ReviewA synthesis of parameters related to the binding of neutral organic compounds to charcoal

- Charcoal-water partitioning coefficients (KD values) were compiled from the literature.
- KD values were correlated with charcoal and organic compound properties.
- Production temperature and surface area were most strongly correlated with KD.

The sorption strength of neutral organic compounds to charcoal, also called biochar was reviewed and related to charcoal and compound properties. From 29 studies, 507 individual Freundlich sorption coefficients were compiled that covered the sorption strength of 107 organic contaminants. These sorption coefficients were converted into charcoal-water distribution coefficients (KD) at aqueous concentrations of 1 ng/L, 1 µg/L and 1 mg/L. Reported log KD values at 1 µg/L varied from 0.38 to 8.25 across all data. Variation was also observed within the compound classes; pesticides, herbicides and insecticides, PAHs, phthalates, halogenated organics, small organics, alcohols and PCBs. Five commonly reported variables; charcoal production temperature T, surface area SA, H/C and O/C ratios and organic compound octanol-water partitioning coefficient, were correlated with KD values using single and multiple-parameter linear regressions. The sorption strength of organic compounds to charcoals increased with increasing charcoal production temperature T, charcoal SA and organic pollutant octanol-water partitioning coefficient and decreased with increasing charcoal O/C ratio and charcoal H/C ratio. T was found to be correlated with SA (r2 = 0.66) and O/C (r2 = 0.50), particularly for charcoals produced from wood feedstocks (r2 = 0.73 and 0.80, respectively). The resulting regression: log KD = (0.18 ± 0.06) log Kow + (5.74 ± 1.40) log T + (0.85 ± 0.15) log SA + (1.60 ± 0.29) log OC + (−0.89 ± 0.20) log HC + (−13.20 ± 3.69), r2 = 0.60, root mean squared error = 0.95, n = 151 was obtained for all variables. This information can be used as an initial screening to identify charcoals for contaminated soil and sediment remediation.

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