Final Activity Report Summary - BIODESOPO (Mechanisms of the biodegradation in soil of biodegradable polymers designed for agricultural applications)
The recent introduction and use of biodegradable polymers in agriculture suggests that agriculture represents one of the most promising areas for further development and applications of specially engineered biodegradable materials (e.g. agricultural mulching films, low tunnel films, nets etc).
Agricultural materials made from biodegradable polymers, eliminate the need and cost for the mechanical removal, as the biodegradable materials can be ploughed directly into the soil. This can be achieved however, provided that their mechanical and physical performance is comparable to the one of their conventional polyethylene or other polymeric counterparts and they are free of ecotoxicity effects. An additional crucial condition for the successful function of biodegradable agricultural materials concerns the rather complicated biodegradation mechanisms and the biodegradation rate of polymeric material in the soil. Thus, for the biodegradable polymers to be accepted for agricultural applications under variable climatic and soil conditions, it is important to identify and get an in-depth knowledge about the basic mechanisms and the range of factors affecting the biodegradation process of the material in the soil that will support the development of appropriate testing methodologies applicable for various climatic and soil conditions. Such reliable methods for testing biodegradation of polymers in soil do not exist today. If the materials used in agricultural applications do not completely biodegrade in the soil, the soil is contaminated irreversibly with severe negative consequences for the environment and for the food safety produced in those soils.
In the framework of this project, the biodegradation behaviour of selected biodegradable polymers based on renewable resources, mainly polylactic acid (PLA) and polyhydroxyalkanoates (PHA), were investigated in soil environment. Biodegradation in soil experiments were performed simultaneously in simulated laboratory (soil and composting) conditions and under real field conditions in Spata (Attiki, Greece). PLA was investigated in different forms (samples of films of various thickness and fibres), as well as other materials claimed by the producers to be biodegradable, in the form of samples of fibres and nets. Two trials were set up to study the effect of the winter period exposure versus the summer conditions on the biodegradation in soil behaviour of the materials under investigation, i.e. period 11 months, starting from October 2007 till September 2008 and 7 months period, starting from June 2008 till January 2009. Samples were removed periodically and characterised. Simulated laboratory results were found to be in agreement with the results obtained from field experiments.
The two typical biodegradable polymers investigated follow different patterns of biodegradation in soil environment. Degradation of PHAs occurs by enzymic hydrolysis, whereas temperature was shown to be the major factor regulating the biodegradation behaviour of PLA.
The analysis of the basic mechanisms and the range of the factors affecting the biodegradation in-soil process of the selected biodegradable polymer materials is expected to help designing appropriate materials for agricultural applications and predict their longterm behaviour of biodegradation in soil.
Agricultural materials made from biodegradable polymers, eliminate the need and cost for the mechanical removal, as the biodegradable materials can be ploughed directly into the soil. This can be achieved however, provided that their mechanical and physical performance is comparable to the one of their conventional polyethylene or other polymeric counterparts and they are free of ecotoxicity effects. An additional crucial condition for the successful function of biodegradable agricultural materials concerns the rather complicated biodegradation mechanisms and the biodegradation rate of polymeric material in the soil. Thus, for the biodegradable polymers to be accepted for agricultural applications under variable climatic and soil conditions, it is important to identify and get an in-depth knowledge about the basic mechanisms and the range of factors affecting the biodegradation process of the material in the soil that will support the development of appropriate testing methodologies applicable for various climatic and soil conditions. Such reliable methods for testing biodegradation of polymers in soil do not exist today. If the materials used in agricultural applications do not completely biodegrade in the soil, the soil is contaminated irreversibly with severe negative consequences for the environment and for the food safety produced in those soils.
In the framework of this project, the biodegradation behaviour of selected biodegradable polymers based on renewable resources, mainly polylactic acid (PLA) and polyhydroxyalkanoates (PHA), were investigated in soil environment. Biodegradation in soil experiments were performed simultaneously in simulated laboratory (soil and composting) conditions and under real field conditions in Spata (Attiki, Greece). PLA was investigated in different forms (samples of films of various thickness and fibres), as well as other materials claimed by the producers to be biodegradable, in the form of samples of fibres and nets. Two trials were set up to study the effect of the winter period exposure versus the summer conditions on the biodegradation in soil behaviour of the materials under investigation, i.e. period 11 months, starting from October 2007 till September 2008 and 7 months period, starting from June 2008 till January 2009. Samples were removed periodically and characterised. Simulated laboratory results were found to be in agreement with the results obtained from field experiments.
The two typical biodegradable polymers investigated follow different patterns of biodegradation in soil environment. Degradation of PHAs occurs by enzymic hydrolysis, whereas temperature was shown to be the major factor regulating the biodegradation behaviour of PLA.
The analysis of the basic mechanisms and the range of the factors affecting the biodegradation in-soil process of the selected biodegradable polymer materials is expected to help designing appropriate materials for agricultural applications and predict their longterm behaviour of biodegradation in soil.