Fate of triclosan in field soils receiving sewage sludge

The anti-microbial substance triclosan can partition to sewage sludge during wastewater treatment and subsequently transfer to soil when applied to land. Here, we describe the fate of triclosan in a one-year plot experiment on three different soils receiving sludge. Triclosan and methyl-triclosan concentrations were measured in soil samples collected monthly from three depths. A large fraction of triclosan loss appeared to be explained by transformation to methyl-triclosan. After 12 months less than 20% of the initial triclosan was recovered from each soil. However, the majority was recovered as methyl-triclosan. Most of the chemical recovered at the end of the experiment (both triclosan and methyl-triclosan) was still in the top 10 cm layer, although there was translocation to lower soil horizons in all three soils. Between 16.5 and 50.6% of the applied triclosan was unaccounted for after 12 months either as a consequence of degradation or the formation of non-extractable residues. ► We study the fate of triclosan in 3 different field soils amended with biosolids. ► Triclosan concentrations were measured over 12 months at 3 depths of soil. ► Methyl-triclosan was identified as a main biotransformation product. ► There was very little movement of triclosan through the soil. ► Only between 16 and 50% of triclosan applied was degraded or leached out of the soil. This paper investigates the mobility and degradation of triclosan in three field soils after receiving an application of biosolids and the persistence of methyl-triclosan.