Potential bioactivity and association of 17β-estradiol with the dissolved and colloidal fractions of manure and soil

The dissolved (DF) and colloidal fractions (CF) of soil and manure play an important role in the environmental fate and transport of steroidal estrogens. The first objective of this study was to quantify the association of 17β-estradiol (E2) with the DF and CF isolated from (i) liquid swine manure (LSM), (ii) a soil:water mixture (soil), and (iii) a LSM:soil:water mixture (Soil + LSM). The appropriate CF and DF size fractions of the Soil, Soil + LSM, and LSM media were obtained by first filtering through a 0.45 μm filter, which provided the combined DF and CF (DF/CF). The DF/CF from the three media was spiked with carbon-14 ([14C]) radiolabeled E2 ([14C]-E2), and then ultrafiltered to isolate the CF (< 0.45 μm and > 1 kDa) from the DF (< 1 kDa). The average recoveries of the [14C] associated with the DF were 67%-72%, 67%-79%, and 76%-78% for the Soil, Soil + LSM and LSM, respectively. For the CF that was retained on the 1 kDa filter, organic carbon and [14C]-E2 were dislodged with subsequent water rinses the Soil + LSM and LSM, but not the Soil. The second objective was to evaluate whether the E2 associated with the various fractions of the different media could still bind the estrogen receptor using an E2 receptor (17β-ER) competitor assay, which allowed E2 equivalent concentrations to be determined. The estrogen receptor assay results indicated that E2 present in the DF of the Soil and Soil + LSM solutions could still bind the estrogen receptor. Results from this study indicated that E2 preferentially associated with the DF of soil and manure, which may enhance its dissolved advective transport in surface and subsurface water. Furthermore, this study indicated that E2 associated with DF solutions in the environment could potentially induce endocrine responses through its interactions with estrogen receptor.