Occurrence, transport, and fate of veterinary growth promoters associated with particulate matter emanating from beef cattle feedyards: a preliminary ecological and human health risk assessment
Year: 2014
Type: dissertation
Abstract: Steroid growth promoter use has become commonplace in modern beef production practices. These growth promoters are used to increase cattle production and profitability. Steroid hormones have demonstrated potential to enter the environment through the use of veterinary growth promoters. In the environment, exposure of ecological receptors to steroid hormones can cause a range of adverse effects. Traditionally, steroid transport has been considered through effluent, runoff, and land application of manure; however, new research shows the potential for steroid transport through airborne particulate matter (PM). This research focused on the fate and transport of steroid hormones in PM from beef cattle feedyards. \nTo better characterize steroid excretion from cattle administered steroid growth promoters, steers were implanted with a combination trenbolone acetate, estradiol implant. In both urine and feces, 17α-trenbolone and 17α-estradiol were predominant metabolites following implantation. Mean concentrations of 17α-trenbolone and 17α-estradiol in feces of implanted steers were 5.9 ± 0.37 ng/g and 2.7 ± 0.22 ng/g, respectively. A best-fit model was developed to predict 17α-trenbolone and 17α-estradiol excretion from steers receiving implants. \nFollowing excretion, steroids potentially degrade through microbial activity in manure. Much research on steroid degradation has focused on land application of manures, thus degradation in manure was determined to better understand steroid fate on feedyard surfaces. Excreta were stored and periodically extracted over 112 d and then analyzed for conjugated and free trenbolone acetate metabolites. The primary trenbolone acetate metabolite, 17α-trenbolone, had a half-life of 5.1 – 9.5 d. Likewise, 17α-estradiol was the predominant estrogen, with a half-life of 8.6 – 53 d. Estrone was the primary metabolite of 17α-estradiol and concentrations of estrone exceeded initial 17α-estradiol concentration in all sample types. These results suggest manure-borne steroids are more stable in excreta than in soil microcosms. \nTransport of steroids via PM has been demonstrates, and an analytical method was validated for the determination of seven steroids in PM. Sample preparation involved liquid-solid extraction followed by cleanup with SPE cartridges. Analytes were separated using reversed-phase liquid chromatography. Samples underwent atmospheric-pressure chemical ionization (APCI) followed by detection using a triple-quadrupole mass spectrometer in SRM mode. The lower limit of quantitation (LLOQ) was ≤0.55 ng/filter for all compounds. Recoveries ranged from 93% - 116%, and coefficient of variation (CV) was ≤16.1% at all spiking levels. \nAir sampling was conducted at commercial feedyards across the Southern Great Plains from 2010-2012. Total suspended particulates (TSP), particulates 10 µm and less (PM10), and particulates 2.5 µm and less (PM2.5) were collected. Steroid analysis was conducted on extracts of PM samples using liquid chromatography mass spectrometry. Estrone and 17α-estradiol were the most commonly detected steroids, identified in over 94% of samples at median concentrations of 10.8 and 20.6 ng/g, respectively. Melengestrol acetate and 17α-trenbolone were detected in 31% and 39% of all PM samples at median concentrations of 1.3 and 1.9 ng/g, respectively. This study demonstrates PM is a viable route of steroid transportation from cattle feedyards. \nA preliminary ecological and human health risk assessment was conducted to highlight receptors at the greatest risk from exposure to pm bound steroid growth promoters. PM bound steroids pose greatest risk to aquatic receptors after potential deposition into water bodies. Of the steroid hormones analyzed, estrogens are present at the highest concentrations and pose the largest risk of adverse effects in ecological receptors. PM bound growth promoters show little risk to human health as exposure is limited to inhalable pm fractions. These small size fractions of PM themselves may pose a greater health risk to humans than steroids bound to the PM.
Author: Brett R. Blackwell
Language: English
Subfield: Pollution
Field: Environmental Science
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W3109603045