The use of polymers in agricultural applications has resulted in their widespread accumulation in agricultural soils. A viable strategy to overcome this accumulation is to replace non-degradable polymers in agricultural applications with polymers designed to biodegrade in soils under formation of carbon dioxide (CO2) and microbial biomass. Promising biodegradable polymers include aliphatic and aliphatic-aromatic polyesters previously shown to biodegrade in compost. However, biodegradation of these polyesters in agricultural soils is poorly studied and understood, reflecting the lack of appropriate analytical approaches. Here, we present a novel analytical work-flow based on incubating 13C-labeled polyesters in soils that allows for (i) monitoring mineralization of polyester carbon by quantifying formed 13CO2 using isotope-sensitive cavity ring-down spectroscopy, (ii) quantifying the amount of remnant polyesters at the end of the incubations by analyzing solvent extracts from soils using proton nuclear magnetic resonance spectroscopy (iii) determining the total amount of added 13C that remains in the soils by combusting soil aliquots and analyzing the formed 13CO2 using isotope-ratio mass spectrometry. We validated this work-flow by incubating 13C-labeled poly(butylene succinate) (PBS) in an agricultural soil. Over 425 days of incubation, 65 ± 1% of the added PBS-13C was mineralized to 13CO2 and 34 ± 2% of the added PBS-13C remained in the soils. The mass balance on added PBS carbon was therefore closed. Most of the PBS-13C remaining in the soil was present as extractable PBS. This finding and the results from kinetic biodegradation modeling of the experimental data pointed at soil-dependent factors, possibly limited nutrient availability, controlling biodegradation rates. The workflow introduced herein will help assess the importance of both polymer- and soil-dependent factors in controlling rates and extents of polymer biodegradation in soils.

Using stable carbon isotope labeling to study the biodegradation of synthetic polymers in agricultural soils

2019 Spring National Meeting

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