Dissipation, transformation and accumulation of triclosan in soil-earthworm system and effects of biosolids application.

Triclosan (TCS), widely used as an antimicrobial ingredient, is usually introduced into soil by biosolids application, and has presented potential risk in agro-ecosystem. The dissipation pathways of TCS in soil were analyzed in the presence and absence of earthworms (including Metaphire guillelmi and Eisenia fetida). Meanwhile the accumulation and transformation potentials of TCS in the two earthworms were evaluated. Results indicated that about 44% of initial TCS amount dissipated in sterile soil after 56-day incubation, which may mainly result from the bound-residues formation. In contrast, TCS in non-sterile soil dissipated more quickly with a t1/2 of 12 days, suggesting that microbial degradation was responsible for TCS dissipation. Triclosan was methylated to methyl triclosan (MTCS) in soil, which however contributed little for TCS dissipation. The presence of M. guillelmi accelerated TCS dissipation with the reduced t1/2 to 8 days, and inhibited MTCS formation in soil, while E. fetida had no significant (P > 0.05) effects on the fate of TCS. E. fetida accumulated more TCS than M. guillelmi, with bioaccumulation factors up to 11 vs. 0.6. It was also proved that methylation metabolism occurred in earthworms (including gut microorganisms), and M. guillelmi had higher metabolic efficiency compared to E. fetida. Even though eliminations of TCS and MTCS were rapid (except for TCS in M. guillelmi), the residues of the two compounds in both earthworms remained at high levels, having the potential to transfer in the terrestrial food web. In addition, results showed that biosolids application changed TCS persistence, as well as bioavailability dependent on earthworm species. When biosolids at 1% added, more residual TCS and MTCS in soil were observed, while TCS accumulation in E. fetida decreased, however, methylation metabolism in both earthworm species was not affected. The findings provide important information for a more precise risk assessment of biosolids land-application. CAPSULE: Triclosan dissipation, methylation and bioavailability in soils were affected by biosolids amendment and dependent on earthworm species with different accumulation and metabolic potentials.