While the threat to the aquatic environment posed by leaching of nutrients from manure-treated fields is well recognized, that posed by leaching of steroid hormones from the manure has received much less attention. The steroid hormones 17b-estradiol (E2) and its degradation product estrone (E1) are of particular environmental concern as both are abundant in slurry from pregnant and cycling pigs and both are potential endocrine disruptors (lowest observable effect level (LOEL) 14 ng/L and 3.3 ng/L, respectively). The present one-year study examines the transport of estrone and 17b-estradiol from manure to tile drainage systems at two field sites on structured, loamy soil.

The study suggests that application of slurry to structured soils poses a potential contamination threat to the aquatic environment in that endocrine disrupting hormones can be transported to water bodies via tile drainage water. This occurred when slurry was applied to the two field sites in accordance with Danish regulations concerning manure doses and methods of application, even when slurry application was followed by soil tillage. The estrogens continued to leach from the root zone into the tile drains in concentrations considerably exceeding the LOEL as long as three months after application, the maximum recorded concentration of E1 and E2 being 68.1 ng/L and 2.5 ng/L, respectively. Transport of estrogens from the soil to the aquatic environment was governed by pronounced macropore flow and consequent rapid movement of the estrogens to the tile drains. These findings are of broad environmental concern as they suggest that the application of manure to structured soils pose a potential contamination risk to the aquatic environment with estrogen, particularly when manure is applied to areas where the majority of stream water derives from drainage water.