An ecological risk assessment for triclosan in the terrestrial environment

Triclosan (2,4,4'-trichloro-2'-hydroxydiphenyl ether) is a broad-spectrum bactericide used throughout North America and Europe for a variety of antimicrobial functions. This paper addresses the risk to terrestrial organisms from several potential exposure pathways: Exposure experienced by earthworms, terrestrial plants, and soil microorganisms as the result of the use of sewage sludge containing triclosan as an agricultural soil amendment; secondary exposure by birds and mammals from consumption of earthworms that have been exposed to triclosan in soil; and secondary exposure by birds and mammals from consumption of fish exposed to triclosan as the result of wastewater treatment discharges. The assessment found satisfactory margins of safety for plants, earthworms, birds, fish, mammals, and soil microorganisms. The lowest margins of safety were for nontarget plants (100 for the typical scenario and 8 for the upper-bound scenario). However, these margins of safety are still above the European Union (EU) recommended fivefold assessment value for nontarget plants and are based on cucumber results from a vegetative vigor study conducted in quartz sand that is of limited relevance for risk assessment. In a pre-emergence study conducted in a more relevant soil (sandy loam), cucumbers showed no response to triclosan at the highest dose tested (1,000 microg/kg). A recent study provides limited field measurements of soil and earthworm concentrations. While that study finds higher soil and earthworm concentrations than were estimated in the present study, even these higher concentrations do not indicate significant risks.