Triclosan Concentrations Over Time In Agricultural Soil Amended with a High Rate of An Alkaline-Stabilized Biosolid.

Triclosan is a broad-spectrum antimicrobial compound that is used in many consumer products, and is commonly detected in sewage biosolids due to partitioning onto organic matter during sewage treatment. Biosolids applied to land have been recognized as a significant source for the introduction of many contaminants into the environment. This study documented soil triclosan concentration over time in an aerobic incubation and a field trial using N-Viro Soil, an alkaline-stabilized biosolid. The amendment rate for the incubation was equivalent to 42 t ha^-1, which is three times the recommended rate for agriculture of 14 t ha^-1, while the field received two applications (Fall, Spring) of 21 t ha^­1, both representing 1.5 times the recommended rate. Triclosan was detected at levels greater than our limit of quantification in both studies. Average triclosan concentration in the incubation study ranged from a high of 143 ng g^-1 on day 3 to a low of 26 ng g^-1 by day 121, representing an 81% decrease over a roughly 4 month period under idealized conditions. In the field, triclosan concentrations following a Fall biosolids application in Oct. 2008 increased to detectable levels (29 to 47 ng g^-1) in all three plots measured in Nov. 2008, which remained elevated (29 to 66 ng g^-1) over the winter period in two out of three plots when sampled in May 2009. Following the Spring application in June 2009, measured triclosan concentrations in July 2009 samples from these same two plots were lower than predicted (33 to 48 ng g^-1) and eventually decreased to levels below the detection limit by the Oct. 2009 sampling. The results indicate that triclosan in Fall-applied biosolids may persist overwinter and could possibly present an increased risk to organisms active in the Spring decomposition process. However, removal of triclosan during the summer months, presumably by aerobic microbial degradation as indicated by the incubation study, led to levels lower than predicted following the Spring application, and levels below our detection limit by the end of the study. Further studies are necessary to evaluate effects on soil communities that may be altered by the presence of a broad-spectrum antibacterial compound.