Assessment of the environmental impact of agar, alginate, and gellan gum carbohydrate gum macro beads biodegradation in a simulated agricultural field system

The necessity to increase crop yields while minimizing adverse environmental impacts, has pushed agricultural practices towards finding new biodegradable materials for various agricultural applications. In this study, three types of carbohydrate beads, prepared of agar, alginate and gellan- gum, were tested for their environmental impact during a soil biodegradation process. To assess this impact the following measurements were taken: (1) soil-respiration (emitted CO2, O2 and CH4) by respirometer, (2) measuring emissions of volatile organic compounds by proton-transfer-reaction-time of flight-mass-spectrometer and (3) residual phytotoxicity in the soil after the degradation process by greenhouse study. The results demonstrate that in a simulation system of soil degradation that lasted 40-days, the alginate macro-beads had the highest respiration rate with ∼217 CO2(mg/g_dw) vs only 40 CO2(mg/g_dw) for agar and none for gellan gum. This study provides evidence for the first time, that a distinctive volatile organic fingerprint cam be detected during the biodegradation process of different carbohydrates (59 m/z for agar, 114, 115 m/z for alginate and 81 m/z for all three). The emission of the volatile organic compounds which dissipated after a week of biodegradation in the soil, suggests that most of the metabolic activity was in the first week. Agar degradation showed a slight residual phytotoxicity affecting the growth of the consecutive crop (disappeared over time). These results can help to establish a future monitoring system for the degradation process of gum-beads that would better estimate the environmental impact and the beads' fate in actual use in soils.