Assessment of total and available polycyclic aromatic hydrocarbons In biochars

Póster presentado en el la XVI Reunión Científica de la Sociedad Española de Cromatografía y Técnicas Afines (SECyTA2016) P‐ENV‐2Eds: González-Pérez, José Antonio.-- Almendros Martín, Gonzalo.-- González-Vila, Francisco Javier.-- Rosa Arranz, José M. de laBiochar may act as a soil conditioner, enhancing plant growth by supplying and retaining nutrients and by providing other services such as improving soil physical and biological properties. Different feedstock, such as organic waste derived from agriculture and forestry or urban wastes including sewage sludge, can be used for biochar production. Feedstock properties and production conditions will drive the properties and composition of produced biochars [1]. Special attention should be paid to polycyclic aromatic hydrocarbons (PAHs), these persistent organic pollutants are highly condensed aromatic structures formed during biochar production due to incomplete combustion (pyrolysis step) [2]. These PAHs may enter the environment when the biochar is applied as soil conditioner, thus the intention of this study was to test a potential hazardous impact due to the presence of PAHs in biochars. Two different PAHs extraction techniques were applied to evaluate the total and available PAHs content in biochars. In order to find a relationship between pyrolysis conditions, feedstock and abundance of PAHs, four biochars produced from different feedstock were analyzed. Three biochars were produced by technical pyrolysis (500‐600 ºC; 20 min) from wood, paper sludge and sewage sludge respectively (samples B1, B2 and B3). The fourth biochar was made from old grapevine wood provided by Bodegas Torres Company (Spain) and using the traditional carbonization method in kilns (kiln‐stack wood biochar; B4). A detailed characterization of these samples can be found in [3]. Exhaustive extraction: The total concentrations of the 16 US EPA PAHs were determined by extracting the biochars during 12h under continuum reflux with 100% toluene. Analysis of PAHs was carried out on an Agilent GC/MS 6890/5973i by on‐column injection of 1 μL of the extract. Chromatographic and mass spectrometric conditions applied are described in [1]. Non‐Exhaustive extraction: Cyclodextrins (CDs) have been proposed as alternative agents to enhance the water solubility of hydrophobic compounds. CDs have a low‐polarity cavity within which organic compounds of the appropriate shape and size can form inclusion complexes [4]. The selected CD was hydroxypropyl‐β‐CD (HPBCD), which has been widely used for this purpose in contaminated soils. ild extractions were performed using an 50 mM HPBCD solution as extractant containing 0.01 M Ca(NO3)2 as background electrolyte and 200 mg L−1 HgCl2 to prevent bacterial growth. Biochar samples (2 g) were placed in glass tubes containing 20 mL of extractant, and the tubes were placed on an orbital shaker at 100 rpm during 24 hours. Total PAHs yielded between 3167 (B3) and 6626 (B4) μg kg‐1. The PAHs concentration of B4 was a 50% higher than B1. Taking into account that both biochars (B1 and B4) are produced from wood, it can be concluded that the pyrolysis process of B4, which was produced by carbonization in traditional kilns, affected significantly the total PAHs levels. The non‐exhaustive extraction procedure resulted in closer abundances of PAHs, which ranged from 978 (B3) to 1585 (B1) μgkg‐1. These data pointed that c. 15‐35% of total PAHs present in biochars are extracted by CDs, and this amount could be considered as the fraction actually bioavailable. This parameter shoud be taken into account to determine the potential hazardous impact of the use of biochar as soil amendment.[1] J.M. De la Rosa et al., J. Soils and Sediments 16 (2016) 557‐565. [2] T. Bucheli et al. (eds) Biochar for Environmental Management (2nded.), Earthscan, London, UK. (2015) [3] J.M. De la Rosa et al., Science of the Total Environment 499 (2014) 175‐184 [4] H. Dodziuk, Cyclodextrins and Their Complexes: Chemistry, Analytical Methods and Applications. Wiley‐VCH Gmbh & Co. KGaA, Weinheim (2006)N