Direct evidence of biodegradation of polymers in agricultural soil
Scientists studying a polyester called PBAT widely used in agriculture have demonstrated its biodegradation in soil – a process that has been suspected to occur, though not conclusively proven, they say. According to the authors, their study suggests that polyesters like PBAT could be a practical solution to alleviate detrimental plastic accumulation in the environment. The widespread entry of plastics into the environment has generated profound discussion and debate. An example of "plasticulture," or the practice of relying on plastic-based materials in agriculture, is the use of mulch films, which are placed on agricultural fields to improve soil conditions. The majority of mulch films are composed of nonbiodegradable plastics and removed improperly after use, posing a threat to the environment. Mulch films made of polymers that biodegrade in soil are an alternative solution, and researchers have suggested that PBAT could be biodegradable based on changes in mass loss and physical-chemical characteristics it exhibits. However, direct evidence of true PBAT biodegradation – including mineralization of PBAT carbon to carbon dioxide (CO2) , or evidence of soil microorganisms incorporating PBAT carbon into their biomass -has not been achieved in agricultural soil, the authors say. Here, Michael Thomas Zumstein and colleagues labelled stable carbon isotopes in three variants of PBAT to demonstrate biodegradation of PBAT in agricultural soil. After soil incubation for six weeks, they used isotope-selective nanoscale secondary ion mass spectrometry (NanoSIMS); they found that soil incubation of all PBAT variants resulted in 13CO2 formation. This, say the authors, confirms that soil microorganisms used carbon from all three forms of PBAT to gain energy. According to Zumstein et al., future work should aim to assess variations in the rate of PBAT mineralization in different agricultural soils over a longer period of time.