Sorption and mineral-promoted transformation of synthetic hormone growth promoters in soil systems

Biotransformation of cyproterone acetate, drospirenone, and megestrol acetate in agricultural soils: Kinetics, microbial community dynamics, transformation products, and mechanisms

The occurrence of biologically active synthetic progestins in agricultural soils is of growing concern due to their potential to disrupt the endocrine function of aquatic fish in nearby surface waters. This study investigated the biotransformation outcomes of cyproterone acetate (CPA), drospirenone (DRO), and megestrol acetate (MGA) in four agricultural soils. The biotransformation data were fitted to a first-order decay model (R2 = 0.93-0.99), with half-lives and first-order decay coefficients ranging from 76.2-217 h and 9.10 × 10-3-3.20 × 10-3 (h-1), respectively. Abundant biotransformation products (TPs) were generated during incubation, with the number and yields varying across the four soils. 1,2-Dehydrogenation was the main transformation pathway of DRO in the four soils (yields of 32.3-214 %). Similarly, 1,2-dehydrogenation was the most relevant transformation pathway of MGA in the four soils (yields of 21.8-417 %). C3 reduction was the major transformation pathway of CPA in soils B, C, and D (yields of 114-245 %). Hydrogenation (yield of 133 %) and hydroxylation (yield of 21.0 %) were the second major transformation pathway of CPA in soil B and C, respectively. In particular, several TPs exhibited progestogenic and antimineralocorticoid activity, as well as genotoxicity. The high-throughput sequencing indicated that interactions between microorganisms and soil properties may affect biotransformation. Spearman correlation and bidirectional network correlation analysis further revealed that soil properties can directly interfere with the soil sorption capacity for the progestins, thus affecting biotransformation. In particular, soil properties can also limit or promote biotransformation and the formation of TPs (i.e., biotransformation pathways) by affecting the relative abundances of relevant microorganisms. The results of this study indicate that the ecotoxicity of synthetic progestins and related TPs can vary across soils and that the assessment of environmental risks associated with these compounds requires special consideration of both soil properties and microbial communities.

Abiotic transformation of synthetic progestins in representative soil mineral suspensions

Altrenogest (ALT), drospirenone (DRO), and melengestrol acetate (MLA) are three highly potent synthetic progestins that can be released into agricultural soils, while their fate in soil minerals remains unclear. This study explored the transformation of these progestins in MnO₂, SiO₂, and ferrihydrite suspensions and identified their transformation products (TPs) via high resolution mass spectrometry and density functional theory calculations. Transformations were only observed for DRO and MLA in SiO₂ suspension and ALT in MnO₂ suspension (half-lives = 0.86 min - 9.90 day). ALT transformation was facilitated at higher MnO₂ loadings, while DRO and MLA transformations were inhibited at higher SiO₂ loadings. These data indicated that hydrophobic partitioning interaction was dominant at higher SiO₂ loadings rather than specific interaction, which limited subsequent surface-catalyzed transformation. ALT transformation rate decreased with increasing pH because MnO₂ reduction requires proton participation. In contrast, relatively high pH facilitated MLA and DRO transformation, indicating that base-catalyzed hydrolysis occurred in SiO₂ suspension. The clustermap demonstrated the formation of abundant TPs. Lactone ring and acetoxy group hydrolysis was the major transformation pathway for DRO and MLA, with estimated yields of 57.7% and 173.2% at 6 day, respectively. ALT experienced C12 hydroxylation and formed the major TP 326g (yield of 15.4% at 8 hr). ALT also experienced allyl group oxidation and subsequent C5 hydroxylation, forming the major TP 344a (yield of 14.1% at 8 hr). This study demonstrates that TPs of metastable progestins are likely the main species in soils and that TP identification is a particular priority for risk assessment.

Biotransformation kinetics and pathways of typical synthetic progestins in soil microcosms

Gestodene (GES), altrenogest (ALT), and medroxyprogesterone acetate (MPA) are three potent synthetic progestins detected in agricultural soils; however, their biotransformation outcomes in soils remain unclear. This study explored the biotransformation of these progestins in five agricultural soils with different physicochemical properties. The biotransformation data were well-described by a first-order decay model (R² = 0.83-0.99), with estimated half-lives ranging between 12.1 and 188 h. Amplicon sequencing indicated that the presence of progestins changed the bacterial richness and community structure in the soils. Linear correlation, canonical correlation, and two-way correlation network analysis revealed that soil properties can affect biotransformation rates by interfering with progestin-soil interactions or with keystone taxa in soils. The clustermap demonstrated the formation of abundant transformation products (TPs). Isomerization and C4(5) hydrogenation were the major transformation pathways for GES (yields of ∼ 13.7 % and ∼ 10.6 %, respectively). Aromatic dehydrogenation was the major transformation pathway for ALT (yield of ∼ 17.4 %). The C17 hydrolysis with subsequent dehydration and hydrogenation was the major transformation pathway for MPA (yield of ∼ 196 %). In particular, some TPs exhibited progestagenic, androgenic, or estrogenic activity. This study highlights the importance of evaluating the ecotoxicity of progestin and TP mixtures for better understanding their risks in the environment.

Migration and abiotic transformation of estrone (E1) and estrone-3-sulfate (E1-3S) during soil column transport

Steroid estrogens have received worldwide attention and given rise to great challenges of aquatic ecosystems security, posing potential adverse effects on aquatic organisms and human health even at low levels (ng/L). The present study focused on understanding the mobility and abiotic transformation of estrone (E1) and estrone-3-sulfate (E1-3S) over spatial and time scales during soil transport. Column transport experiments showed that the migration capacity of E1-3S was far stronger than E1 in soil. The calculated groundwater ubiquity score and leachability index values also indicated the high leaching mobility of E1-3S. The hydrolysis of E1-3S and abiotic transformation into estradiol and estriol was observed in the sterilized soil. Furthermore, possible transformation products (e.g., SE₂₃₉, E2₃₇₈, E1 dimer₅₃₈, E1-E2 dimer₅₄₁) of E1 and E1-3S in soil were analyzed and identified after the column transport experiments. The estrogenic activity was estimated by 17β-estradiol equivalency values during the transport process in aqueous and soil phases. Additionally, the potential leaching transport to groundwater of E1-3S requires further critical concern.

Chronic Exposure to Two Gestagens Differentially Alters Morphology and Gene Expression in Silurana tropicalis

Gestagens are active ingredients in human and veterinary drugs with progestogenic activity. Two gestagens-progesterone (P4), and the synthetic P4 analogue, melengestrol acetate (MGA)-are approved for use in beef cattle agriculture in North America. Both P4 and MGA have been measured in surface water receiving runoff from animal agricultural operations. This project aimed to assess the morphometric and molecular consequences of chronic exposures to P4, MGA, and their mixture during Western clawed frog metamorphosis. Chronic exposure (from embryo to metamorphosis) to MGA (1.7 µg/L) or P4 + MGA (0.22 µg/L P4 + 1.5 µg/L MGA) caused a considerable dysregulation of metamorphic timing, as evidenced by an inhibition of growth, narrower head, and lack of forelimb emergence in all animals. Molecular analysis revealed that chronic exposure to the mixture induced an additive upregulation of neurosteroid-related (GABA_A receptor subunit α6 (gabra6) and steroid 5-alpha reductase 1 (srd5α1) gene expression in brain tissue. Chronic P4 exposure (0.26 µg/L P4) induced a significant upregulation of the expression hypothalamic-pituitary-gonadal (HPG)-related genes (ipgr, erα) in the gonadal mesonephros complex (GMC). Our data suggest that exposure to P4, MGA, and their mixture induces multiple endocrine responses and adverse effects in larval Western clawed frogs. This study helps to better our understanding of the consequences of chronic gestagen exposure and suggests that the implications and risk of high gestagen use in beef cattle feeding operations may extend to the aquatic environment.

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.

Sorption and desorption of seven steroidal synthetic progestins in five agricultural soil-water systems

Manure fertilization and wastewater irrigation can introduce the biologically potent synthetic progestins into agricultural soils, causing endocrine disruption in organisms of nearby surface waters. Therefore, this study investigated the sorption and desorption potential of etonogestrel, medroxyprogesterone, gestodene, norgestrel, cyproterone acetate, levonorgestrel, and dienogest in five agricultural soil-water systems. Sorption data were well-described by the linear sorption model. In most batch systems, cyproterone acetate exhibited the highest affinities for soils, followed by etonogestrel, medroxyprogesterone, levonorgestrel, gestodene, norgestrel, and dienogest. The sorption magnitudes (logK_oc or logK_d) were significantly correlated with the progestin hydrophobicities (R² = 0.72-0.86, p < 0.05). The K_d values of the progestins were also significantly correlated with organic carbon content and pore volumes of the soils (R² = 0.68-0.98, p < 0.05). In addition, 0.5 M urea resulted in 3-19% decreases in K_d values of the progestins. Taken together, these data indicated that hydrophobic partitioning interaction, hydrogen bonding interaction, and pore filling were the sorption mechanisms for the progestins in soil-water systems. No significant desorption hysteresis was observed for the progestins, indicating that they can be readily desorbed under rainfall or irrigation events. Based on the sorption and desorption data, we estimated the dynamic transport of the progestins in conventional agricultural management systems, and predicted the concentrations of the progestins as a function of soil-sorbed concentration, water-soil ratio, and dilution factor of receiving waters. This study will improve the understanding of the risks posed by the progestins under field-scale hydrological conditions.

Spatio-temporal distribution and transformation of 17α- and 17β-estradiol in sterilized soil: A column experiment

The environmental behaviors of steroid estrogens (SEs) associated with land irrigation and application are of critical concern worldwide. Understanding the spatio-temporal distribution and transformation process of these estrogenic compounds in soil is greatly significant. In this study, laboratory soil column experiments were conducted to investigate and explore the migration and abiotic transformation of 17α-estradiol (17α-E2) and 17β-estradiol (17β-E2) over spatial and time scales. Results indicated that the migration tendency of 17α-E2 and 17β-E2 was similar. Discrepancies in transport for different SEs groups might be due to the competitive sorption and isomeric transformation in the binary-solute system. 17α-E2 and 17β-E2 can also undergo the abiotic transformation during soil column transport. The soil with naturally abundant mineral substances (e.g., iron and manganese oxides) indicated that E2 isomers tended to mineral-promoted racemization, oxidation, reduction, and radical coupling reactions. Some possible transformation products (e.g., SE₂₃₉, E2₃₇₈, and SE dimer₄₇₆) were identified and proposed in soil samples. Compared to the single compound tests, the estimated 17β-estradiol equivalency (EEQ) values of E2 mixture were higher during SEs migration process.

Sorption, transport, and transformation of natural and synthetic progestins in soil-water systems

Natural and synthetic progestins are emerging endocrine disruptors that can be transported from livestock farms and agricultural fields to receiving waters via surface runoff. The transformation of progestins during transport is expected to affect the efficiencies of runoff management systems. Therefore, this study explored the sorption, transport, and transformation of progesterone, norethisterone acetate, medroxyprogesterone acetate, cyproterone acetate, dydrogesterone, and norethisterone in agricultural soil-water systems. The sorption coefficients and retardation factors (R) were positively correlated with the progestin hydrophobicities, indicating that hydrophobic interactions dominated the sorption and transport processes. During transport, dydrogesterone and progesterone were transformed into 9-10 products. The breakthrough curves of the parents and products exhibited periodical patterns over extended times. Specifically, the R values of the parents and products were positively correlated with chromatographic retention times (hydrophobicities) when the products were generated before transport. In contrast, a negative correlation (R² = 0.75-0.88) was observed when products were successively generated during transport, indicating that the transformation kinetics changed the retardation of these solutes in the columns. These observations also demonstrated that the transport potential estimates based on traditional metrics of steroid hydrophobicity are not always accurate and that runoff management measures are less effective for metastable progestins.

Sorption and transport of trenbolone and altrenogest photoproducts in soil-water systems

This study evaluated the sorption and transport potential of seven phototransformation products of 17α-trenbolone, 17β-trenbolone, trendione, and altrenogest, along with the parent trienone steroids in batch and column soil-water systems. In batch systems, the target solutes exhibited linear isotherms, with values for sorption coefficients (log Koc) of parent steroids (2.46-2.76) higher than those for photoproducts (1.92-2.57). In column systems, the estimated retardation factors (Rsol) for parents (2.7-5.1) were ∼2-5 times higher than those for photoproducts (0.84-1.7). The log Koc (R2 = 0.75) and Rsol (R2 = 0.89-0.98) were well correlated with measured log Kow values, indicating that hydrophobic partitioning governed the soil-solute interaction of these biologically potent compounds in soil-water systems. These data indicated that photoproducts exhibited reduced sorption affinity and increased transport potential relative to more hydrophobic parent structures. In agroecosystems, traditional runoff management practices would be expected to exhibit reduced treatment effectiveness for photoproducts relative to the parent compounds of commonly used trienone steroids.

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.

Emerging investigator series: development and application of polymeric electrospun nanofiber mats as equilibrium-passive sampler media for organic compounds

We fabricated a suite of polymeric electrospun nanofiber mats (ENMs) and investigated their performance as next-generation passive sampler media for environmental monitoring of organic compounds. Electrospinning of common polymers [e.g., polyacrylonitrile (PAN), polymethyl methacrylate (PMMA), and polystyrene (PS), among others] yielded ENMs with reproducible control of nanofiber diameters (from 50 to 340 nm). The ENM performance was investigated initially with model hydrophilic (aniline and nitrobenzene) and hydrophobic (selected PCB congeners and dioxin) compounds, generally revealing fast chemical uptake into all of these ENMs, which was well described by a one compartment, first-order kinetic model. Typical times to reach 90% equilibrium (t_90%) were ≤7 days under mixing conditions for all the ENMs and <0.5 days for the best performing materials under static (i.e., no mixing) conditions. Collectively, these short equilibrium timescales suggest that ENMs may be used in the field as an equilibrium-passive sampler, at least for our model compounds. Equilibrium partitioning coefficients (K_ENM-W, L kg^-1) averaged 2 and 4.7 log units for the hydrophilic and hydrophobic analytes, respectively. PAN, PMMA and PS were prioritized for additional studies because they exhibited not only the greatest capacity for simultaneous uptake of the entire model suite (log K_ENM-W ∼1.5-6.2), but also fast uptake. For these optimized ENMs, the rates of uptake into PAN and PMMA were limited by aqueous phase diffusion to the nanofiber surface, and the rate-determining step for PS was analyte specific. Sorption isotherms also revealed that the environmental application of these optimized ENMs would occur within the linear uptake regime. We examined the ENM performance for the measurement of pore water concentrations from spiked soil and freshwater sediments. Soil and sediment studies not only yielded reproducible pore water concentrations and comparable values to other passive sampler materials, but also provided practical insights into ENM stability and fouling in such systems. Furthermore, fast uptake for a suite of structurally diverse hydrophilic and moderately hydrophobic compounds was obtained for PAN and PS, with t_90% ranging from 0.01 to 4 days with mixing and K_ENM-W values ranging from 1.3 to 3.2 log units. Our findings show promise for the development and use of ENMs as equilibrium-passive samplers for a range of organic pollutants across soil/sediment and water systems.

Effect of rainfall timing and tillage on the transport of steroid hormones in runoff from manure amended row crop fields

Runoff generated from livestock manure amended row crop fields is one of the major pathways of hormone transport to the aquatic environment. The study determined the effects of manure handling, tillage methods, and rainfall timing on the occurrence and transport of steroid hormones in runoff from the row crop field. Stockpiled and composted manure from hormone treated and untreated animals were applied to test plots and subjected to two rainfall simulation events 30days apart. During the two rainfall simulation events, detection of any steroid hormone or metabolites was identified in 8-86% of runoff samples from any tillage and manure treatment. The most commonly detected hormones were 17β-estradiol, estrone, estriol, testosterone, and α-zearalenol at concentrations ranging up to 100-200ngL^-1. Considering the maximum detected concentrations in runoff, no more than 10% of the applied hormone can be transported through the dissolved phase of runoff. Results from the study indicate that hormones can persist in soils receiving livestock manure over an extended period of time and the dissolved phase of hormone in runoff is not the preferred pathway of transport from the manure applied fields irrespective of tillage treatments and timing of rainfall.