DEGRADATION OF ESTROGENS IN DAIRY WASTE SOLIDS: EFFECTS OF ACIDIFICATION AND TEMPERATURE

Abstract

Manure–borne estrogens are increasingly recognized as a potential ecological hazard. However, sample–handling protocols for these compounds are not clearly delineated in the literature, nor are comparisons between assays for estrogens. A study was conducted to explore the degradation of estrogen in separated dairy manure waste solids (press cake), using three popular assay types. Estrogens were measured by enzyme–linked immunosorbent assay (ELISA), gas–chromatography mass–spectroscopy (GC–MS) and a recombinant yeast estrogen reporter assay. As measured by GC–MS, background estrone concentrations were approximately 100 ppb, while 17
–estradiol concentrations were one–third of the estrone concentration, and 17–estradiol concentrations were below the detection limit (10 ppb). In contrast, background 17–estradiol concentrations as measured by ELISA were 53 ppb. In press cake samples spiked with 17–estradiol, ELISA and GC–MS 17–estradiol concentrations from all experiments were well correlated (r 2 = 0.93), although the ELISA values were higher than the GC–MS values. The yeast estrogen assay was also highly correlated with GC–MS results (r 2 = 0.94). The rates of total estrogen removal in press cake samples spiked with 500 ppb 17–estradiol and incubated over a range of 5–50 ³ C were characterized by a 1 st –order decay constant (k). The k values increased with temperature and ranged from 0.029 d –1 to 0.12 d –1 . Rate constants observed in unspiked press cake samples agreed with the values derived from the spiked samples. Over a 7–d period, acidification of samples (pH < 2) and storage at 5 ³ C reduced 17–estradiol losses to 15% and total estrogen losses to 17%, whereas unacidified samples lost 90% of 17–estradiol and 40% of total estrogen. The results of this study strongly suggest the need for acidification and cold storage of environmental samples being tested for estrogens. In this study, no single assay met all the desirable criteria of speed, sensitivity (<1 ppb), and detection of both 17–estradiol and estrone. Therefore, the use of multiple assays for the detection of environmental estrogens is warranted.