Fate and Biological Activity of Endocrine Disrupting Compounds in the Waste of a Commercial Swine Operation.

摘要

Over the past two decades, emerging evidence has unequivocally demonstrated the potential for endocrine disrupting compounds (EDCs) found in waste effluents to adversely impact aquatic species. The waste of animal feeding operations (AFOs), including swine, cattle, and poultry operations, generally receives less treatment than human waste. Thus, these operations have been implicated as potentially major sources of manure-borne EDCs to the aquatic environment, with steroid hormones and phytoestrogens being of particular concern. In order to develop a more comprehensive understanding of the occurrence of these EDCs in AFO waste, this study seeks to assess the mass flux of steroid hormones, phytoestrogens, and estrogenic activity in the waste of a prototypical commercial swine operation. This study additionally aims to evaluate the capacity of classical in vitro estrogen screening assays to predict estrogenic effects in exposed fish, and delineate the ligand interactions that drive the piscine estrogenic response. A field study was conducted to assess the flux of hormones, phytoestrogens, and estrogenic activity through all major operational units of a prototypical commercial swine sow AFO. Sampling was conducted on repeat occasions between 2008 and 2011, and attenuation of analytes in soil was assessed over a 61-day sampling period following the sprayfield application of slurry in the spring of 2011. In the anaerobic lagoon, which is the largest repository of waste on the farm, steroid hormones, phytoestrogens, and estrogenic activity were detected at high levels. Estrone and equol were the predominant estrogen and phytoestrogen species in the lagoon, respectively. Almost all analytes were found to be significantly elevated in the particulate phase relative to the aqueous phase of the lagoon slurry, and markedly elevated loads of hormones, phytoestrogens, and estrogenic activity were observed in the lagoon sludge. To assess analyte flux through the whole system, levels of these compounds in the lagoon were compared to that of urine, feces, and of collection pits located beneath the barns. It was found that sow urine and feces contain a variety of free and conjugated hormones, with progesterone being the most abundant steroid hormone. During waste storage in barn pits and the lagoon, the mass ratio of these compounds shifts, with androgens, progesterone, and phytoestrogens attenuated relative to steroidal estrogens. Both estrone and equol appear to be formed along the waste disposal route, with estrone being the predominant compound contributing to estrogenic activity across all units of the farm. In soil, analytes and estrogenic activity were generally attenuated from initial levels within 2 days of land application, but compounds including estrone, androstenedione, progesterone, and equol were still detectable in soil at 61-days post-application. Estrogenic activity on the farm was assessed using the yeast estrogen screen (YES) and T47D-KBluc in vitro screening assays, and was generally found to track well with reported analyte concentrations. To evaluate the capacity of these in vitro assays to predict estrogenic effects in fish, laboratory exposures were conducted using Japanese medaka (Oryzias latipes). Male medaka were exposed to steroidal estrogens (estrone, 17beta-estradiol, 17beta- estradiol, or estriol) or to an extract of swine lagoon slurry, with all exposures calibrated to be of equal potency in the YES assay. These exposures were found to elicit significantly different magnitudes of hepatic vitellogenin and choriogenin induction in exposed medaka. Using ligand binding assays, it was observed that compounds which elicited the greatest magnitude of vitellogenin and choriogenin gene expression had preferential binding affinity for the medaka estrogen receptor beta (ERbeta), supporting recent observations that ERbeta plays a critical role in vitellogenesis and choriogenesis. Results suggest that incorporation of multiple ER subtypes into estrogen screening protocols may increase predictive value for the risk assessment of aquatic systems, including assessment of complex mixtures such as livestock waste effluents.