Conazole Fungicides and Biochar in the Soil Environment

The charred, coal-like residues of organic matter from incineration under oxygen-limited conditions (pyrolysis) are commonly found in soils and sediments as a result of forest or crop fires, crop flaring, or atmospheric deposition of soot. They possess a strong attraction especially to poorly water- soluble organic chemicals, which can become strongly sorbed to these particles over time. On the other hand, the industrial production of similar materials, referred to as biochars (BC), from a variety of feedstocks (including organic waste materials and sewage sludge) and their large-scale application to arable soils has been suggested to improve soil fertility, crop yield and contribute to carbon sequestration as a climate benefit. However, the affinity of pesticides to BC-particles has been observed to substantially reduce the effect of pest control, resulting in overapplication to prevent crop loss. On the other hand, BC may help to reduce risks from long-term soil pllution, including residues of pesticides. The interactions between soils, biochars and agrochemicals determining the fate of selected pesticides, the conazole fungicides tebuconazole and epoxiconazole, and the effects on soil organisms (microbes, earthworms and plants), is investigated in the present project. Both a large number of arable soils from AT and CZ and biochars (each >70), and their mixtures under exposure to weathering conditions are tested to obtain a statistical connection between fungicide sorption and the molecular and structural properties of the sorbents, and their change over time when exposed to air and humidity (weathering). Characterization methods include infrared spectroscopy, sorption/desorption tests, mineral oxide chemistry, scanning electron microscopy, crystallography, and the investigation of the growth of selected fungi, bioavailability of CFs to plants and earthworms. The overall hypothesis is that molecular interactions between soil, BC and fungicides manifest themselves on fungicide transfer to soil biota and plants. In more detail: (i) the prediction of conazole fungicide sorption/desorption based on biochar and soil properties, or pyrolysis conditions, is possible, (ii) soil oxides and hydroxides cover BC sorption sites over time, thus reducing BC sorption capacity, (iii) fungal producers of specific, highly reactive enzymes are able to transform the recalcitrant BC fraction, (iv) fungicide bioavailability to earthworms and plants is reduced by BC. These mechanisms have not been investigated before to this extent. The high number of soils and BCs allow for a reliable characterization of the involved processes. Moreover, little data is available on the stability of BC in soils. The understanding of the effects related to changes of pesticide fate, behaviour and bioavailability in soils treated with BC is a prerequisite for its potentially beneficial environmental application. 1

The charred, coal-like residues of organic matter from incineration under oxygen-limited conditions (pyrolysis) are commonly found in soils and sediments as a result of forest or crop fires, crop flaring, or atmospheric deposition of soot. They possess a strong attraction especially to poorly water-soluble organic chemicals, which can become strongly sorbed to these particles over time. On the other hand, the industrial production of similar materials, referred to as biochars, from a variety of feedstocks (including organic waste materials and sewage sludge) and their large-scale application to arable soils has been suggested to improve soil fertility, crop yield and contribute to carbon sequestration as a climate benefit. However, the affinity of pesticides to biochar particles has been observed to substantially reduce the effect of pest control, resulting in overapplication to prevent crop loss. On the other hand, biochar may help to reduce risks from long-term soil pollution, including residues of pesticides. The interactions between soils, biochars and agrochemicals determining the fate of selected pesticides and the effects on soil organisms (microbes, earthworms and plants), was investigated in the present project. Both a large number of arable soils and biochars, and their mixtures under exposure to weathering conditions were tested to obtain a statistical connection between fungicide sorption and the molecular and structural properties of the sorbents, and their change over time when exposed to air and humidity ("weathering"). The overall hypothesis was that molecular interactions between soil, biochar and fungicides manifest themselves on fungicide transfer to soil biota and plants. These mechanisms have not been investigated before to this extent. Moreover, little data is available on the stability of biochar in soils. The understanding of the effects related to changes of pesticide fate, behaviour and bioavailability in soils treated with biochar is a prerequisite for its potentially beneficial environmental application.