Impacts of Colloidal Material On the Fate of Estrogens in Soils.

The application of animal manure and biosolids to improve soil fertility carries the risk of contaminants entering the ecosystem. Estrogenic compounds are commonly detected in animal manure and pose a biological hazard therefore it is important to understand their fate. Estrogens are non-polar and strongly adsorbed to soil organic matter, which limits their miscible transport, but presents another possible transport vector. The movement of colloids that are rich in organic matter may facilitate the transport of estrogens to surface water. As a first step in considering colloidal transport mechanisms, our objective in this study is to determine the rate, intensity, and capacity for adsorption and desorption of 17β-estradiol (E2) by colloidal and fine-particulate components of swine manure and three Iowa soils.

The soils selected range from 70 - 400 g /kg in clay content, 7 - 30 g/kg in organic C, 12 - 60 cmol/kg CEC, and 7 - 11 in C/N ratio. Using a chemical and physical fractionation scheme we have fractionated a sample of farrowing house swine manure and determined that a large proportion of the manure sample consisted of flocculable particulates (52% of the dry mass), and a small proportion was colloidal material (~4%).

We determined adsorption isotherms for E2 binding to Zook and Hanlon soils. In earlier work, we had found that E2 was linearly sorbed to the soil materials, with Kd values ranging from 29 L kg-1 (Hanlon) to 584 L kg-1 (Zook) using Na azide to suppress biological activity. When samples were autoclaved before the sorption experiment, the Kd values fell to ~6 L kg-1 for the Hanlon soil materials and 41 L kg-1 for the Zook soil materials. The log Koc for the soils ranged from 2.93 - 3.13.  Preliminary results from one soil suggest that the colloidal material has about ten times the sorption capacity of the whole soil which also correlates to the order of magnitude increase in organic carbon content.