Impact of two contrasting biochars on the bioaccessibility of ¹⁴C-naphthalene in soil

This study investigated the impact of two different wood biochars (BioC1 and BioC2) on the extractability and biodegradation of ¹⁴C-naphthalene in soil. Both biochars had contrasting properties due to difference in feedstocks and pyrolytic conditions (450–500 °C and 900–1000 °C, designated as BioC1 and BioC2, respectively). This study investigated effects of biochar on the relationship between ¹⁴C-naphthalene mineralisation and calcium chloride (CaCl₂), hydroxypropyl- β-cyclodextrin (HPCD) or methanol extraction in soil amended with 0%, 0.1%, 0.5% and 1% BioC1 and BioC2 after 1, 18, 36 and 72 d contact times. Total extents of ¹⁴C-naphthalene mineralisation and extraction were reduced with increasing concentrations of biochar; however, BioC2 showed greater sorptive capacity. Good linear correlation existed between total extents of ¹⁴C-naphthalene mineralisation and HPCD extractions in BioC1 (slope=0.86, r²=0.92) and BioC2 (slope=0.86, r²=0.94) amended soils. However CaCl₂ and methanol extractions underestimated and overestimated extents of mineralisation, respectively. These results indicate that biochar can reduce the bioaccessibility of PAHs and the corresponding risk of exposure to biota, whilst HPCD extraction estimated the bioaccessible fraction of PAHs in soil. Bioaccessibility assessment is vital in evaluation of biodegradation potential and suitability of bioremediation as a remediation option.