Using metabolomic profiling to inform use of surrogate species in ecological risk assessment practices

The U.S. EPA frequently uses avian or fish toxicity data to set protective standards for amphibians in ecological risk assessments. However, this approach does not always adequately represent aquatic-dwelling and terrestrial-phase amphibian exposure data. For instance, it is accepted that early life stage tests for fish are typically sensitive enough to protect larval amphibians, however, metamorphosis from tadpole to a terrestrial-phase adult relies on endocrine cues that are less prevalent in fish but essential for amphibian life stage transitions. These differences suggest that more robust approaches are needed to adequately elucidate the impacts of pesticide exposure in amphibians across critical life stages. Therefore, in the current study, methodology is presented that can be applied to link the perturbations in the metabolomic response of larval zebrafish (Danio rerio), a surrogate species frequently used in ecotoxicological studies, to those of African clawed frog (Xenopus laevis) tadpoles following exposure to three high-use pesticides, bifenthrin, chlorothalonil, or trifluralin. Generally, D. rerio exhibited greater metabolic perturbations in both number and magnitude across the pesticide exposures as opposed to X. laevis. This suggests that screening ecological risk assessment surrogate toxicity data would sufficiently protect amphibians at the single life stage studied but care needs to be taken to understand the suite of metabolic requirements of each developing species. Ultimately, methodology presented, and data gathered herein will help inform the applicability of metabolomic profiling in establishing the risk pesticide exposure poses to amphibians and potentially other non-target species.

Cross-Taxa Distinctions in Mechanisms of Developmental Effects for Aquatic Species Exposed to Trifluralin

Standard ecological risk assessment practices often rely on larval and juvenile fish toxicity data as representative of the amphibian aquatic phase. Empirical evidence suggests that endpoints measured in fish early life stage tests are often sufficient to protect larval amphibians. However, the process of amphibian metamorphosis relies on endocrine cues that affect development and morphological restructuring and are not represented by these test endpoints. The present study compares developmental endpoints for zebrafish (Danio rerio) and the African clawed frog (Xenopus laevis), 2 standard test species, exposed to the herbicide trifluralin throughout the larval period. Danio rerio were more sensitive and demonstrated a reduction in growth measurements with increasing trifluralin exposure. Size of X. laevis at metamorphosis was not correlated with exposure concentration; however, time to metamorphosis was delayed relative to trifluralin concentration. Gene expression patterns indicate discrepancies in response by D. rerio and X. laevis, and dose-dependent metabolic activity suggests that trifluralin exposure perturbed biological pathways differently within the 2 species. Although many metabolites were correlated with exposure concentration in D. rerio, nontargeted hepatic metabolomics identified a subset of metabolites that exhibited a nonmonotonic response to trifluralin exposure in X. laevis. Linking taxonomic distinctions in cellular-level response with ecologically relevant endpoints will refine assumptions used in interspecies extrapolation of standard test effects and improve assessment of sublethal impacts on amphibian populations. Environ Toxicol Chem 2020;39:1797-1812. Published 2020. This article is a US government work and is in the public domain in the USA.

Effects of Louisiana crude oil on the sheepshead minnow (Cyprinodon variegatus) during a life-cycle exposure to laboratory oiled sediment

Determining the long-term effects of crude oil exposure is critical for ascertaining population-level ecological risks of spill events. A 19-week complete life-cycle experiment was conducted with the estuarine sheepshead minnow (Cyprinodon variegatus) exposed to reference (uncontaminated) sediment spiked with laboratory weathered South Louisiana crude (SLC) oil at five concentrations as well as one unspiked sediment control and one seawater (no sediment) control. Newly hatched larvae were exposed to the oiled sediments at measured concentrations of < 1 (sediment control), 50, 103, 193, 347, and 711 mg total polyaromatic hydrocarbons (tPAH)/kg dry sediment. Juveniles were exposed through the reproductively active adult phase at measured concentrations of <1 (sediment control), 52, 109, 199, 358, and 751 mg tPAH/kg sediment. Throughout the exposure, fish were assessed for growth, survival, and reproduction. Resulting F1 embryos were then collected, incubated, and hatched in clean water to determine if parental full life-cycle exposure to oiled sediment produced trans-generational effects. Larvae experienced significantly reduced standard length (5-13% reduction) and wet weight (13-35% reduction) at concentrations at and above 50 and 103 mg tPAH/kg sediment, respectively. At 92 and 132 days post hatch (dph), standard length was reduced (7-13% reduction) at 199 and 109 mg tPAH/kg dry sediment, respectively, and wet weight for both time periods was reduced at concentrations at and above 109 mg tPAH/kg dry sediment (21-38% reduction). A significant reduction (51-65%) in F0 fecundity occurred at the two highest test concentrations, but no difference was observed in F1 embryo survival. This study is the first to report the effects of chronic laboratory exposure to oiled sediment, and will assist the development of population models for evaluating risk to benthic spawning fish species exposed to oiled sediments. © 2015 Wiley Periodicals, Inc. Environ Toxicol 31: 1627-1639, 2016.

Developmental toxicity of Louisiana crude oil-spiked sediment to zebrafish

Embryonic exposures to the components of petroleum, including polycyclic aromatic hydrocarbons (PAHs), cause a characteristic suite of developmental defects and cardiotoxicity in a variety of fish species. We exposed zebrafish embryos to reference sediment mixed with laboratory weathered South Louisiana crude oil and to sediment collected from an oiled site in Barataria Bay, Louisiana in December 2010. Laboratory oiled sediment exposures caused a reproducible set of developmental malformations in zebrafish embryos including yolk sac and pericardial edema, craniofacial and spinal defects, and tissue degeneration. Dose-response studies with spiked sediment showed that total polycyclic aromatic hydrocarbons (tPAH) concentrations of 27mg tPAH/kg (dry weight normalized to 1 percent organic carbon [1 percent OC]) caused a significant increase in defects, and concentrations above 78mg tPAH/kg 1 percent OC caused nearly complete embryo mortality. No toxicity was observed in Barataria sediment with 2mg tPAH/kg 1 percent OC. Laboratory aging of spiked sediment at 4°C resulted in a nearly 10-fold decrease in sensitivity over a 40-day period. This study demonstrates oiled sediment as an exposure pathway to fish with dose-dependent effects on embryogenesis that are consistent with PAH mechanisms of developmental toxicity. The results have implications for effects on estuarine fish from oiled coastal areas during the Deepwater Horizon spill.

Exposure of three generations of the estuarine sheepshead minnow (Cyprinodon variegatus) to the androgen, 17beta-trenbolone: effects on survival, development, and reproduction

Estimating long-term effects of endocrine-disrupting chemicals on a species is important to assessing the overall risk to the populations. The present study reports the results of a 42-week exposure of estuarine sheepshead minnows (Cyprinodon variegatus) to the androgen, 17beta-trenbolone (Tb) conducted to determine if partial-(F0) or single-generation (F1) fish exposures identify multigenerational (F0-F3) effects of androgens on fish. Adult F0 fish were exposed to 0.007, 0.027, 0.13, 0.87,and 4.1 microg Tb/L, the F1 generation to < or =0.87 microg Tb/L, the F2 fish to < or =0.13 microg Tb/L, and the F3 fish to < or =0.027 microg Tb/L. The highest concentrations with reproducing populations at the end of the F0, F1, and F2 generations were 4.1, 0.87, and 0.027 microg Tb/L, respectively. Reproduction in the F0, F1, and F2 generations was significantly reduced at 0.87, 0.027, and 0.027 microg Tb/L, respectively. Fish were significantly masculinized in the F1 generation exposed to 0.13 microg Tb/L or greater. Female plasma vitellogenin was significantly reduced in F0 fish exposed to > or =0.87 microg Tb/L. Gonadosomatic indices of the F0 and F1 generations were significantly increased at 0.87 and 0.13 microg Tb/L in the F0 and F1 generation, respectively, and were accompanied by ovarian histological changes. Reproduction was the most consistently sensitive measure of androgen effects and, after a life-cycle exposure, the daily reproductive rate predicted concentrations affecting successive generations. The present study provides evidence that a multiple generation exposure of fish to some endocrine-disrupting chemicals can result in developmental and reproductive changes that have a much greater impact on the success of a species than was indicated from shorter term exposures.

Multigenerational exposure of the estuarine sheepshead minnow (Cyprinodon variegatus) to 17β-estradiol. II. Population-level effects through two life cycles

The evaluation of multigeneration, population-level impacts is particularly important in the risk assessment of endocrine-disrupting compounds, because adverse effects may not be evident during the first generation of exposure. Population models were developed for the sheepshead minnow (Cyprinodon variegatus) exposed to 17β-estradiol (E2) for two complete generations (F1 and F2) to determine population-level effects of multigenerational exposure to a model estrogen. Stage-structured matrix models were used to determine interactions between treatment and the number of generations exposed. Reproduction was significantly reduced in both the 0.08 and 0.2 μg E2/L treatments in both generations, and embryo and larval stages experienced reduced survival at 0.2 μg/L in the second generation only. However, increased female to male sex ratio in these treatments compensated for the loss in reproductive output, and significant population-level effects only occurred in the 0.2 μg E2/L treatment of the F2 population. The F2 population in the 0.2 μg E2/L treatment also had an altered, stable stage distribution relative to the control population of both generations and the Fl population in the 0.2 μg E2/L treatment, resulting in additional population-level effects. These results demonstrate that continued exposure to E2 had compounding effects on sheepshead minnow populations and that long-term exposures may be necessary to understand the risk that exposures to environmental estrogens pose to native populations. Although population-level effects did not occur in the Fl generation, a risk decision based on Fl organism-level effects would be protective of the population exposed for two generations.

Multigenerational exposure of the estuarine sheepshead minnow (Cyprinodon variegatus) to 17 β-estradiol. I. organism-level effects over three generations

A 280-d study examined the effects of 17β-estradiol (E2) on reproduction and development of the sheepshead minnow (Cyprinodon variegatus) exposed from the parental (F0) through three subsequent (F1, F2, and F3) generations and evaluated the need for multigenerational assessments of the risks of endocrine-disrupting chemicals. This first three-generation study exposed adult F0 and F1 fish to measured concentrations of 0.01, 0.04, 0.08, 0.2, and 0.3 μg E2/L; the F2 and F3 generations were exposed to 0.2 μg E2/L or less. The cumulative 21-d production of normal embryos was significantly reduced in the F0 generation at 0.3 μg E2/L and in the F1 and F2 generations at 0.08 μg E2/L or more. The daily reproductive rate was significantly reduced in all three generations at 0.08 μg E2/L or more during spawning days 8 to 14 and 15 to 21. The proportion of infertile eggs from F1 fish was significantly increased above that of the solvent controls at 0.04 and 0.2 μg E2/L and from F2 fish at 0.04 μg E2/L or more. Changes in liver, kidney, and gonadal tissues were seen in the F0 and F1 generations exposed to 0.2 μg E2/L or more. The female gonadosomatic index was significantly decreased at 0.3 μg E2/L in the F0 and F1 generations. Estradiol affected the hepatosomatic index only in female F1 fish, but not in a dose-dependent manner. All F1 fish in 0.3 μg E2/L appeared to be phenotypically female. Our results indicate that life-cycle exposure to E2 significantly decreased embryo production by F1 and F2 fish at concentrations lower than those affecting the F0 generation, and they emphasize the importance of evaluating the impact of an estrogenic chemical on reproduction through a minimum of two (F0 and F1) generations.

Development of a methodology for successful multigeneration life-cycle testing of the estuarine sheepshead minnow, Cyprinodon variegatus

Evaluation of effects on fish reproduction and development during chemical exposures lasting for multiple generations is sometimes limited by variable reproductive responses and the time required for the exposure. Established testing methods and the short life cycle of the sheepshead minnow, Cyprinodon variegatus, make this species particularly suitable for use in identifying potential impacts of contaminants in estuarine and marine environments. This study describes the refinement of life-cycle exposure methods that increased the reliability of reproduction in sheepshead minnows and reduced the time to maturation for larvae and juvenile fishes. A test of three spawning chamber designs, three sex ratios, and two photoperiods identified conditions that reduced the coefficient of variation in egg production from >100% to as little as 32%. The most reliable results were produced with groups of three female and two male fishes (all of similar size) when they were placed in a rectangular chamber and acclimated for 12 days. A test water temperature of 26.5 +/- 2 degrees C and a 14L:10D photoperiod resulted in fish producing a mean of 74 embryos per female per day, with a coefficient of variation of 31.8%. Egg fertility exceeded 90%, with a hatch rate of 95% for normal embryos (>or=80% yolk) and a hatch rate of <or=45% for embryos containing <or=77% yolk. The length of time to grow larvae to spawning adult fish was reduced to approximately 60 days posthatch by feeding them flake food twice daily to satiation for 15 min, and it was observed that size (>or=2.7 cm standard length) was critical for spawning readiness. Adult fish were prepared for the spawning assessment by adding frozen brine shrimp to their diet. Results of these experiments provide methods that are of particular interest in assessment of endocrine-disrupting chemicals that are known to affect reproduction.

Comparison of estrogen-responsive plasma protein biomarkers and reproductive endpoints in sheepshead minnows exposed to 17beta-trenbolone

Protein profiling can be used for detection of biomarkers that can be applied diagnostically to screen chemicals for endocrine modifying activity. In previous studies, mass spectral analysis revealed four peptides (2950.5, 2972.5, 3003.4, 3025.5m/z) in the plasma of estrogen agonist-treated male and gravid female sheepshead minnows (Cyprinodon variegatus, SHM), which served as distinct estrogenic biomarkers. In this study, a 21-day reproductive assay with adult SHM was conducted to investigate possible dose-related effects of the synthetic androgen, 17beta-trenbolone, on expression of these four estrogen-responsive peptides. In addition, the response of the peptide biomarkers were compared to traditional reproductive endpoints of fecundity, histopathology, secondary sex characteristics, length, weight, hepatosomatic index, female gonadosomatic index and plasma vitellogenin (VTG) levels. Fish were continuously exposed to 0.005, 0.05, and 5.0 microg/l, a solvent control (triethylene glycol, TEG), and a seawater control (SW) using an intermittent flow-through dosing system. Plasma was analyzed for the presence of the four peptide biomarkers by MALDI-TOF MS and VTG protein by quantitative ELISA. Male fish from the trenbolone treatments and controls showed no expression of the four peptide biomarkers or measurable levels of VTG. The estrogen-responsive biomarkers and plasma VTG were constitutively expressed in females from the SW, TEG, 0.005 and 0.05 microg/l exposures. All four peptide biomarkers were significantly reduced (p<0.0002 to p<0.005) at the 5.0 microg/l treatment level which corresponded with significant reductions in fecundity and changes in ovarian morphology. A distinct but non-significant reduction in VTG was also observed in female fish from the 5.0 microg/l treatment. Results of this study suggest application of these estrogen-responsive protein biomarkers may be a cost effective alternative to fecundity measures which are labor intensive and expensive to conduct.

Characterizing coral condition using estimates of three-dimensional colony surface area

Coral reefs provide shoreline protection, biological diversity, fishery harvests, and tourism, all values that stem from the physically-complex coral infrastructure. Stony corals (scleractinians) construct and maintain the reef through deposition of calcium carbonate. Therefore, assessment of coral reefs requires at least some measurement endpoints that reflect the biological and physical condition of stony corals. Most monitoring programs portray coral quantity as live coral cover, which is the two-dimensional proportion of coral surface to sea floor viewed from above (planar view). The absence of the third dimension, however, limits our ability to characterize coral reef value, physiology, health and sustainability. A three-dimensional (3D) approach more realistically characterizes coral structure available as community habitat and, when combined with estimates of live coral tissue, quantifies the amount of living coral available for photosynthesis, growth and reproduction. A rapid coral survey procedure that coupled 3D coral quantification with more traditional survey measurements was developed and tested in the field. The survey procedure relied on only three underwater observations--species identification, colony size, and proportion of live tissue--made on each colony in the transect. These observations generated a variety of metrics, including several based on 3D colony surface area, that are relevant to reef management.

Vitellogenin mRNA regulation and plasma clearance in male sheepshead minnows, (Cyprinodon variegatus) after cessation of exposure to 17 beta-estradiol and p-nonylphenol

Research was conducted to determine the kinetics of hepatic vitellogenin (VTG) mRNA regulation and plasma VTG accumulation and clearance in male sheepshead minnows (Cyprinodon variegatus) during and after cessation of exposure to either 17 beta-estradiol (E2) or para-nonylphenol (NP). Adult fish were continuously exposed to aqueous measured concentrations of 0.089 and 0.71 microg E2 per l, and 5.6 and 59.6 microg NP per l for 16 days using an intermittent flow-through dosing apparatus. Fish were sampled on days 8 and 16 of exposure followed by sampling at discrete intervals for up to 96 days post-exposure. At each interval five fish were randomly sampled from each concentration and hepatic VTG mRNA and serum VTG levels for individual fish determined by slot blot and direct enzyme-linked immunosorbent assay (ELISA), respectively. Exposure to E2 and NP resulted in a dose dependent increase in hepatic VTG mRNA and plasma VTG over the course of the 16-day exposure period. Mean plasma VTG levels at day 16 were >100 mg/ml for both high doses of E2 and NP, and >20 mg/ml for the low exposure treatments. Within 8 days post-exposure, hepatic VTG mRNA levels returned to baseline in both high and low E2 treatments but remained elevated 2-4 fold in the NP treatments. Due to a shortened sampling period, a clearance rate for plasma VTG in the 5.6 microg NP per l treatment could not determined. In the 0.089, 0.71 microg E2 per l, and 59.6 microg NP per l treatments, VTG levels began decreasing within 4 days after exposure cessation and exhibited an exponential rate of elimination from plasma. Clearance rates for 0.71 microg E2 per l and 59.6 microg NP per l were not significantly different (P=0.47), however, both demonstrated significantly higher rates of clearance (P<0.02) than observed in the 0.089 microg E2 per l treatment. Our results indicate that hepatic VTG mRNA rapidly diminishes after cessation of estrogenic exposure in sheepshead minnows, but plasma VTG clearance is concentration and time dependent and may be detected at measurable levels for months after initial exposure to an estrogenic compound.

Relationships between tissue contaminants and defense-related characteristics of oysters (Crassostrea virginica) from five Florida bays

Evidence linking bivalve defense responses with pollutant exposure is increasing. Contaminant effects on immune or defense responses could influence the ability of an organism to resist infectious disease. This study explored relationships between xenobiotic chemicals accumulated in oyster (Crassostrea virginica) tissue and various measures of putative oyster internal defense activities and physiological condition. Defense-related and physiological measurements were made on individual oysters collected from 22 sites at five Florida bays and pooled oyster tissue from each site was analyzed for polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs), metals and certain pesticides. Chemical concentrations, physiological condition, and hemocyte and hemolymph characteristics varied across bays and among sites within a bay. Within-bay comparisons showed that sites with high oyster defense-related activities often had accompanying high tissue concentrations of one or more classes of xenobiotic chemicals. Correlation analysis performed across bays demonstrated significant positive relationships between most defense-related characteristics and at least one contaminant, including various PAH, PCB and trace metal analytes. In combination with other recent studies, these results strengthen the hypothesis that certain xenobiotic chemicals may be associated with elevated oyster hemocyte activities, even though the ultimate influence on disease resistance remains unknown.

Effects of p-nonylphenol, methoxychlor, and endosulfan on vitellogenin induction and expression in sheepshead minnow (Cyprinodon variegatus)

Temporal and dose-response relationships of vitellogenin (VTG) mRNA induction and subsequent plasma VTG accumulation were established for sheepshead minnows (Cyprinodon variegatus) treated with p-nonylphenol (an alkylphenol) and the organochlorine pesticides methoxychlor and endosulfan. Thirty-two adult male fish per treatment were continuously exposed to measured concentrations of 0.64, 5.4, 11.8, 23.3, and 42.7 micrograms/L p-nonylphenol; 1.1, 2.5, 5.6, 12.1, and 18.4 micrograms/L methoxychlor; and in two separate tests, 15.9, 36.3, 68.8, 162, 277, 403, 590, and 788 ng/L endosulfan using an intermittent flow-through dosing apparatus. Separate triethylene glycol (50 microliters/L) and 17 beta-estradiol (65.1 ng/L) treatments served as the negative and positive controls, respectively. Four fish were randomly sampled from each test concentration on days 2, 5, 13, 21, 35, and 42 of exposure, and levels of hepatic VTG mRNA induction and serum VTG accumulation were determined for each individual. Overall, fish exposed to p-nonylphenol or methoxychlor demonstrated a rapid, dose-dependent synthesis of VTG mRNA up to day 5 of exposure, followed by a relatively constant dose-dependent expression through day 42. Both chemicals showed a dose-dependent increase in plasma VTG over the entire time course of exposure, with significantly elevated VTG levels by the fifth day of exposure to p-nonylphenol at concentrations of 5.4 micrograms/L or greater and to methoxychlor at concentrations of 2.5 micrograms/L or greater. Exposure to 0.64 microgram/L p-nonylphenol resulted in highly variable plasma VTG levels of less than 6 mg/ml. Exposures with endosulfan failed to induce measurable levels of either hepatic VTG mRNA or serum VTG at the chemical concentrations tested. Our results demonstrate that the sheepshead minnow bioassay is a suitable estuarine/marine teleost model for in vivo screening of potentially estrogenic substances.