Application of sewage sludge and sewage sludge biochar to reduce polycyclic aromatic hydrocarbons (PAH) and potentially toxic elements (PTE) accumulation in tomato

The effects of sewage sludge (SS) and its derived biochar (SSBC) on the availability and uptake of polycyclic aromatic hydrocarbons (PAHs) and potential toxic elements (PTEs) by Solanum lycopersicum (tomato) fruits grown in contaminated urban soil were investigated. Increasing application rates of SS and SSBC (2, 5, and 10 %) decreased PAH availability and, correspondingly, PAH accumulation (22-39 and 48-62 %, respectively) into tomato. SSBC was more effective in this regard. The available concentrations of PAHs (Sigma 16PAH) in the SSBC treatments were significantly reduced (from 30.0-47.3 %) as compared to the control treatment. The availability of high-molecular-weight PAHs (containing four to six benzene rings) was greatly affected, while low-molecular- weight PAHs (containing two to three benzene rings) was less affected by SSBC amendments. The addition of SSBC showed the least effect on bioaccumulation of naphthalene (two-ring PAH; 24.5-32.6 %), while the highest effect was observed for benzo(b) fluoranthene (five-ring PAH; 3.1-86.8 %) and benzo(g, h, i) perylene (six-ring PAH; 51.8-84.2 %). In contrast, increasing application rates of SS successively increased PTE (As, Cd, Cu, Pb, and Zn) availability and accumulation (15-139 %) into tomato while SSBC successively decreased PTE availability and accumulation (1791 %). Changes in accumulation varied with PTE and the extent to which PTE concentrations in soil was elevated.