Surface and subsurface attenuation of trenbolone acetate metabolites and manure-derived constituents in irrigation runoff on agro-ecosystems

Ractopamine and Other Growth-Promoting Compounds in Beef Cattle Operations: Fate and Transport in Feedlot Pens and Adjacent Environments

The current study represents a comprehensive investigation of the occurrence and fates of trenbolone acetate (TBA) and metabolites 17α-trenbolone (17α-TBOH), 17β-TBOH, and trendione (TBO); melengesterol acetate (MGA); and the less commonly studied β-andrenergic agonist ractopamine (RAC) in two 8 month cattle feeding trials and simulated rainfall runoff experiments. Cattle were administered TBA, MGA, or RAC, and their residues were measured in fresh feces, pen floor material, and simulated rainfall runoff from pen floor surfaces and manure-amended pasture. Concentrations of RAC ranged from 3600 ng g^-1, dry weight (dw), in pen floor to 58 000 ng g^-1 in fresh feces and were, on average, observed at 3-4 orders of magnitude greater than those of TBA and MGA. RAC persisted in pen floors (manure t_1/2 = 18-49 days), and contamination of adjacent sites was observed, likely via transport of windblown particulates. Concentrations in runoff water from pen floors extrapolated to larger-scale commercial feedlots revealed that a single rainfall event could result in mobilization of gram quantities of RAC. This is the first report of RAC occurrence and fate in cattle feedlot environments, and will help understand the risks posed by this chemical and inform appropriate manure-management practices.

A critical review of the environmental occurrence and potential effects in aquatic vertebrates of the potent androgen receptor agonist 17β-trenbolone

Trenbolone acetate is widely used in some parts of the world for its desirable anabolic effects on livestock. Several metabolites of the acetate, including 17β-trenbolone, have been detected at low nanograms per liter concentrations in surface waters associated with animal feedlots. The 17β-trenbolone isomer can affect androgen receptor signaling pathways in various vertebrate species at comparatively low concentrations/doses. The present article provides a comprehensive review and synthesis of the existing literature concerning exposure to and biological effects of 17β-trenbolone, with an emphasis on potential risks to aquatic animals. In vitro studies indicate that, although 17β-trenbolone can activate several nuclear hormone receptors, its highest affinity is for the androgen receptor in all vertebrate taxa examined, including fish. Exposure of fish to nanograms per liter water concentrations of 17β-trenbolone can cause changes in endocrine function in the short term, and adverse apical effects in longer exposures during development and reproduction. Impacts on endocrine function typically are indicative of inappropriate androgen receptor signaling, such as changes in sex steroid metabolism, impacts on gonadal stage, and masculinization of females. Exposure of fish to 17β-trenbolone during sexual differentiation in early development can greatly skew sex ratios, whereas adult exposures can adversely impact fertility and fecundity. To fully assess ecosystem-level risks, additional research is warranted to address uncertainties as to the degree/breadth of environmental exposures and potential population-level effects of 17β-trenbolone in sensitive species. Environ Toxicol Chem 2018;37:2064-2078. Published 2018 Wiley Periodicals Inc. on behalf of SETAC. This article is a US government work and, as such, is in the public domain in the United States of America.

Environmental transport of endogenous dairy manure estrogens

Although estrogens originating from dairy manure applied to agricultural soils as a fertilizer can potentially contaminate surface water and groundwater, the variables that control transport are poorly understood. Our objective was to assess the potential for off-site movement of endogenous dairy cattle estrogens when manure is applied on fields at agronomically relevant fertilization rates. Estrone (E1), 17α-estradiol (α-E2), and 17β-estradiol (β-E2) were used in laboratory sorption, desorption, and transformation incubations with both manure and an agriculturally relevant soil. Sorption on manure containing 44% organic carbon exceeded sorption on soil containing 0.8% organic carbon by 20 to 150 times, following the pattern of β-E2 > α-E2 > E1. Approximately 20% of E1 and 17% of α-E2 were desorbed from manure, whereas only about 4% of β-E2 was desorbed. Thirty to seventy percent of α-E2 and β-E2 were converted to E1 in soil and manure, making it imperative that transformation reactions be considered when predicting transport and potential biological effects in the environment. Overall results indicate that high organic carbon concentrations and relatively low amounts of desorption inhibit the potential for off-site transport of endogenous dairy manure estrogens.

Trenbolone acetate metabolite transport in rangelands and irrigated pasture: observations and conceptual approaches for agro-ecosystems

To assess the relative ecological risks of trenbolone acetate (TBA) use in agro-ecosystems, we evaluated the spatiotemporal dynamics of TBA metabolite transport during irrigation and rainfall events. Within a pasture, TBA-implanted heifers (40 mg TBA, 8 mg estradiol) were briefly penned (24 h) at high stocking densities (500 animal units (AU)/ha), prior to irrigation. Irrigation runoff concentrations of 17α-trenbolone (17α-TBOH) 0.3 m downslope were 11 ng/L in the wetting front, but quickly decreased to ∼0.5 ng/L, suggesting mass transfer limitations to transport. At 3 and 30 m downslope, efficient attenuation of 17α-TBOH concentrations is best explained by infiltration and surface partitioning. At plot scales, transport through vegetated filter strips resulted in <0.5-7 ng/L 17α-TBOH concentrations in rainfall-induced runoff with partial subsequent attenuation. Thus, even under intense grazing scenarios, TBA-metabolite transport potential is expected to be low in rangelands, with ecological risks primarily arising from uncontrolled animal access to receiving waters. However, 17α-TBOH concentrations in initial runoff were predicted to exceed threshold levels (i.e., no observed adverse effect levels [NOAELs]) for manure concentrations exceeding 2.0 ng/g-dw, which occurs throughout most of the implant life. For comparison, estrone and 17β-estradiol were modeled and are likely capable of exceeding NOAELs by a factor of ∼2-5 in irrigation runoff, suggesting that both endogenous and exogenous steroids contribute to endocrine disruption potential in agro-ecosystems.