Animal manures applied to soils as nutrient amendments are potential nonpoint sources of endocrine-disrupting chemicals (EDCs) to water bodies. Numerous studies have investigated the distribution of EDCs like 17ß-estradiol (E2) between solid and liquid phases of soils. Some of these studies have suggested that the movement of EDCs in soils can be retarded or facilitated by the colloidal portion of either soils or manure. To date, however, there is limited information about the distribution of EDCs in manure colloids in the presence of soil colloids.

Thus, we initiated an investigation to measure the sorption of E2 (up to 2 mg L^-1) by manure colloids (0.45 – 1.0 µm) in the presence of soil colloids. The study also describes the sorption of E2 to a second manure component (1 -71 µm) in the presence of soil colloids. Colloidal fractions from two soils that differ in organic C content were separated via sedimentation. Dialysis tubing was used maintain separation of the two competing sorbents without acting as a barrier to the estrogen. At the end of a 24-h sterile incubation in the dark, the concentration of E2 in the liquid phase was quantified by HPLC while the E2 concentration in the soil colloids was quantified after E2 was desorbed from the colloidal material using solvent extraction. The quantity of E2 unaccounted for was assumed to be sorbed by the manure component.