Location: Soil and Water Management ResearchTitle: Determination of polycyclic aromatic hydrocarbons in biochar and biochar amended soil Author
Submitted to: Journal of Analytical & Applied Pyrolysis
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/1/2012
Publication Date: 9/1/2013
Publication URL: http://handle.nal.usda.gov/10113/57850
Citation: Fabbri, D., Rombola, A.G., Torri, C., Spokas, K.A. 2013. Determination of polycyclic aromatic hydrocarbons in biochar and biochar amended soil. Journal of Analytical & Applied Pyrolysis. 103(2013):60-67. Interpretive Summary: A potential abatement strategy to increasing atmospheric levels of carbon dioxide (CO2) is to sequester atmospheric CO2 into a more stable form through the use of pyrolysis. Biomass feed stocks are used to generate a more stable carbon form (biochar) that is returned to the soil sequestering atmospheric carbon into a slower cycling pool, resulting in alterations in plant growth/yield and microbial soil processes. However, the mechanisms behind the “biochar effect” have not been fully elucidated. In the present work, we have developed an analytical method for the evaluation of sorbed polycyclic aromatic hydrocarbons (PAH), specifically in regards to the analyses of biochar and biochar + soil combinations. We have optimized, the solvent used and extraction time, with the analysis being conducted by GC-MS. The sum of the USEPA PAH compounds sorbed to biochar ranged from 1.2 to 19 µg g-1, as a function of pyrolysis technique, temperature, and feedstocks. These findings could provide additional insight and direction in the evaluation of biochar prior to the soil application. These results are significant to farmers and policy makers and will assist scientists and engineers in developing improved biochars based on properties to minimize greenhouse gas implications and improve soil carbon management.
Technical Abstract: A method for the determination of the 16 USEPA polycyclic aromatic hydrocarbons (PAHs) in biochar and soil amended with biochar was developed. Samples were Soxhlet extracted with acetone:cyclohexane 1:1, and PAHs were analysed by GC-MS after silica gel clean-up. In a comparative study based on reflux extraction, the solvent system acetone/cyclohexane exhibited a higher extraction efficiency of low molecular weight (LMW) PAHs (e.g. naphthalene) than toluene or dichloromethane. The method was applied to a reference biochar utilized in field experiments provided recovery of deuterated PAHs (acenaphthene, phenenthrene, chrysene) in the 67-88%, precision (as assessed by relative standard deviations) between 8-18%, and limit of detection (LOD) in the 0.08-0.3 ng g-1 ranges. The method was successfully validated through the analysis of a certified soil material, and was capable to quantify PAHs once the biochar was embedded into the soil at 1% level. The concentration of the 16 USEPA-PAHs along with the 15 EU-PAHs (priority hazardous substances in food) was determined in a suite of currently available biochars for agricultural field applications deriving from the pyrolysis of different feedstock under different conditions. The total levels ranged in the 1.2 to 19 µg g-1 and 0.2-5 µg g-1 interval for USEPA and EU PAHs, respectively, while benzo[a]pyrene ranged between 0.01 and 0.16 µg g-1. Considering a typical application of 20-60 t biochar ha-1, the degree of PAHs contamination will be dependent on the presence of background PAHs in soil and the sorbed concentrations of PAHs in the biochar. Our data, along with PAH levels determined in other studies, suggest that biochars produced by slow pyrolysis from woody biomass possess the lowest level of sorbed PAHs (< 10 µg g-1).