Sand to Root Transfer of PAHs and PCBs by Carrots Grown on Sand with Pure Substances and Biosolids Amended Sand

A study on behaviour of trace organic compounds (Polycyclic Aromatic Hydrocarbons, PAH, and Polychlorinated Biphenyls, PCB) in a sand-plant system has been carried out, with the reclamation of wastewater treatment plant biosolids for agriculture in mind. Carrot plants (Daucus carota) were grown on soilless culture (sand), to provide optimal transfer conditions, in plant containers inside a temperature regulated greenhouse. There were two types of experiment. The trace organic compounds have initially been introduced as pure substances. A second experiment has been carried out under the same conditions, but using biosolids. Plant development has been unaffected by the presence of the pure substances and the biosolids. The transfer of the trace organic compounds has been followed in the peel, the core and the leaves of the carrot plants. Results obtained are expressed as fluxes of the trace organic compounds into the plant. The results clearly show that trace organic compounds accumulate in the carrot peel. INTRODUCTION In Europe, 40% of the annual production of biosolids from wastewater treatment plants is recycled in agriculture (Ademe, 1996). New Water Framework Directive (2000/60/EC) is currently under examination to standardise acceptable levels of trace organic compounds (TOC) in biosolids. It would appear essential, in the interests of public health, to study the transfer potential into plants of these TOC’s (Diercxsens et al, 1987). According to the French ministerial order of 8 January 1998, the maximum quantity authorized for land application of biosolids is 30 tons dry matter per ha per 10 years. Carrots (Daucus carota L.) have been reported to be the crop having the greatest potential for organic uptake due to their high lipid content (Wild and Jones, 1992). In addition, carrots can be separated easily in peel, core and leaves in order to follow organic compounds transfer. Sand has no organic matter content thus applied organic compounds may be more bioavailable. So a root crop growing in sand can be considered the worstcase scenario to study behaviour of trace organic compounds. The aim of this study was to investigate the transfer of Polycyclic Aromatic Hydrocarbons (PAHs) and Polychlorinated Biphenyls (PCBs) compounds from biosolids amended sand into a food-chain crop under “worst-case” operational practice (Morard, 1995). MATERIALS AND METHODS Fifteen days after germination, seedlings of carrots cv. Amsterdam A.B.K Bejo were transplanted into glass pots containing sand only (check, C1), sand with PAH or PCB as pure substances (i.e. pure substance experiment) and containing sand only (check,