Environmental Fate of Trenbolone Acetate Used in Animal Agriculture: Mechanistic Studies of Hormone Biodegradation in Various Redox Conditions

Recent studies have been reported that natural and synthetic hormones are major endocrine-disrupting contaminants (EDCs) that can cause contaminant-associated reproductive and developmental alternation on aquatic organisms. In particular, synthetic steroids such as trenbolone acetate (TBA) are widely used as growth promoters in beef cattle. It has been reported that livestock excrete potential endocrine disrupting hormones such as the TBA metabolites (17á-trenbolone, 17â-trenbolone, and trendione) into aquatic environments. Although livestock likely contain much higher levels of steroid contaminants due to the increased use of growth-promoting hormones, relatively little is known about the fate of these synthetic steroids under various aquatic environments. Therefore, this study undertook a series of experiments using biodegradation microcosms to develop a mechanistic understanding of the fate of TBA metabolites in various redox conditions. Redox potentials were controlled by using reagents (titanium(III) citrate, L-cysteine, and dithiothreitol) to develop anaerobic (Eh 100 mV), although abiotic losses in sterile controls were observed for three androgen steroids, 17á-trenbolone and 17â-trenbolone were degraded by as much as 80% and 40% by biotic processes over 10 days. However, trendione degraded by only 20% biotic processes during 3 days, with slight increased after 3 days. Half-lives of 17á-trenbolone, 17â-trenbolone, and trendione were 0.9, 1.5, and 2.7 days in aerobic experiments, respectively. In anaerobic (-438±149 mV), anoxic (-269±45 mV), and suboxic (-100±22 mV) conditions, losses by abiotic processes were observed for all three conditions. In anaerobic and anoxic conditions, observed losses of 17á-trenbolone, 17â-trenbolone, and trendione in sterile controls were around 70% and biotic processes were only responsible for about 20% of attenuation. In suboxic conditions, losses of 17á-trenbolone and 17â-trenbolone were nearly 30% in sterile controls, and observed biotic processes may have contributed 20% to degradation. Half-lives of 17á-trenbolone, 17â-trenbolone, and trendione were 19.2, 8.8, and 7.8 days in anaerobic conditions, respectively. In anoxic conditions, half-lives of 17á-trenbolone and 17â-trenbolone were 3.3 days and 3.2 days, and in suboxic conditions half-lives of 17á-trenbolone, 17â-trenbolone, and trendione were 2.7, 2, and 3.6 days. Although uncertain due to the losses in sterile controls, ORP (oxidation-reduction potential) values obviously affect biodegradation rates for all three androgen metabolites. From the data, aerobic conditions seem to be more favorable conditions than suboxic, anoxic, and anaerobic conditions for 17á-trenbolone, 17â-trenbolone, and trendione degradation