The unavoidable presence of hazardous PAHs in biochar is a matter of concern due to possible health and ecological risks associated to its application in soils. Besides the direct effect of increased environmental PAH concentrations resulting from its use, a variety of indirect and ancillary factors may affect the behavior of biochar amended soils as a sink or source of PAHs. Understanding the impact of biochar on soil quality needs a considerable effort from laboratory and field studies. This contribution reports on the levels of PAHs in a cultivated soil one year after the addition of biochar. Biochar, deriving from slow pyrolysis of pruning orchard, was superficially distributed in the inter-row space of a vineyard at a rate of 22 t ha-1 in 2009 following a randomized block layout with 5 replicates and incorporated into the soil with a chisel plow tiller in the 0-30 cm depth. Soil is a sandy clay loam with sub-acid pH (5.4). Two soil sampling campaigns were made in August and December 2010. An analytical procedure targeted to the determination of PAHs in both biochar and soil matrices was recently developed [1]. Briefly, samples were spiked with surrogate PAHs, then PAHs were soxhlet extracted for 36 hours with an acetone/cyclohexane 1:1 mixture, purified by silica gel solid phase extraction (SPE) and analysed by GC-MS(SIM). The method was validated with the certified reference soil CRM (ERM-CC013a). All the US EPA PAHs were detected in the utilised biochar and summed up to 3.5 µg g-1, with naphthalene as the most abundant species followed by phenanthrene. The untreated soil samples exhibited total PAH concentrations two orders of magnitude lower than that of biochar and with a different distribution pattern characterised by higher abundance of phenanthrene and fluorene. After almost one year following biochar application, the total mean concentration values of PAHs in amended soils resulted higher than those of the untreated soils, both in August (52 vs. 31 ng g-1) and December (35 vs. 27 ng g-1). However, the differences were not statistically significant due to the high dispersion of PAH values between samples withdrawn from the same parcel (n = 5). The lower concentrations observed in winter for the treated soils suggest a seasonal variability superimposed to sampling heterogeneity. These preliminary results suggest that the soil contamination by PAHs following biochar application is not significant at the application rates currently recommended in agriculture (20–60 t ha-1) and the PAH load typically found in biochar from slow pyrolysis [1]. The long term persistence of PAHs and their potential to be bioaccumulated is under investigation. [1] D. Fabbri, A.G. Rombolà, C. Torri, K. A. Spokas, J.Anal.Applied Pyrol., 2012), http://dx.doi.org/10.1016/j.jaap.2012.10.003.
Determination of polycyclic aromatic hydrocarbons (PAHs) in an agricultural soil treated with biochar
ROMBOLA', ALESSANDRO GIROLAMO;FABBRI, DANIELE;TORRI, CRISTIAN;
2013
Abstract
The unavoidable presence of hazardous PAHs in biochar is a matter of concern due to possible health and ecological risks associated to its application in soils. Besides the direct effect of increased environmental PAH concentrations resulting from its use, a variety of indirect and ancillary factors may affect the behavior of biochar amended soils as a sink or source of PAHs. Understanding the impact of biochar on soil quality needs a considerable effort from laboratory and field studies. This contribution reports on the levels of PAHs in a cultivated soil one year after the addition of biochar. Biochar, deriving from slow pyrolysis of pruning orchard, was superficially distributed in the inter-row space of a vineyard at a rate of 22 t ha-1 in 2009 following a randomized block layout with 5 replicates and incorporated into the soil with a chisel plow tiller in the 0-30 cm depth. Soil is a sandy clay loam with sub-acid pH (5.4). Two soil sampling campaigns were made in August and December 2010. An analytical procedure targeted to the determination of PAHs in both biochar and soil matrices was recently developed [1]. Briefly, samples were spiked with surrogate PAHs, then PAHs were soxhlet extracted for 36 hours with an acetone/cyclohexane 1:1 mixture, purified by silica gel solid phase extraction (SPE) and analysed by GC-MS(SIM). The method was validated with the certified reference soil CRM (ERM-CC013a). All the US EPA PAHs were detected in the utilised biochar and summed up to 3.5 µg g-1, with naphthalene as the most abundant species followed by phenanthrene. The untreated soil samples exhibited total PAH concentrations two orders of magnitude lower than that of biochar and with a different distribution pattern characterised by higher abundance of phenanthrene and fluorene. After almost one year following biochar application, the total mean concentration values of PAHs in amended soils resulted higher than those of the untreated soils, both in August (52 vs. 31 ng g-1) and December (35 vs. 27 ng g-1). However, the differences were not statistically significant due to the high dispersion of PAH values between samples withdrawn from the same parcel (n = 5). The lower concentrations observed in winter for the treated soils suggest a seasonal variability superimposed to sampling heterogeneity. These preliminary results suggest that the soil contamination by PAHs following biochar application is not significant at the application rates currently recommended in agriculture (20–60 t ha-1) and the PAH load typically found in biochar from slow pyrolysis [1]. The long term persistence of PAHs and their potential to be bioaccumulated is under investigation. [1] D. Fabbri, A.G. Rombolà, C. Torri, K. A. Spokas, J.Anal.Applied Pyrol., 2012), http://dx.doi.org/10.1016/j.jaap.2012.10.003.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
