Degradation or stabilisation of methanol, glutamic acid and glucose by photochemical reactions

The most important resource after water is soil. It consists of weathered rocks and minerals and soil organic matter (SOM) derived from the degradation of plants. SOM has numerous positive functions and interacts with mineral particles forming associations that are important for soil physical, chemical and biological properties. SOM is the most important factor for the maintenance of soil fertility. Studies have shown that many areas in Europe present great percentages of soil loss and low contents of organic matter. Consequently, an understanding of the processes that mineralise SOM is essential for sustainable management of soils. The loss of SOM is attributed to many factors. For example, deforestation and practices used in cultivation of land can lead to SOM mineralisation by creating favourable conditions of moisture, aeration and temperature, which enhance biological activity. They can also expose protected organic matter to conditions that increase its decomposition. Iron-bearing minerals are ubiquitous in soil. Many studies connect the presence of iron with higher concentrations of SOM. The creation of complexes between SOM and metal ions, like iron, is a process of organic matter stabilisation. It is possible that photochemical reactions that may occur on the surface of iron-bearing minerals, such as haematite and olivine, could play a role in the mineralisation or stabilisation of SOM. Here we report preliminary results from experiments that are being conducted on the photochemical decomposition of glutamic acid, glucose and methanol on the surfaces of haematite and olivine. The photochemical experiments are carried out in batch vessels. Solutions of each organic in suspensions with a mineral are created and exposed to UV light, with wavelength 365nm. Samples are taken every 24 hours and the concentration of the organics measured with UV-vis spectroscopy. The initial concentration of the organics was 1mM and of the minerals is 20g.L-1. Prior to beginning experimentation each suspension was stirred for approximately 1 hour, under no light, to normalize the adsorption before illumination. Control experiments in the dark, but otherwise under the same conditions, are conducted in parallel. Results indicate that the concentration of the organics in solution decreased after exposure to UV light. We believe that the presence of haematite and olivine promoted degradation of the three organic substances. The results of this study are linked with research into soil degradation and loss of organic matter since iron-bearing minerals in soil interact with organic matter. We propose that iron-bearing minerals may play a role in the degradation of organic matter when exposed to UV light. In the era of climate change and new patterns of cloud cover, SOM may become more vulnerable in the future not only due to temperature rise but also because of less cloud cover and hence increased exposure to UV light.