Reductions in hepatic vitellogenin and estrogen receptor alpha expression by sediments from an agriculturally impacted waterway

Previous studies have reported alterations in the endocrine function of fathead minnows (Pimephales promelas) collected and deployed in the Elkhorn River. The goal of the current study was to determine whether sediment from the Elkhorn River watershed could act as a source of endocrine-active compounds. To accomplish this, four aquaria containing sexually mature fathead minnows and polar organic chemical integrative samplers (POCIS) were established. The aquaria contained either: (1) laboratory water only, (2) Elkhorn River water only, (3) laboratory water and Elkhorn River sediment or (4) Elkhorn River water and Elkhorn River sediment. Steroid hormones were not detected in the extracts of POCIS or sediment. Pesticides were detected in POCIS extracts from tanks containing Elkhorn River water, but were not detected in the extracts of sediment or POCIS suspended in the tank containing laboratory water and Elkhorn River sediment suggesting that sediments do not act as a significant source of the 14 steroid hormones or 24 pesticides that were analyzed for in the current study. The hepatic mRNA expression of vitellogenin (vtg) and estrogen receptor alpha (ERalpha) in fathead minnows from each group was assessed. Female minnows exposed simultaneously to sediment and water collected from the Elkhorn River experienced defeminization as indicated by significant reductions in both vtg and ERalpha expression. Significant reductions in vtg mRNA expression were also observed in females exposed to laboratory water and Elkhorn River sediment, but not in females exposed to Elkhorn River water only. This finding suggests that exposures to sediments, rather than water, collected from the Elkhorn River lead to the defeminization of females. However, the compound(s) responsible for this effect have yet to be determined.

Agrichemicals in Nebraska, USA, watersheds: occurrence and endocrine effects

The objective of the present study was to determine the occurrence and endocrine effects of agrichemicals in four Nebraska, USA, watersheds--the Elkhorn, Platte, Niobrara, and Dismal rivers. Land use in the Elkhorn River and Platte River watersheds is characterized by intense agriculture, including row crop and beef cattle production. In contrast, land within the Niobrara River and Dismal River watersheds consists primarily of grasslands. Polar organic chemical integrative samplers (POCIS) and caged fathead minnows were deployed at a site within each watershed for 7 d. The POCIS were analyzed for pesticides and hormones, while the caged minnows were analyzed for the expression of estrogen- and androgen-responsive genes. Amounts of pesticides recovered in POCIS extracts from the Elkhorn and Platte rivers were higher than those recovered from the Niobrara and Dismal rivers. Furthermore, female minnows deployed in the Elkhorn River experienced significant reductions in expression of two estrogen-responsive genes (vitellogenin and estrogen receptor α) relative to females deployed at the other sites, indicating alterations in endocrine function. However, the defeminization of these females could not be definitely linked to any of the agrichemicals detected in the POCIS recovered from the Elkhorn River.

The endocrine activity of beef cattle wastes: do growth-promoting steroids make a difference?

The primary objective of this study was to compare the endocrine activity of wastes from trenbolone acetate:estradiol (TBA:E)-implanted steers to that of wastes from unimplanted steers. To accomplish this, fathead minnows (Pimephales promelas) were exposed to urine or fecal slurry from TBA:E-implanted or unimplanted steers for 7 days. Following exposures, hepatic vitellogenin (vtg) mRNA expression and secondary sexual characteristics were assessed. Among both males and females, there were no differences in vtg mRNA expression between fish exposed to urine from implanted or unimplanted steers at any of the concentrations tested. Furthermore, concentrations of steroid hormones in the urine of implanted and unimplanted steers were similar. These findings indicate a lack of differences in the endocrine activity of urine from TBA:E-implanted and unimplanted steers. With regard to the fecal slurry exposures, there were no significant differences in vtg mRNA expression among females from any of the groups; however, significant differences in male vtg mRNA expression were detected. Specifically, males exposed to 1600 mg dry feces/L from implanted cattle experienced an 840-fold increase in vtg mRNA expression relative to both unexposed males and males exposed to the corresponding fecal concentration from unimplanted steers. These males also appeared to experience a reduction in male secondary sexual characteristics. These findings suggest that steroids associated with the wastes from TBA:E-implanted steers have both feminizing and demasculinizing effects on male fish. Furthermore, these effects are most likely due to the presence of estrogenic compounds, which were detected in the liquid portion of the fecal slurry from TBA:E-implanted steers, but not in that of unimplanted steers. The findings of this study indicate the presence of endocrine-disrupting compounds in the urine and feces of cattle and suggest that the implant history of cattle alters the endocrine activity of feces, but does not alter the endocrine activity of urine.

The environmental impact of growth-promoting compounds employed by the United States beef cattle industry: history, current knowledge, and future directions

The current state of knowledge regarding the environmental impact of growth-promoting compounds associated with the U.S. beef cattle industry is extensive in some areas but virtually nonexistent in others. The compounds administered to the cattle are quite well understood, as are bovine metabolism and excretion. If the sex and age of the cattle on the feedlot are known, the metabolites excreted by the cattle should be predictable with a great deal of accuracy. The fate, transport, and biological effects of growth-promoting compounds are just beginning to be studied. Most of the research conducted on the fate and transport of growth-promoting compounds has focused on 17beta-E2; however, much of this research was not conducted using feedlot runoff or manure. Studies are needed that focus specifically on manures and runoff from experimental or commercial feedlots. To date, the degree to which growth-promoting compounds are released from feedlots in a bioavailable form remains a point of speculation. The environmental fate and transport of TBA, P, and MGA have not been well studied. Comparisons between the fate and transport of T and 17beta-E2, however, make it clear that compounds with similar structure may behave very differently once released into the environment. Considering that 17beta-E2 is a naturally occurring estrogen and that TBA is a nonaromatizable androgen, it is not surprising that these compounds directly impact the reproductive physiology of fishes. The effects of these two compounds have been well documented, as has been described here; however, the effects of P and MGA exposures have gone largely uninvestigated. This is a serious critical gap in our knowledge base because progestogins play an important role in sex steroid synthesis and reproduction. Clearly, additional research on the consequences of exposures to P and MGA is warranted. The majority of research investigating the effects of 17beta-E2 and TBA metabolites on fish has been conducted in the laboratory and has typically focused on continuous, pharmacological exposures to single compounds. These exposures may not bear much similarity to environmentally relevant exposures, and as such may offer little information regarding biological effects seen in nature. Cattle feedlot runoff is likely to contain a suite of growth-promoting compounds rather than any single compound. Clearly, deciphering the biological effects of exposure to complex mixtures containing androgenic, estrogenic, and progestogenic compounds will remain an important area of study for the next few years. A second complexity associated with the biological runoff from cattle feedlots is the discontinuous nature of the release. It is likely that inadvertent entry of growth-promoting compounds will follow spring snowmelt or rainstorm events. These events will result in intermittent, pulsed exposures to high concentrations of these compounds interspersed by long-term exposures to lower concentrations. The effects of exposure timing and duration should be considered to generate a clearer understanding of the biological consequences of exposures to growth-promoting compounds. To date, a very limited number of studies (only one!) have sought to determine whether fish living in waterways receiving runoff from cattle feedlots are adversely affected by growth-promoting compounds associated with the runoff. Clearly, more field studies need to be conducted before a relationship between cattle feedlot effluent and biological consequences can be elucidated.

Occurrence and biological effect of exogenous steroids in the Elkhorn River, Nebraska, USA

Recent studies of surface waters in North America, Japan and Europe have reported the presence of steroidogenic agents as contaminants. The current study has three objectives: 1) to determine if steroidogenic compounds are present in the Elkhorn River, 2) to determine if sediments collected from the Elkhorn River can act as a source of steroidogenic compounds to aquatic organisms, and 3) to determine if site-specific biological effects are apparent in the hepatic gene expression of fathead minnows. Evidence was obtained using three approaches: 1) deployment of polar organic chemical integrative samplers (POCIS), 2) deployment of caged fathead minnows, and 3) a laboratory experiment in which POCIS and fish were exposed to sediments from the deployment sites. Deployment sites included: the Elkhorn River immediately downstream from a Nebraska wastewater treatment plant, two waterways (Fisher Creek and Sand Creek) likely to be impacted by runoff from cattle feeding operations, and a reference site unlikely to be impacted by waste water inputs. The POCIS extracts were analyzed for a number of natural steroids and metabolites, as well as four different synthetic steroids: ethinylestradiol, zearalonol, 17beta-trenbolone and melengestrol acetate. Estrogenic and androgenic metabolites, as well as progesterone and trace levels of melengestrol acetate were detected in POCIS deployed at each site. POCIS deployed in tanks containing field sediments from the four sites did not accumulate the synthetic steroids except for ethinylestradiol, which was detected in the aquarium containing sediments collected near the wastewater treatment plant. Fish deployed in Sand Creek and at the wastewater treatment plant experienced significantly elevated levels of gene expression for two genes (StAR and P450scc) relative to those deployed in Fisher Creek. Fish exposed to the sediments collected from Sand Creek had significantly higher levels of hepatic StAR and P450scc gene expression than did fish exposed to sediments from the two other field sites, as well as the no-sediment control tank.

IN CONCLUSION

1) detectable levels of steroidogenic compounds were detected in passive samplers deployed in the Elkhorn River, 2) sediments do not appear to be a significant source for steroidogenic compounds, and 3) site-specific differences were found in mRNA expression among the different treatment groups of fish; however, a functional explanation for these differences is not readily forthcoming.

Cadmium exposures in fathead minnows: are there sex-specific differences in mortality, reproductive success, and Cd accumulation?

The primary goal of this experiment was to determine whether cadmium (Cd) exposure has sex-specific effects on the reproductive success of fathead minnows as measured by time to first spawn, spawning frequency, clutch size, fecundity, fertilization success, hatching success, and offspring mortality to 2 d post hatch. Prior to breeding, minnows were either exposed to 50 microg/L Cd or sham exposed for 21 d. After exposures, minnows were paired (male x female) into one of four breeding groups-control x control (C x C), control x exposed (C x E), exposed x control (E x C) or exposed x exposed (E x E). Pairs of minnows were subjected to a 21-d breeding study during which the reproductive parameters mentioned above were measured. During the breeding study, minnows in the E x E pairs had significantly higher mortality than minnows in the C x C pairs; however, the mortality of minnows in the C x E and E x C did not differ from that of C x C pairs. Presumably, behavioral alterations in both males and females exposed to Cd accounted for the increased mortality in the E x E group. The results of the breeding study did not reveal any significant differences among any of the reproductive parameters measured with the exception of offspring mortality. Offspring from C x E pairs did not differ from offspring from C x C pairs with regard to mortality; however, offspring from pairs containing exposed males (E x C and E x E) had significantly higher mortality than offspring from C x C pairs suggesting that paternal exposure to Cd leads to an increase in offspring mortality.

Cadmium exposures during early development: do they lead to reproductive impairment in fathead minnows?

The primary objective of this study was to determine whether cadmium (Cd) exposures during embryonic and larval development alter the reproductive performance, reproductive physiology, and sex ratio of fathead minnows (Pimephales promelas). Embryonic exposures were conducted by exposing adult female fathead minnows to 0, 25, or 100 microg/L Cd for 8 d prior to breeding. Larval exposures were conducted by exposing the larvae to waterborne Cd at 0, 12.5, 25, or 50 microg/L from 8 to 29 d posthatch (the time period associated with female sexual differentiation). Minnows from each exposure period were raised to maturity, at which time their reproductive success, secondary sexual characteristics, gonadosomatic index (GSI), plasma 11-ketotestosterone (11-KT) concentrations, and sex ratios were assessed. Results from the embryonic study reveal that Cd exposures alter the secondary sexual characteristics of male fathead minnows but do not alter reproductive performance, GSI, 11-KT concentrations, or sex ratios. Larval exposures, during the period of female sexual differentiation, significantly reduce the frequency of adult spawning and increase clutch size but do not alter fecundity, secondary sexual characteristics, GSI, or 11-KT. Subtle alterations in sex ratio were observed, indicating that larval Cd exposures may increase the proportion of females in an exposed population.

Cd exposures in fathead minnows: effects on adult spawning success and reproductive physiology

The primary objective of this study was to determine whether cadmium (Cd) exposures alter reproduction in fathead minnows (Pimephales promelas). Pairs of sexually mature minnows were exposed to waterborne Cd at 0, 12.5, 25, or 50 microg/L for 21 days. During this exposure period, the reproductive success of pairs was assessed. Following the exposure, gonadosomatic index (GSI), male secondary sexual characteristics, male plasma 11-ketotestosterone (11-KT) concentrations, and female plasma estradiol (E2) concentrations were determined. Results of this study show that Cd exposures impair reproduction in fathead minnows. Pairs exposed to 50 microg/L experienced a significant decline in spawning frequency and fecundity relative to unexposed minnows. Cd exposures also caused alterations in male secondary sexual characteristics, as males exposed to 25 microg/L had significantly fewer nuptial tubercles than controls. Furthermore, males exposed to 12.5 microg/L Cd experienced a significant increase in plasma 11-KT concentrations relative to controls. No alterations in GSI or female plasma E2 concentrations were observed.

Acclimation to Cu in fathead minnows: does age influence the response?

This study had two primary objectives. The first was to determine if the length of exposure necessary for acclimation to Cu to develop in larval fathead minnows (Pimephales promelas) is different than that for juveniles. The second objective was to determine whether the acclimatory response, as determined by organism survival, is consistent with acclimation as determined by whole-body Na+. Six experiments were conducted: four using larval (<20-d-old) and two using juvenile (<60-d-old) fathead minnows. Within each experiment, fish were allocated to one of four groups: unexposed, continuously exposed, episodically exposed or naïvely exposed. The continuous group was exposed to a sublethal Cu exposure (125 microg/L) for 8, 12, 16 or 20 d and then subjected to a survival test at a lethal dose (375 microg/L). Fish in the episodic group were exposed to the sublethal dose for either 4 or 8 d, given a depuration period of varying lengths (4-16 d) then subjected to a survival test. Naïve minnows were maintained in clean water then given the survival challenge. Results from survival tests show that the larvae acclimate after only a 4-d sublethal exposure to Cu. In contrast, juveniles require a 16-d exposure to acclimate. Once acclimation had developed, there was a strong relationship between larval survival and whole-body Na+. Acclimated larvae maintained whole-body Na+ relative to unexposed fish, while unacclimated larvae did not. Interestingly, this was not the case for juveniles, as acclimated and unacclimated groups did not differ with respect to whole-body Na+ concentrations. The results of this study show that age influences the time course and possibly the mechanisms of acclimation in fathead minnows exposed to Cu.