Peer Review #3 of "The effect of biochar amendments on phenanthrene sorption, desorption and mineralisation in different soils (v0.1)"

Abstract

The contamination of soils and waters with organic pollutants, such as polycyclic aromatic hydrocarbons (PAHs), affect a large number of sites worldwide that need remediation. In this context soils amendments can be used to immobilise PAHs while maintaining soil functioning, with biochar being a promising amendment. In this experiment phenantrene (Phe) was used as a frequent PAH contaminating soils and we studied the effect of three biochars at 1% applications to three different substrates, two agricultural topsoils and pure sand. We evaluated the changes in soil properties, sorption-desorption of Phe, and mineralisation of Phe in all treatments. Phe in pure sand was effectively sorbed to olive pruning (OBC) and rice husk (RBC) biochars, but pine biochar (PBC) was not as effective. In the soils, OBC and RBC only increased sorption of Phe in the silty soil. Desorption was affected by biochar application, RBC and OBC decreased water soluble Phe independently of the soil, which may be useful in preventing leaching of Phe into natural waters.Contrastingly, OBC and RBC slightly decreased the mineralisation of Phe in the soils, thus indicating lower bioavailability of the contaminant. Overall, biochar effects in the two tested soils were low, most likely due to the rather high soil organic C (SOC) contents of 2.2 and 2.8% with Koc values in the same range as those of the biochars. However, OBC and RBC additions can substantially increase adsorption of Phe in soils poor in SOC.PeerJ reviewing PDF | Abstract 18 19 The contamination of soils and waters with organic pollutants, such as polycyclic aromatic 20 hydrocarbons (PAHs), affect a large number of sites worldwide that need remediation. In this 21 context soils amendments can be used to immobilise PAHs while maintaining soil functioning, 22 with biochar being a promising amendment. In this experiment phenantrene (Phe) was used as a 23 frequent PAH contaminating soils and we studied the effect of three biochars at 1% applications 24 to three different substrates, two agricultural topsoils and pure sand. We evaluated the changes in 25 soil properties, sorption-desorption of Phe, and mineralisation of Phe in all treatments. Phe in 26 pure sand was effectively sorbed to olive pruning (OBC) and rice husk (RBC) biochars, but pine 27 biochar (PBC) was not as effective. In the soils, OBC and RBC only increased sorption of Phe in 28 the silty soil. Desorption was affected by biochar application, RBC and OBC decreased water 29 soluble Phe independently of the soil, which may be useful in preventing leaching of Phe into 30 natural waters. Contrastingly, OBC and RBC slightly decreased the mineralisation of Phe in the 31 soils, thus indicating lower bioavailability of the contaminant. Overall, biochar effects in the two 32 tested soils were low, most likely due to the rather high soil organic C (SOC) contents of 2.2 and 33 2.8% with Koc values in the same range as those of the biochars. However, OBC and RBC 34 additions can substantially increase adsorption of Phe in soils poor in...