The influence of sunlight and oxidative treatment on measured PAH concentrations in biochar
2015
Khalid, Fathima N. M. | Klarup, Doug
The concentration changes of 18 different polycyclic aromatic hydrocarbons (PAHs) in two different biochars were assessed after (1) chemical oxidative treatment with a solution of H₂O₂ and Na₂S₂O₈, (2) exposure to sunlight with intermittent wetting, and (3) exposure to sunlight with intermittent wetting after mixing in ZnO and Na₂S₂O₈. Chemical oxidative treatment of biochars derived from gasified wood biochar and a gasified wood/Arundo donax mixture led to decreases in six-ring PAHs, but overall significant increases in measured PAH concentration sums for both biochars (from 225 ± 7 to 312 ± 18 μg g⁻¹ for wood-derived and 165 ± 3 to 244 ± 7 μg g⁻¹ for mixture-derived). Sunlight exposure of the mixture-derived biochar led to increases in some three- and four-ring PAHs, but overall decreases in summed PAH concentrations (165 ± 3 to 60 ± 1 μg g⁻¹ with wetting only and 165 ± 3 to 41 ± 4 μg g⁻¹ when Na₂S₂O₈ and ZnO were included). The mass losses in the sunlight-exposed samples primarily were due to losses of low molar mass (two-ring) PAHs, though high molar mass (five- and six-ring) PAH concentrations also decreased. This result implies sun and rain exposure to biochar, prior to agricultural application, will help reduce potential PAH soil contamination from the biochar.
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