Steroid estrogens and estrogenic activity are ubiquitous in dairy farm watersheds regardless of effluent management practices

Steroid estrogens contamination has been linked to adverse effects on exposed aquatic biota. Steroid estrogens are excreted by all mammals and are found in most agricultural wastes including dairy manure and dairy shed effluent (DSE). Some previous studies have demonstrated elevated levels of free and conjugated estrogenic steroids in DSE and this source has increased as New Zealand has experienced rapid expansion and intensification of dairy farming. This research used an approach incorporating analytical chemistry and bioassays to evaluate the levels of estrogenic activity in environmental samples from representative dairy watersheds with differing DSE management practices: either land-applied or discharged to water. The results demonstrated that estrogenic activity and steroid estrogens were prevalent in the waterways within all the studied dairy watersheds. Estrone was the predominant steroid measured in watershed waters because of its presence in dairy cow wastes and as a degradate of the main dairy cow estrogen, 17α-estradiol. Measurable estrogenic activity (17β-estradiol equivalents, EEq) was found at low levels in 83% of the stream samples (highest 1.44 ng L−1 EEq) and 75% of the groundwater samples (≤0.15 ng L−1 EEq). While estrogenic activity was generally <1 ng L−1, one (of 10) stream with measurable estrone, 17α- and 17ß-estradiol had activity of 1.4 ng L−1, a level potentially harmful to aquatic biota. Comparable steroid estrogen concentrations and estrogenic activity were found whether DSE was spray irrigated on farm paddocks or directly discharged into waterways. This suggests that direct access of cattle to streams, the direct input of DSE into waterways and runoff from land application all require more intervention and effective management.