Fate of flame retardants and the antimicrobial agent triclosan in planted and unplanted biosolid-amended soils.

A comprehensive understanding of the fate of contaminant-laden biosolids is needed to fully evaluate the environmental impacts of biosolid land application. The present study examined the fate of several flame retardants and triclosan in biosolid-amended soil in a 90-d greenhouse experiment. Objectives included evaluating the persistence of these compounds in soil, their phytoaccumulation potential by alfalfa (Medicago sativa), and potential degradation reactions. Concentrations of the polybrominated diphenyl ether (PBDE) congeners BDE-47 and BDE-209 and the antimicrobial triclosan declined significantly over time in biosolid-amended soil planted with alfalfa and then reached a steady state by day 28. In contrast, no significant losses of those analytes were observed from soil in nonvegetated pots. The amount of an analyte lost from vegetated soil ranged from 43% for the flame retardant di(2-ethylhexyl)-2,3,4,5-tetrabromophthalate to 61% for triclosan and was significantly and negatively related to the log octanol-water partition coefficient. Alfalfa roots and shoots were monitored for the compounds, but no clear evidence of phytoaccumulation was observed. Methyl triclosan formation was observed in the biosolid-amended soils during the study period, indicating in situ biotransformation of triclosan. The present study demonstrates that, although they are highly recalcitrant, PBDEs, selected alternate brominated flame retardants, and triclosan are capable of undergoing dissipation from biosolid-amended soils in the presence of plants.