Non-Ideal Transport of Agricultural Hormones and Antibiotics From Animal Waste Ponds.

Naturally lined animal-waste ponds contain veterinary pharmaceuticals and hormones and leak leachate at a rate of ~1 mm/d, which equates to ~2,000 L/d (~530 gal/d) for a small half-acre pond. The ponds often act as point sources of groundwater pollution, but it is scientifically unclear how hormones and antibiotics transit the unsaturated zone to the water table without being retarded and degraded. We will test three hypotheses derived from our preliminary studies: 1) Variably-Saturated Soil Beneath Ponds: Because organic seals control the flux of leachate from ponds, coarse textured soils beneath ponds are less saturated than fine textured soils. Less saturation increases the leachate pore velocity (but not the flux), resulting in less retention time within the vadose zone.  On the contrary, less saturation increases the air-water interface inducing a more aerobic state, which is conducive to biodegradation; 2) Colloid-Facilitated Transport: adsorption of hormones to mobile colloids reduces the adsorption of hormones to stationary soil matrix, and 3) Co-Existence Effect: antibiotics present within ponds interfere/sanitize the hormone degrading bacteria, reducing hormone degradation. These hypotheses will be tested through (1) a batch sorption study that discerns the adsorption and degradation properties, (2) soil column experiments using dairy waste to examine the mechanisms of hormone and antibiotic fate and transport, and (3) field-based experiments using small waste ponds to validate findings from the laboratory tests to further improve scientific understanding and provide more defensible results for regulatory bodies.