© 2015 Gregory et al. We examined the effect of biochar on the water-soluble arsenic (As) concentration and the extent of organochlorine degradation in a co-contaminated historic sheep-dip soil during a 180-d glasshouse incubation experiment. Soil microbial activity, bacterial community and structure diversity were also investigated. Biochar made from willow feedstock (Salix sp) was pyrolysed at 350 or 550°C and added to soil at rates of 10 g kg < sup > -1 < /sup > and 20 g kg < sup > -1 < /sup > (representing 30 t ha-1 and 60 t ha < sup > -1 < /sup > ). The isomers of hexachlorocyclohexane (HCH) alpha-HCH and gamma-HCH (lindane), underwent 10-fold and 4-fold reductions in concentration as a function of biochar treatment. Biochar also resulted in a significant reduction in soil DDT levels (P < 0.01), and increased the DDE:DDT ratio. Soil microbial activity was significantly increased (P < 0.01) under all biochar treatments after 60 days of treatment compared to the control. 16S amplicon sequencing revealed that biochar-amended soil contained more members of the Chryseobacterium, Flavobacterium, Dyadobacter and Pseudomonadaceae which are known bioremediators of hydrocarbons. We hypothesise that a recorded shortterm reduction in the soluble As concentration due to biochar amendment allowed native soil microbial communities to overcome As-related stress. We propose that increased microbiological activity (dehydrogenase activity) due to biochar amendment was responsible for enhanced degradation of organochlorines in the soil. Biochar therefore partially overcame the co-contaminant effect of As, allowing for enhanced natural attenuation of organochlorines in soil.
Gregory, S. J., Anderson, C. W. N., Camps-Arbestain, M., Biggs, P. J., Ganley, A. R. D., O’Sullivan, J. M., & McManus, M. T. (2015). Biochar in co-contaminated soil manipulates arsenic solubility and microbiological community structure, and promotes organochlorine degradation. PLoS ONE, 10(4). https://doi.org/10.1371/journal.pone.0125393