Overall conclusion

1. Geoffrey Marchal gfm@dmu.dk Geoffrey Marchal1, Kilian E. C. Smith1,Arno Rein2, Anne Winding1, Lis Wollesen de Jonge3, Stefan Trapp2 and Ulrich Gosewinkel Karlson1 Phenanthrene | silicone | Sphingomonas sp. 10-1 (DSM 12247) | desorption | biodegradation | soil amendment Objectives In order to investigate the potential of different soil amendments (activated charcoal (AC), charcoal (biochar), compost) to sorb PAHs and their effect on bioaccessibility and biodegradation of PAHs in soil, a method was developed that can determine simultaneously the changes in PAH dissolved concentrations and their bioaccessibility. Phe desorption from the soil plus amendments Phe mineralization sorbed to the soil plus amendments Objective Objective Compare the abiotic desorption, KOC,and Cfree of Phe from the different soil amendments Study the biodegradation of Phe sorbed to soil amendments by a Phe degrading bacterium comparing to the abiotic desorption A method to simultaneously determining the reduction in PAH dissolved concentrations and bioaccessibility in carbon amended soils Method Method • 14C Phe 5 mg kg-1 • Sphingomonas sp. (DSM 12247) • Specific soil amendment (AC, biochar or • compost) • Agricultural soil • Scintillation glass vial (20 ml) with aluminum cap • Minimal salt solution • Shaking (150 rpm) at room temperature • 14CO2 trap (KOH) • 14C radiolabeled Phe as a model PAC (5 mg kg-1) • Specific soil amendment (AC, biochar or compost) • Agricultural soil • Minimal salt solution (MSM) • Scintillation glass vial (20 ml) with aluminum cap • Shaking (150 rpm) at room temperature • Silicone O-rings (n=5) as a sink for Phe • Sequential abiotic extraction Results Results Fig. 2. Mineralization of 14C phenanthrene, as a % of initial radioactivity (●), in agricultural soil suspensions with either AC, charcoal or compost in MSM contained in glass vials and maintained for 15 days at 150 rpm at room temperature. Phenanthrene mineralization is compared to the cell density (■) for each time point. The controls were soil suspensions without any soil amendment. The initial phenanthrene concentration was 5 mg kg-1 and initial cell density was 9 x 104 cell ml-1. Each point represents the mean % of phenanthrene of initial radioactivity and the mean cell density, error bars indicate the range (n =5). The lines serve to guide the eye. Fig. 1. Sequential abiotic desorption of 14C phenanthrene (●), as a % of the initial radioactivity, from the AC, charcoal or compost plus agricultural soil suspensions in MSM to the silicone O-rings contained in glass vials and maintained for 24 days at 150 rpm at room temperature. Phenanthrene desorption is compared to freely dissolved concentration (Cfree, ■) in the soil suspension for each time point. The initial phenanthrene concentration was 5 mg kg-1. The controls were soil suspensions without any soil amendment. Each point represents the mean % of phenanthrene of initial radioactivity and the mean of freely dissolved concentration, error bars indicate the range (n = 5). The lines serve to guide the eye. • Maximum mineralization during the first 3 days • Amount of Phe mineralized increase with increasing desorption • compost negatively affect the mineralization but increase bacterial growth • Rapidly removable fraction desorbed within 0.5 to 6 days followed by slower desorption of residual phenanthrene • Total amount desorbed: AC << charcoal < compost • Cfree decrease concomitantly with a decrease of desorption • Conclusions • Correlation between phenanthrene desorption and mineralization • Mineralization of 4% for AC, 12% for charcoal, 18% for compost, and • 28% for control • Conclusions • Phenanthrene partly desorbable from AC and biochar, but almost fully • desorbed from compost • Method allows desorption, KOC, and Cfree to be measured efficiently and • reproducibly • Overall conclusion • Total Phe desorption, KOC, Cfree and mineralization measured efficiently, rapidly and reproducibly • Up to 200 vials can be processed in a single run • Sequential abiotic desorption predicts the mineralization trends, but still overestimates the extent of mineralization • Shaker with up to 200 scintillation glass vials • 40 different treatments with 5 replicates 1 Department of Environmental Sciences, Aarhus University, Box. 358, Frederiksborgvej 399, DK 4000 Roskilde 2 Department of Environmental Engineering, Technical University of Denmark, Miljøvej building 113, 2800 Kgs. Lyngby, Denmark 3 Aarhus University ,Department of Agroecology and Environment, Research Centre Foulum, Blichers Allé, Postbox 50DK-8830 Tjele