Using laboratory-generated biosolids to evaluate the microbial ecotoxicity of triclosan in a simulated land application scenario.

Land application accounts for approximately 50% of wastewater solids disposal in the USA. Yet, little is known regarding the ecological impacts of many non-regulated chemicals found in biosolids. In most previous studies aimed at assessing ecological impacts, a model biosolid is generated by spiking high concentrations of the target chemical into a soil or biosolid. This approach does not account for the interaction of the chemical of interest with the solids throughout the biosolids production process (a.k.a., aging) which may impact the bioavailability and, thus, ultimate toxicity of the chemical. In the present study, using a lab-scale wastewater and digestion treatment system, we generated biosolids which contained aged triclosan and compared ecological impacts to that of spiked biosolids. Ecotoxicity was assessed based on functional and community structure changes to soil denitrifiers, microorganisms critical to nitrogen cycling. A decrease in denitrifier abundance and diversity was observed in the aged biosolids at concentrations of 17.9 ± 1.93 μg/kg while decreases in activity were observed at 26.9 ± 4.6 μg/kg. In the spiked biosolids treatment, lower denitrifier abundance, diversity, and activity were observed at triclosan (TCS) concentrations of 68.6 ± 26.9 μg/kg. This difference suggests a need to better understand TCS bioavailability dynamics.