Impact of soil amendments and the plant rhizosphere on PAH behaviour in soil

Carbonaceous amendments reduce PAH dissolved concentrations (C_free), limiting their uptake and toxicity. A soil contaminated with PAHs was mixed with activated carbon (AC), charcoal or compost and planted with radish (Raphanus sativus L.), and C_free, chemical activities and diffusive uptake of the PAHs measured over 2 months. For AC, C_free and diffusive uptake were decreased by up to 94% compared to the unamended soil within one week. In addition, the sum chemical activity of the PAHs remained below the threshold for baseline toxicity. In contrast, charcoal and compost only led to modest reductions in C_free and diffusive uptake, with sum chemical activities that could potentially result in baseline toxicity being observed. Furthermore, both C_free and diffusive uptake were lower in the planted compared to unplanted soils. Therefore, only AC successfully reduced PAH acute toxicity in the soil, but plant-promoted microbial degradation may also play an important role in PAH attenuation.