Compensatory response of fathead minnow larvae following a pulsed in-situ exposure to a seasonal agricultural runoff event.

Agriculturally-dominated waterways such as those found throughout the Midwestern United States often experience seasonal pulses of agrichemical contaminants which pose a potential hazard to aquatic organisms at varying life stages. The objective of this study was to characterize the developmental plasticity of fathead minnow larvae in a natural environment subject to a seasonal episodic perturbation in the form of a complex mixture of agricultural stressors. Fathead minnow larvae were maintained at the Elkhorn River Research Station for a 28-d in situ exposure to an agrichemical pulse event. Minnow larvae were sampled after 14 and 28days to characterize developmental plasticity through growth measures and relative gene expression. Concentrations of agrichemical contaminants measured in water using polar organic chemical integrative samplers and composite sediment samples throughout the 28-d exposure were quantified using gas chromatography-mass spectrometry. Elevated concentrations of acetochlor, atrazine, and metolachlor were indicative of inputs from agricultural sources and were associated with reductions in body mass, condition factor, and androgenic gene expression in river exposed fathead minnow larvae. However, following a 14-d in situ depuration during the post-pulse period, river exposed larvae overcompensated in previously suppressed biological endpoints. These results indicate that fathead minnow larvae are capable of compensatory responses following episodic exposure to agrichemical stressors.

Impact of sediment particle size on biotransformation of 17ß-estradiol and 17ß-trenbolone.

Soil/sediment particle size has been reported to influence the sorption and bioavailability of steroid hormones in the environment. However, the impact of particle size on biotransformation has not been well elucidated. The present study investigated the dissipation of 17ß-estradiol and 17ß-trenbolone and the formation and degradation of the subsequent transformation products in different size fractions of a sandy and a silt loam sediment. The results showed that the decay of 17ß-estradiol and 17ß-trenbolone associated with fine particles followed a biphasic pattern with more rapid decay in the initial phase followed by a second phase with slower decay of the residues compared to their decay rates in the sand fraction. Estrone and trendione were detected as a primary biotransformation product for 17ß-estradiol and 17ß-trenbolone, respectively. The parent-to-product conversion ratios and the degradation rates of estrone and trendione varied among different size fractions, but no consistent correlation was observed between decay rates and sediment particle size. Estrone and trendione decayed in the whole sediments at rates not statistically different from those associated with the fine fractions. These results indicate that fine particles may play an important role in influencing the persistence of and the potential risk posed by steroid hormones in the aquatic systems.

Bioavailability and Fate of Sediment-Associated Progesterone in Aquatic Systems.

The environmental fate and bioavailability of progesterone, a steroid hormone known to cause endocrine-disrupting effects in aquatic organisms, is of growing concern due to its occurrence in the environment in water and sediment influenced by wastewater treatment plant and paper mill effluents, as well as livestock production. The objective of this study was to evaluate the fate of progesterone in two natural sediments and the corresponding alteration of gene expression in three steroid-responsive genes; vitellogenin, androgen receptor and estrogen receptor alpha. When exposed to progesterone-spiked sand, fathead minnows (Pimephales promelas) exhibited significant reductions in the expression of vitellogenin and androgen receptor expression. In contrast, fish exposed to progesterone associated with the silty loam sediment did not show a biological response at 7 days and only realized a significant reduction in vitellogenin. In both sediments, progesterone degradation resulted in the production of androgens including androsteinedione, testosterone, and androstadienedione, as well as the antiestrogen, testolactone. Differences in compound fate resulted in organism exposure to different suites of metabolites either in water or associated with the sediment. Results from this study suggest that environmental progestagens will lead to defeminization at environmentally relevant concentrations, and that exposure is influenced by sediment properties.

The effect of particle size on sorption of estrogens, androgens and progestagens in aquatic sediment.

There is growing concern about the biologic effects of steroid hormones in impacted waterways. There is increasing evidence of enhanced transport and biological effects stemming from steroid hormones associated with soils or sediments; however, there are limited studies evaluating how steroid hormone distribution between various particle sizes within whole sediments affects steroid fate. In this study, sorption of 17ß-estradiol, estrone, progesterone, and testosterone was evaluated to different size fractions of two natural sediments, a silty loam and a sandy sediment, to determine the steroid sorption capacity to each fraction and distribution within the whole sediment. Sorption isotherms for all steroid hormones fit linear sorption models. Sorption capacity was influenced more by organic carbon content than particle size. Interactions between size fractions were found to affect the distribution of steroids within the whole sediments. All four steroids preferentially sorbed to the clay and colloids in the silty loam sediment at the lowest aqueous concentration (1 ng/L) and as aqueous concentration increased, the distribution of sorbed steroid was similar to the distribution by weight of each size fraction within the whole sediment. In the sandy sediment, preferential sorption to fine particles was observed.

Bioavailability and fate of sediment-associated trenbolone and estradiol in aquatic systems.

Endocrine disrupting effects in aquatic organisms have been observed in systems influenced by steroid hormones. Associating endocrine disruption with aqueous concentrations of steroids alone may overlook the influence of source-sink dynamics in sediments on steroid hormone bioavailability. The objective of this study was to determine the fate of 17ß-estradiol and 17ß-trenbolone in two field sediments and to evaluate the corresponding bioavailability of the compounds to the fathead minnow (Pimephales promelas). Steroid fate was evaluated using analytical chemistry and verified by assessing the biological activity using yeast based in vitro assays. Effective bioavailability of the steroids was inferred from changes in hepatic vitellogenin expression (increased expression in males exposed to 17ß-estradiol, and reduced expression in females exposed to 17ß-trenbolone). In experiments conducted with 17ß-estradiol, no induction of hepatic vitellogenin mRNA expression was observed in male fish exposed to sediment-associated 17ß-estradiol. In contrast, female minnows exposed to sediment-associated 17ß-trenbolone experienced significant reductions in hepatic vitellogenin compared to negative controls. In both systems, the parent compounds were shown to degrade rapidly to the more persistent metabolites, estrone and trendione, both of which were found predominantly associated with the sediments. Results from the yeast estrogen screen indicate a reduction in biological activity as biotransformation of 17ß-estradiol occurs; results from the yeast anti-estrogen screen were inconclusive and unable to substantiate 17ß-trenbolone fate in aquatic systems. Collectively, these data support the contention that steroid hormones associated with the sediment can become bioavailable to fish, and that sediment characteristics influence the observed bioavailability of these compounds.

The anti-estrogenic activity of sediments from agriculturally intense watersheds: assessment using in vivo and in vitro assays.

The goal of the current study was to determine whether sediments from agriculturally intense watersheds can act as a potential source of anti-estrogenic endocrine-disrupting compounds. The specific objectives of the current study were to determine (1) whether female fathead minnows (Pimephales promelas) experience alterations in endocrine function when exposed to sediments collected from agriculturally intense watersheds and (2) if these sediments display anti-estrogenic activity in an in vitro assay. In addition, sediment samples were analyzed for the presence of steroid hormones and pesticides associated with local agricultural practices. To accomplish this, sediments and water were collected from three sites within two agriculturally intense Nebraska watersheds (Bow Creek and the Elkhorn River). In 2009, minnows were exposed to sediment and/or water collected from the two Bow Creek sites (East Bow Creek and the Confluence) in the laboratory, while in 2010, minnows were exposed to sediment and/or water from East Bow Creek, the Confluence and the Elkhorn River. Following the 7-day exposure period, the hepatic mRNA expression of two-estrogen responsive genes, estrogen receptor α (ERα) and vitellogenin (Vtg) was determined. In 2009, females exposed to Confluence sediments, in the presence of laboratory water or Confluence water, experienced significant reductions in ERα expression relative to unexposed and Confluence water-exposed females. The defeminization of these females suggests the presence of a biologically available anti-estrogenic compound in sediments collected from this site. In 2010, sediments were assessed for anti-estrogenic activity on days 0 and 7 of the exposure period using a 4-h yeast estrogen screen. Lipophilic extracts (LEs) of day 0 sediments collected from the Confluence and the Elkhorn River induced significant reductions in the estrogenic reporter activity of treated yeast cultures suggesting the presence of a lipophilic anti-estrogenic compound in these extracts. Chemical analysis revealed the presence of a variety of steroid hormones, including those associated with the production of beef cattle (i.e. ß-trenbolone, α-zearalanol and α-zearalenol), in sediments indicating that compounds utilized by local beef cattle operations are capable of entering nearby watersheds. Overall, the results of this study indicate that an environmentally relevant anti-estrogenic compound is present in sediments from agriculturally intense watersheds and that this compound is bioavailable to fish. Furthermore, the presence of steroid hormones in sediments from these watersheds provides evidence indicating that steroids are capable of sorbing to sediments.