Properties of soil particle size fractions and their effects on fate and transport of hormones in soil environments

Hormones detected in environments have aroused wide public concern due to their possible adverse effects to humans and ecosystems. Currently, information is still very limited on the fate and transport (F/T) of hormones in the soil environment. This study provides a new perspective by separating soils into particles of different size fractions (DSFs), and then investigating the sorption-desorption properties of these soil particles and the distribution information of hormones among these particles with batch reactors. Also the mobile behavior of hormone associated with soil particles and manure in runoff and leachate under rainfall simulation tests was evaluated.;The results showed that the sorption and desorption of hormones associated with soil particles were highly particle size dependent. The sorption affinity ranked as clay > silt > sand, depending mainly on both TOC content and surface area of the soil particles with the TOC weighting higher. The main sorption mechanism of environmentally relevant concentration (20--150 ng/L) of testosterone was electrostatic attraction for sand, mainly hydrogen bonding and functional groups for clay, and electrostatic attraction, hydrogen bonding and functional groups for silt. Of the whole soil, testosterone was sorbed mainly by silt-sized aggregates (STA) even though STA had a lower sorption affinity; smaller particles (< 2000 nm) contributed more than 30% of sorbed testosterone even though their mass percentage was only ~5% of the whole soil. The partially-dispersed soil particles of DSFs should be used as testing materials to predict the transport of hormone in runoff because the fully-dispersed method would overestimate the transport potential while the whole soil method would underestimate the result. The rainfall simulation tests demonstrated that more than 88% of the manure-borne testosterone stayed in the bulk soil; the runoff facilitated the transport of testosterone through both solute and sorbed phases with the corresponding mass ratio being ~7 to 3; no testosterone was detected in the leachate, indicating that the transport of testosterone through the soil was slow when there was no preferential flow.;This research provides a new perspective and methodology to better understand the F/T of hormones in soils. The new fractionation methodology and rainfall simulation slab system can be used to study the F/T of other micro-pollutants in the soils. In the future, a new framework concerning the effects and roles of partially-dispersed soil particles on the F/T of micro-pollutants should be set up with the corresponding separation procedure being standardized.