biodegradable plastic that is used, for example, for food packaging, organic waste bags and mulch films. Particles from three different size ranges (50 to 200 micrometers, 200 to 500 micrometers and 0.63 to 1.2 millimeters) were added in varying concentrations to a sandy loam soil on the one hand and a loamy soil on the other. Over a period of four weeks, the scientists measured the amounts of CO₂ released from the soils.

No impact of LDPE on the soil’s CO₂ emissions was identified during the course of the research. In contrast, the effects of PBAT are significant. “The smaller the biodegradable microplastic particles are and the higher their concentration in the soil, the more CO₂ escapes from the soil into the earth’s atmosphere. We observed increases in CO₂ emissions of 13 to 57 percent, depending on the size of the particles, their concentration in the soil and the soil properties. Sandy loam soils released more CO₂ than pure loam soils,” the lead researcher said.

As the Bayreuth research team found out, the increase in CO₂ emissions goes hand in hand with the increase in microbial biomass: If small, biodegradable PBAT particles enter the soil in high concentrations, the amount of bacteria and fungi, which make up the majority of the microbial biomass here, increases. The biological composition of the biomass may also change in the process.